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Stop here! Let's talk about brakes

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Comments

  • swschradswschrad Member Posts: 2,171
    you are doing a self-adjust in the backup and stop routine, and that should stay. if it doesn't, that might indicate rusty junk in the adjuster mechanism needing replacement.

    also, it's possible if the RR is parked in a puddle or downhill or something, or in the shadow so the night dew never burns off, that that drum is rusting faster than the one on the left, and after a few brake applications, they'd be back to balanced anyway. just for the heck of it, park differently so the left rear wheel is where the right was a couple times and see if the issue moves to the other side. if it does, you won't need to replace anything.
  • fear_hopefear_hope Member Posts: 90
    Thanks both of you for your input. Turned out the shoes were fine, no contamination to speak of. My front pads were gone though and the rotors had been turned once before so...to the tune of $371 ;~( my brake system was repaired.
  • fleetwoodsimcafleetwoodsimca Member Posts: 1,518
    Once again light is shed on the fact that those who are willing and trained to work professionally on vehicles do get paid well for doing so. (:¤]
  • wainwain Member Posts: 479
    who makes brembo rotors?
    they are supposed to be good
  • alcanalcan Member Posts: 2,550
    Brembo makes Brembo rotors:


    http://www.brembo.com/group_na.htm

  • r42bxr42bx Member Posts: 2
    I have a 1997 Camry. I am the only driver. The first front pads lasted 56000. The second set of front pads lasted 21000. In February 2002 the pads were 8/32. On October 10, 2002 they were 3/32. The dealer had told me over the phone that they were 2/32 but he changed his mind when he returned the parts to me. All three sets of pads are Toyota brand. The dash parking brake light had been comming on intermitantly. The dealer claims he turned the rotors again and charged me for it.

    The question I have is why would the second set of brakes wear out in 21000 miles ? Why would they go from 8/32 to 3/32 in 8 months ? There has been and still is some brake groaning after stopping.
  • swschradswschrad Member Posts: 2,171
    in my case, ford parts stocks two different pad sets for my 2000 exploder. both are OEM grade or better. one set is softer and quieter, the other is harder, more fade-resistant, but may squeak a couple times if there is a little brake rust, until it has been ground off the rotor. list price is about $20 different for the two-wheel set on my fronts.

    being I am set for towing, and because I don't like to keep paying the same labor charge for reworks in fewer miles, I choked out the cost of dinner out for the better pads. they're about the same I got in my trailer towing package upgrades.

    I would bet a dollar to a donut that you didn't, and that there are severe-service pads on the shelf that would have given you brake life closer to what you had in the OEM. I will also bet the only practical difference in use unless you are at the limits of the vehicle is that the more costly pads last longer.
  • fleetwoodsimcafleetwoodsimca Member Posts: 1,518
    That's an excellent point! You will save more in the long run by buying the premium pads if you are paying someone else to do the brake work. In my case, I do most brake pad and shoe exchanges on my own vehicles, but I don't exactly seek out the opportunity to do it. I have read arguments that the softer, faster wearing pads are easier on the rotors and drums, so one can factor that in as well, I suppose. One thing is for sure: Keeping your brakes up is of paramount importance.
  • wainwain Member Posts: 479
    lets see they sell:
    brutestop for street rods- thats clear
    another label for taxis - thats clear
    then
    quiet stop - to cure noise problems
    noise solution - to cure noise problems
    and professional grade plus -

    which are closest to a toyota OE pad for 94 camry? . Maybe I just better stick with Toyota OE????
  • swschradswschrad Member Posts: 2,171
    and tell 'em what you are after and how you drive. for real, not what you tell Mom and Dad how you drive. they can fit you with the most appropriate parts.
  • wainwain Member Posts: 479
    I would ask, but some countermen are more/less smart than others, and sometimes there is a promo on "pushing" certain stuff that may taint ones opinion, so I like to read what the company says too.
    In this case compnay has too many choices
  • fleetwoodsimcafleetwoodsimca Member Posts: 1,518
    Well, for what it's worth, I know a pro mechanic who has told me what he recommends for the vast majority of his clients:

    http://www.raybestos.com/pgplus.htm
  • wainwain Member Posts: 479
    Thanxx
  • 94acura94acura Member Posts: 12
    History, 94 Acura integra with 140K on it, did not touch the car for 3 weeks with break handle lifted. The moment I drove it, I hear constant sound from the rear wheels.When I push the break paddles, I can feel the vibration of the break. I then went to mechanics, they changed the pads and rotors and the sound went away for 3 days. Yesterday and today, I hear the same sound again after couple of miles driving( This time the sound is lighter, more like a sqeaky break but only happens at each spin.). After couple of more miles driving, the sound went away. I am wondering if it is a serious problem. Do I need some adjustment for my rear wheels or there is something wrong with the break system? I also checked the break dust of my rear wheels, the left side has more dust than the right side. Anyone can give me a hint? Thanks
  • hengheng Member Posts: 411
    When the car sits for days, the rotors rust. But after driving a little and working the brakes, the rust comes off. That is what I believe is happening.

    The brake dust being heavier on one side is more of a concern. That sounds like a caliper is hanging up but don't jump to conclusions until you get a few hundred miles on the new brakes. They need some use to seat the pads in.
  • acuraowneracuraowner Member Posts: 57
    I have a question, a friend of mine offered to do the brakes on my Neon for $50 if I buy the parts. The Dodge dealership wants $160 plus tax.

    Anyways, I am on a budget and was wondering if there was any recommendation for good/cheap pads. I have made the mistake of getting "the cheapest thing you have" on my Integra and my brakes made all types of noise and did not brake very well.

    I am just looking for standard brakes. Im not into the high performance scene, just looking for quiet but good brakes.

    Thanks
  • fleetwoodsimcafleetwoodsimca Member Posts: 1,518
    Raybestos and Bendix come to mind. Why don't you look into these brands and check the selection of grades and prices? These two companies are known for excellence and a wide range of high quality products, tailored specifically to brands and models of vehicles.
  • bolivarbolivar Member Posts: 2,316
    ...in my area.

    OReilly, Autozone, NAPA.

    Each of these have complete Internet Sites, with parts and prices. You can see various brands and levels of prices, for your specific vehicle.
  • tnjrobi1tnjrobi1 Member Posts: 41
    I have a 96 200SX SE with only 83,000 miles. I've replaced the brake pads twice since I bought the car new. The last time I changed pads I put on EBC Greenstuff pads. These pads have great stopping power, but I'm beginning to hear grinding noises and screeching coming from the front brakes. I pulled the wheel and looked at the rotors and everything looks fine (still plenty of pad too.) So what's making the grinding & screeching noise?

    Please any advice would be helpful.
  • fleetwoodsimcafleetwoodsimca Member Posts: 1,518
    Did you check the rear shoes? I am assuming you do not have disks all around.
  • burdawgburdawg Member Posts: 1,524
    Are the rotors original? If so, have you ever had them machined when replacing the pads?
  • tnjrobi1tnjrobi1 Member Posts: 41
    fleetwoodsimca:

    I thought about the rear shoes. And I changed them. Still have the problem.

    burdawg:

    They are the original rotors and I haven't had them turned. But they seem smooth to the touch. Do I still need to have them turned even if there not scored?
  • burdawgburdawg Member Posts: 1,524
    You mentioned that the pads had been changed a couple of times before, so I assume that your on your fourth set. Probably by now the rotors have a pretty good inner and outer ridge built up as they have worn. It could be the pads contacting these ridges that are causing your noise.
  • fleetwoodsimcafleetwoodsimca Member Posts: 1,518
    ...turn 'em or replace 'em. Maybe you could get one of the brake outfits to look at them for free, and advise you what they think (or what they think you will believe). It wouldn't hurt, and just might reassure you on where you're headed on this deal.
  • roadrascalroadrascal Member Posts: 35
    Hope someone can help me out. I'm going to replace the front brake pads and rotors on my 2001 Windstar fairly soon (rotors are warped at 31,000 miles). According to the Ford factory service manual, the bolts that hold the brake caliper anchor to the steering knuckle need to be replaced with new ones once I take them off. This isn't mentioned in either the Hayne's or Chilton's manuals that I have, nor have I done this to other vehicles before. Other than telling me "because Ford says so", any good reason why I need to get new ones? They're about $4.00 a piece from the dealer (I need 4) which isn't a big deal, except I have never heard of replacing these bolts before. Thanks for the advice.

    Tom K.
  • alcanalcan Member Posts: 2,550
    The original bolts have locking compound on the threads. Replace with new or purchase a tube of Loctite Blue (medium strength) thread locker and use one or two drops on each. Also, clean off all corrosion and rust scabs from the hub flanges to ensure the rotors have no runout after installation.
  • haspelbeinhaspelbein Member Posts: 227
    I have a '97 Ford Ranger (2wd, 2.3L) that had recently developed a slight pull to the right, which I discovered was a slow leak in the passenger side front tire. Since the tires had about 60K miles on them (and were 6 years old), I replaced them all.
    Now the truck tracks straight as an arrow. However, when I apply the brakes there is still a slight pull to the right. It's only noticable when you take your hands off the steering wheel and brake. It is very minute, but it bugs me.

    I replaced the front brakes (pads & rotors about 7K miles ago) and the calipers looked fine at that point. Any ideas what I should take a look at next ?

    P.S.: Happy New Year !
  • fleetwoodsimcafleetwoodsimca Member Posts: 1,518
    I suppose the most likely culprit is the caliper, even though it may look good. I had a 1978 Chrysler New Yorker that pulled right. I let it go until it got so bad that I could detect that it got worse after enough braking to warm up the pads, rotors, and calipers. Visual inspection on "repair day" convinced me not to replace the rotors. I put in new calipers and pads on both sides (of course). Voila! Done deal. Cured.
  • moonshadowmoonshadow Member Posts: 256
    If you are straight with no braking then a caliper may be a little tighter than the other

    This is a common problem when doing brakes that enough people do not pay attention to.

    It may not be the caliper itself, however , rather it is the mechanism that the caliper rides on....

    Check your caliper with a helper. Have them apply the brakes and then release as you watch with a good light to ensure that the piston is coming out and then relaxing when the pedal is relaxed. Watch the piston bootseal for motion. If the piston seems to move in and out(very slighty of coarse, remember that disc brakes work on zero clearences) then your problem may be the sliders or caliper housing rust.

    I normally inspect the sliders/ braces that the caliper housing slides on. If you have a rust build up in this area, it will cause the caliper to either
    1. not relax as much as the other side,

    2. drag, relative to the other side, while pressure is being applied

    As a result when you apply the brakes the sticky /rusted caliper tends to make contact with the rotor sooner than the other side or fetch up and not make as much contact as the other side.

    I like to fit the caliper into the steering knuckle without the pads or rotors and check for drag. I then slip the pads into their appropriate positions and check for fit to ensure the contact points of the metal backing plates of your pads are not fetching up. These should be just right, not tight or binding, its a feel that you get use to. If you can not move or slide them, then your caliper will have a hard time as well. I use a scrapper/wire brush to knock off just the rust and apply a very thin layer of never-seize to these metal on metal contact points to help prevent the rust from re growing. Its takes about an extra half hour to do this but I do not have complaints.

    All caliper units/mechanism/assembly designs are different. You have to analyze your design and look for contact points of the caliper and the pads metal backing plates.
    Pay close attention to the piston pad as it normally moves within the caliper housing and some replacement pads sometimes have the piston spring slightly off which causes the pad to make agressive contact with the inside of the caliper.

    My Father old Dynasty had an interesting problem where the calipers where very stiff to return. It turned out to be a rust buildup under the rubber sleeve inside the caliper which the slide pin/bolts were inserted.(ten year old calipers) I carefully stuck a small screwdriver up under the sleeve around its perimeter to free it from the rust and then pull it out. Used a rat tail file and a fine brush to knock down the rust, slapped in a sliver of never seize, re inserted the rubber boots, installed the pins and presto, I was able to push the caliper back and forth. no more binding.

    Normally , rust build up causing binding or premature pad wear is why calipers get sent back for rebuild, but late at night when nothing is open,one has to improvise. hey, why waste money on perfectly good calipers when a half hour of fiddling fixes you up. Besides, bleeding lines because of caliper change is a bigger pain. If the piston slides well then rust is a suspect.

    Sometimes a ridge build up on the rotor may cause an applied pressure imbalance as one set of pads come in contact with the rust ridge sooner than the other, however, the pull is only noticed at first and as more pressure is applied then the car goes straight. nevertheless you got new rotors so that is probably not your issue.

    Some things to check for and good luck.

    Make sure you keep your pads and rotors clean of never seize finger prints. If you do a good brake cleaner washes it up good. Remember, just a sliver, enough to wet the metal contact points. If you dont have never sneeze then any greese will do.
  • fleetwoodsimcafleetwoodsimca Member Posts: 1,518
    Some years ago, I bought a tube of brake caliper slider lubricant from NAPA. It is purpose packaged and sold, and replaces antiseize. It is great stuff, but the tube it came in proved weak. I continue to use it every time I do a brake job.
  • moonshadowmoonshadow Member Posts: 256
    Sounds interesting. I'll check it out! Sometimes when you find a good solution you tend to stop looking for something even better,,,

    Man these boards are great. Nothing like first hand experience.
  • haspelbeinhaspelbein Member Posts: 227
    I was afraid that the calipers may be the reason. I doubt that the rotors or pads are to blame, as their are essentially new. I may first give them a good cleaning, though.
    If that doesn't help, I may have to find myself a compessor and get the calipers out of the brake shoes.
    Also, thanks a lot for the reference to the brake slider lubricant.

    Martin
  • fleetwoodsimcafleetwoodsimca Member Posts: 1,518
    From your user profile, I noted you might be living in Alberta. Speaking of brake work, about 27½ years ago, I got an emergency brake job done at the International Harvester company store in Grand Prairie. I was on my way to Alaska. What a great group of people they were. I still look back on the experience with gratitude.
  • moonshadowmoonshadow Member Posts: 256
    Nope. New brunswick.

    When I signed up several years ago I selected Canada and I guess I just breezed over the rest.

    While checking my profile I see that the first state/ province is Alabama. Funny that the system didn't catch me on that. Oh well I have edited it to properly reflect correct data.

    Thanks for the inadvertent heads up.

    Places like the outfit you found are great. Its to bad all shops don't work the same, they would; get better mileage.

    My brother travelling through ontario lost the fuel pump in his van and managed to be towed to a Canadian tire 10 minutes before they closed up .

    The buddy there, stayed late to diagnose and then drove the family and all their luggage to a hotel, Arranged to pick up a new pump from a junk yard as the local dealer had none in stock. He came in early the next day with the pump, set everything all right and then called my brother and picked him up.

    My brother was extremely grateful and wrote a letter to CTC about this guys above and beyond the call of duty. They sent him back a letter stating that buddy was going to get an award for his efforts.

    When my brother was telling this story when he got back, we were all waiting for the shoe to drop because the service was so unbelievable good. He just plain luck out big time. People and places like this and yours need more recognition because they are a rarity.

    When any place treats me right, I always try to talk to the manager and let them know. They love it because they normally get negative feedback only.

    Thanks again for the heads up.
  • fleetwoodsimcafleetwoodsimca Member Posts: 1,518
    I'll update mine, too!
  • craniumcranium Member Posts: 40
    Ok, I know I posted this months ago, but the problem has gotten worse. I have a 1989 Buick Century, newish brakes all around (maybe a year ago). This car is my winter car, so was driven every couple of days over the summer, so I could work the bugs out.
    Over the summer, when I went to drive it, after it was sitting for a few days, the rear wheels, prticularly the right rear, would lock up. I would ususally drive in reverse, tapping the brakes, and this would fix the problem. If not, after a few sloooooow stops, the locking up would go away. If I drove the car everday, I almost never had this problem.
    Now, it's winter time. Snow is on the road, and this car is my daily driver. I'm getting the same symptoms every day. It's extremely dangerous now with alittle snow on the ground, the rear tends to lock up too often. Again it goes away after a while, but now it happens in the morning, when I go out for lunch, when I leave work, etc. If the car sits for more than a few hours, I have this problem.
    I do not want to put ANY money in to this, as I'm going to sell it or use it as a trade in the spring. I've had "brake specialists" look at it in the summer, and they adjusted it, but nothing has resolved the problem.

    Please let me know what you think.
    Thanks, and sorry for the long post.
  • fleetwoodsimcafleetwoodsimca Member Posts: 1,518
    It surely sounds, doesn't it, like something is contributing to not allowing the brake fluid to move in the direction of the master cylinder. Instead, something like a bad wheel cylinder, or a partially obstructed brake fluid line is holding pressure in the direction of the wheel, and acting like a temporary one-way valve. Your economic position on the matter sounds very reasonable to me. So, it would appear you must find the "obstruction" and eliminate it, or just nurse the poor old thing along until spring...
    By the way-- right now is a good time to buy cars. The market is depressed. Were I you, I'd be shopping not later than this afternoon. (:o]
  • craniumcranium Member Posts: 40
    I would love to go car shopping this afternoon, but we have a new little one in the home, and i'm the only one working. We need to wait 5 more months, then my Jetta is paid off, and that will free up some funds for an Odyssey, or Sienna.

    I'm not sure if there is a problem with the fluid returning to the MC, because the wheel releases as soon as I take my foot off the pedal. The problem really is, when I touch the pedal, the rear lock up, before the front even start to grab. I was thinking that I should try to bleed the rear, but I figure the "brake shop" would have already done this simple task.

    Is there possibly some kind of brake proportioning valve or something?

    BTW, I'll probably sell this car in March, before the inspection is up (I'm in NY), and we'll trade in the Civic for the honda or toyota van
  • fleetwoodsimcafleetwoodsimca Member Posts: 1,518
    I should have gone back and read the history, but I didn't! Your right. That sounds like a proportioning valve gone bad, or at least a junction block with a problem that favors fluid going to the rear at the expense of the front. It still has room to be a partial blockage, just located in perhaps an even more unfriendly place. Take a look very near the underside of the master cylinder and trace down from there as far as you can to find a "splitting block" in the line/lines. I still think your time would be better spent looking at new cars!
  • craniumcranium Member Posts: 40
    Well, that's not what I wanted to hear! If it's easy, and I can do it for under $20 I'll fix it. I couldn't find "proportioning valve" at napaonline, or autozone. That is what it's called right? Any idea what this part would cost? I won't have a chance to look under the hood today, probably tomorrow after work.

    Are you a salesman fleetwood? :) You really want me to buy a new car don't you? hee hee hee..
  • alcanalcan Member Posts: 2,550
    Proportioning valves rarely fail. More likely the rear brake shoes.
  • bolivarbolivar Member Posts: 2,316
    On this vehicle you probably have drum rear brakes.

    I also don't think a Proportioning Valve would do this. These valves usually only separate the front disks from the rear drum, so problems would effect both rear wheels.

    My guess is something is mis-assembled, broken, rusted up, and/or bent on one of the rear wheels. The one locking up 'might' be ok, with the problem in the other side.

    The pins and springs that hold the brake shoes to the backing plate should be all examined. If a pin or spring is broke, missing, or bent it will cause very nasty 'grabbing'. The contact points where the shoes contact the backing plate should be checked and should be greased to allow them to 'move' on the backing. The entire set of cables and springs should be checked for correct installation and freedom of movement. The auto adjusters should be checked - one could be adjusted out much too far. Or one side might be adjusted in - too loose - and this side is not contributing to braking at all.

    In other words, everything on the rear should be checked. By someone that knows what they are doing, and will and can fix the problems found.

    If this has been happening for a year, and the brakes are a year old, I bet someone did a bad job of re-assembling them. Or a pin/spring has broken.
  • moonshadowmoonshadow Member Posts: 256
    Lots of good advice coming. here is some more.

    Does sound like a rear mechanical type problem. Depending on year the proportional valve may separate the LF and the RR from the RF and the LR, ie diagonally.

    Nevertheless, like bolivar suggested, your first and easy step is to check your hardware. The fact that backing up and braking temporarily fixes you up would indicate this, as this is how the majority of the self sticking useless self adjuster are supposed to work.

    Commonly as well. the emerg brake cable should be checked for motion. This cable connects to the emerg brake lever which then connects at a pivot point near the top on the rear shoe. Very common seize point for idle shoes. Play close attention to the cross bar that slides under the cylinder and makes contact with both shoes. The ends are notched differently and must go in the right way.

    You should as well, check for a sticky piston . Do this by pushing on one shoe to drive the piston in and watch for the other side to move out. Then push on the other to accomplish the same as before. They should have equal pressure. The cylinder is mearly a hollow tube that recieves fluid from the rear and pushes out the two piston in opposite directions when pressure is in the line.

    The only other thing inside the cylinder is a light spring pushing each piston outward when no pressure is present. Therefore, pushing on one piston will cause the spring and fluid to apply tension/force on the other and make it slide out the other end. This is easier to see if your new to it if the shoes et al are removed. Note: do not push one piston in so far as to cause the other to pop right out of its boot, make a mess of fluid and a bleed process..

    Ie: if you hold one fixed and push on the other it should push itself back out. Idle brakes may cause a rust ridge to build up on the piston walls and bind them.

    Long story Good luck.
  • moonshadowmoonshadow Member Posts: 256
    Remember with a disc/drum setup, the front recieves from 60 to 80 percent of the braking power. As you may know the disc works on zero clearance and the back does not.

    The pads are virtuall resting on the rotors and need only a few thou of travel to make contact, where as the drums have anywhere from 1/32 to 1/8 inch clearance (depending on how they are adjusted). They also pivot on an arc so that the shoe surface gradually makes contact with the drum

    This means that if your drums are activating instantly, then some thing is probably stuck in there or is not assembled properly. Of coarse something could be blocking that line, or another could be blocked causing all pressure to be going to that one wheel as fleetwood suggested.

    Without actually seeing the problem we are just hypothesizing
  • craniumcranium Member Posts: 40
    Yes, I do understand how the drum brakes work, so I guess that is a start. Over the summer, I did take the wheel off, and inspected everything on the wheel that "normally" locks up (I say that because if it's slippery, both will lock up quite easily). Everything looked normal, and I did test the cylinder to see if it was fried. It moved back and forth smoothly, so it's not, well, at least not on that side. Looks like I'll take it to Monroe this weekend, and have them do a "free" estimate for me, and then I'll fix myself. But like I said before, others have looked at it and they could not find a problem.

    I'll also go to the library today, and take out my trusty Haynes. Keep the suggestions coming guys!
  • moonshadowmoonshadow Member Posts: 256
    Curiouser and curiouser. Is that ever weurd.

    I would be interesting to see if the front wheel on the diaagonal to your rear locking brake gets
    pressure when the pedal is applied. LIft that wheel off the ground and have someone do the pedal and see if the wheel get braking.

    Since you have verified all the mechanics to that wheel then you very may well have a blockage /defect in the fluid distribution.

    How dark is the fluid in the resovoir?

    Very wierd and very interesting.
  • craniumcranium Member Posts: 40
    it should be red/pink right? I can safely assume tht this is the original fluid in the car, and should I also assume that it's dot 3, so it does absorb water after a while right? Would old fluid cause this? I would think that if it was because of old fluid, it would have symptoms (not necessiarly (sp?) this symptom) at all 4 wheels.

    Concering the front left getting power (assuming the proportioning valve is the diagonal type), wouldn't I feel the vehicle pull to one side or the other if one of the brakes up front were stopping and the other wasn't?

    I'm still baffeled
  • moonshadowmoonshadow Member Posts: 256
    Definitly a baffling problem for sure, until its solved.

    The fluid new should be clear. 12 year old fluid has probably discolored to the a dark brown.

    It will absorb water and this causes the metal lines to form corrison with causes the fluid to rust up. Yeh, you are correct that it would pull I was just surmissing on a guess that if the one front or both fronts were plugged some how, then your back would get all the juice. Very wierd though.

    A couple months back a buddy came to see me and he had about a 1/4 inch of sediment at the bottom of the masters resavoir and the fluid was the color of a 10000 mile oil change. He had no problems except a emerg cable stuck, but we cleaned out the crud and bleed the whole system anyway.

    With all this crud he had no blockage problems. If your fluid (guessing again ) is crudy then perhaps just one line or the front could be plugged who knows. Its like your blood, you only seem to get one clot or plugged artery at a time until they eventually one by one plug up.

    To eliminate the plugging possibilty yo u could open up each bleeder screw and have someone push the pedal and check for flo. Providing the bleeder hole is not plugged up with rust.

    at this point , it could be any thing. Start with the simple and work your way up to magic. If i was a gambler , i think my money would be on the rear mechanism though. Very strange , very interesting.

    Good luck
  • alcanalcan Member Posts: 2,550
    Every car and light truck sold in North America since 1967 has a dual or tandem brake master cylinder and hydraulic system. RWD vehicles split the hydraulics front-rear. FRW split the system diagonally, one circuit for the left front and right rear, the other circuit for right front and left rear. A proportioning valve (2 required on FWD, one for each rear circuit) is used to limit rear brake pressure under medium to hard braking, to prevent premature rear lockup at higher speed due to weight transfer from the rear tires to the fronts. Up to about 500 psi system pressure (the split point) the prop valve is wide open, no restriction to flow to the rear brakes, wheel cylinder pressure is the same as master cylinder and front caliper pressure. Above the split point, the prop valve starts operating, limiting any additional pressure rise in the rear brake circuits to about 70% of any additional master cylinder pressure rise (the slope). So a master cylinder and front caliper pressure of 600 psi results in rear brake pressure of about 570 psi; m/c at 700 psi, rear brakes at 640 psi; etc. It ain't a proportioning valve causing this problem.

    GM has had a chronic problem with rear brakes locking up on some carlines, primarily because they've retained the duo-servo design brake. Almost everyone else uses the single anchor type. To fix it, there isn't a silver bullet. Look at rear shoes out of adjustment (most likely, and probably caused by seized up star wheel adjuster and/or parking brake, as previously mentioned), cheap shoes (probably), weak return springs (it's old, so are the springs), and poor drum finish, in that order. Every GM with rear lockup concerns that I've serviced has been corrected with new Delco shoes, new spring and hardware kit, machine drums, and proper assembly and adjustment.

    Btw, brake fluid should be a clear, amber colour. Dark fluid indicates lack of maintenance and is full of water. More info on that here:
    http://www.batauto.com/articles/brkfld.shtml
  • swschradswschrad Member Posts: 2,171
    if you have dark fluid, have it all purged now, and THEN start replacing bad parts as you find them. bleeding from that point on will clear the little crud you dislodged from the bad part right away. you don't want to be pushing rust and sludge and little mystery chunks into the new parts by purging the rotten rusty wet old fluid after they are installed.
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