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Chevy C/K Series Maintenance and Repair

69flh69flh Posts: 10
edited March 14 in Chevrolet
I have a 1990 K2500 Chevy pickup with RWAL.
I have had problems for quite sometime with the right rear wheel locking up when applying the brakes. I installed new rear shoes and it really compounded the problem. I then installed a new master cyl. & wheel cylinders and the problem still exists. Sometimes it feels as though the drum is warped as I get a vibration when applying the brakes but not always. I checked the drums and they are within .010 roundness. Is there any way to check the combination valve? This valve is pretty expensive and I hate to replace it and still have the same problem.


  • PF_FlyerPF_Flyer Pennsylvania Furnace, PAPosts: 5,854
    We were in need of a "problems & solutions" topic for C/K series trucks, so I'm going to rename this one to make it the general problems topic where ALL C/K problems and fixes can be discussed...

    PF Flyer
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  • catamcatam Posts: 331
    It actually sounds like your wheel speed sensor may be bad. This is the sensor that tells the ABS whether or not the wheel is actually turning. I would check that next.
  • dustykdustyk Posts: 2,926
    A bad speed sensor would be my first guess, too, but if I understand the problem correctly I would suspect the one that's bad is on the other side.

  • 69flh69flh Posts: 10
    From what I can find this truck has one speed sensor located on the tail shaft of the transmission. I have not been under the truck yet to look at it and was wondering if anyone knows what is involved to replace it?
  • akjbmwakjbmw Posts: 231
    Do you know that the left rear wheel brake is working correctly? Getting less pressure?
    If one wheel locks and the other doesn't, the drive shaft will turn twice as fast.
    If the sensor is on the drive shaft, it would see increased speed and apply some strange engineered logic control? It could be comparing front speed to rear speed and reduce braking to the slower of the two. If there was a weak/blocked pressure on one side, the problem could be exaggerated. How are those flex brake hoses?
  • 69flh69flh Posts: 10
    Lines look good. When I bled the brakes, the fluid coming out of the bleeders did not appear restricted. You are right about "strange logic control". Sometimes the brakes really act up, especially when wet. Other times they are fine.
    I am still wondering about the combination valve,
    (the proportioning part of it.
  • dustykdustyk Posts: 2,926
    I'm sorry, my brain was turned off when I sent that last message.

    Many manufacturers with RWAL Brakes only use one sensor. Dodge uses an encoder (they call it the exicter ring) made out of steel internal with the differential and mount a sensor on the rear axle housing.

    Since Dodge uses the GM-made American Axle on some of its trucks, I suspect yours is the same way.

    So, I take back what I said earlier. You could have a pinched brake line on the side that isn't over-applying. If you've inspected everything at the rear brakes on both sides and everything looks good and operates static, then I think you'll find you have a bad hydraulic control unit (HCU) or ABS Control Computer. Since it is a GM product I think this HCU high on the suspect list. I've seen quite a few of them fail.

    Good luck,
  • bassmanbassman Posts: 1
    I have developed a "bearing knock" when engine is cold. Noise goes away after warm up. These is a Tech. Service Bulleton on this problem. It is TSB #99-06-01-003 issued in April 1999. Does anyone have any information as to what the TSB says?
  • mcmike06mcmike06 Posts: 1
    Hey to everybody out there. I just recently (as in tonight) came across a problem with my 1990 Chevy C1500. This is what happened, I went outside to my truck & got in it started it up & moved it out of our driveway then I backed into our driveway except when i shut off the truck & got out my tail lights were still on. I have looked all around the truck for problems that I could see & I saw none. I was just wondering if anybody had any idea as to why they wont go off or what's causing this I would really be thankful for it.
  • rayt2rayt2 Posts: 1,208
    The TSB says it's normal and no fix required. Did'nt you always want a truck that sounds like a diesel when it first starts up ? It's not the bearing knock but rather "piston slap" do to poor design, tolerances are to loose when cold, when it warms up they expand and piston slap goes away (on 90% of them). My knocker has 48k so far and only makes the noise during cold startup. I had read of a fellow knocker turning over 100k on his with no ill effects other than embarrassment.

    MCMike: The tailights were known on the older trucks 1988 & up to corrode the curcuit board on lamp holder. I had same problem on my 88. You need to replace taillamp holder assembly with upgraded unit. The holder unscrews from the lense once you take the entire unit off truck. Another problem was that the lights would melt the lenses from the short which kept the lights on all the time.

    Ray T.
  • catamcatam Posts: 331
    Is it your tail lights or brake lights??
    If its your brake lights check the brake pedal sensor switch to see if its working properly, I had this problem once on a GM car.
    If its your tails lights see the previous post.
  • 69flh69flh Posts: 10
    I have a 1990 K2500 with the 4 speed, (granny gear), that is making a rather loud clicking noise in reverse while in 4 wheel drive. I do not notice it in 2 wheel drive. Any ideas??
  • rojo87rojo87 Posts: 2
    The temp gauge on my '87 silverado is stuck on max hot even when engine is cold and ignition off. The oil needle also fluctuates wildly but mostly stuck on max. Approximately 500 miles ago I had the heater core replaced and a/c switched over from freon to another type (can't remember the R#). All of this was done by my local Chevy dealer.

    Any idea what would cause these gauges to suddenly start acting act so strangely?
  • I have a 02 Chev Duramax w/ ALLISON, after 25000 miles suddendly @ startup no power brakes or steering, locked up for @ least 20 minutes , called dealer, checked out fine w) no codes, occured again & again, Dealer said no TSB on problem, finally bulletin came out & Chevy said there was no fix & would have to live with it,
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,391
    You'd have to "live with it?!" That's one way of losing customers....

    While I'm here, can anyone tell me if the lug bolt pattern on the C20 has changed over the last 35 years? I have a 1969 C20 camper conversion w/ step side long bed that has 68K original miles and all original equipment. Having original rims and hubcaps is great, but it makes for expensive tires. Living in Fairbanks, AK, I have considered for many years to get a set of winter rims that were more up to today's standards. The 16.5 rims make it difficult to find tires and when I do, they are expensive. I don't typically haul too heavy of loads in the winter other than the 900 lbs of sand to give me enough traction to stay on the road, so a rim/tire set wouldn't need to be capable of the load rating 'D' I use now.

    Any suggestions?
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,391
    Is it possibly a fuel filter issue? Not sure what year of truck so I'm just going with basics here.
  • This is a 1998 Chevy full size pickup. Would the fuel filter cause pressure to build up in the tank? Or could it be the evaporator box that one of the lines run to under the hood?
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,391
    Admittedly, I am well out of my element with a '98. I was queing in more on the hesitation than the tank presssure. My '69 will hestitate when I punch the pedal to pass, etc, if the fuel filter gums up at all. I think the filter is either undersized for the vehicle or it is suffering some minor but continuing ill effects of having sat for 20+ years without use....

    Just thinking about it intuitively, it doesn't seem like tank pressure should negatively affect the flow of fuel to the engine - vacuum, yes, but pressure, no. But, with all the interconnected electronic gizmos and sensors on vehicles anymore, who can tell? You might check a repair manual for your rig's year to help figure out what systems are in place for evaporative control. I know that mine breathes through the gas cap, but newer ones probably try to internalize the evaporation to prevent fumes from escaping the vehicle. There's likely a block in the evaporative system somewhere and if you had some diagrams to help lead you through an inspection, you might find the culprit.

    Good luck!
  • xwesxxwesx Fairbanks, AlaskaPosts: 8,391
    Oh, and thinking about it a little more, if there WAS a block in the system and it was a negative feed system (meaning that vacuum draws the gases through the system), perhaps it IS causing the hesitation because the vacuum is too strong on the up-system side of the block. So, you're getting increased vacuum on one side and increased pressure on the other.

    Just some thoughts.
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