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Chevy Silverado/GMC Sierra's w 8100/Allison



  • 4x4man4x4man Posts: 222
    Not sure where else to find info on the 6 speed setups, you don't hear much about the 6spd in the gasers....sorry no help to you there.

    Upgrading is all up to you, however I don't think I would want a half ton pulling 6,000lb loads every few weekends, like a camper or boat or something like that. Sure the truck can move it, but after a while, the stress on the drivetrain wear it out not to mention your nerves. Trust me, been there done that, never gonna do that again!! We upgraded our truck because we knew we would be selling the boat and buying a 5er sometime. As it turns out that sometime is this year!! Glad I have a truck that I know will pull this 5er. It weighs about 7500 lbs before food, gear, etc. I figure after the wife gets done loading all of the "necessities" we will be close to the GVW of the trailer at 10,000lbs!!

    By the way I got the 4.10 gears in my truck because I was planning on upgrading the tires. I am getting the same mileage as others with the 8.1L and 3.73's and other people are reporting the same thing. Get the 4.10's and don't look back!!

  • kg11kg11 Posts: 530
    If you want a 8.1/6 spd you'll have to order it.I paid invoice for my 8.1/Allison but the best deal I could find ordering one was $1200 over invoice and a 3-4 month delivery time.
  • noobie1noobie1 Posts: 326
    Am I reading you right? Cheverolet does not require speedo or ABS recalibration with 265-75 upgrades?
    And, what exactly does overly sensitive ABS feel like?

  • wheeler2wheeler2 Posts: 13
    You have answered some of my questions. Thanks for the towing advice, after my experiences I really had to wonder about the viability of towing the large loads I have read/heard about with 1/2 ton trucks. The trailer I may be buying is about 6000 GVW plus toys in the truck bed and passengers = another 1000. We're supposed to be calming nerves not frazzling them! Your comment about 4.10 gearing and mileage is interesting, it also helps insure one will be able to tow whatever they need to. If I understand the GM propaganda brochure, if I buy the six speed the only axle ratio available with it is the 4.10?

    I ordered my '99 Ram QC and paid invoice, I like ordering because I get what I need/want and don't have to fight with a salesman over bells & whistles I don't want to pay for (and I don't mind waiting). Planning on ordering a 2003, will be checking some of the other discussions to see if there is early news on changes and improvements. Hopefully I will be able to get close to invoice again.
  • mikeusnmikeusn Posts: 1
    REF: Msg 349 Experienced the same, exact thing. Immediately after starting up, and before putting the vehicle in gear, a loud clunk came from what I thought was the rear end. It caused me to look in my rear-view mirror where I saw a guy exiting his car parked behind my vehicle. My first impression was that he bumped me while parking his small, insignificant automobile. That was not the case though. This has happened only one time, and I hope it is not a recurring thing.

    Vehicle data: 2001 GMC 2500HD LT 8.1L w/Allison transmission.
  • kanton1kanton1 Posts: 41
    There is a bulletin out about the clunk. It is the intermediate steering shaft that is making the noise. The bulletin is for a "lube job." It does not solve the problem, however it does make it a little better. I had my done about three weeks ago. Also, GM says the rattle is a bad bearing somewhere in the upper steering shaft or steering box?? Supposedly working on a fix, should be out soon.

    MPG... most of these HD speedometers are reading fast by 2-3 mph with the stock 245's. There are big discussions over on the about this. Many of the guys are comparing speedo to their GPS units and finding the diff. My speedo reads 3 mph faster. Now if I up graded to 265's my speedo would be just about perfect.

    Also, remember if the speedo is reading fast, we are actually getting better MPG that what we believe and we are getting to the end of our warranties sooner than 36K!! Hmmm...something to ponder!! A GM money saving scheme?

    Good Luck,
  • noobie1noobie1 Posts: 326
    Good points. I've long suspected this speedometer indicates faster than actual, although 2-3 seems light. It seems more like the error is a percentage: the faster the 'wronger'. Are you indicating 3 mph error throughout? I've had the same thought about 265's, except for the possibility of some critical oversight, which is why I'm quizzing 4x4man in regard to his comments about recalibration not being necessary. I've also heard here something about the Allison needing correct input from the speedometer for proper cooling during towing, but really have no clue about it. I guess a stop by my dealer and see if they have one.

  • 4x4man4x4man Posts: 222
    Sorry for the late reply, didn't have internet access for a while...

    I didn't say Chevrolet does not require recalibrations for 265's, just stated it wasn't necessary, I should have stated it was my opinion, sorry. Chevrolet doesn't even want you to upgrade your tires. In fact there is a tsb stating if you are complaining about performance or transmission shifting you must have the 245's on before they will even look at it.

    I have not checked my speed with a GPS, but have read that the rolling distance between the 245's and 265's is so little (like 2% or 3%) that it is not necessary from other peoples opinions to recal, that is why I didn't. Sorry should've explained better in my earlier post. You can have the speedo recalibrated for 265's, at least that is what my service manager told me. However it is $100!! No thanks, I'll put that towards the higher gas prices thank you.....

    To clarify the over-sensitive abs I had and others have reported. It is when you are braking and go over the slightest bump and your abs kicks in pulsating the brake pedal and then not applying as much force to the brakes so you don't slow down as quickly. Now with the 265's when braking going over minor bumps or expansion joints, the abs does not kick in extending my stopping distance. Hard to explain I guess, but when ever my abs kicked in with the 245's on dry roads, my stopping distance increased!!

    I didn't notice any shifting issues from the Allison going up to 265's. I have a hard time believing there would be a cooling issue with the Allison while towing or empty as the 265's don't decrease your rpms by much, maybe 200 rpms?? I am not an expert, but the two Allison guys on the diesel page haven't stated that it will be a problem. I think one of them even has upgraded his tires to 265's or 285's!!

  • minikinminikin Posts: 389
    change was noticeable to me in both shift points and braking. Thought maybe I was imagining it until I recalibrated the truck. But when I did, I dialed the speedo in dead-on, so the difference may have been a bit larger than just the change in tire size.
    -- Don
  • 4964me14964me1 Posts: 15
    Anybody done the oil change themselves? I haven't been inder the truck yet, but I'm hoping the filter is in the same place Chevy always put it in their V-8's. Anybody out there know how many grease fittings there are, and where they're at? (i.e., upper and lower ball joints, inner and outer tie rod ends, pitman arm, idler arm, & center link/etc.) Also, that Alison filter is just a spin it off - lube the gasket - spin the new one on - add 1/2 qt. deal, right?

    Can't see paying anyone to do that when I can do it myself in 10 minutes.

    Do they ship the Alison with synthetic ATF? The owner's manual talks about the Castrol transynth or whatever it's called, but it doesn't say if that's what's actually IN IT. I figure I'll just prime the filter (fill it) first, especially since that Alison supposedly has circulation problems anyway.
  • eric2001eric2001 Posts: 482
    The oil filter is on driver's side (right above the front drive shaft - unless you have 2WD) in the usual location. I use a piece of aluminum foil to direct the flow over the driveshaft into the catch bucket. Think you covered the grease points, also check if you have any on the universals or the carrier bearing (2 piece driveshaft).

    As for the transmission filter, there is a magnet on the filter that needs to be removed (right on the top around threaded hole) cleaned & placed on the new filter.
  • noobie1noobie1 Posts: 326
    To add to Eric's comments, just crawled under my truck (2500HD,4WD) to double check. Ten fittings in all; upper and lower ball joints plus six across the steering linkage. One piece drive shaft, u-joints are sealed. A reminder: careful about screwing on those new filters. Being new to GM, I just went through a real tussle removing the filter I replaced on the last (my first) change. The instructions on the Delco box indicate after lubing the gasket well, contact plus one revolution. THAT'S TOO TIGHT! I tried five different wrenches before I found one that would work; Actually broke one of them. The winner was a geared, three pronged devise that fits over the bottom of the filter (NAPA, 6.99). The gears work to tighten the grip the harder it's turned. Though it accepts a 3/8" drive, I put a 1/2" adapter and extension on it and cranked it right off with a torque wrench. I screwed the new one on, contact plus one half revolution. We'll see how that works.
    I also replaced the Allison filter and, as has been stated here previously, it pays to shop. I got quotes from GM ranging from 18.00 to 44.00. An Allison dealer charged 8.25. I bought three. By the way, Allison told me #29537268 has been discontinued. The new number is #29539579. I can see no difference from outside appearance.
    If you'll check your manual, (page 7-27) you'll see that DEXRON-III is the prescribed fluid. Castrol TranSynd is the recommended fluid if you switch to synthetic. There's a lot of information about it on the Allison site. Happy wrenching.

    Bob; Thanks for the info. No problem about the wait. Because of my situation I also have limited access to my computer. I stopped by my dealer today and asked about recalibrating the speedometer after a 265 upgrade. At first they were all, "Yeah, yeah, ABS" and "computer controls everything and yada, yada". But when I pressed, "You mean for just one tire size"? they were'nt quite so affirmative. I'll just keep checking.
    BTW, does anyone know of or if GM techs use an all-in-one device for diagnostic and recalibration? If so, what is it? Cost? Thanks.

  • noobie1noobie1 Posts: 326
    Additionally, haven't experienced any of the ABS sensitivity you describe.

  • I have 14K miles on my 2001 8.1 Allison Crew Cab 4X4. Have had piston slap getting progressively worse along with oil consumption getting right at 1qt per 2K miles. Did a boresope inspection on the cylinders and found deep vertical scratches in #8 along with 10 PSI lower compression. Of course GM says its "NORMAL". The new (last spring) GM TSB on oil consumption states usage up to 1 QT per 2K miles is normal for all their engines with less than 36K miles if in a vehicle of less than 8500 GVWR. Does anyone know what they consider "NORMAL" oil consumption for the HD? Does anyone know what other manufacturers consider to be "NORMAL" oil consumption? Theres a lot of good info on Piston SLap along with a .wav file where you can listen to it at
  • 4964me14964me1 Posts: 15
    Nice site. So you've confirmed what we all suspected all along, these motors are beating themselves to death. My experience was nearly identical. I took it in, and the service advisor listened to it, said "Yeah, there's definitely something wrong with it. I had my manager check it out, too. We even started one on the lot, and that one was quiet." BUT when I got all my paperwork back, my invoice said "COULD NOT DUPLICATE CONCERN; NO ABNORMAL NOISE HEARD" Which they subsequently refused to change, because "Once it's in the computer I can't change it." They also put me on an "Oil consumption watch", which they remedied by overfilling the crankcase by almost a quart. I went to a second dealer, who wrote WORD FOR WORD the exact same thing on my invoice, but told me later that it was an piston condition where there's some abnormal contact with the cylinder walls. They tend to "rattle around a little until it warms up" Well, any idiot knows that ain't good, but they INSIST that it's a "NORMAL CHARACTERISTIC" of that engine, and it's not detrimental to the life of the engine. Basically all that means is "GM is going to gamble that the warranty runs out before your motor explodes"
    Well, now that I've heard everyone is getting the same BS, I'm even more pissed than I was before. $37,000, and they can't build the fu&king motor right. GM won't do anything, and they've got the dealerships reading right off the script.

    Here's my idea.
    Send an e mail to:

    If they get enough of them, they'll listen. General Motors + consumer fraud = BIG STORY.

    Send a letter to the EPA. (Defective engines getting 10MPG, burning oil) they'll have a field day.

    Then, try:

    60 Minutes
    524 West 57th St.
    New York, NY 10019

    You seem to be on the right track, but a few dissatisfied customers obviously mean nothing to GM. When 60 minutes comes knocking at their door you can bet your [non-permissible content removed] they're going to start doing something about it, though.
    BBB doesn't work, lemon laws don't work, let's see if bad publicity works.
  • 4964me14964me1 Posts: 15
    Hi gang:
    Just got an e mail back from the folks at Dateline. Sent them the whole stiry. Apparently, the e mail adress is only for correspondence on show topics that have aired already. They DID say that if you have a story idea, send it to:

    Dateline NBC
    30 Rockefeller Plaza
    New York, NY 10112

    The more letters they get, the better chance we ALL have. I'll tell them about MY experience with the dealerships and GM being less than helpful, but unless you guys do it too, it's really not a story. One guy with a bum truck? So what? But 10? 100? Now we're talking. Come on guys, what's one more letter? Who wants their truck fixed?
  • gmctxguygmctxguy Posts: 1
    I have a 2001 GMC 2500HD 4x4 w/8.1 Allison, and just put on a new set of 285s, but need some tips on where to get the speedo recalibrated (new to site, sorry if already discussed).....Hypertech Programmer III won't work with Allison tranny so SOL there for the recalibration and shift pt adjustments. (Truck sure looks good with those bigger tires!) Any ideas?
  • For folks who are interested, there is now a borescope photo of cylinder bore damage caused by piston slap on a 2001 8.1 Liter GM engine with only 14K miles in addition to the .wav file of the sound at

    This is the only knocking cylinder which is approximately down 10 PSI on compression when compared with the average of the other cylinders. The engine knocks at all temperatures (although louder at cold start) and is now using approximately 1.2 qts per 2K miles of oil. Borescope inspections of the other non-knocking cylinders showed only the original factory machining.

  • I've read about the GM 6.0 and 8.1 engunes experiencing piston slap. Now a borescope picture confirms that a cylinder is damaged in just a few miles. Wake up and smell the roses GM field reps. There is definitely a problem! I know that sticking your head in the sand is a good career survival technique but.... there are a lot of good folks out here who need your help! Corporate snobbery isn't going to further GM's plan to better serve their customers. If you want to be aloof, get a job in another field. T o those who are experiencing problems; why not get a consumer fraud lawsiut going as a class action? All it take is a leader and organizer. GM doesn't like those kinds of actions happening or getting adverse publicity in the media.
  • rmartin3rmartin3 Posts: 10
    I enjoy the board. I have found the truck I want...8.1L, 2WD, long bed, single wheel, BUT with 3.73. My '96 GMC with 4.10 gear 7.4L (290HP, 410 ft/lbs) pulls an 8500# travel trailer great. Any idea how to compare the ability of a 4.10 7.4L to a new 8.1L with a 3.73? Would I be getting as much towing ability (uphill towing grunt)? Thanks for the help
  • kg11kg11 Posts: 530
    The Allison 5spd trans that comes with the new 8.1 has a much lower 1st gear than the previous A/T ,so you won't loose anything off the line.If you have the 5 spd stick,the new 8.1 is available with a 6spd but not here in CA so I never got a chance to compare.


    BTW I got the 4.10 gears and avg 13.3 @70 mph and REAL BAD MPGs in town with my lead foot.
  • 4964me14964me1 Posts: 15
    With more HP (340) and torque (455), the 8100 should handle anything you can throw at it. It's spec'd at 12,000 lb towing capacity with your configuration. I went with the 3.73 on mine, figuring I'd save a few MPG. I get 9 around town, and close to 12 on the highway (empty). If I knew all I was going to get was 9MPG I'd have gone with the 4.10, not because you need it, but just to give me a little more off the line. If you liked your 454, you'll like the 8100. (provided you get one that doesn't knock)
  • rmartin3rmartin3 Posts: 10
    I just bought the chevy 2500HD long bed, 8.1L, crew cab I mentioned a couple of posts ago. Outstanding so far (after 2 days). I lost the directions to my Kelsey brake controller. It has 4 thick, white, blue, and black. Would anyone know where to connect these wires to the included brake wiring harness, which has a thick red and blue, and thin light blue, black, and brown wires. I am a novice at this kind of thing. Thanks for any help
  • eric2001eric2001 Posts: 482
    Red is your connection to brake lights (switch)
    Black is battery positive
    White is battery negative (chasis ground)
    Blue is connection to trailer brakes

    These connect to factory harness (if you have) which are labeled on the harness. The brown wire (illumination) is not used, and if the trailer has a battery connection, the 40 amp fuse gets plugged into post #1 in electrical center under the hood.

    The factory harness gets plugged into connection @ top left of the panel under dash at driver's left foot. There is a cover which needs to be removed to see. Remove plastic nut holding cover in place, connect harness & reinstall cover.

    Hope this helps.
  • nomoregmnomoregm Posts: 158

    Seeing as Anti-GM sites are on the endangered-species list 'round here....Come, join the carnage!

  • rmartin3rmartin3 Posts: 10
    Hooked up the brake controller great.
    In my '96 7.4, 4.10, while going up a big hill while towing, I would downshift to "low 3" and the transmission would downshift 1 gear, and increase about 750 rpm. While test towing today with the Allison 8.1L, whether in tow-haul or not, if I downshift to "low 3" at the start of a big hill, going 70 mph, the tranny would downshift 1 gear, go up to about 3000 rpm, then every time, would after about 2 seconds, downshift again, and the rpm would increase to 4000 rpm...even though the extra downshift didn't appear to be needed to hold speed. Is the approved solution to always tow in overdrive, and put up with the searching for gears while going up an incline.... or drive in "low 3" and see 4000 rpm?
    Thanks again.
  • kg11kg11 Posts: 530
    3rd gear in the Allison is not much(if any) higher than 2nd in your '96. There are 5 gears in the Allison ,4th is 1 to 1 ratio just like 3rd in your '96 and 1 thru 3 cover the a slightly wider and lower range as the first 2.Leave it in drive and select tow/hual mode.

  • bamatundrabamatundra Posts: 1,583
    Even if you buy their ludicrous excuse that it does not affect the longevity of the engine - Why would anyone want to drive a truck that sounds like a paint shaker? Shouldn't GM fix this?

    This brings up the question of what a warranty is for. GM is merrily handing out extended warranties to anyone with a knocking truck because they know that they can get away with not honoring them. (Just like they are not honoring the original warranty).

    Would you buy a new GM truck knowing that there is a good chance that your engine will knock loudly and GM will tell you to take a hike when you attempt to get it fixed?
  • tomh12tomh12 Posts: 240
    Why does Toyota not offer a full size 1/2 ton, let alone a 3/4 or 1 ton? Do they have any V8's larger than the 4.7 available? Why would someone who owns one of these tiny wanna be 1/2 tons be posting garbage in this topic?
    Go spam your own site some more.
  • bamatundrabamatundra Posts: 1,583
    Why doesn't GM offer a "full size" truck that doesn't knock? According to GM knocking is normal.

    Remember - this topic is about GM trucks - not Tundras. As painful as I know it is to own a knocker, can we please try to stay on topic?
This discussion has been closed.