View Full Version : SLACK IN TAKE-OFF
Mine still has a bump or feels like loose drive train on take-off from a stop. I need some help on this, when I took it in to the dealership they replaced the transmission, but I still have this problem. Is this just a quirk of the Allison or is it a GM driveline problem? I now have over 30,000 miles on this truck and this is my only complaint. Everytime you take off from a stop it goes bump, feels like you have a round of slack in the drive train.
a64pilot
11-19-2001, 19:34
Joe,
Watch your tach. as you leave from a stop. Is your tranny starting out in second and then shifting into first? Did the dealer also replace the TCM? If not I would think that it would be a simple troubleshooting procedure to temporarily install a new one. I have read in this forum that you can reset the fast learn of this xmsn by driving at 60 mph and placing the selector in 1 and coasting down to a slow speed. Do this three times. This has apparently helped other people with strange tranny problems. I have not tried this, your mileage may vary. (apparently the xmsn will only downshift at the correct speed and will not over-rev the eng.) http://www.62-65-dieselpage.com/ubb/smile.gif
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2001 C3500 LT Charcoal Grey
CC/Longbed Putco boss boards,
virtual grill,mudflaps,sill protectors Rhino liner,
bug deflector. Looking into Boost/EGT gague
sonofagun
11-19-2001, 20:34
Joe,
Mine does not do this at all. I'd stay after the dealer. Sorry for your misery. Good luck.
Bob
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2001 GMC 2500HD D/A olympic white, Manik
SS brush guard and nerfs, Hella driving lamps, Velvet rides, HD Air Lifts and Compressor
Snugtop cover, Linex, Yakima rails on cover (mt. bikes), Amsoil 2 stage airfilter. XM Radio.
ECM upgrades. One piece driveshaft.
43 gal across the bed aux. tank.
1966 Chevelle convetible 396 4SPD (restored)
_ _ _ _ _ _
Working on EGT/Boost guage, 4" exhaust.
GOD BLESS AMERICA and those who walk in harms
way to protect us all!!
I'm not sure if this is an ongoing problem or a new development but there have been problems with the 2 piece driveshaft on hard accelerating takeoffs. Surely your dealership would have ruled this out.
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'01 Silverado 2500HD Dmax/Allison Ext 4x4 SB - "I drive a 2500HD"
Joe,
I know what your going through. My 02 does the same thing. I have about 5500 miles on it and I get the same bump when I take off. It feels like slop in the drive train, but I think it is coming from the Allison. It also bumps right before I come to a complete stop and when I take off it does it again. The real strange thing about this is that it doesn't do it all of the time. Once in a while (like once a week) it will take off just fine. It is really the only problem I'm having with the truck. Compared to all of the other problems I'm hearing with the Allison, I guess I should be happy. I took it to my dealer and he said it was an Allison trait and they all did it. I don't believe that because you're the first person I've heard that posted that complaint. Keep me posted if you find anything out. Thanks!
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duramax170
11-19-2001, 20:59
not sure if this is the same thing but when i don't quite make a complete stop then accelerate the truck will rev like it is in nuetral and then all of a sudden drop into gear, this doesn't happen very often, but now when it does it i just let off the pedal and then reapply and everything is okay
DmaxMaverick
11-20-2001, 03:15
There are several different issues being discussed here (and other posts), and sounds like all are looking for a single solution.
1. The 2 - 1 shift. This is when you come to a stop (or nearly) and the tranny doesn't shift to first until you try to accelerate...RPM's increase...CLUNK...CHIRP... and all is normal from there. A longer or full stop with zero throttle input should cure it, and the downshift to first described above made mine happen less often. It appears to me that this is the result of the TCM attempting to minimize shift business, and the nature of the Allison to be a "slow shifter".
2. The bump after a stop, before taking off again. This could be a dry or insufficiently lubed output spline. If it doesn't slip easily, it will bind and release suddenly, causing the "bump" feeling. This could also be chassis windup from braking. This is the differential forces between the front and rear brakes. The energy from the "bind" is stored in the springs/drivetrain until the brakes are released, then a "bump" or "surge" can be felt.
3. The surge while slow maneuvering could be the idle surge, or "lunge", complained about, and I believe there is an update for it (ECM). This is when the throttle is "tapped" and the idle RPM increases by about 300, then idles back down after a couple seconds. Mine does this and I can duplicate it at will. I have had no updates, and mine has the "first release" programming.
Hope this helps some of you with your diagnosis. Good luck.
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2001 GMC 2500HD SLT 4X4 E/C SB loaded -D/A- Indigo Blue - Amsoiled bumper to bumper - Delivered November 2000
1985 K Blazer 6.2L N/A 500K+ original miles on Engine/Tranny (2 transfer cases, 1 pump, and a few rear ends)
Synthetic Oil!!
Thanks for all the input, the transmission takes off in low, they checked it with the scan tool, I have tried the retrain, but not at 60 mph. I tried it at 40 mph, couldn't bring myself to do it going any faster. The transmission does not have a slip yoke, this is done by the 2 piece driveshaft, at least that's what it looks like to me, the driveshaft bolts up just like it did on my old 4 wheel drive or like a transfer case type hookup. It could be the slip joint in the driveshaft, which has no grease fitting, the clamps on the rubber boot are not removeable without destroying them and I'm not going to tear up anything while the truck is under warranty. So I guess I'll just wait until somebody can pinpoint the problem. It's really no big deal, it just annoys me to no end. Thanks again for the suggestions.
hogbreth
11-20-2001, 12:33
It's interesting that this subject should be discussed at this time. I've put 800mi on my new 3500 D/A 4X4 and love it's performance and handling.The only problem I have noticed is this same launch problem. If I come to a complete stop at a traffic signal when I release the brake to accelerate I notice something that feels like the suspension unloading. Dmax Maverick did a good job of analysing the problem. If while you are waiting for the light to change and you shift to 1st it doesn't seem to do it.I believe that its tied to the trans. the feeling you get when this happens is so subtle that I don't think this is a major but it is annoying especilly since Iam aware of it. If I don't come to a complete stop everything is fine that's why I initially thought it was the suspension wraping up.
mguebert
11-20-2001, 18:25
I have this same exact problem with my truck, I have had it to the dealer twice and they tell me it is normal. It does not do it all of the time, but mostly it does. It varies in intensity, sometimes being pretty bad other times barely noticeable. It is also noticeable when stopping. It is definitely not the tranny because I have tried to pull it into low gear before I come to a stop and it still does it.
It really aggravates me and is one of two complaints I have with my truck. The other is excessive oil consumption. Both of which GM is refusing to do anything about.
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2001 Chevrolet Silverado LS 2500HD 4x2 Ext Cab LWB,SRW Duramax
Banks EGT and Boost Gauge
ISSPRO Turbo Timer
STR8PIPED!
Line-X Over the Rails
Roll-n-Lock bed cover
I had the one piece driveshaft installed today and it helps correct 90+% of this problem! I know it doesn't make sense, but trust me that the two piece driveshaft causes more problems than you think.
Lone Eagle
11-21-2001, 17:26
DmaxMaverick hit the nail on the head with his # 2 comment. My 99 1500 had the same thump. The amount of thump was directly related to how much brake was used to stop. Believe it or not the factory fix was to flush the transfer case and add a different type of oil. Didn't find out what kind because I was selling the truck. The front spline on the drive line must slide in and out smoothly or it will thump. Later! Lone Eagle
mguebert
11-21-2001, 17:33
Lone Eagle and csimo,
Thats great for you guys, but for those of us with 2wd trucks the TSB does not apply and the dealership will not perform the update to the single piece driveshaft.
The problem feels to me a lot like a bad u joint.
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2001 Chevrolet Silverado LS 2500HD 4x2 Ext Cab LWB,SRW Duramax
Banks EGT and Boost Gauge
ISSPRO Turbo Timer
STR8PIPED!
Line-X Over the Rails
Roll-n-Lock bed cover
Any of you guys get an actual fix for this? Mines developed the same issue, a bump right before stopping and a bump when taking off from a a stop. Doesn't do it all the time, but it's there.
mguebert
04-03-2002, 19:21
Nope,
Still living with it, now have over 22K and it is as bad as ever. It sucks knowing my expensive truck rattles like a chevette :mad:
I've heard that there are new transmission calibrations for both the 2001 and 2002 trucks that may help address some of the downshift issues. There have been some comments made in other threads regarding improvements after getting the new calibration. I agree that some of the problem may be something other than the transmission, such as driveline. It certainly couldn't hurt to ensure that the transmission has the latest updates IMHO. There's nothing as pretty as seeing the sun come up over the hood of a HD. Wellll, almost nothing!!! :D
ropadopa2000
04-05-2002, 14:20
i have the symptom of when i come to a complete stop and boom almost feels like some one rearended me,. what i belive to be is that the trany is ****ing back into 1st is this normal it dosent happen all the time but it still cathces me of guard some times.
Looking at the GM calibration site:
http://vci.ecomm.gm.com/vci
For my '02 it doesn't appear any tranny updates are available. Only thing new showing are some updates for false trouble codes, misfire detection, and California emissions.
Temp has something to do with it some how. Today was around 70 in the Dallas area and in traffic it did it quite often. Feels like some slack in something. U-joint, converter, something. When it comes to a stop feels like something in the bed slid up and hit the cab giving the whole truck a bump in the back. Then after this happens and you start to take off, letting off the brake often gets another bump in the drivetrain. Almost like the tires were spinning and suddenly caught. It's wierd and isn't repeatable every time.
Could it be the front rear brake proportioning is out of whack maybe? Dunno, grasping at straws.
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