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sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 22988
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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GM 2500 HD: I HAVE A 2007 CLASSIC CHEVY 2500 hd diesel w/ allison

Customer Question

I HAVE A 2007 CLASSIC CHEVY 2500 hd diesel w/ allison trans. When I pull up to a stop sign or light, a little fast on the brake. The truck will want to keep going and when I push harder on the brake, sometimes it feels like someone rearends me. What might be the problem?
Submitted: 2 years ago.
Category: Car
Customer: replied 2 years ago.
the truck has 100k on it.
Expert:  sprinkles08 replied 2 years ago.
Hello and welcome to JustAnswer!
It sounds as if the torque converter clutch is turning on. In the front of the converter is a disc clutch that is turned on at higher steady speeds to give a mechanical lock between the engine and trans. If the converter clutch comes on when stopping then it will drag the engine down and kill it with a gas engine, but with a diesel it will have the power to keep running and will try to keep pulling.
The problem could be with the converter itself, a valve body or solenoid issue, but if it happens when stopping suddenly only then it may be a fluid level issue. If the level is low then the pump can suck air and cause this. The first thing I would recommend is checking the fluid level.
Customer: replied 2 years ago.
I checked the oil way before I asked the question. It stopped lunging forward for a few days but has returned.
Expert:  sprinkles08 replied 2 years ago.
Are any fault codes setting?
Has anything else been tested or replaced that was not mentioned?
Customer: replied 2 years ago.
I took it to a local transmission specialist and the tested the tranny. I was told it was fine and it was my rear leaf springs that were weak. I am not sure if this could be it, so tommorrow I am going to go pick it up and look it over. They said that the leafs are shifting sometimes when I stop. I do tow a 5th wheel but it is only 10k lbs.
Expert:  sprinkles08 replied 2 years ago.
I thought that the truck tried to keep pulling away against the brakes when trying to stop?
Customer: replied 2 years ago.
It does that but they seem to think it's the springs. I was looking online for other people with my same symptom and found that sometimes the slip yoke on the driveshaft will bind some on the output shaft when decreasing speed at a stop sign and will feel like someone rearends you due to the release of the pressure on the splines if there is insufficient lube on them. Also if adding lube to the splines does work but only temporary, GM has a nickel plated yoke you can change out as a permanent fix. By the way the truck will feel like it is lunging forward but I can stop it with more pressure on the brakes. I lubes up the yoke and will see if it cures the problem, hopefully it will. I did talk to a spring specialist and the said it may be the springs as they see it in alot of 2500HDs. The only thing is they say it is more of a slap than a pushing forward when the springs go bad(weak). I hope it is the yoke due to the 450 to 600 price tag. It may be the torque converter but the tranny shop said the drivetrain worked great and it was definately the spring but not so sure.
Expert:  sprinkles08 replied 2 years ago.
If you're feeling something shifting in the rear rather than the truck continuing to pull then it could definitely be a slip yoke or rear suspension related issue.
Customer: replied 2 years ago.
Well I lubed up the slip yoke and it felt ok that evening but today we went for a long drive and it did it more. When I almost stop I hear a clunk towards the rear of the truck and it will push me forward maybe a few inches or so and feels like I got tapped in the rear or the rearend loaded up and released all of a sudden at almost stopped speed. The spring shop said it was more of a spring slap sound. I just hope if I take it to the spring shop and let them ad the leaf to each side and the bushings it cures the problem. I am mechanically inclined and can possibly put a set of heavier springs for less than the 450 the shop is asking, hmmm.
Expert:  sprinkles08 replied 2 years ago.
If the spring bushings are loose then the bushings or springs will definitely need to be replaced either way. I would recommend repairing that issue first and re evaluate it.
Customer: replied 2 years ago.
I can't see how the bushings or springs could make it feel like I am being shoved from behind a few inches. I guess I don't understand.
Expert:  sprinkles08 replied 2 years ago.
I agree. Loose rear suspension will cause a noise, a shift or loose feeling but it isn't going to cause the truck to try to keep pulling against the brakes while stopping.
Customer: replied 2 years ago.
sorry for the delay of my chatting. I still have the problem. I have spent money to fix the springs and I have changed the slip yoke to a nickel plated one and changed the u-joints to no success. I am still with the problem. I do know that it will only happen once the tranny warms up to operating temps according to my gauges.
Expert:  sprinkles08 replied 2 years ago.
If you pop the shifter into neutral at the end of a stop does it still happen?
Customer: replied 2 years ago.
When I switch the trans to neutral while doing a rolling stop it does not do it.
Expert:  sprinkles08 replied 2 years ago.
I'd recommend getting another opinion from a trans tech at a dealer. I think you're back to the torque converter clutch most likely coming on.
Customer: replied 2 years ago.
I just thought of something. A few months ago I changed the brakes on the rear of the truck. On the drivers side the pads were shot and I had to replace the rotor on that side due to very excessive wear and I had the passenger side reground (replaced both sides with new rotors and kept the regrind for later use). I remember that the noise and bumping started not too long after this. Could it possibly be something at the rearend causing problem or should I just take it to the service bay at GM? The calipers opened back up nicely when I serviced the brakes but just wondered if this was a sign of a possible alternative solution that had not been thought of before. Thanks ahead of time and thank you for your patience.
Expert:  sprinkles08 replied 2 years ago.
If you aren't having any whining or growling noise from the rear differential I doubt the differential is causing what you're feeling.