Chevy and GMC Duramax Diesel Forum banner

07 lbz "bump" when stopping

6K views 15 replies 7 participants last post by  Dan9812 
#1 ·
My lbz duramax has been giving me a bump feeling a few times a day when coming to a stop. I can see on my edge programmer that it's shifting late to 1st. After I've already come to a complete stop. It's been pretty frequent and I've also noticed that the edge shows me when I'm slowing down to a complete stop the truck will shift from 2nd to 1st, then back to 2nd real quick and real quick back to 1st. It will do that just coming to a regular stop. I haven't felt the bump feeling every time it does that but a couple. I did see a tsb about harsh shifting so I'm not sure if that's what it is or what. It also feels like the antilock brakes are kicking in sometimes when I stop
 
#2 ·
I know doing a "re-learn" on the trans can solve some minor things sometimes. Also common to change the spin on filter and clean the magnet (hopefully it's still there)
How's the up shifting feel? and have you tried placing it in manual mode and down shifting while decelerating that way?

Those are things I'd try first, but hopefully an expert will chime in soon
 
#3 ·
Up shifting seems fine. Sometimes shifting from drive to reverse gives a nice bang I don't like but other than that it seems fine. The bump is definitely noticeable, my girlfriend thought we got rear ended the other day. I may try the relearn after manual shifting
 
#4 · (Edited)
Does it feel like you got rear ended lightly as you stop? My LBZ did that a few times -- I recall maybe 5 or 6 times. See this recent thread for more discussion and a possible solution by cleaning and re-greasing the output shaft splines. I never thought to watch my edge display when it occurred because it was so rare for me. http://www.duramaxforum.com/forum/transmission-shop/780378-tranny-bumps-if-someone-hit-me-rear.html

As for the abs, do you live in an area where salt or other corrosive is used on the roads in the winter? I experienced my abs kicking in just as I came to a stop. The pedal would drop just before I came to a complete stop and I felt the abs pulse in the pedal. I replaced the abs sensors once with little improvement. The rust on the top of the wheel bearing apparently pushed the sensor out of the hole a hair; enough to screw with the sensor. I took a die grinder to the top of the wheel bearing to remove the rust and corrosion from the mounting surface, then re-replaced the sensor an it's been perfect since.
 
#8 ·
Yes, if that was directed at my mistake.

Yea it does feel like I just got rear ended. Mine does it over and over especially on quick stops, versus a slow rolling stop u can't feel it as much. I'll check the splines out. I think I did read about the abs sensor issue that your talking about. I live in Michigan so things definitely get corroded here
I live in Michigan as well.
 
#6 ·
Yea it does feel like I just got rear ended. Mine does it over and over especially on quick stops, versus a slow rolling stop u can't feel it as much. I'll check the splines out. I think I did read about the abs sensor issue that your talking about. I live in Michigan so things definitely get corroded here
 
#9 ·
I just did some manual shifting everything was fine, I haven't messed with the splines yet. I did the trans relearn and after it pushed to do it my edge cs shut off, don't know if that's normal but it definitely felt like it was relearning because it was down shifting harder than usual but I think it's still doing the bump. I recorded a short video of the programmer showing the truck shifting from 2nd to 1st and back and forth but I guess u can't upload videos on here
 
#10 ·
Based on other threads involving transmission issues, inquiring minds will want to know if any codes are present. Your edge might only read a generic trans fault code. It's my understanding that if the Allison is acting up, it should leave a code
 
#11 ·
I just had it at a performance shop and he didn't say anything about trans codes. And I know he had his tablet looking thing hooked up to it. The truck was in for other things but I mentioned the trans issue to him but it didn't do it to him and he all he said was try a flush and maybe adding a "sump" to the trans, if I'm remembering right
 
#12 ·
Is the bump happening right when you come to a stop, like when the truck rocks back? If so, I'd check the splines in your slip yoke first. Spray it with brake clean, then lube it with ATF. That's a really common issue and can damage your t-case over time if it's not lubed. That's a cheap and easy way to either fix it or narrow the possibilities.
 
#13 ·
Nope not when the truck rocks back, but just before the truck stops. It's done it 3 times today and every time it down shifts from 2nd to 1st, then back to 2nd real quick and then once it's goes back to 1st it gives me the bump I feel
 
#14 ·
I'm having the same issue in my lmm. from what I can tell it's the e valve dragging in the valve body I'm hoping a sonnax spring will fix it
 
#15 ·
I had this occurring on my 07 classic and it ended up being a broken valve body spring...I pick up the truck tomorrow...apparently it's not uncommon or "life-threatening" but will cause worse damage if left as is over time...you might consider a TransGo Jr. install and see if you can get this swapped out...it's either that or a U-Joint or transfer case yoke issue...
 
#16 ·
Well I took my truck in and they dropped the trans pan and said it didn't look good. There was slot of clutch material on the filter so they said they think the trans is going. Originally they were going to check the valve body but once they saw that they didn't. I wish they would have . My truck has never gone into limp mode, and I also do have the trans go Jr. Installed
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top