Car jerks when on or off gas

Technical Discussions - Got a mechanical problem?

Moderator: bajabob

Post Reply
Footie570
Scoobytruck Lurker
Posts: 14
Joined: Tue Jun 28, 2016 6:11 pm

Car jerks when on or off gas

Post by Footie570 » Wed Aug 03, 2016 11:00 am

I've got a 2003 baja 2.5 manual transmission. When I'm driving and let off the gas, no matter how gradually, the car jerks fairly hard (just once). It does the same thing when I apply the gas as well after coasting, it jerks back fairly hard, one time. It has nothing to do with my shifting or my clutch. It has done it before and after my full engine rebuild and brand new clutch. It's suuuuuper annoying and any help anyone could offer to solve this problem would be greatly appreciated.

User avatar
kamesama980
Scoobytruck Master
Posts: 260
Joined: Mon Feb 29, 2016 6:54 am

Re: Car jerks when on or off gas

Post by kamesama980 » Wed Aug 03, 2016 11:47 am

driveline slop mainly, worn suspension can aggravate it. Seems to be an element of poor programming in the transition from idle to off-idle and back that doesn't help either. Mine does it too but not horribly. Check for play in the diffs, axles, and driveshaft first. Unless you find a smoking gun, next inspect the suspension bushings and linkages, preferably on ramps or a drive-on rack so you can see them at ride height. If you have someone you trust a lot, have them get in, start the car and ease off the clutch to apply a little torque to the driveline alternating forward and reverse while you're underneath seeing what moves.
-Russell
"You don't get to judge me for how I fix what you break"
03 sport 5mt
05 turbo 5mt vf39 and other STI bits, 3" turbo-back

User avatar
anarchy1024
Scoobytruck Master
Posts: 312
Joined: Mon Apr 12, 2010 4:07 pm
Location: Santa Clara, CA (Originally Toronto, ON)

Re: Car jerks when on or off gas

Post by anarchy1024 » Wed Aug 03, 2016 5:50 pm

Could worn engine mounts or rear differential bushings do that? Read a bit about the rear diff bushings wearing out quickly...

Footie570
Scoobytruck Lurker
Posts: 14
Joined: Tue Jun 28, 2016 6:11 pm

Re: Car jerks when on or off gas

Post by Footie570 » Thu Aug 04, 2016 7:23 pm

I highly doubt it's the motor mounts as they are brand new, along with pretty much all my engine internals. When we rebuilt my engine my friend said my rear tranny mount might be shot. Think that could be it?

User avatar
anarchy1024
Scoobytruck Master
Posts: 312
Joined: Mon Apr 12, 2010 4:07 pm
Location: Santa Clara, CA (Originally Toronto, ON)

Re: Car jerks when on or off gas

Post by anarchy1024 » Thu Aug 04, 2016 8:29 pm

It sounds Iike it could be, but I haven't had that problem before. If the mount is worn out, the transmission could rotate when accelerating, then rotate the opposite direction when decelerating. That extra movement could act as driveline slop, and could be felt as jerks during that transition or when loading/unloading the drive train. At least, seems to make sense in my mind...

polypolyman
Scoobytruck Lurker
Posts: 5
Joined: Thu Nov 05, 2015 10:59 am

Re: Car jerks when on or off gas

Post by polypolyman » Thu Aug 11, 2016 7:35 pm

Have you replaced the pitch stop mount?

User avatar
kamesama980
Scoobytruck Master
Posts: 260
Joined: Mon Feb 29, 2016 6:54 am

Re: Car jerks when on or off gas

Post by kamesama980 » Fri Aug 12, 2016 11:18 am

anarchy1024 wrote:Could worn engine mounts or rear differential bushings do that? Read a bit about the rear diff bushings wearing out quickly...
Footie570 wrote:I highly doubt it's the motor mounts as they are brand new, along with pretty much all my engine internals. When we rebuilt my engine my friend said my rear tranny mount might be shot. Think that could be it?
anarchy1024 wrote:It sounds Iike it could be, but I haven't had that problem before. If the mount is worn out, the transmission could rotate when accelerating, then rotate the opposite direction when decelerating. That extra movement could act as driveline slop, and could be felt as jerks during that transition or when loading/unloading the drive train. At least, seems to make sense in my mind...
While I could probably tell the difference between slop in rotating bits and loose mounts for rotating bits by sound, I don't expect someone that haven't spent a few years in a shop diagnosing such things to do so, so I will say yes, worn engine, transmission, differential, sub-frame, or suspension bushings/mounts could also do it. Heck I've seen sway bar links that clicked under the suspension articulation from a change in torque input.
-Russell
"You don't get to judge me for how I fix what you break"
03 sport 5mt
05 turbo 5mt vf39 and other STI bits, 3" turbo-back

jdlmodelt
Scoobytruck Contributer
Posts: 44
Joined: Sat Dec 12, 2015 12:59 pm
Location: SW Colorado

Re: Car jerks when on or off gas

Post by jdlmodelt » Sun Jan 08, 2017 4:30 pm

i've been trying to diagnose my noise issues. There is a shudder with mine, automatic, non turbo when starting from a stop. I can feel the thump/shudder center and behind me. I'm guessing its either/or the transmission mount worn out and the drive shaft center bearing rubber support. I'm also considering the engine mounts. The vehicle has 156,000 miles on it. CV's are clean and boots are good. It also howls around 60-65mph. My mechanic things wheel bearing, which it might be, but perhaps the drive shaft center bearing? Any ideas besides the center differential?

User avatar
kamesama980
Scoobytruck Master
Posts: 260
Joined: Mon Feb 29, 2016 6:54 am

Re: Car jerks when on or off gas

Post by kamesama980 » Wed Feb 01, 2017 2:52 pm

jdlmodelt wrote:
Sun Jan 08, 2017 4:30 pm
i've been trying to diagnose my noise issues. There is a shudder with mine, automatic, non turbo when starting from a stop. I can feel the thump/shudder center and behind me. I'm guessing its either/or the transmission mount worn out and the drive shaft center bearing rubber support. I'm also considering the engine mounts. The vehicle has 156,000 miles on it. CV's are clean and boots are good. It also howls around 60-65mph. My mechanic things wheel bearing, which it might be, but perhaps the drive shaft center bearing? Any ideas besides the center differential?
Is the shudder on takeoff directly proportional to speed (driveshaft RPM)? if so, then carrier bearing would be my first suspect. If it's disproportional to speed, it might be something on the input side of the auto trans. Mounts tend to be more of a single clunk as the assembly they are supposed to fix in place shifts.

Worst case it's the carrier AND a wheel bearing....no, not worst case, just less good case.
-Russell
"You don't get to judge me for how I fix what you break"
03 sport 5mt
05 turbo 5mt vf39 and other STI bits, 3" turbo-back

Footie570
Scoobytruck Lurker
Posts: 14
Joined: Tue Jun 28, 2016 6:11 pm

Re: Car jerks when on or off gas

Post by Footie570 » Wed Feb 01, 2017 3:22 pm

Update from me, I forgot to post up when I replaced my transmission mount: It helped the problem quite a bit, but its still there a little bit. I also have since put the engine and transmission into a legacy body, broke my brand new tranny mount in the process, and the problem is way worse than before.... gotta love working on cars :lol:

Post Reply