LOST JEEPS :: View topic - What's that "thunk" when I let off the brake?

So I'm at a full stop and the light turns green--time to go. I let off the brake and hear/feel a gentle but definite "thunk" before I even get my foot over to the gas (er, diesel) pedal. The truck shifts/runs fine in all other respects... Any ideas? Seem to have plenty of ATF and brake fluid.

usa591 wrote:

My 05 CRD has this exact same problem, mine also runs and shift completely fine, it bothers the crap out of me, i posted something on here before about it but didn't get much for replies, maybe ill tear the wheels off and grease all the caliper sliders today since i have the day off. they get all corroded from the salt in the northeast winters up here, worth a try i guess. i was thinking U-joint at first but the driveshaft had no play in it with it in neutral and it wasnt making any noise when i shifted into reverse

Have you checked for play in the upper balljoint on the rear end?

CATCRD wrote:

Like was posted above, it's not brakes, it's your rear driveshaft slip yoke. Just unbolt the rear end of your driveshaft, unclamp the boot at the front end and slide it off. Wipe some grease in the splines and reverse. I do it about every 2 years.

what type of grease do you recommend? i had a similar problem on my 2006 gmc sierra and i used high temp synthetic marine grease.

Author:	usa591 [ Mon Sep 06, 2010 3:27 am ]
Post subject:	What's that "thunk" when I let off the brake?
So I'm at a full stop and the light turns green--time to go. I let off the brake and hear/feel a gentle but definite "thunk" before I even get my foot over to the gas (er, diesel) pedal. The truck shifts/runs fine in all other respects... Any ideas? Seem to have plenty of ATF and brake fluid.

Author:	Glend [ Mon Sep 06, 2010 5:33 am ]
Post subject:	Re: What's that "thunk" when I let off the brake?
You might have a brake sticking. I have the same problem occasionally. Mine seems to be in the rear. Started after a big trip in sand and mud. I suspect a good cleaning of the caliper will fix it up.

Author:	Joe Romas [ Mon Sep 06, 2010 8:57 am ]
Post subject:	Re: What's that "thunk" when I let off the brake?
This is an old jeep thing It's the slip joint on the tail shaft of the transmission and rear drive shaft needing lubed. Some older XJ's even had a grease fitting but that's too easy

Author:	bakersoil [ Mon Sep 06, 2010 1:56 pm ]
Post subject:	Re: What's that "thunk" when I let off the brake?
In my case its the transmission not down shifting into 1st until I let off the brake and it moves ever so slightly after the dead stop. Sometimes it will down shift very hard like it broke something if you give it a little to much throttle on take off.

Author:	salden77 [ Mon Sep 06, 2010 3:31 pm ]
Post subject:	Re: What's that "thunk" when I let off the brake?
usa591 wrote: So I'm at a full stop and the light turns green--time to go. I let off the brake and hear/feel a gentle but definite "thunk" before I even get my foot over to the gas (er, diesel) pedal. The truck shifts/runs fine in all other respects... Any ideas? Seem to have plenty of ATF and brake fluid. My 05 CRD has this exact same problem, mine also runs and shift completely fine, it bothers the crap out of me, i posted something on here before about it but didn't get much for replies, maybe ill tear the wheels off and grease all the caliper sliders today since i have the day off. they get all corroded from the salt in the northeast winters up here, worth a try i guess. i was thinking U-joint at first but the driveshaft had no play in it with it in neutral and it wasnt making any noise when i shifted into reverse

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Author:	CATCRD [ Mon Sep 06, 2010 4:03 pm ]
Post subject:	Re: What's that "thunk" when I let off the brake?
salden77 wrote: usa591 wrote: So I'm at a full stop and the light turns green--time to go. I let off the brake and hear/feel a gentle but definite "thunk" before I even get my foot over to the gas (er, diesel) pedal. The truck shifts/runs fine in all other respects... Any ideas? Seem to have plenty of ATF and brake fluid. My 05 CRD has this exact same problem, mine also runs and shift completely fine, it bothers the crap out of me, i posted something on here before about it but didn't get much for replies, maybe ill tear the wheels off and grease all the caliper sliders today since i have the day off. they get all corroded from the salt in the northeast winters up here, worth a try i guess. i was thinking U-joint at first but the driveshaft had no play in it with it in neutral and it wasnt making any noise when i shifted into reverse Like was posted above, it's not brakes, it's your rear driveshaft slip yoke. Just unbolt the rear end of your driveshaft, unclamp the boot at the front end and slide it off. Wipe some grease in the splines and reverse. I do it about every 2 years.

Author:	salden77 [ Mon Sep 06, 2010 5:37 pm ]
Post subject:	Re: What's that "thunk" when I let off the brake?
Like was posted above, it's not brakes, it's your rear driveshaft slip yoke. Just unbolt the rear end of your driveshaft, unclamp the boot at the front end and slide it off. Wipe some grease in the splines and reverse. I do it about every 2 years.[/quote] what type of grease do you recommend? i had a similar problem on my 2006 gmc sierra and i used high temp synthetic marine grease.

Author:	ptsb5a [ Mon Sep 06, 2010 5:39 pm ]
Post subject:	Re: What's that "thunk" when I let off the brake?
Have you checked for play in the upper balljoint on the rear end?

Author:	salden77 [ Mon Sep 06, 2010 5:51 pm ]
Post subject:	Re: What's that "thunk" when I let off the brake?
no not yet, ill have to jack it up and check for play

Author:	LibertyCRD [ Mon Sep 06, 2010 8:21 pm ]
Post subject:	Re: What's that "thunk" when I let off the brake?
ptsb5a wrote: Have you checked for play in the upper balljoint on the rear end? Bingo. I have the exact same problem, and this is what I suspect the problem is. I will eventually get under there and check.

Author:	CATCRD [ Tue Sep 07, 2010 12:04 pm ]
Post subject:	Re: What's that "thunk" when I let off the brake?
salden77 wrote: CATCRD wrote: Like was posted above, it's not brakes, it's your rear driveshaft slip yoke. Just unbolt the rear end of your driveshaft, unclamp the boot at the front end and slide it off. Wipe some grease in the splines and reverse. I do it about every 2 years. what type of grease do you recommend? i had a similar problem on my 2006 gmc sierra and i used high temp synthetic marine grease. It's not a high temp application so I wouldn't go buy high temp just for this. Just use whatever multipurpose stuff you have on hand. I may drill and tap for grease fittings next time I have to take off the driveshaft.

Author:	salden77 [ Tue Sep 07, 2010 4:25 pm ]
Post subject:	Re: What's that "thunk" when I let off the brake?
i already have the grease, and grease fitting sounds like a good idea, i might do that when i take mine off.

Author:	danoid [ Tue Sep 07, 2010 9:28 pm ]
Post subject:	Re: What's that "thunk" when I let off the brake?
The more permanent solution involves nickel chroming the spline. Problem is that also changes the size of the spline so it's a bit of a bother to do after the fact. Would have been real easy to do from the factory though.

Author:	usa591 [ Tue Sep 07, 2010 9:41 pm ]
Post subject:	Re: What's that "thunk" when I let off the brake?
Thanks for all the responses, amigos!

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Author:	usa591 [ Fri Sep 02, 2011 1:21 pm ]
Post subject:	Re: What's that "thunk" when I let off the brake?
problem solved: my mechanic greased the splines--no more thunk.