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| Bump from dead stopped at release of brake http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=35132 |
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| Author: | LiberD [ Sun Aug 17, 2008 12:20 pm ] |
| Post subject: | Bump from dead stopped at release of brake |
I would appreciate any opinions on what might be causing a bump or jolt forward when I first let off of the brake foot pedal from a dead stop just as the Liberty begins to roll. Thanks. Mitchell |
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| Author: | Uffe [ Sun Aug 17, 2008 3:07 pm ] |
| Post subject: | Re: Bump from dead stopped at release of brake |
LiberD wrote: I would appreciate any opinions on what might be causing a bump or jolt forward when I first let off of the brake foot pedal from a dead stop just as the Liberty begins to roll.
Thanks. Mitchell I think people here would agree to have your engine mounts checked 
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| Author: | LiberD [ Sun Aug 17, 2008 7:55 pm ] |
| Post subject: | Bump from dead stopped at release of brake |
Thank you Uffe. The bump occurs without any foot on the accelerator. It happens just when I take my foot off of the brake pedal from a standstill. Does that still sound like mounts? Mitchell |
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| Author: | gmctd [ Sun Aug 17, 2008 8:41 pm ] |
| Post subject: | |
Could just be the driveshaft slip joint binding from rust - gives a thump as it unbinds |
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| Author: | chrispitude [ Sun Aug 17, 2008 8:46 pm ] |
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Hi Mitchell, Is it any worse if you brake hard to a stop, versus gently coming to a stop? On vehicles with a lot of suspension travel, I've noticed that stopping hard will cause the suspension to load up as the wheels come to a stop, which keeps them in a somewhat loaded position. As soon as you let off the brakes, the tire is able to rotate and unload. When coming gently to a stop, this doesn't happen. - Chris |
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| Author: | CATCRD [ Sun Aug 17, 2008 8:46 pm ] |
| Post subject: | |
Mine has always done this, especially when coming to a hard stop. I chalk it up to backlash in the drivetrain. |
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| Author: | danoid [ Sun Aug 17, 2008 9:46 pm ] |
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gmctd wrote: Could just be the driveshaft slip joint binding from rust - gives a thump as it unbinds
I'll second that, although it's not necessarily rust. The slip joint of the rear driveshaft can bind. Harder braking pitches the car forward more and the the reaction torque from the brakes turns the axle. If the slip joint binds this leaves the axle twisted (around the tire rotation axis). When you release the brakes (release the torque) the axle returns to it's normal roation position and you feel a bump. The fix is a nickel plated slip joint (either the yoke or the spline). But since the nickel adds thickness to a tighly toleranced involute spline, just adding plating to the existing parts will make things much worse. The spline needs to be more open (before plating so plating can fill the gap) and that takes either a newly machined yoke or shaft. The work around is to always brake gently as you're coming to a stop and allow the slip joint to slip. (Until of course it starts to rust and then it will always bind.) Group buy anyone? I'd love to get rid of that little annoyance. |
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| Author: | LiberD [ Sun Aug 17, 2008 11:05 pm ] |
| Post subject: | Bump from dead stopped at release of brake |
Thanks for all of the input. I will have to see just how much deceleration it takes to cause the bump. I usually feather the brakes from a distance and do not brake sharply, but I'll try to see if I can cause the bump on purpose. I have been getting an intermittent ESP/BAS and Stability Control Light which go out after I restart. I posted this elsewhere here. Could these be related? Mitchell |
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| Author: | gmctd [ Sun Aug 17, 2008 11:16 pm ] |
| Post subject: | |
Most definitely - need to get a Starscan on it - Mr MoService can handle that |
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| Author: | LiberD [ Sun Aug 17, 2008 11:33 pm ] |
| Post subject: | Bump from dead stopped at release of brake |
gmctd, I think you are suggesting taking to Dealer Service. In another post I was asking how to get the dealer to fix it because I had brought it in with the ESP/BAS and Stab. Ctrl. lights on and they could not solve. This because they could not get those lights to repeat coming on ( I have, I don't know how) and the stored codes identified nothing. So what do I say to get them to replace Wheel Sensors or whatever else is needed? Mitchell |
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| Author: | KeighJeigh [ Mon Aug 18, 2008 2:35 pm ] |
| Post subject: | |
My 05 does 2 versions of this: 1) The driveline backlash is the sloppiest I’ve ever experience in any car I’ve owned including older Jeeps and 4X4 pickups. I’ve assumed this is just the way it is – but it makes clunking noises when going in and out of gear, or from forward to reverse, or if I go into neutral while sitting in heavy traffic, or if I put it into 1st or 2nd gear to use the engine as a brake and then accelerate, or in general when I engage the 4WD. Lots of clunkiness in general. I have crawled underneath it and checked and found no damage….but there is a lot of slop when I turn the driveshaft back and forth. It hasn’t gotten any worse, so I assume it is just a Jeep-ism. They probably manufactured mine on the very edge of acceptable tolerances (perhaps 2 mating gears with minimum tooth size) so the rear differential gears are especially sloppy. I brought it to the stealer when I first noticed these issues but they told me there was nothing wrong and that these cars were a bit sloppy in general. (surprise surprise) 2) There is something strange about the suspension/rear brake combo that causes a different kind of clunk under certain conditions. It happens when I come to a slow stop at a stoplight and leave my foot on the brake. When I release the brake and just before I hit the accelerator I hear a clunk. It’s been very tough for me to diagnose because it is intermittent and only under certain conditions. My theory is it one of two things: Worst case is that the car is rocking forward on some loose suspension component and then rocking back when released. The wheel pulls the suspension backward when it is braking and then pushes it forward when accelerating. Perhaps a loose upper control arm bushing? Or, it could be the rear brake sticking and then popping loose. This has gotten no worse since I’ve owned the car so I have written it off as a Jeep-ism as well. - Chris |
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| Author: | CHessMaster [ Mon Aug 18, 2008 5:22 pm ] |
| Post subject: | |
This is definitely a slip yoke binding problem. I have had this same complaint in my Liberty twice now and lubing the slip yoke solved the problem both times. The first time, the dealer fixed it after I told them exactly what to do, but they didn't put enough grease on the splines and it only lasted about 20k miles. To fix it properly, you need a special "slip yoke grease". It is a light greenish/blue color and is relatively expensive. Any good driveline shop should be able to fix it for you using this special grease. I've fixed lots of GM trucks this way with the same complaint. The shop I worked for has used the same 1 quart can of this stuff for about 5 years now, it goes a long way....... DO NOT use regular bearing or lithium grease on the slip yoke assembly! It would be just about as expensive to buy a can of the lube, or just have a driveline shop do it for you with the correct (small) amount of lube. I can get the General Motors part number for the grease in question if anyone needs it. If you want to go "aftermarket" or "Chrysler" with the grease, your on your own  .
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| Author: | BVCRD [ Mon Aug 18, 2008 5:32 pm ] |
| Post subject: | |
I had this same issue on an F150. Slip yoke needed greased every 12K miles. I havn't bothered with the CRD. Just let it do it's thing knowing it isn't causing any damage. |
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| Author: | LiberD [ Mon Aug 18, 2008 6:18 pm ] |
| Post subject: | Bump from dead stopped at release of brake |
Thanks for everyone's input. Yeah, I will mention it to the dealer when I go in for the next issue that comes up, although I still have the intermittent ESP/BAS & Stab. Lights coming on. I will just put them on notice by having it written up. Until then, I think I will let it ride. Mitchell |
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| Author: | johnyrr [ Mon Oct 06, 2008 2:23 pm ] |
| Post subject: | |
I havent looked is there a zerk, if not how do you lube the slip-yoke? Sorry for the newbie question |
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| Author: | CHessMaster [ Mon Oct 06, 2008 9:16 pm ] |
| Post subject: | |
johnyrr wrote: I havent looked is there a zerk, if not how do you lube the slip-yoke? Sorry for the newbie question
You have to remove the rear drive shaft and lube the splines (t-case output and driveshaft yoke) with the above mentioned special grease. Make sure you get a new "band clamp" as you might possibly damage the old one that holds the rubber dust boot on the yoke. |
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| Author: | mcnaughb [ Sun Nov 09, 2008 2:32 am ] |
| Post subject: | |
Quote: 2) There is something strange about the suspension/rear brake combo that causes a different kind of clunk under certain conditions. It happens when I come to a slow stop at a stoplight and leave my foot on the brake. When I release the brake and just before I hit the accelerator I hear a clunk. It’s been very tough for me to diagnose because it is intermittent and only under certain conditions. My theory is it one of two things: Worst case is that the car is rocking forward on some loose suspension component and then rocking back when released. The wheel pulls the suspension backward when it is braking and then pushes it forward when accelerating. Perhaps a loose upper control arm bushing? Or, it could be the rear brake sticking and then popping loose. This has gotten no worse since I’ve owned the car so I have written it off as a Jeep-ism as well.
My 06 exhibited this exact problem. Ended up being motor mounts. |
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| Author: | BVCRD [ Sun Nov 09, 2008 3:34 pm ] |
| Post subject: | |
mcnaughb wrote: Quote: 2) There is something strange about the suspension/rear brake combo that causes a different kind of clunk under certain conditions. It happens when I come to a slow stop at a stoplight and leave my foot on the brake. When I release the brake and just before I hit the accelerator I hear a clunk. It’s been very tough for me to diagnose because it is intermittent and only under certain conditions. My theory is it one of two things: Worst case is that the car is rocking forward on some loose suspension component and then rocking back when released. The wheel pulls the suspension backward when it is braking and then pushes it forward when accelerating. Perhaps a loose upper control arm bushing? Or, it could be the rear brake sticking and then popping loose. This has gotten no worse since I’ve owned the car so I have written it off as a Jeep-ism as well. My 06 exhibited this exact problem. Ended up being motor mounts. It it is the exact same thing, how can the motor mounts be the cause if the engine is at a dead stop, and the only action taken is a release of the brake pedal? |
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| Author: | Wobbly [ Sun Nov 09, 2008 4:02 pm ] |
| Post subject: | |
This may be unrelated, but when parking on a grade the vehicle always moves a bit after setting the parking brake, putting the transmission in park, and then releasing the brake pedal. As I'm getting out I always wonder for a split second if I forgot to set the parking brake. |
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| Author: | mrkake [ Mon Nov 10, 2008 12:50 am ] |
| Post subject: | |
Wobbly wrote: This may be unrelated, but when parking on a grade the vehicle always moves a bit after setting the parking brake, putting the transmission in park, and then releasing the brake pedal. As I'm getting out I always wonder for a split second if I forgot to set the parking brake.
That's just your brakes unloading. The best way to do it is set your park brake, slip the tranny into neutral and then release the brake pedal letting the park brake take the load, then put it into park. Least ways that's what my daddy taught me. |
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