rear end bumping while braking

[whitefirebird96]

I recently changed out my rearend from a open 3.23 to a lsd 3.42. shortly after completely it, I notice that while I brake and the car is not in gear( it is a manual) there is a rhytmic bumping coming from somewhere in the rear. if i brake while the car is in a gear, the sound isn't there. I know I should use the transmission to help with the braking, but i was wondering if the bump is the lsd 'settling' in, or if it a serious problem and someone may be able to help me diagnose it before it becomes a major problem. thanks

[hockeyman]

Re: rear end bumping while braking

Could be a loose bearing in the pinion gear, loose or worn driveshaft u-joints, loose axle pin, worn c-clip(s), etc. There are a variety of items that can cause a noise like you are describing. I would prop the veh up from the frame, leave the trans in neutral and get under there and move stuff around to see if I coud re-create the noise. I definately wouldn't be driving it until I located and fixed the problem. If you have a loose or worn c-clip, your axle can slide out when you're going down the road!

[Publican]

Re: rear end bumping while braking

Also check your ABS - did you put the proper reluctor ring on and were the brakes functioning properly before you buttoned it up?

[whitefirebird96]

Re: rear end bumping while braking

I got the whole rearend assembly from tacreationsusa.com out of florida. I was told it was out of a 98 with about 60000 miles on it. I did take off the differential cover before I put it on, and i didn't notice anything really out of place. Of course this isn't my specialty and all those ideas sound like small things that can cause a big problem. Is there anyway you can help me narrow it down? I would like to elimate a few of those options if anyone knows how. I don't mind pulling the cover back off and looking, but would prefer to get the rest of the possiblities out of the way first. thanks a lot

[whitefirebird96]

Re: rear end bumping while braking

well I got under the car the other day and rotated the driveshaft back and forth while the car is in neutral. while going in one direction and then pausing and turning in the opposite direction, I fell it kind of catch and make a bump. Felt kind of like there were no teeth catching for that fraction of a second. It felt similar to the way it does while braking. I can't figure out why only the braking of the car would cause it to bump. But I hope this description helps someone help me determine what the cause may be. Thanks a lot

[hockeyman]

Re: rear end bumping while braking

Sounds like either worn gears or a broken tooth in the gear(s).

It makes total sense why you hear the noise when braking. As the car is cruising or on acceleration, you're pushing on the one side of the worn gears. When you brake, you slam them into the other (worn) side.

This is just a possibility though. I'd take them to a reputable place and get their opinion first. Don't go to PepKids (boys) or similar, try to find a professional transmission or gear shop that's been around for a while. This way you know you're getting an exact diagnosis, not a "i'm not sure but I'll ask the manager" diagnosis.

[whitefirebird96]

Re: rear end bumping while braking

do you think I got a bad deal from tacreationsusa.com?

[hockeyman]

Re: rear end bumping while braking

do you think I got a bad deal from tacreationsusa.com?

It depends... I don't know how much you spent, or what the previous driver did to the rear. I've seen high mileage cars that were in better shape than excessive low mileage cars. Just depends on how they drive and how well it was maintained.

How long have you had this rear and how many miles did you put on it?

Also, just pulling the diff cover really won't reveal too much if you don't know what you're looking at or looking for. There are gears burried deep in there that you must unbolt outter gears to see.

[whitefirebird96]

Re: rear end bumping while braking

I have had the rear in my car about a week now.

[hockeyman]

Re: rear end bumping while braking

I have had the rear in my car about a week now.

:eek: WOW! Yeah, I'd definately call them!!!

[whitefirebird96]

Re: rear end bumping while braking

ok, called them, not a bad rear end. My ineptitude has shown through. The nut on the pinion flange is super sensitive. I thought I had marked the original position when I changed the pinion seal. Obviously not, I believe I have pulled the pinion out too far from the gears. Am working on it now and will update. TAcreationsusa.com walked me through the diagnosis, they are great

[whitefirebird96]

Re: rear end bumping while braking

ok, so I may have forgotten to mention that I also put in a new LS1 aluminum driveshaft. With the diameter of the shaft being larger than my original 2 pc steel one, I came into problems. The yoke on the pinion end was not the same shape as the 2 pc. It was about an inch larger in diameter. So what was happening was when I would brake hard, the car would kind of flex upward in the middle due to my brake upgrade. When it did this, the trailing arm( that runs next to the driveshaft) didn't like being so close to the larger driveshaft, and it would rub on each side of the yoke. I am currently going to pull it off and dremel the edges to make it clearance better, because I don't want to put the 2 pc back in just to alleviate the noise.