willhammond20

Hi all, I’m getting a rumble from the rear when accelerating through 4/5000 revs. Like a vibration. I’ve an idea of what it might be but wondered if anyone else has had the same issue? Thanks in advance.

engifineer

Sounds like CV cup pitting. Easiest fix is to swap the cups side to side (free other than new grease). If they have already been swapped you can use spacers to fix. It typically is felt most under acceleration from about 40 mph to 70mph or so.

willhammond20

Thanks. So I guess this will work until the other side gets pitted? Then replace them?

engifineer

Nope, can do it multiple times. This time, swap the cups. If it happens again, use axle spacers (moves the bearings away from the pitted portion). It it does it again, swap cups back and still use axle spacers. After that, yes you would need to replace axles.

willhammond20

Thank you!

engifineer

this is of course assuming the cups have never been swapped. When you do it, clean all the old grease out and add new. When clean, you can see the pitting in them and check to see if there is pitting on both sides of the channels. If so, then go straight to spacers since they have already been swapped. When you see them it become apparent where the pitting occurs and where the stress is when moving the car. The cup "pushes" the bearings in the CV joint when driving so look at the edges of those channels.

willhammond20

Perfect, thank you very much. So providing they haven’t been swapped it’ll sort the issue for a while?

engifineer

It should. There are some that have similar symptoms when prop shaft joints are going, but the most common cause are the CV cups. Unless abused heavily, they should last as long swapped as they did originally. I have pitted mine twice but the 2nd time was after a bunch of 6000 rpm launches on an autox practice day so pretty sure that time was just that abuse coupled with normal wear.