Replacing Differential Bearings - Questions...

[RRjr]

Hello everyone, hoping someone can help with a few a questions...

 

I'm attempting to change the differential carrier bearings on my 2002 Boxster S manual tranny after narrowing a whining sound together with a knocking sound when getting on and off throttle - we're pretty sure it's coming from the differential. We've ruled out other possibilities like axle CV joints, wheel bearings, etc. My local Porsche specialist also checked the car and agreed it was coming from the diff - most probably worn carrier bearings. 

 

We've removed the differential and upon inspection I have a few questions: 
1. I don't see any shims installed on either side of the differential. Is this normal? I thought there were always shims used to adjust backlash, etc. Would I only see them if I remove the bearings??
2. There are some engravings on the ring gear.,..anyone know what those refer to?

 

Thanks in advance for any info!!

 

 

 

Edited November 14, 2023 by RRjr

[JFP in PA]

Welcome to RennTech 

 

The carrier shims are outside the carrier bearings, item #10 in this diagram:

 

 

Pre load measurement:

 

The backlash or free play should be in the range 0.12 to 0.22 mm. Here's a picture showing its measurement with factory tools.

 

 

Have fun..................😉

[RRjr]

thanks!

[JFP in PA]

And just as an observation: Noises when loading or unloading the drive line are rarely related to the side carrier bearings; the more likely suspect is the pinion bearings......

[RRjr]

thanks again...when I grab the pinion gear and rotate it doesn't seem to have any play side to side - feels pretty solid. Is this something I would notice moving it by hand? 

[JFP in PA]

2 hours ago, RRjr said:

thanks again...when I grab the pinion gear and rotate it doesn't seem to have any play side to side - feels pretty solid. Is this something I would notice moving it by hand? 

 

Not necessarily. The other thing you need to consider is having to do it all over again if you guess wrong on which bearing it is, which is why most shops replace ALL the bearings when there is a problem.  

[RRjr]

Fair enough - thanks again for your help, will continue investigating. 

[JFP in PA]

1 minute ago, RRjr said:

Fair enough - thanks again for your help, will continue investigating. 

 

And just as a by-the-by, that pinion bearing is a $500 item at retail 😮

[RRjr]

Indeed, not to mention the transmission needs to be taken apart if I'm not mistaken...

FYI - this knocking sound on and off throttle regardless of gear only started about a month ago, together with a whining/vibrating noise only on acceleration. I thought bad bearings get slowly worse over time, but there was no knocking sounds before then...it's quite audible and distinct, although not always consistent. Here's a video showing us moving the axles by hand - first both in the same direction, then one by itself...

 

 

Any thoughts would be appreciated...☺️ 

[JFP in PA]

That is definitely not "opportunity knocking".

 

To replace the pinion bearing, the entire gear "tree" has to be disassembled, and some special tooling is involved as well (surprise, surprise).  Another reason why for most, this is not a DIY project, but usually farmed out to one of the specialty gearbox shops.

[elsabeth]

In many differential setups, especially those in Porsche vehicles, shims are used to adjust the backlash and preload of the differential gears. However, in some cases, the shims might not be immediately visible without disassembly, as they can be located between the bearing and the differential housing, or within the precision bearing itself. If you don’t see any shims, they might be internal or integrated into the bearing setup. After removing the bearings, you should be able to see if there are shims present. During reassembly, you will need to ensure the backlash and preload are set correctly, which might involve measuring and adjusting the shims. Porsche typically has precise specifications for these adjustments.

Edited August 14 by elsabeth