Loose CV axle and damaged front drive unit differential

[glankford]

Hello everyone, I just purchased a 2020 model 3 performance with some damage on the front right side. The inner CV boot was damaged so decided to replace the CV axle on that side. When I went to pull it out, i noticed that it was pretty loose and wobbly where it met the front drive unit. After removing the old one, I discovered the bushing part of the differential (next to the spline) was pretty chewed up and scored on both the axle and mating surface inside the drive unit. There isn't a replaceable bushing inside the drive unit from what I can see. I don't really need a limited slip differential from Unplugged Performance but don't see anywhere else where I can get one. I pulled the motor out and got everything apart and found that the bearing on that side was damaged from metal debris created by the axle.

I've rebuilt plenty of engines and transmissions so disassembly doesn't scare me.

Thanks in advance!

 

[one2many]

3 words come to mind - junk Yard

 

[NewbyMaybe]

I don't know much about M3's but the issue with most drive units is the software/firmware. Does the unplugged unit swap easily?

Put a cable cam in your drive unit to see how bad it is.

 

[glankford]

It does swap without too much fanfare. The worst part was draining the coolant and ATF=9 fluid. Here are some pics of the internals if anyone is interested. The last pic shows the chewed up surface where the CV axle mates up. I'm going to try a local machine shop first to see if they can sleeve the differential.

 

[MobileClimate]

any update on what you can use ? this is some of the reason why they say NO LUBE on the splines ..because that axle sits in that bearing you dont want that to slip

 

[buckets0fun]

because that axle sits in that bearing you dont want that to slip

'That axle' is inside of the differential. The differential has a bearing on it that rests in a raceway within the DU case's casting.

OP- Curious to see what your axle's spines look like. Happen to have a photo?

 

[MobileClimate]

It’s also possible to install the axl without the snap ring which would cause a lot of damage when you first try to drive it

 

[tesdpr]

This may be a weird question but if the jam nut on a tie rod end is loose, which it was from factory on my 22 MYLR, and I felt nothing on the driving experience, can the drive shaft on CV joint also be damaged from the back and forth of the tie rod end moving slightly while not secured by the jam nut? If so can the DU differential that ties to the CV axle be damaged from this as well?

 

[tesdpr]

This may be a weird question but if the jam nut on a tie rod end is loose, which it was from factory on my 22 MYLR, and I felt nothing on the driving experience, can the drive shaft on CV joint also be damaged from the back and forth of the tie rod end moving slightly while not secured by the jam nut? If so can the DU differential that ties to the CV axle be damaged from this as well?

I am presuming because the CV has two boots with clevis inside each boot that there is enough decoupling from the spline to CV connection in the DU all the way to the wheel hub such that if a tie rod issue were to occur that it would have to be catastrophic failure for a cascading failure to the CV - correct?

 

[buckets0fun]

This may be a weird question but if the jam nut on a tie rod end is loose, which it was from factory on my 22 MYLR, and I felt nothing on the driving experience, can the drive shaft on CV joint also be damaged from the back and forth of the tie rod end moving slightly while not secured by the jam nut? If so can the DU differential that ties to the CV axle be damaged from this as well?

No. You’d snap the shank on the loose tie rod and cause major damage before the cv was stressed.

It’s also possible to install the axl without the snap ring which would cause a lot of damage when you first try to drive it

damage would only come if the axle came out of the fdu. It would take some serious magic for that to happen without the driver hearing horrendous noises and likely the case of the fdu being destroyed.

 

[MobileClimate]

The snap ring keeps it locked in there and your not supposed put lube on the splines because you want that locked in there tight ..the joint can have lots of play in all directions ..if you have play on the half shaft it’s going be at the joint .the axl is either in all the way or not ..you’ll know right away if it comes out ..there’s a YouTube video of a guy that has a shop put in wrong he didn’t get too far

 

[tesdpr]

No. You’d snap the shank on the loose tie rod and cause major damage before the cv was stressed.

damage would only come if the axle came out of the fdu. It would take some serious magic for that to happen without the driver hearing horrendous noises and likely the case of the fdu being destroyed.

Thx!

 

[glankford]

'That axle' is inside of the differential. The differential has a bearing on it that rests in a raceway within the DU case's casting.

OP- Curious to see what your axle's spines look like. Happen to have a photo?

Sorry for the late reply. I don't have a picture but it looks like every other CV axle I've seen in my 30+ years as a shadetree mechanic.

 

[Bellington]

It does swap without too much fanfare. The worst part was draining the coolant and ATF=9 fluid. Here are some pics of the internals if anyone is interested. The last pic shows the chewed up surface where the CV axle mates up. I'm going to try a local machine shop first to see if they can sleeve the differential.

View attachment 849347View attachment 849348View attachment 849349

I'm having the same play on both drive units. I'm having a problem understanding the wear. Is the the worn part in the differential the side gear, or a spacer? I assumed it was where the non-splined section of the half shaft was supported in the side gear. If so, the half shaft part that goes into the side gear should always turn with the side gear and never wear at that point. What am I missing, or am I not explaining my question sufficiently?

 

[brainhouston]

this is some of the reason why they say NO LUBE on the splines ..because that axle sits in that bearing you dont want that to slip

u do understand that everything inside FDU or similar gearbox is submerged to the same oil... hence the output shaft seal...
splines don't slip

OP, ck eBay also, maybe someone took one apart n selling just the part u need.
FYI, its possible that damage come from driving after accident, like to pull over or just happened at full speed
Maybe axle partially came out n rattled in there

 

[MobileClimate]

u do understand that everything inside FDU or similar gearbox is submerged to the same oil... hence the output shaft seal...
splines don't slip

OP, ck eBay also, maybe someone took one apart n selling just the part u need.
FYI, its possible that damage come from driving after accident, like to pull over or just happened at full speed
Maybe axle partially came out n rattled in there

You dont understand that you dont put lube on splines and you dont put lube on the inside of a bearing race...that why tesla says dont put lube there its not rocket science

 

[brainhouston]

You dont understand that you dont put lube on splines and you dont put lube on the inside of a bearing race...that why tesla says dont put lube there its not rocket science

Yeah, cause everything will be covered in oil the minute u drive

 

[AlanSubie4Life]

You dont understand that you dont put lube on splines and you dont put lube on the inside of a bearing race...that why tesla says dont put lube there its not rocket science

Tesla is clear that the outer splines at the hub should not be lubed. But that is a different location.

Clicking noise when accelerating