gearbox crown wheel bearing preload

[andyblackman777]

I've read the service notes and various other threads about this but there is one thing I'm unsure about.

When tightening the crown wheel nut I assume it forces the bearing race out towards the crown wheel. If you then decided its to tight, then undoing it would not draw the race back as its pressed into the case. or am I missing something here

any thoughts?

Cheers 

Andy

[andyblackman777]

I can answer my own question.😀 If you tighten to much you have to press the race back in a bit and start again

 

[andyblackman777]

Just  thought I'd post here on my experience of doing this. I fitted new bearings to my diff with the original shim. I assembled the cases dry with no shafts, just the diff in place. I then tightened the preload nut until the diff just started to feel resistance. I then used a spring balance and some string wrapped around the diff body as explained in the service notes. I measured the resistance by pulling on the string to get the diff to rotate, taking the measurement from the gauge while the diff was turning. I tightened the nut a little bit at a time until I got the reading in the middle of the specified range. If you reuse the old bearings you just need to check the diff rotates freely with no play when assembled as described.

Next was the reassembly of the complete box and to check the backlash. I did this without sealing the cases. to make it less messy/work if I did have to change the diff shim. ( the shim thickness is what governs the diff backlash) not the preload nut. (Having said that I think it  can effect the backlash but its not the correct way to do it).  I measured the backlash with a dial gauge and found it to be at the tighter end of the tolerance 0.1mm. It is essential to lock the secondary shaft in position I used a large adjustable wrench on the rear nut . Holding it by hand doesn't work. Interestingly I measured again after reassembly and sealing the cases with the Renault anaerobic sealant. The measurements were the same. Thickness of the sealant is tiny, I would like to know what difference the next size shim would make on the preload. The lotus ones come in 1.0, 1.1, 1.2, 1.3 mm and so on and the back lash is between 0.1 and 0.2 mm. so I'm curious what effect a 0.1 mm shim size change would make to the Backlash. As I was in tolerance I decided not to completely strip the box and diff to see if the next size shim would put me in the centre of tolerance, so I can't answer this question. if anyone does know please comment here.

I made a short video of this here, which is quite boring!

 

 

[jannickz]

You're correct in your understanding. Tightening the crown wheel nut typically pushes the bearing race outwards against the crown wheel. However, simply loosening the nut won't necessarily pull the race back perfectly due to friction and potential deformation during tightening. As you tighten the nut, it applies pressure to the bearing race, pushing it outwards against the crown wheel. This increased pressure preloads the bearing, reducing play and ensuring smooth operation.