Help me diagnose my gearbox whine.

[kamaro]

I just did my 1st drive after installing a SBH 930 gearbox in my car, The previous owner of the 930 box has taken the LSD unit out of it and put in an open diff. instead, so I knew that I might need to set the backlash on it, so I did a pattern check before I install it in the car :




I took the chance and installed it as it is, it turned out I pushed my luck too far, as I can hear a whine when ever I exceed about 30 mph, and it clearly a R&P noise as it would still be there even if I press the clutch. I can drop the engine at anytime with no issues, but I need to figure out how to approach setting up the R&P correctly, I have done more than a dozen muscle cars rear ends with ease, but I never did a Porsche!, I can't even think how do I suppose to check the backlash with the whole diff assembly hiding inside the housing. Please let me know if you have any tips/tricks, thanks!

[kevingross]

You need to set both the diff carrier bearing preload as well as backlash (freeplay). Can't be done with the marking fluid in your pictures. The workshop manual describes the process and tools needed.

[kamaro]

Originally Posted by kevingross

You need to set both the diff carrier bearing preload as well as backlash (freeplay). Can't be done with the marking fluid in your pictures. The workshop manual describes the process and tools needed.

To be honest, I read the procedure in the manual but I feel that I need to clarify it more from someone that already did it before.

Are the bearing preload and the backlash can be done by using different shims on the carrier? If so, I think it can be set while the trans still in the car, right?

[lite75]

Recommend removing the transmission and making adjustments on a motor stand. If the pinion gear hasn’t been changed should only require shimming the diff.

[kamaro]

Originally Posted by lite75

Recommend removing the transmission and making adjustments on a motor stand. If the pinion gear hasn’t been changed should only require shimming the diff.

The pinion has not changed, the PO only replaced the differential unit but kept the original pinion and gear.

Where do I find the shims/bearings and the s[special tools to make the measuring/adjustments for it? I have searched the whole Pelican parts with no luck.

[Matt Monson]

A 385 tool is a rare beast these days. I paid several thousand for mine.

[Marc Bixen]

I'd still like to find one Matt. I borrow P.Z.'s when I need one.

[Jon B]

Originally Posted by kamaro

Are the bearing preload and the backlash can be done by using different shims on the carrier? If so, I think it can be set while the trans still in the car, right?

Kamaro, to check or adjust the backlash, the pinion shaft must be locked. To do that properly, the front housing must be removed.
You might be able to do a basic preload check in the car, but to check the bearing drag the pinion must be removed. And any adjustment to the preload will probably alter the backlash.

The whole process cannot be done properly with the transmission in the car.

[lite75]

You can check the bearing drag by removing the ring gear, much easier in this case.

[Jon B]

Originally Posted by lite75

You can check the bearing drag by removing the ring gear, much easier in this case.

Yes, it can be done that way, so it's possible to check the bearing drag and preload with the transmission in the car.
If you remove the ring gear, you would then need to clean the gear and the diff housing, re-mount the ring gear, re-torque the 12 bolts and install and peen 6 new lock plates.

If the guide fork plate is removed from the transmission, it might be possible to lock 3rd or 4th gear and in effect lock the pinion shaft. Possibly with an improvised tool bolted to the case.
It would require a complicated work-around from the normal process, and the results may be questionable.

The best and most accurate way to do all this is out of the car, properly, with the parts cleaned and dry except for some oil on the bearings.