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Re: Transmission Noise - Diff Preload? Posted by CMyles [Email]  (#1126) [Profile/Gallery]
(more from CMyles) on Tue, 10 Apr 2007 17:16:00
In Reply to: Re: Transmission Noise - Diff Preload?, pjkbrit, Tue, 10 Apr 2007 14:52:59 Members do not see ads below this line. - Help Keep This Site Online - Signup |
Muddy,
Here is something to consider; in salvage yards they look at these units and think "Good to sell except for that one funky inner driver". They then swipe an inner driver assembly from another unit and do the swap without considering the consequences of mis-shimming the differential. To make the backlash tighter they would have to leave shims out of the right (passenger) side assembly so maybe see if there is evidence of recent tampering there. In addition to decreasing the backlash that would increase the preload on the differential side bearings too so they may be hurt if the car was driven much. Of course the only way to be sure of the backlash is to measure it with a dial indicator set up or do a contact pattern test. You can do either with the unit in the car (but it's no fun) and make the correction. Proper backlash is typically 0.17 mm on the dial indicator (when set up for this) so you're "feeling" for only about 0.007" of movement. If you were comparing a good unit to an old worn one you may think that the good unit is too tight so be careful with that. The good news is that if this is the case it's something you can fix without pulling the unit out, provided that the R&P gears haven't been damaged. You can replace the diff. side bearings at the same time if indicated. So that's how I would address that issue. I think that based on your description it is just as likely to be a breakdown of the fifth gear assembly. What sometimes happens there is that the nut on the front end of the mainshaft (aka. pinion shaft) works loose and rubs on the back of the input shaft while also letting the fifth gear hub wander. That causes the fifth slider to wander and when it's engaged it may ride against the fifth shift fork unevenly and make noise. I think that usually happens on gearboxes that have been rebuilt as I didn't used to see that problem on virgin units (which would make me wonder about the veracity of the mileage claim on that salvage unit). Some rebuilders don't torque or stake the nut properly. I have always put red Loctite on those threads as an added measure. If that's the problem then the fix requires total disassembly of course (at which point the box should be completely rebuilt). The entire counter gear assembly is unloaded when in fifth and except for the final drive dynamics, which are present in all gears, the mainshaft has limited radial load when in fifth. The load on the input shaft bearings is minimized when in fifth as the torque is transmitted through the fifth gear hub and slider. The same logic applies to the upper chainwheel bearing, if bad it would be noisy in fourth or third when accelerating from xxxx RPMs the same as in fifth. So check out your differential and if it's not that then your gonna have to pull it out and disassemble it regardless of which internal part has failed. There's no shame in trying some different oil. I've come to like the special MTLs like Redline or Amsoil because they are designed to work with synchromesh assemblies but any experiment is sometimes worth trying. Good luck, let us know what develops.
posted by 206.123.221...
, Tue, 10 Apr 2007 22:28:16, Tue, 10 Apr 2007 17:16:00 <-- Viewing This Message
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