Here's my .02 worth:
The inner race of the pinion head bearing is located against the pinion and
is in turn held in place by a spacer, a shim pack, the innner race of the
tail bearing, the input flange and the nut. The whole assembly is bolted up
solid - there can be no relative movement between the inner races of the
bearings and the pinion shaft. The outer races of the tail and head
bearings are located in the differential case, with the actual location of
the pinion relative to the crown wheel being determined by another shim pack
between the outer race of the head bearing and the differential case. Thus,
as this shim thickness is changed in order to get the pinion to mesh
correctly with the crown wheel, the shim thickness between the tail bearing
inner race and the bearing spacer must be adjusted in order to maintain the
correct preload on the two bearings. This preload is accomplished solely by
changing the shim thickness - tightening the input flange nut will not
change the preload UNLESS THE SHIM IS TOO THIN. This is why there is a
turning torque quoted - if it takes more than a few inch pounds to turn the
whole pinion assembly after everything has been tightened, then the shim is
not thick enough, and if the turning torque is too low the shim is too
thick. The input flange nut should be tightened to around 100 ft-lbs. This
is required simply to hold the whole thing together - the input flange
undergoes many thousands of torque reversals and if the nut is not tightened
enough it will eventually loosen. If any of you have tightened the this nut
to 100 in-pounds instead of 100 ft-lbs, my advice is to get under the car
and torque it up ASAP!!
-----Original Message-----
From: Pete & Aprille Chadwell <dynamic@transport.com>
To: triumphs@autox.team.net <triumphs@autox.team.net>
Date: Thursday, May 06, 1999 10:37 AM
Subject: RE: Pinion Nut Torques
>
>Chris Lillja wrote:
>>I think it's important to note that at least one of the specifications in
>>the manual for the pinion pre-load is a spec for how much torque it takes
to
>>TURN the pinion (with the diff sitting on a workbench) not how tight the
nut
>>should be. (I think.)
>>
>>Perhaps that the source of the confusion?
>>
>>7.5-10 ft lbs to turn the pinion "freely" with the nut torqued to 90-100
>>FT./lbs? That sounds right.
>
>Well, that may not be a bad idea, except remember that whatever the
>pre-load is, the engine has to overcome it in order to turn the rear
>wheels. Not that the engine couldn't easily top 7.5-10 ft lbs, but I would
>assume that the PRE-LOAD would indeed be expressed in inch pounds. Foot
>pounds seems like it would be a little tight, but God knows I've been wrong
>before!
>
>Literally, the "source of the confusion" is simply that in the Bentley
>manual on page 54 it specifies 90 to 120 FOOT POUNDS and on page 346 it
>clearly states 90 to 120 INCH POUNDS. Both of these specs are clearly for
>the pinion nut torque, not the bearing pre-load. Apparently the former is
>correct.
>
>Given that, I guess it would be wise after all to second-guess the pre-load
>specification as well. In this case, it is given on page 346 as 15 to 18
>inch pounds, (this would be equivalent to one-and-a-half foot pounds) and
>glancing at the metric equivalent, given as .17 to .21 kgf m, that looks to
>be about right. I think.
>
>Someone help us out here!
>
>Pete Chadwell
>1973 TR6
>
|