1950s 1951 Differential rebuild: few questions due to the lack of any specs

[Caddy Chris UK]

Hi All

RE: 1951 Coupe De Ville Differential (photo included).

As a follow-on to my recent 'draft video guides post'... since the diffs were only meant to be rebuilt in the factory, I'm struggling to find specs for reassembly / set-up.

I'd be grateful if you have any technical specifications / guides / input on re-assembly (I've not found any despite searching).  I've seen the existing forum posts on pinon shaft pre-load, pinon nut torque settings and bearing pre-load torque checks – which I can follow (very handy, thanks).  So I'm now only working on a few items listed below, or on any areas which commonly cause problems when reassembling diffs, that would really help. Many thanks:

1.    BACKLASH. I'm currently aiming to achieve between 8 and 10 thou. This seems to be quite common for modern diffs. Any reason that the older diffs (different materials?) might need a different spec? (The backlash on my diff was about 15 thou before disassembly). What is the spec for backlash on a 1951 diff? Will 8 - 10 thou be okay? Thanks.

2.    CARRIER BEARING PRE-LOAD: Without any spec, I'd go with a small amount of pre-load to guarantee that there was no end float. The TIMKEN general guidance is that maximum bearing life results from a slight pre-load. What is the spec for the carrier bearing preload (for these 'pedestal and pinch-bolt' arrangements)? Thanks.

3.    PINCH BOLT TORQUE: The torque setting for the bearing support 'pinch' bolts in the pedestal mounts? My, current plan, with a lack of any info, is simply to put them back 'as they were' – i.e. align to the marks made prior to removal. Thanks.

Many thanks for any help...
Chris

[Dave Shepherd]

Was the rear noise free? Pinion preload with used bearings is around 20-25 in/lbs rotating torque, with a new seal. Try 008-0010 lash, look at the tooth contact pattern. Carrier bearing preload is pretty much by feel in this case. Agreed on the pinch bolt tightening. These are the specs a newer diff would use, in general.

[Caddy Chris UK]

Many thanks for the input Dave, very helpful and much appreciated - thank you.
Chris.