TR4/4A Rear end questions

[Rut]

I’m in the process of cleaning up the TAs, hubs, and diff from a TR6 in preparation of possibly using them in my 67 TR4a restoration. I also wanted to use these extra parts to learn on since this is my first time. The TAs are stripped and the bushings removed and some of the hub mounting studs need attention. My plan is to blast the TAs and clear coat them. The bearings and U joints are extremely smooth which really surprised me considering the surface rust, but there’s absolutely no slop. The diff has been partially disassembled and the pinion nut marked and removed so I can replace the pinion seal. I’ll check the preload (15-18 in lbs) on assembly, but would that change with a new pinion seal and would you feel safe putting the nut back in the marked position or would you go with preload? The diff was smooth before I started and should be good to go with a new seal. Is my idea of using these TR6 parts on my 4a off base?
Thanks, Rut

 

[bobhustead]

I think the torque spec is for new parts. Since yours are already worn in (despite condition), full torque might be too much. The Haynes manual for my 3 said mark it, break it loose with hand tools, and count the turns off, returning it to the same number of turns. If you didn't count turns, I guess you could go the to spec preload and back it off til the marks line up.
Bob

 

[TRopic6]

Rut,

The trailing arms are different in that the TR6 has the upper rebound rubber mounted on the arm; on the 4A it mounts on the body and there is a smooth spot on the TA for it to contact on. I'm going from memory though; I once got a set of 4A TAs with half-shafts and noticed that. You can adapt them to work I think.

Jeff

 

[Rut]

Thanks guys, I did mark the nut relative to the pinion as well as noting number of turns. I now see the difference between the 4a and 6 TAs and will use some of the 4a TAs for the restoration, but I’ll continue to restore the 6 rear end for experience. I’m guessing the 6 and 4a hubs and half shafts are the same, but I’ll confirm that.
Thanks, Rut

 

[TR3driver]

On the diff, I think it depends on whether you have the earlier unit with shims, or the later unit with the crush sleeve.

With shims, torque the nut to spec. If preload is significantly off, you have to change the shim pack. Probably not necessary, but if you want to accurately check preload, you have to do a trial assembly without the seal.

With the crush sleeve, your only hope is putting it back exactly where it came from (don't go past and then back off). Even that is iffy; you really should replace the sleeve and re-crush the new one. Again, you have to stop going in, you can't go past and back off.

Most of the force from the nut has to be taken by the sleeve, up to the front bearing race and pinion gear. Only a tiny fraction of that is applied to the bearings. (But the preload comes from the tiny fraction.)

 

[TR3driver]

On the diff, I think it depends on whether you have the earlier unit with shims, or the later unit with the crush sleeve.

With shims, torque the nut to spec. If preload is significantly off, you have to change the shim pack. Probably not necessary, but if you want to accurately check preload, you have to do a trial assembly without the seal.

With the crush sleeve, your only hope is putting it back exactly where it came from (don't go past and then back off). Even that is iffy; you really should replace the sleeve and re-crush the new one. Again, you have to stop going in, you can't go past and back off.

Most of the force from the nut has to be taken by the sleeve, up to the front bearing race and pinion gear. Only a tiny fraction of that is applied to the bearings. (But the preload comes from the tiny fraction.)

PS, On the Stag diff (only manual I've got handy), a wider range is allowed for pre-load when you have the crush sleeve. 13-20 INCH pounds rather than 15-18.

 

[Rut]

Randall,
Thanks for the info! I don’t know what year or ratio this diff is, but I can get it back to where it was after I install a new pinion seal. I’ve found a variety of cast numbers, but nothing stamped and I haven’t opened it up yet to count the teeth. If I put it back to the same position on the pinion nut and I’m within spec on the preload will that be ok? This car will be a Frankenstein in some regards with an OD tranny from a 62, possibly a TR6 engine with a little extra, etc. unless I go nuts with the M3/Getrag I like so much. My plan is this, I don’t have a clue...
thanks, Rut

 

[TR3driver]

Yeah, should be OK even with shims.

Only a slim chance it will be anything other than 3.70 ratio. The housing and carrier remain the same, the gear sets interchange. On earlier cars, there was supposedly a paint mark indicating factory ratio, but it could have been changed. I don't know if the paint continued into TR6 or not.

 

[Rut]

I cleaned up the TAs and diff which has a 37 tooth ring gear, derusted the driveshaft, etc. The diff is in great condition and the TAs have no cracks and only one stud needed a helicoil, the rest were secure. All in all, this was a really good exercise and I learned a lot...I’m ready to tackle the 4a rear end now.
Thanks, Rut