TR4/4A Diff gear wear

[cjimj]

Before my question, here's my sad story. I've owned my 4A since about 1976. It was in bad shape when I bought it, so I started a full body off restoration around 1980.

One wife, two kids and 32 years later I finally started making some progress https://www.youtube.com/watch?v=Z7y6uXelPzw&list=UU1fZlKoBvlFAhWovwPdCfjw&index=1&feature=plcp

Another two years later I'm picking up speed and now have the front suspension ready to reassemble and am working on getting the diff ready for the rear suspension.

I don't recall any problems with the diff when I parked the car way back then, but I figure the car has around 75-100k miles and the backlash measures 0.006 inches. I made a stab at checking the contact pattern, which shows full contact across the full width on the top half of the tooth. The info I've found says the pinion is set too shallow, but I haven't found any mention of what full contact across the tooth means.

Can someone tell me from this info whether the gears are worn excessively or do they just need to be readjusted?

Thanks,
Jim

 

[TR3driver]

Can't really tell from that, until you get the pattern centered the other way. Probably means some wear, but maybe not enough to replace the gears. Of course, I did over 200,000 miles on a diff that was much worse than that when I got it, and it was still working fine when the car got totaled.

 

[cjimj]

The info I've come across is either how to set up presumed good gear sets or else pictures after the damage had occurred. Nothing in between. I suspect they're OK, but if I've got to go to all the trouble of resetting them, I'd like to be reasonably sure I'm not reusing questionable parts.


Do you know if resetting the pinion depth can be expected to narrow the contact patch so that it's less than across the full tooth?

Thanks,
Jim

 

[CJD]

Jim, could you include a picture of your contact pattern? For a well used set of gears, it is normally best to set it how it has been running, and not worry much about the backlash. The two gears wear in together, so it is often difficult to get a perfect "book" pattern on a used set. That said, it should not be completely foreign looking.

If it was quiet when they ran, then they are likely good. If they had a whine at 30, 60, and 90 mph...then I've found it's unlikely it can be fixed by trying to adjust the pattern.

 

[cjimj]

The gray line about 2/3rds down the tooth is the edge of the contact patch. Everything above was wiped clean by the pinion.



Thanks

 

[CJD]

I think you are right, that the pinion could use just about .002" extra shim to try to move the contact patch further into the teeth, and off the edge. It appears the ring gear is good, but you have to check the pattern after the extra shims are added. The amount of shimming is just a guess. If you take pictures for each thickness adjustment of shims, you'll start to get a feel for how the patch changes.

Setting dif gears is an art that takes patience. I've had sets that took me 2 days playing with shims before I was happy with the pattern. Once in a while you hit it right off, but that's not common. It's well worth the time spent, as the dif will last the life of the car if set up properly.

 

[cjimj]

Thanks very much for sharing your insight. Time to build the spreader and get to work!

Thanks again,
Jim

 

[TR3driver]

Time to build the spreader

Up to you, of course, but the spreader is not strictly required.

 

[cjimj]

LOL, I had hunch someone would pipe up to say a spreader isn't required. I saw your pictures earlier and thought about using your procedure to extract the diff from my extra live rear axle, but after dinging a corner just removing a seal I figured I'd be wise to 'do it right.' Besides, it doesn't look that hard to make one, though making one that WORKS might be another story...

Take care,
Jim

 

[TR3driver]

Not "my" procedure really, rather passed down to me by "those who have gone before" (as somebody put it). Note that you have to careful with the spreader as well, there's a big warning in the manual that overspreading will damage the case.

PS, I've used the pry bars on solid axles as well, just didn't take any photos.

 

[titanic]

Jim-I have a home made spreader and an extra diff (blatant commercial message). I am located in Albany. PM if interested.
Berry