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Rear Differential Concern???


Senior Member
Country flag

While out for a nice drive to see all the fall colours this Canadian Thanksgiving weekend, I notice a lot of noise coming from the rear end of my TR4 when in third and fourth gears. I was a bit annoying. It was definitely more noticable under load then when just coasting. I am going to check the oil level, and being an optimist, hopefully it's something as simple as that. I'm not holding my breath though. So, with all that, I thought I'd throw it out there for input from the forum. What might be the problem I'm looking at?

......Thanks, Alex


Great Pumpkin - R.I.P
The one currently in my TR3 howls something awful in 3rd & 4th. I'm pretty sure it is due to wear in the gear teeth (they are visibly grooved) but might also be due to the gears not being set up properly.

Fortunately it doesn't seem to be getting any worse, but I am still planning to replace it.

I'm currently trying to find some substitute for the pinion setting tool and dummy pinion, Churchill M.84. But most likely I'm going to give up and just use trial and error to get the gear pattern just right. It's a Pain in the Anatomy, but ...


Jedi Knight
If you do the best job you can setting up a diff, it will still make some noise in all likely hood.This can be mitigated with a mix of STP/Lucas gear additive and the 90/140 you get OTC at your store of choice.I have used this mix since the 60's and while excessive HP can shatter old gears,I never had one blow from bad bearings.
The howl could be in the trans also, and if this is the case, suspect the counter gear bearings on a tr4/6 box.If the 3 box is still in place dont look here they had better bearings on the counter gear,though the shaft could be worn out....
MD(mad dog)


Jedi Warrior
Country flag
Randall-I wouldn't be too concerned about the pinion setting tool. After reading and re-reading the big red Tr2-3 factory manual, I came to the conclusion it really isn't necessary. From what I understand the Churchill tool was used to determine the thickness of the shim pack necessary to achieve the magic number of 3.4375" as measured from the thrust face of the pinion to the centerline of the axle. The dimension is used to replicate the position of the R&P when they were lapped together. However, this dimension only represents a starting place as the tooth contact markings will determine the actual shims needed. Bottom line is that you can use the existing shims to start with. Since the only variable is any difference in the thickness of old vs new bearings.
Having said that, I made a useable substitute for the Churchill tool, but I don't think it was really necessary. A valuable lesson I learned from overhauling the diff is to use new lockwashers and loctite on the ring gear bolts. I had 1 bolt come loose and put a hole in the cover plate (TR6).


Great Pumpkin - R.I.P
Unfortunately, I didn't save the shim pack when taking it apart. It used to be that you could trust new bearings to be the same thickness as the old ones, but it seems that is no longer true. I got burned on the last diff I did : kept taking out shims .002 and .003 at a time trying to get the pinion preload right ... took me some 15 tries before it was finally right! Plus this diff had already been messed with, so I wouldn't have any confidence it was right anyway.

This time I measured the bearings more carefully. The "no name" pinion carrier bearings I got at first weren't even the same as each other! I replaced them with Timken bearings and they match the originals; but the pinion bearing is still different by a few .001" even Timken to Timken.

You're quite right about the tooth pattern, but it can be quite tedious to do trial & error until it is just right. I was hoping to get fairly close first.

BTW that previous diff was dead quiet. Actually kind of surprised me, after so many people said they always make noise after being rebuilt. Guess I just got lucky.



Country flag
Beautiful pattern Randall!

Many guys will engage the parking brakes when setting the pattern, to load the gears and come closer to seeing what the pattern will be under engine load. Another alternative is to favor the heel of the ring gear just a bit. Then, under load the pattern will move back to look like the one in your pic.

It is a bear. I have spent a week on a dif before I was satisfied with the pattern. Somtimes I have to just walk away and come back when less frustrated! But it is worth it, as the gear set will last a couple hundred k without noise or issue. If the pattern is off, you may only get a couple k out of the set.

I've never had the luxury of a pinion setting tool either. I always started with no shims and work up, based on how far the pattern is astray. Probably explains why it takes me so long, though.


Don Elliott

Obi Wan
I once allowed the oil level to get to low in the diff and it sounded like I had just changed to winter snow tires. The noise was there in all gears but would only make this noise during load (accelerating) or at a constant speed.

I topped it up and it seemed to get quieter - but then the noise cam back and got worse. I bought a new pinion and crown gear set from Roadster Factory (I figured that the "Made in Italy" was a good sign), removed the axle and took it in to a diff specialist here in Montreal. In all, it cost me about $1000. for the parts and labour to install the gears and do the set up properly.


Senior Member
Country flag
Thanks everyone! I now have a few things to try. I suspect the rear diff on my car has never been looked at before and more than likely needs attention. I'll do the easy thing for now and try the a gear additive mixed with my regular oil until the end of the season and then remove and inspect the diff. I actually have another ring and pinion that's in great shape. I'll compare the two and rebuild it with the better bits.

Thanks All.

........Cheers, Alex


Freshman Member
I've set up many crown wheel and pinions in many different cars and trucks over the years. I've always simply used a dial indicator to set backlash and then dye blue to get a good pattern. It can indeed be time consuming, but once you get the feel for it, it's not so bad.


Senior Member
Country flag
First off, thanks for the responses. I was definitely low on fluid. But the day after filling up the differential and transmission oil levels, I found this lovely pool of nice clean oil on the garage floor below my differential. Upon further investigation it is clear, very clear, that the oil had leaked out the front of the diff. So I do a little reading and this seems to be not usual, but the oil leaked without any load. That can't be good! Apparently there is a leather (?) seal that may be the culprit and needs to be replaced. Is that correct, or am I in for a lot more work? Is it possible to replace this seal by simply detaching the drive shaft to access it?


Great Pumpkin - R.I.P
Well, "simple" isn't exactly the right word, but it can be done. After you take the driveshaft flange loose and prop the shaft up out of the way, you'll need to remove the cotter pin and undo the big nut inside the flange, which should be torqued to something like 100 ftlb.

I don't like pulling that hard against a car while I'm under it, so I made up a tool to keep the flange from turning (which also makes it easier to turn the breaker bar IMO). Basically just a flat steel bar, drilled to take two of the driveshaft bolts, and ground a little bit to clear the socket. (You won't have to grind if you get the holes off to one side.) Others have made do by just locking the wheels with the handbrake, but I have pulled a car off the jackstands before and I do not care to repeat the experience!

Then you can tap the flange off, pry the old seal out and tap the new seal into place. Sometimes they will go in just by tapping all around the edge, but most likely you'll need some sort of tool again, to fit over the exposed shaft and press on the seal all around. I used a big socket. I like to smear a little Hylomar around the outside of the seal, and some grease inside, but it's not essential.

Also inspect the sealing surface on the input flange. If it is scored or damaged, you need to either polish away the damage or install a Speedisleeve. Spread a coat of grease on the sealing surface before installing it. Torque it to 85 ftlb, then just enough more to get one of the cotter pin slots to line up with one of the holes in the shaft. Insert and turn the cotter pin, then reinstall the driveshaft flange. If you are still using nyloc nuts, use new ones. I prefer all-metal 'Stover' nuts as even new nylocs seem to work loose for me.

Here's a shot of the holding bar (holding a Stag flange in the vise, but you get the idea).

Don Elliott

Obi Wan
Alex - I have used a "Speedi-Sleeve" at least once to fix the leaking problem. The last time, I had it all apart and my neighbour with a lathe turned about 0.010" off the diameter of the input shaft and we got a new seal that was sized for the smaller diameter. No leaks since.

Google "Speedi Sleeve" for info.
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