TC Differential

[Steve Simmons]

The previous owner of TC9849 took the differential apart. He apparently also got donor parts from two others. So now I have three diffs worth of parts in a box together that I have to figure out. Since the center carriers are machined to match (or so I've been told), I assumed there would be witness marks of some kind. I do find some stamped numbers, but nothing matches from one to the next. There is also one half that is a bit different from the others, as seen in the second photo (look at the bolt cutouts).

I did manage to weed out a bad set of gears, so most of what is left is from two diffs. Anyone have any tricks to figure out which parts went together? Or a way to take two non-matching parts and make them work? Of primary concern is the carrier halves. I think I already know the answer.

[Ray White]

Steve. I am not an expert but what I have learned about this kind of problem is that it all depends on whether or not you expect to end up with a silent (or at least quiet) rear axle. The crown wheel and pinion more than anything needs to be a matched pair. Of equal importance are the bearings and the pre load. The diff gears themselves are often fine but again the bearings suffer wear and the diff cage can often be found to have cracked. Replacements, as you may know, are available from Roger Furneaux here in England. He provided excellent instructions when I replaced mine.

[Duncan M]

Patina on the metal surface in the 3rd pic appears to show a match for the two on the right.

[ROGER FURNEAUX]

hi Steve - the first thing to do is check for cracks: do this by simply holding each half by the threaded end between finger and thumb, and tapping the flange with a small hammer or a spanner (wrench). Good ones will ring like a bell. Obviously bearings and nuts have to be removed.

Now line them up: the lock ring slots always line up side-to-side. They are nearly always stamped (often 33 for some reason) in more than one place. In your 2nd. photo you have three with cut-outs for the nuts, and one (centre) is the CW side. Hopefully you can match them up.

If you have any cracked ones (you can also use Flawfinder dye penetrant) I can get them repaired with a complete new end piece welded in and machined concentric on a jig. I also have new billet steel centres in chrome-moly, much stronger than the originals.. And every other part of course.

Always use new bolts, NEVER the old ones which are probably stretched, even if they don't have any "necking". I use 8mm HT bolts and self-locking all metal nuts (Stover or cone nuts, in 10 grade). I also only use taper-roller bearings which take a little while longer to set up, but are certainly long-lived! The first one I did 30 years ago is still running...

Roger
TC0978
MGBGT V8
MGB Roadster

[Steve Simmons]

Thanks Roger, I'll do that. I also noticed this on a couple of them. How much wear is acceptable?

Can you please email me a quote for all the bolts (for center and for ring/pinion) as well as bearings?

[ROGER FURNEAUX]

This is just about acceptable: other cars have domed bronze thrust washers on the outer faces of the spider gears, but I have not found any the right size.. Surely you can get bearings and bolts in California Steve? Postage is not cheap these days.

Roger

[Steve Simmons]

I can get them here, just need to figure out exactly what to order. One stop shopping is just convenient. There is a supplier here that sells the stuff also, but at a big markup. So I have to go to several sources to get everything.

I haven't found a domed washer to fit either. Everything I've seen is too big and too thick.

[timberstone]

Hope this is an appropriate posting thread to discuss what might go wrong with overhauling a TC differential, and to determine some cause for concern with the overhaul.
Thirty Seven years ago, the differential on MGTC0820 came out and underwent inspection and adjustment. No change in crown wheel or pinion ratio when it was installed back. However the differential was hardly used since then due to long term storage.
Then when doing the recent rebuild of the entire chassis, and seeing on this forum -- and the article by Roger Furneaux -- that there were issues with the differential bearings, as a precautionary measure the unit was removed and sent to a prominent Stateside shop for rebuild in accordance with Roger's article and installation of modern bearings.
After a few hundred miles the differential oil was drained and sent to a testing lab where it was found to be within specification.
After another 1500 miles the differential oil was sent to the same lab and came back with: "....Your copper and lead readings are a little high compared to those we've seen, maybe showing a little bronze wear."
Another 1500 miles passed and the differential oil was drained again and tested: "Copper and lead were on the high side in the previous sample, and they increased quite a lot this time so we're a bit more concerned about wear now. Not only is there more microscopic metal in the oil, we also noted visible metal in the sample bottle, which isn't a great sign. Some of the metal particles in the bottle had a copper-like appearance, and some of it reacted to a magnet (steel). There were a few larger steel pieces, but for the most part, the visible metal was very fine. Insolubles tested at limits....."

Also, mentioning that there seems to be more whining noise from the rear than normal.

Understandably now there is great concern about the situation in the differential. Should there be resignation to removal and sending it somewhere (else) for a look? If so, what should be the instructions and recommendations for a good place that can do the work properly, and maybe not just Stateside.

Octagonally yours,
BOXLEY (Robert and MGTC0820)

[Steve Simmons]

I'm not a differential expert but I can show you what it looks like when the original bronze bearing blows apart. The rest of the parts didn't look a whole lot better. This was the original part out of the diff I was asking about earlier.

That said, if you replaced all the bearings with modern then I'm wondering where the bronze in your oil came from.

[Duncan M]

Robert-

From the whine you hear--to the bits of metal in the oil, it sure sounds an awful lot like the pinion ball bearings are gone and getting ground up. The only thing keeping the whole thing from exploding is a straight roller bearing--also on the pinion. You need to disconnect the driveshaft at back, and see if there is any sideways movement of the pinion. Of course it could be something else, but those original style pinion bearings (brass caged double row ball bearing by R&M) were just no good. Have you noticed leaking from the pinion cap scrolls? That is a sign the pinion shaft is getting loose and wiping out the scrolls on the cap. You should check those pinion bearings before you drive the car again.

[timberstone]

Think there will soon be removal of the unit and look inside.
Will report then.
Octagonally yours,
BOXLEY (Robert and MGTC0820)

[ROGER FURNEAUX]

hi Robert - if your diff. was rebuilt according to my instructions, it should have four taper-roller bearings, which have no bronze. Even if they used modern bearings 3305 & N305 such as Moss supply, they have steel cages. The only other sources of "yellow metal" are the oil scrolls in the axle ends. With worn hub bearings (a possible reason for the whine?) the half-shafts move about a lot and wear away the brass scrolls. I have seen them worn smooth, with the inside ends almost gone, due to flexing of the half-shafts.

Regarding the original Ransome & Marles bearings with their bronze cages, the diff. I rebuild mostly all still have them. The CW side bearings are usually in perfect condition, but I replace them anyway (so I have plenty of good used R&M LJT35s if anybody wants them!). The 3MDJT25 double row thrust bearings which Steve shows, break up because they are not up to the job. I very much doubt that they are attacked by additives in the oil, as shown by near-perfect LJT35s. They are now obsolete, but I have a few NOS if anybody really wants to stay original!

As regards rebuilding your diff. you are welcome to send it to me here in Olde England, but the courier cost would be horrendous! I make diff. drain plugs, with a better head size and a magnet to catch all those pesky particles.

Roger
TC0978
MGB
MGBGTV8