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MG TC
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Ray White



Joined: 02 Dec 2014
Posts: 3199
Location: Derby

PostPosted: Tue Dec 31, 2019 9:05 pm    Post subject: Reply with quote

I am at my wit's end with the diff rebuild. The meshing of the Crown wheel and pinion is not going well. There is a variation in the back lash and a runout of up to 0.04 mm. The maximum should be 0.01mm - any more than this and the axle will be noisy.

I suppose this is what happens when you try to make a silk purse lout of a pig's ear. Crying or Very sad
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Farmer John



Joined: 18 Feb 2010
Posts: 167
Location: Manawatu NZ

PostPosted: Wed Jan 01, 2020 2:33 am    Post subject: MG TC diff Reply with quote

Hi Ray
The runout tolerance looks to be pretty tight, max 1.6 thou of an inch?
Getting the runout down is most likely a matter of checking and resetting the side bearings and then doing the same to the crownwheel to carrier fit.
Take it apart and wash it all using fresh cleaning liquid and a perfectly clean brush. You will need a perfectly clean surface to place the parts on and let them drip dry.
Inspect the mating surfaces for absolutely anything abnormal like scratches or dings or dents. Run over them with a razor blade or similar if you can to feel for damage. Do not expect to find anything but you must check. Running a file over is not accurate for the tolerance you are chasing.
Have a good look at the corner radius where the side bearings fit, you do not want the bearing touching there.
After the checking wash it all again. I really want to say wash it three times with clean washing liquid each time.
Of course you will have the crownwheel preloaded when checking the runout.
Tighten the bolts as evenly as you can (which means the threads must be perfect) a flat at a time. If you still have exactly the same runout there are a couple of options. Do it all again is one, or knowing the highest reading dismantle again and pay attention to the relevant parts of the carrier and wheel. The wheel could be fitted half a turn round and see what changes.
Personally I would dismantle check and clean three times before even thinking of any other action because I have been through this sort of thing before, taking a crankshaft out of a partially assembled engine and washing the shaft caps and bearings again for example. Happens to all sorts of parts.
Just bear in mind Ray that cleanliness is crucial, wash the outside of your washing pan, wash all the tools you are going to use, clean clothes the works. It is not surgery though, your "C" is not going to get infected or catch some virus. Good luck, it is only work that will achieve your desired outcome.
John
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Ray White



Joined: 02 Dec 2014
Posts: 3199
Location: Derby

PostPosted: Wed Jan 01, 2020 2:57 am    Post subject: Reply with quote

Thankyou for your helpful reply, John. As it happens the crown wheel and pinion are brand new...as are the bearings. I have gone for taper roller bearings.

The parts that are old are the diff and carrier itself (and the casings, of course). I checked the run out with the c/wheel bolted to the carrier before trying to mesh the pre loaded pinion and it seemed fine. I was quite happy with it. The problem only seems to have appeared since tightening up the adjuster nuts.

Although it is definitely not cracked, I think this diff has suffered a trauma at some time in the past as the pinion was missing a tooth and the front bearing cage had broken up.

Also, one of the large (2 1/16") adjuster nuts was incredibly tight and required considerable effort to move it. I have worked it back and forth a lot of times and freed it off - but it is still tight compared to the other side which is fairly loose. I don't know if there is some kind of distortion that shows up when these nuts are tightened for mesh adjustment?

I can take it apart again and reposition the c/wheel to see if it makes any difference but if there is no discernible run out as before then I don't know what to do.

If I end up with a noisy axle I will never be satisfied with the car. Perhaps I may have to substitute with a refurbished 3.9:1 Morris Minor unit.?
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Farmer John



Joined: 18 Feb 2010
Posts: 167
Location: Manawatu NZ

PostPosted: Wed Jan 01, 2020 4:06 am    Post subject: MG TC diff Reply with quote

Hello Ray. When a tooth breaks off, even disregarding the force that caused the break, the broken piece of tooth can lie in the valley and get run over by the other gear, or the other gear try to ride up on the broken stub, causing a massive load on the carrier which could easily be enough to distort or break it. If there is damage to the crownwheel teeth that you think fits this scenario you could pretty well write off your carrier.
Another check Ray. If you can somehow arrange the dial gauge so that it reads radially somewhere on the wheel edge, that will tell you whether the wheel has any "rise and fall". If it does you have confirmation that one of the side gear stubs is at fault. That is enough reason to instantly discard that carrier. Tightening the adjusters would load up the stub it seems.
Whether you look at second hand items is your decision as you certainly have the knowledge and equipment to check any you find.
John
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peter scott



Joined: 18 Dec 2007
Posts: 6137
Location: Edinburgh

PostPosted: Wed Jan 01, 2020 11:55 am    Post subject: Reply with quote

Hello Ray,

I'd be inclined to just try it and see if it's noisy and be prepared to strip again if it is.

Peter
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Ray White



Joined: 02 Dec 2014
Posts: 3199
Location: Derby

PostPosted: Wed Jan 01, 2020 12:46 pm    Post subject: Reply with quote

peter scott wrote:
Hello Ray,

I'd be inclined to just try it and see if it's noisy and be prepared to strip again if it is.

Peter


Hi Peter. I am hoping to get the axle finished before fitting the new body. I don't really want to rush things or cut any corners if I can help it so if it costs a bit more to get it right first time then I am prepared for it.

The new crown wheel and pinion came from Roger Furneaux in Devon and he can supply me with either a refurbished carrier for not much money - or a new one for about 400 (which is about 1/3rd less than Moss). The question is whether to go all out and buy new diff gears as well - but I am not sure about that if the noise is only likely to come from the c.w.p.?

An alternative would be a high ratio Morris Minor unit that could fit into my casing without much fettling but I am reluctant to change course having invested in the MG parts.


Last edited by Ray White on Wed Jan 01, 2020 1:18 pm; edited 1 time in total
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Keith D



Joined: 16 Oct 2008
Posts: 951
Location: Upper Swan, Western Australia

PostPosted: Wed Jan 01, 2020 12:58 pm    Post subject: Reply with quote

Ray, get that diff right the first time. If you do not, it will fester in your mind during the remainder of your restoration and spoil the enjoyment you will get when the MG is back on the road, completely refurbished.

You have one of the most desirable classic cars of all time, (IMHO) so I would strongly suggest you don't shortcut anything, just keep heading for a gorgeous car that will be as new.

Keith
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1932 Austin Seven RN long wheelbase box sedan
1950 Austin A40 tourer
1999 BMW Z3

You are either part of the problem or part of the solution
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Ray White



Joined: 02 Dec 2014
Posts: 3199
Location: Derby

PostPosted: Wed Jan 01, 2020 1:25 pm    Post subject: Reply with quote

Keith D wrote:
Ray, get that diff right the first time. If you do not, it will fester in your mind during the remainder of your restoration and spoil the enjoyment you will get when the MG is back on the road, completely refurbished.

You have one of the most desirable classic cars of all time, (IMHO) so I would strongly suggest you don't shortcut anything, just keep heading for a gorgeous car that will be as new.

Keith


Thanks for the kind words and encouragement, Keith. I really hope to have an eminently usable classic sports car when it is finished.

This is likely to be my last rebuild and I am investing my savings into it. I try not to worry about the cost which is huge and think about the fun I might get from it. Very Happy
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Ray White



Joined: 02 Dec 2014
Posts: 3199
Location: Derby

PostPosted: Fri Jan 03, 2020 1:39 am    Post subject: Reply with quote

Today I finally threw in the towel with the distorted diff housing and ordered a new one from Roger Furneaux. If at first you don't succeed,,,, etc.

On a different matter, I received my new armoured brake pipe kit. The box contained the correct sections of pipe complete with end fittings. I will bend the pipes and fit with new clips (which I have forgotten to order) but if it all goes together without hassle then I think it was 100 well spent. I just can't afford the time to make up all the Cunifer brake pipes; let alone spin yards of armour cladding from binding wire.

In preparation I made a neatly fitting master cylinder heat shield from polished stainless steel.(Proprietary ones cost 100!) At one side it meant making two small holes in the chassis to accept 1/8" BSF fasteners and the other side was discretely held in place by the gearbox mounting nuts. These new mountings look so much nicer than the old ones.

The shield insulation material is unorthodox in that it is just a flexible silicon mat usually found in the kitchen!

Another job that I finished was fitting new oilite bushes in the recently painted pedals and mounting them on a new shaft in the pedal box. I am not entirely satisfied with the fit which still seems a little sloppy.

Perhaps one day I will modify the design by having a longer shaft that goes right through the chassis and have a central drilling with a grease nipple the end - accessible from the outside. I think brass bushings would make a better job and the split pins could be replaced with cir clips.

The master cylinder was installed... only to find that the new push rod / ball joint had insufficient clearance where the threaded part screws into the bottom of the brake pedal. All I needed was another 1/32" but in the end I had to undo the heat shield, remove the pedals from the shaft and unbolt the master cylinder from the chassis. GRRR!!

Having got the assembly greased and re fitted (with very tricky spring loaded split pins) I called it a day.
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Ray White



Joined: 02 Dec 2014
Posts: 3199
Location: Derby

PostPosted: Sun Jan 12, 2020 1:49 am    Post subject: Reply with quote

I have finally resolved my diff back lash problem. When I took it apart again I examined the mating surface of the crown wheel to the diff carrier. There was nothing obvious at first but then I tried rotating the crown wheel on the housing and noticed a slight resistance and a slight noise at one point. I discovered that the crown wheel could actually "rock" very slightly and on closer examination discovered a blemish on the mating surface at the edge of one of the six bolt hole lugs.

With a needle file I was able to remove the burr and get the crown wheel to sit nicely on the carrier. I then bolted it back down again.
After ensuring the right bearing load by carefully adjusting the side nuts, I reassembled the diff with the pinion and checked for between 5 and 7 thou backlash. This time the reading was consistently within tolerance. PHEW!!!



The odd looking item in front of the diff is a template for measuring the distance the pinion needs to be for correct meshing with the crown wheel. With this set the shim size in front of the end cap on the pinion housing can be established.
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Ray White



Joined: 02 Dec 2014
Posts: 3199
Location: Derby

PostPosted: Sat Jan 25, 2020 4:59 pm    Post subject: Reply with quote

Before and after.





That's better!
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Ray White



Joined: 02 Dec 2014
Posts: 3199
Location: Derby

PostPosted: Thu Jan 30, 2020 6:47 pm    Post subject: Reply with quote

One small item that seems to be missing from many T types is the correct Lucas fog Lamp. My car was no exception. I have a Raydot lamp but it is incorrect for the car.

I was successful in winning an Ebay auction for a Lucas FST 462 fog lamp. The lamp arrived today and is better than I had dare hope. It will need re chroming but other than that it is unspoilt.

If 47 plus 4 postage seems steep,,, new replicas are available from NTG for 440 plus postage... Shocked

https://www.ebay.co.uk/itm/223856277300
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Rick
Site Admin


Joined: 27 Apr 2005
Posts: 20851
Location: North-west UK

PostPosted: Thu Jan 30, 2020 8:27 pm    Post subject: Reply with quote

Ray White wrote:
...

https://www.ebay.co.uk/itm/223856277300


We often go to a steam bash held in the seller's neck of the woods, one year I took big Dodge to it. That event was mostly memorable for us overtaking a lengthy line of steamrollers and traction engines on the return leg.

Nice lamp, probably one of the rarer ones being quite small.

RJ
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Various 1920s-1960s - Austin, Morris, Commer, Dodge etc.
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Ray White



Joined: 02 Dec 2014
Posts: 3199
Location: Derby

PostPosted: Wed Feb 12, 2020 12:06 am    Post subject: Reply with quote

I am hoping to restore the fog lamp so it was good to find the following :

http://www.mgtcownersclub.com/restorers-corner/brass-lucas-lamp-restoration

On this occasion, I am tempted to keep everything as original as possible.
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Ray White



Joined: 02 Dec 2014
Posts: 3199
Location: Derby

PostPosted: Fri Feb 14, 2020 11:47 pm    Post subject: Reply with quote

I sometimes glance at this photo of a newly restored XPAG ready for installation. It has been painted in the same combination of dark red and silver grey that I am having my engine.

This is not my engine but how I want mine to look.
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