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MG MGA - Replacement crown wheel and pinion query.

I have recently ordered a 9/41 4.555:1 differential gear set from Moss (Part No 267-185 ) and note that it requires a different pinion flange and nut, see
http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29225#18
Interestingly, they show the 3.9 gear set only requires a replacement nut and the 4.8 does not require either - Why is this so?

I note in the Brown & Gammon catalogue that they also offer 4.1, 4.3, 4.55 & 4.875 gear sets but make no reference about requiring a replacement flange and/or nut for the non standard ratio gear sets (I emailed them asking did their 4.55 gear set need a replacement flange and nut but have had no reply as yet).

Mike


Mike Ellsmore


Note that only the 4.55 is available from Moss. I'm pretty certain this is new Hindustan production. The 3.9 would have been MGB production. The 4.875 and 4.3 were MGA era production. So, the older ones use the old nut and flange, the 3.9 requires the later flange but uses the old nut, and Himdustan have made some change that requires the MGB flange and a different nut. The Hindustan plant is a state of the art modern gear plant, and wouldn't surprise if they went to metric threads.

FRM
FR Millmore

The MGA 1600 factory Service Parts List shows the 9/41 rear axle gear set as an option.
It does not specify that a different flange nor a different nut are required.
It appears that the supplier to Moss has put a different spline and thread on the pinion.

Mick

Typed before FRM's comment but posted later.
M F Anderson

When I get the Moss bits I will measure the splines and thread. The 10/43 MOWOG gear set I am replacing in this diff has 10 splines (1.0" OD) and the thread is 0.75" OD 16 tpi (3/4 UNF). I also have a 11/41 diff so when it is dismantled I will measure that also.
Mike
Mike Ellsmore

oops...I meant to write "I also have an 11/43 diff so when is dismantled I will measure that also".
Mike Ellsmore

Mike-
About 5-6 years ago, on one of these boards, somebody said that they had gotten a 4:55 from Moss, and there were no setup numbers on the gears. A Moss spokesman said they had asked Hindustan about this. The answer was that the new equipment was so good that they just scrapped any gearset that was not "zero-zero", ie exactly on spec. Said that it made life much easier for the mechanics off in the mountains, who had neither tools or ability to set up gears properly. I was hoping they would make up a bunch of different ratios for us!

FRM
FR Millmore

If FRM's theory that the new gear sets may have a metric pinion nut is correct I would be concerned that the threads in the crown wheel, for securing it to the carrier, may also be metric.

Mick
M F Anderson

Mick-
I expect Moss would say so, and sell you special bolts.
But I doubt it. Big external threads are generally cut, or ground, in the same setup that the rest of the part blank is made in. The new machinery for that may well be standard in metric, but special for inch threads = cheaper to change the nut, also standard.
Small internal threads are mostly still made with taps, so setup is just putting different taps in the machine. Plus it avoids having to ream the carrier holes or make special shouldered bolts.
I think these are service parts only now, not new production parts; seems to me I read that Hindustan finally retired the A50!

FRM
FR Millmore

Received the pinion and crownwheel (4.555:1) from Moss today - great work by UPS - ordered Fri, here in Oz Wed.
Surface quality of the gears was a shock - looks like they are sand blasted rather than the polished finish usual found on gearsets! Thought it might have been some kind of preservative but didn't come off with thinners. Took around to my diff. specialist and he also said he had not seen new gears looking like this! Buffed of some of the gray stuff with a wire buff but no high polish underneath. We have decided to assemble the diff and see how it runs!
The reason Moss sells a replacement pinion flange for these gear sets is these pinions only have 6 splines (as against 10 on original gearsets) - both 1.0" diameter. The thread on the pinion is different also M18 x 1.5 mm pitch (original 3/4 UNF 16TPI). Checked threads in crown wheel and these are 3/8 UNF (same as original). Also the untapped hole is missing on the replacement crownwheel. I guess these are the diff gears running around in the Mumbai A50 taxis.
Has anyone use tried these gearsets previously in an MGA?
Mike

Mike Ellsmore

More photos.
Mike

Mike Ellsmore

Mike,

I wonder if the gears have been "tuftrided" like some of the rocker shafts? Is the surface powdery?

I wiped a new tuftrided rocker shaft down with a bit of oil and a mild 3M pad to get to a smooth surface.

John
jbackman

The grey finish is a form of phosphate treatment, similar to (and possibly licensed from)Parkerizing. It forms an extreme pressure break-in lube, and incidentally acts as an anti-corrosion coating as well. Do not try to remove it!

http://parkerhq.com/zinc_phosphate.htm

Most commonly known as a finish on guns etc., it is also commonly used on hi-torque fasteners, and cams and similar that have very high pressure sliding loads, like hypoid gears.

http://en.wikipedia.org/wiki/Parkerizing

This is an area of lubrication/materials technology that has been growing like crazy in recent years, so your gears may have had some even better witches' brew processing.

FRM
FR Millmore

John has a point, Tufftriding is another possibility.

http://www.durferrit.de/media/pdf/Tenifer_QPQ_eng.pdf

In either case, any part running in soft metal bearings would need to be polished, as the crystalline surfaces would eat white metal or bronze bearing materials. Parkerized camshafts and Tufftrided crankshafts always have polished bearing journals, but cams/followers and gears (sliding loads) are not polished normally.

FRM
FR Millmore

I have emailed Moss to find out what the coating is and also asked if they have a comment to add to this thread.
Mike
Mike Ellsmore

When i worked at David Brown Gears they used this process which we called Parkoluberising.It actually eats its way into the metal and when oil is added it soaks in.This way the oil is not just on the surface of the gear but also inpregnated into it.
I used to Parko small parts for painting as the paint soaks into the metal and leaves a great finish.
P D HEWITT

Moss replied to my query and said (short and sweet)finish is protective coating - don't worry about cleaning it off - have fun driving!
Barney has updated his Tech guide with info about these gears. If any problems after installation I will update the thread.
http://mgaguru.com/mgtech/rearaxle/ra202b.htm
Mike
Mike Ellsmore

Just noticed a brand new 3.9 diff assembly on ebayuk number 260978322651 - bit pricey at £200 link is below -

http://www.ebay.co.uk/itm/260978322651?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649#ht_500wt_1413
Cam Cunningham

The saga continues - my differential specialist assembled the diff with the Moss gears and has advised if I used this differential people would hear me coming down the street from two blocks away! He says these gears have not been lapped during manufacture. It is impossible to get it turn on the bench without a significant rumble that alone at road speeds. He has advised me not to use the gears and return them to Moss. (He has been in business as a diffential specialist since 1983 and is renowned in Melbourne for his work). I intend to take the matter up with Moss. (freight from US to Aust for 12 lbs is ~$110).
Has anyone used the Moss 4.555:1 crown wheel and pinion gearset without problems?
Mike
Mike Ellsmore

Mike, you might find it easier to look for a ZB Magnette diff.
M Wellard

Thanks M Wellard,
Yeah I realise that now. I thought buying a new crown wheel and pinion would provide me with trouble free motoring (hillclimbs, motorkhanas, sprints plus a bit of touring) but rather it has left my bank balance poorer!
I have had a bad run with big items imported from the US. An alloy cylinder head required $450 of modifications to make it useable (valve seats need re-cutting, valve guides needed reaming plus a couple of other smaller issues) - not Moss supply that time!
Mike
Mike Ellsmore

Mike, can the diff specialist lap the diff for you. It should be possible (suggest that Moss contribute in some way). Cheers, Mark
M Wellard

This thread was discussed between 10/03/2012 and 16/03/2012

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