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MG MGA - 3.9 Differential Conversion - Again

I asked about this topic back in April for converting my 1500 back axle with WW to a 3.9 ratio.

My 3.9 diff arrived in the post on Saturday - a win on Ebay. So I am on the way at last.

From the previous thread, following FRM's notes plus Barney's pictorially illustrated process, I have dismantled the diff as described and extracted the side gears. I am now just waiting for a suitable window to do the swap over. New gasket is on order.

In the meantime is there anything useful I can check out on the partly dismantled diff on my bench? Cursory look suggests all is well.

Steve
Steve Gyles

Hi Steve, Good luck with your differential rebuild. Always ready to give a hand if needed - believe you are in Preston only 15 miles from me -email me if needed.By the way our club meets this Thursday for our Pride of Ownership -if you want to visit - see our website - www.westlancsmg.co.uk
Cam Cunningham

Hi Steve,

Ref your 3.9 diff, try and get somebody to give your diff a once over, I use a gearbox repairer ( one man band) who is excellent, he has just done my 4.1 diff.
Have a good look at the crown wheel teeth, any wear will show as discolouration to the teeth where they mesh, if the teeth are visibly worn it will need replacing, along with the pinion. 'Blueing' is caused by heat through lack of oil and it will whine. Check all the teeth for pitting, the planet wheels suffer, new bearings are recommended as well as a pinion seal. If all your teeth look like 'mirrors' they're probably OK, check for slack on the planet wheels. I'm going to change my 3.9 to a 4.1, the 3.9 is high geared, third give's you 85-90 mph, I've got to slow down a bit! 3 points already.


Regards

Terry
Terry Drinkwater

Cam

Sorry for not responding sooner, been at the Farnborough Airshow for a couple of days. I will see if I can get down tonight but no promises.



Terry

Thanks for the information. My first impression was that all was in very good condition and no apparent wear on the teeth etc. I will now have a good look. Who do you use for speedo recalibration? I have forgotten where I sent mine after I converted to the 5-speed gearbox.

Steve
Steve Gyles

Hi Steve

I could bore you with a very long story about instruments, but not now. I had an unbelievable saga with Adrian Sidwell ( he goes to quite a few auto jumble's and classic car shows ) Avoid him like the plague. I was finaly sorted out by Speedy Cables who were excellent, website www.speedycables.com hope this helps


Terry
Terry Drinkwater

When I changed from 4.3 to 3.91 final drive I sent my 1450 speedometer (25x58) to Mo Ma where then changed the 58 tooth ratchet sprockets to 53 teeth for correct ODO reading, and re-magnetized the armature for correct speedometer reading. It cost $113 including shipping in early 2004. When finished they blacked out the "1450" on the face and wrote "1325" on the back.

It would have been neat if they could have stenciled the new model number and "1350" in the original locations on the front, because the factory did have that model as a production option to go with the optional 43/11 final drive (for competition use). The model number would be SN.6104/15. Very rare.

Mo Ma Manufacturing - (instrument repair)
1321 Second Street. NW, Albuquerque, NM 87102
Ph (505) 766-6661 - Fax (505) 766-5419 - Email momanm@aol.com
Barney Gaylord

Oops, typo. That 1350 should be 1325.
Barney Gaylord

Terry

Yep, that's triggered my memory, it was Speedy Cables. Just found my receipt. £47 incl P&P 6 years ago. Many thanks

Steve
Steve Gyles

I dont think you need to remagnetise the magnetic coupling to change the range of the speedo Barney? It is a matter of increasing or decreasing the range spring length/tension.
Bob (robert) I am turning? yes I once owned an MGWasp!!

Clock springs ar a pain to fiddle, and I wouldn't know where to by a replacement. The ones in the MG speedo and tach are not easily adjustable for rotation. You could increase or decrease tension on the clock spring by repositioning the indicator needle on the shaft, but that can lead to gross nonlinearity in the speed indication.

When you have the right tools, adjusting the strength of magnetism in the armature is as easy as turning a knob. When my speedo came back after recalibration it was spot on at 47 mph (test speed with my electric drill) but a little non-linear. It reads about 5% high in the 60-100 mph range, very close to correct at lower speeds.
Barney Gaylord

Steve

Keith Swindell in Warrington - search the archive. Good, cheap and reliable
dominic clancy

Thanks Dominic. Will check him out.
Steve Gyles

Terry,
Can you e-mail me with your phone number. I'd like to talk about Adrian Sidwell. I am having ongoing problems with my fuel gauge and sender unit and have already spoken to him and arranged to send both to him over next Winter for refurbishment and setting up.
Steve, if you get details of Keith Swindell can you put them up please.
David Grahame

David

These are the contact details that Dominic posted in 2004:

Keith Swindells, 30 Warwick Ave, Newton-le-willows, WA12 8PS, UK. tel +44 1925 224592

Steve
Steve Gyles

Steve ,
Many thanks. David
David Grahame

This thread was discussed between 17/07/2006 and 24/07/2006

MG MGA index

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