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MG MGB GT V8 Factory Originals Technical - rear axles

i would like some advice on any other suitable rear axles for my 1975 mgb gt v8 conversion. i currently have the standard 1800 rear axle.

regards graham
graham young

The very best option is an MGC axle with a 3.3 to 1 ratio.
Chris at

I would have said 3.07 ('69 C) but otherwise agree with Chris. Actually, depends a bit on the tranny used: if a TR8 box, 3.07; if a T-5, 3.3 (the T-5 has a higher o/d ratio). Also depends what you'd most like to emphasize, relaxed highway cruising or all-out acceleration. I don't know why, but MGBs and Cs were made with rear axles fully prepared for WWIII ... I mean, they are not Dana 60s but they are much more robust than, say, a Ford 8". If you can scare up an MGC axle with a Quaife, that is absolutely optimal but is bound to be mighty pricey.

Also add the consideration of wheel and tyre sizes. Actually rather than consider the axle ratios, use overall gearing as a guide and then tailor the transmission rations to suit that goal. I feel that around 26mph per 1000rpm in 5th gear, where the ratios are evenly spread, is a good balance between really sharp performance and sensible cruising ability. For the real cruisers then 30 or more MPH per 100 is best and this can be achieved using the high 5th cruiing gearboxes.

My 26mph per 100rpm is achieved via a 3.07 axle and 14" wheels and tyres. A 3.3 with 15" wheels would be about the same.

One thing to be very careful with is axle condition. Always have the lid off and examine internally. As 3.3 is an MGC fit only you have a very old axle and few spare CW&P's.

Roger Parker

I had the V8 Conversation done not long ago. Since I run the car on freeways the original rear end was geared to low. ( First gear was not needed) There is a supply of 3.07:1 available from England. This is the one Andy installed. As far as the performance goes this is ideal for driving the freeways and is a good overall set up. But the whining at speeds from 40MPH to 80MPH is unbearable. I wish I had went with the FORD rear end.

2000 engine RPM's gets me 69 MPH. When passing the engine has enough power to get around. If I am in a real big hurry than I shift down to 4th. My milage on a trip is 25- 30 MPG. The higher if I can stay out of the four-barrel!

Leroy Cook


That's terrible, sounds like something was installed wrong. There shouldn't be any whine at all. One possibility is, if you started out with a regular B rear rather than a C, the 3.07 cw&p being a tad larger than their B counterparts, the diff housing is supposed to be machined out. Did they do this? I'd take it back and have it torn apart and checked, admittedly not a small undertaking. A regular C rear end doesn't whine at all.

I used a chrysler 8-3/4" that has been narrowed to fit a MGB. Its a little large for this application, but I'll never break it! The main reason I went with this diff. is because it has limited slip and 3.23 gears. With a .73 5th gear (T5) and 14 inch tires, at 70mph the engine rpm is 2300-2400. First gear is 2.95 to 1 and very usable with this rear ratio.

3.07 to 3.43 should be a good choice depending on over-drive ratios and tire size.

bill jacobson

Setting up of the 3.07 CW&P in the B axle is an ongoing problem here too with many instances of excessive gear noise. I fear that the specs that are known for the axle do not include the details of those who built the things up and somehwere in the past a vital additional piece of informantion has been lost. It was a known fact that setting these axles up at the factory was very difficult and needed the finest of skilled touches to get right.

Doesn't excuse the excess noise as there are many axles that are converted to quiet operation. Just shows a history of this problem.

Roger Parker

What about the 3.07 gearset makes them particulary finicky? I ask because I am about to have a Quaife LSD installed in my V8's MGC 3.07 rear end, and I imagine they'll have to take everything apart to get it in there. It doesn't whine at all now and I sure don't want it to simply because some hamfisted shop didn't know how to get it right.

(Incidentally, the car's up near NYC ... anyone know of a shop up there that can handle this sort of work?)

Just found this bbs. Looks like good participation, nice to see Roger Parker involved.

I ended up using the new 3.07 gears (from Ian Pender/Mike Satur)in my '78. They were installed and set up at great expense by a former BL dealership mechanic, now employed by a local high-profile Jaguar restoration shop. They howl like a banshee above 35 mph.

I am now back in the hunt for a good set of MGC gears, 3.3, 3.07, or 3.7 in order of preference. But, I would like to retain my axle housing, as it has the factory sway bar mounts and all new bearings and seals. I know the sway bar mounts can be welded onto an earlier tube axle case, but I am trying to keep everything as factory stock as possible.

Is it possible to pull a good diff assembly complete from one axle case and install it in another without having to go through the entire micrometer/shimming/unavailable crush sleeve ordeal again?
Scott Pontius

It is posible, but it is helped if the A & B dimensions on the axle case are the same between the two cases.

Look either side of the centre case on the tube locating part - there should be A +3 and B -2 or something similar - this indicates the amount off standard dimension that that particular case has been machined.

The pinion also needs to be set up - in practice I have found that lightly nipping up the crushable spacer will return preload close to ideal.

The key dimension is getting the right backlash on the crownwheel as engraved on the wheel - usually 8 thou.

By swapping the washers around, I can usually gt this spot on.

Bearing preload on the diff assy bearings doesn't seem to be critical - I certainly have never had to use a stretcher to remove or insert an assy into the case.
Chris at

FYI If anyone is looking, I have just put a 69 CGT automatic parts car up for sale. Storage trouble forces me to sell it. Should have the 3.307 to 1 rear axle ratio in it. Has not run in years. Rusty, no title, late serial number car that is complete for $1200.00 FIRM. In Ohio.
Sold as-is for parts. jpegs available to serious.
Will not seperate. delivery possible.
Safety FastER, Bill
William Eberhardt

On a related note, I have long wondered: is a C 3.07 rear end the same thing as a factory V8 3.07 rear end, but for the narrower stance (most of the C rears being wire wheel axles, to my knowledge) ... I'm talking about inside the pumpkin?

This thread was discussed between 20/12/2000 and 02/01/2001

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