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MG MGB GT V8 Factory Originals Technical - WTB: Ford rear end ... advice needed

I'd like to buy a Ford rear end for my new GTV8 conversion. I guess they come in 8", 8.8" and 9" -- what does that pertain to (?size of the ring gear?) and which one is best?

I would like gearing of about the same as a late MGC rear (3.07) and I would like a posi.

If anyone has one of these for sale or knows where I can get one prepped for an MG please let me know. I'm not very experienced with diffs and severely time-constrained, so a rebuilt, ready-to-rock unit would be best.

Also ... do I need a new driveshaft? If so, would this also be a Ford part? The car has a Rover 5-speed trans if that matters.

Thank you.
David Duquette

David, you are correct the numbers refer to the size of the ring gear. there is also a 7.5 Ford axle. The closer you will get to a 3:07 is a 8" Ford with a 3:00
Next gear would be 3:55. The best place that I know is Currie Enterprizes in Anahaim Ca. On a GM 12 bolt you can get a 3:08.
Posi traction units go for $250 to $350.
Your present driveshaft can be mod to fit the new rear end by a shop that works on drivelines. In NJ should be a place where you can buy a complete axle ready to run and shorten to 51 or 52 inches. Take advantage of this and go for the 50 or 51 and place wider wheels and tires without rub on the rear fenders.

Check with the Hot Rodders for a place in NJ.
Just a though with a V8 a good performer would be a 10 bolt GM with a 3:23 with a 5 speed a good all around ratio for a V8. Just thinking at load.

r/ Bill

Bill Guzman

Bill, thanks. I called a place and they sell 9" Fords for $685 rebuilt, cut to taste. I forgot to ask what gears I can get. But they said that I need to "specify spline". What the hell are they talking about?

Also, do you need to get them to weld on those bumps that locate the leaf spring u-bolts on an MG? As I recall there's also a little nub on the bottom that goes into a hole into the springs to locate them, no?(I have only fiddled with leafs once, and a while ago -- can't recall exactly what's there!) Plus I should probably get some sort of attachment welded on in case I ever put a traction bar on the car.

What would be super is if I can somehow describe to them everything that needs to happen so that I can walk out of there with a complete unit, that only requires putting the hubs and brakes on.

David Duquette

David you can also get ford 8" and 9" in 3.25 ratio. ford 9" come in 28 and 31 spline axles, 31 being the strongest. Steve

OK, getting closer. Sounds like an 8" is fine up to 300HP, and it's lighter than a 9" so I'll go with that.


1. They come in 3.00 and 3.25; which would be better? (car has 4.2 & Rover 5-sp)

2. I told the guy I'd need it cut to 51", and he said, "whatever you want, but which flange am I measuring to?" Can anyone translate to English?

3. They need to know the exact angle of the pinion relative to the leaf spring mounts; anyone know this offhand? Eyeballing it, it looks like maybe 5 degrees but they need it right on the money.

4. They sell these things complete with brakes, either discs or drums. If there's room under the car for discs, maybe a tad better, although they cost a lot more. _But how do you make sure the rear brakes aren't too strong?_ ... add a proportioning valve? Is this how you guys have done it, or have you been able somehow to re-use your MG brakes? (I forgot to ask the guy if, as I expect now that I think about it, I am supposed to supply him with my MG hubs.)

5. They will happily weld on a fitting for an anti-tramp bar, if I can tell 'em what kind and where it should go. Any suggestions? While the getting's good ...

Thanks for advice to a V8 newbie. Is there a dimensioned drawing of an MGB diff somewhere? That'd make life really easy.
David Duquette

How wide can you get under STOCK MGB rear end? How about the front?
I have heard 195/50(or60)R15 is the best that can be done, but I look forward to hearing what you have found!!

My thoughts were going different sizes front/rear.. maybe 195/60r15 up front and like 215 or 225/50r15 in back to help keep that power on the ground. Might also help with the MGB oversteer..

PS - I will be lower the car to chrome bumper standard
Larry Embrey


You can if you use Panasport wheels with "MG offset" from K-Speed. I am running 225/50-15 front and 245/50-15 rear, Goodyear ZR-1. Rims are 6"front and 7" rear with 51" width rear end and fender lips rolled up in rear(not recommended unless you want to repaint the area.

Mark Marchbanks

Larry, Mark is right. From the axle mounting to the inner fender is about 5 1/2 < >inches of clearence minus 1" if using 51" axle. I use a 3 inch back space on a 15X8 wheel with 225X50X15 there is plenty on room left.
Call Panasport directly and talk to Mash he will help you, they have a 22mm back space wheel that will house a 205X60X15 Also look at wheels for a Nissan 240/260 they have same bolt pattern.

r/ Bill
but I would recommend using the 195X60 tire dia and wietgh depends on manufactures.
Bill Guzman

David, is best to talk to the that is doing your axle. Tell then what you are trying to accomplish.

Axle gear selection depends on many factors; tire dia. Cam torque output rpm, transmission type.and type of driving. These are the must important.

If you have a manual 5 speed with .85 ratio 5 gear, 23 tire dia, and a cam that starts producing at 1800 rpm I would then choose the 3:25 or 3:55

The rear axle is measured from the back of the backing to backing plate, or from flange to flange.

Dont guess at the angle. Measured with a angle finder. 5 degrees is way to much. The norm is 3 man ideal 1 to 1 degrees. This is to keep the two parallel lines between the trans and the differential one is above the other.

Disc brakes required a plan. Different master cylinder should be used and braking area match to the original rear brakes. If other type of shoe brake is use then do the same match the area and wheel cylinder dia. A proportional valve will cure the dia size.

Traction bars come in different styles. Take them to the shop and have them weld the necessary brakets

David I would take the axle of the car and take it to the shop. Have them match yours. They can also weld your MG axle hubs to use the original brakes.

I hope this helps you, dont get to exited and rush it, call other shops and ask them the same questions until you are satisfied with one them. Ask them if the axles are welded type, are the gears new, who is the manufacture of the posi traction and what type of warranty it has, also Locker or clutch type posi (either one is OK) Some axles are cut and then weld the splines, the best are the ones that are
re spline. The first are cheaper. The 8 has taper axles there fore they cannot be re spline, unless you cut about 4 from each side. Welded axles are OK for street and occasional drag race.

Happy USA July
r/ Bill
Bill Guzman

Wow Bill!! Talk about a brain dump!! That will be going in my V8 notebook for sure. Sounds like I look for 9" rears.

Well from what it sounds like, I should be able to put on some 225/50r15's mounted on 15x7 wheels on all corners if I use a 52" axle and 22mm or 3" backspaced wheels?? That will also fit under the front as well??

I am looking at wheels other than Panasports, (I just don't care for them, no offense to those running them) so I would not want to call them and get all this info and not buy from them... I have a listing of cars that use the same bolt pattern, now it is a matter of getting the correct backspace or offset.
Larry Embrey

Please clarify ... why have so many of you headed for Ford rear-ends? Aren't they _much_ heavier than the MG's? I mean, a 9 inch Ford diff is a massive thing. So far my C rear end seems to be handling the V8's output OK, that's why I ask.
Art Phillips

Art, I think it comes to many issues. Mind you these are targeted to those in the US.

EASE of finding donor unit.
VERY CHEAP to find used. (~$50 complete drum to drum if you are willing topull it yourself)
Wide variety of parts available and easy to buy in any Auto parts store.

Most people I know with a V8 use the smaller 8" rear, I am only targeting the 9" due to it being easier to cut and re-spline, as well as even easier to find and install parts in. At least that is what I have been told.
Larry Embrey

Art, Larry gave you some reasons why. But the main reason is choice of gear ratios, the 9" is not that much heavier, dimensions are not much different than the stock unit.

r/ Bill
Bill G.

I think that one of the main reasons for usin the Ford 8 inch or 9 inch rear ends is the ease of changing gear ratios once the rear end is installed. The Ford rear end uses a removable third member or "Pumpkin" that can be replaced without going through the process of setting up the ring and pinion cleareances. This along with availability and cost make it attractive. Also some of the early Mustang, Mavricks and Grenadas share the same bolt pattrern as the MGB.

Larry Diede

Found a 76' Mustang II V-8 car with an 8 inch in it.
The thing is only one inch wider than my 80' MGB's
axle on both sides, has 3.00 gears, is limited slip,
and has MG bolt pattern. Going to run some back
spacing on the rims to make up the width. Cost...
$50....complete. Works for me.

I was just informed last night by a "fellow swapper" that the S-10 Blazer axle is 47" backplate to backplate.
I have not yet confirmed this, or seen what ratios are available. But it's worth a look-see.
Randy Forbes

no need to stop that press. I posted months ago the I was using the s-10 axle. I don't remember the exact length, but I think that it is only 1-2 inches longer. Cut off brackets from mg axle-weld them on s-10 axle, you're done in a day. Number of gear ratios from factory. I'm using 3.08. The bolt pattern is 5 by 4/3 - s10 series, camaro, corvette. Great for anybody with no time/money to have one custom made - however, having one made with posi and disks is even better. Also, those drum brakes are huge and will instantly lock up rear brakes first on hard stop and will need to be addressed.

I used the 6 cylinder Maverick rear which had the 4 on 4 1/2 spacing and did the wheel offset thing you mentioned rather than narrowing the rear end. Are you sure the Mustang II isn't 4 on 4 1/4 inches?
George B.

Anybody using a postal jeep rear end? Seems to be right width, 3:09, limited slip. $70...

This thread was discussed between 21/06/2000 and 17/07/2000

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