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MG MGB GT V8 Factory Originals Technical - rear disc brakes

I've already posted a similar question on the mgb tech page, but with little result. Does anyone have the address of a good web resource for info on installing a rear disc conversion? I am especially interested in a conversion on an SD1 axle narrowed to fit an mgb. I intend to narrow the halfshafts at the hub end; now seems to be a good time to replace the hub completely with one more suited to carrying a disc. I have a pair of 4wd ford sierra rear calipers already (they have a handbrake facility on them).
I have already fitted 4-pot vitesse sd1 calipers and vented pug 505 discs to the front; eventually I will be using 15 inch wheels with wider tyres than standard (once I have finalised the axle width and hopefully retained the mg stud spacing). I am not worried about brake balance at the moment as I will be using a balance valve if required.
Nick Bentley


Strange halfshafts cound be used and specified for a disc set up. Terry Brown of FRC was considering a rear disc brake kit for SD1 but not heard much on this for sometime.


I have done a rear handbrake conversion but on the B axle. If you Have MGB stud spacing then a rear disc from a rover 800 might fit.
I think if you use the 4wd sierra cosworth calipers you will need wider vented discs.
Rally design sell vented discs in various sizes that fit ally mounting bells. You could have a bell made up to the right dimensions for the SD1 axle.
With my 2wd cosworth rear calipers I never managed to get the handbrake working satisfactorily so I am using a hydraulic handbrake but the cable is still attached so it fools the MOT test.


OOOPS I meant Rear disc conversion not handbrake conversion.

I have fitted to my v8conversion all round disc braking, pedal box with balance bar, hydraulic handbrake, brake proportioning valve for the rear.
Mark, please, question, for the MoT inspection the hydraulic handbrake is it a problem?. (my hydraulic hanbrake work very well)

Nick, I fitted a 240 series Volvo rear axle to my MGA V8. There are many different gear ratios available, limited slip is very inexpensive, 240 series rearend assemblies are a dime a dozen and pretty much indestructible. After removing all of the usless brackets, I had the assembly narrowed about 5" so the wheels would fit inside the fenders. I'm told that if you get wheels with the correct back spacing (front wheel drive wheels) the rear end assembly will fit the MGB without narrowing.
With the rear end narrowed, I positioned the axle on the MGB axle mounts to the hanging springs and rewelded them in place.
For the handbrake, I then shortened the Volvo cables and fabricated pieces to connect the cables to the existing handbrake. I'm using an MGB dual circuit master cylinder. I now have four wheel disc brakes that haul the MGA down very well. You can check out these modifications on my website (


Nick, I forgot to mention, I had the axle hubs redrilled to accept the MGB 4 lug wheels.


Hi Nick,

I also have a Volvo rear axle. It has a limited slip diff and I will run a 3.55 ratio. The half shafts and casing have been shortened by 5 1/2 inches to make it the same width hub to hub as the MGB steel wheel axle.

The axle tubes are the same diameter as those on an MGB so I have just cut the rear spring mounts off a scrap axle housing. I am still waiting for some blank discs so that they can be drilled with the MGB stud pattern. I haven't done the hand brake cable yet, but as John found, it doesn't look too complicated.

MG David

Thanks for the info everyone. Due to the lack of breaker's yards up here, car modifiers tend to work with what they already have or can beg or borrow from their mates. A volvo axle sounds like the way forward, but I am going to persevere with my rover SD1 axle for the time being. Do rover 800 discs slip over the wheelstuds or bolt behind the hub like mgb front discs? (My great plan is to cut the end off the halfshafts and adapt mgb front hubs to fit them... mg front solid discs could then be used at the rear). Then it should be easy enough to make carriers for the calipers to bolt onto the axle flange ends.
Any other guidance?
Thanks as ever.
Nick Bentley

Rover 800 rear discs slip over the wheel studs but the central hole has to be enlarged slightly.


Thanks Mark. So if I adapt mgb rear hubs to fit on the ends of SD1 halfshafts it should all be pretty sraightforward. Just a thought.... does anyone know if the spline pattern on the inner end of an mgb tube axle halfshaft is the same as on the inner end of an SD1 halfshaft? I have an axle in the back of the garage but haven't took the shafts out yet to check.
Thanks again.
Nick Bentley

Quick update.... after going over the pros and cons of fitting an SD1 axle, I have decided to retain the mgb axle and fit new saab 900 rear discs and calipers. (Nice article in the archives about this.) At some point I will fit a v8 diff to sort the gearing. Thanks for all the advice so far.
Nick Bentley


From looking at your web site I noticed that you used a Volvo Rearend with a 3.55 ratio. Is there a plate or any other indentifying marks on the diff to indicate the ratio and whether or not it is limited slip?


Al Wulf

This thread was discussed between 21/09/2005 and 29/09/2005

MG MGB GT V8 Factory Originals Technical index

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