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MG MGB GT V8 Factory Originals Technical - same old questions

Im getting my 74 gt back from the spray shop next weekend am im embarking on the long job of putting a 3.5 rover conversion together, originally started by someone else. Ive read through the archives and am confused on a few things, namely i cant trace a 3.07 axle but have been offered a 3.31 axle of a late mgc with steel wheel hubs, will this be ok if i use 15 inch wheels. And secondly there seems to be a lot of confusion on which brakes to use, people say not to use the SD1 2 pots, but surely if they can stop a big rover saloon care they will stop an Mg with ease, any thoughts will be appreciated as i start to get the old gall on her feet again soon after spending the last 7 years sat in a garage with all the bits in boxes, many thanks Dean.
dean stanton

forgot to add that im also using the sd 1 gearbox as well for the axle question.

cheers Dean
dean stanton

Dean, a 3.31 axle will do you right. I run 3.07, but if anything 3.21's probably preferable. I'd use 6" wheels and 195/60/R15 tires. As far as the brakes, mine are bone stock non-boosted MGB albeit with drilled/slotted rotors and Greenstuff pads. They're more than adequate.

Dean, What I have found out on the 3.07 & the 3.31 is a grand total of 200r.p.m. is all. I have run them both & I like the 3.31 over the 3.07.when running around from town to interstate. I have to use the 3.0 for when I pull my 3,000 lbs. trailer for I will not use 5th. in the rover 5sp., for it is the weak link & I have broke it. I tell people that the C rear is VERY good but it needs some help. What I do is lighten the flywheel to 20-22 lbs. to help take the bang out of the rear when I let it rip & I will not shift at max. tork. (3500 to 5,000 r.p.m.) for with a power shift you will twist an axel. When I let her go I run her up to 6,000 r.p.m. to get her out of the tork. & into the horsepower. I have a C axel that has 400,000 miles on it & the only thing that I did was put stainless steel thrust washers on the spider gears, were you might be able to find brass ones over there. My 74.5 G.T. has 449,000 miles on her with a rover 3500 (185hp.) & the C rear axel is the best set up I have seen.
Glenn Towery

If you want the 3.07, you can buy the crownwheel and pinion and fit them, or have them fitted, to your own axle. They have been remanufactured and are sold by several V8 specialists. But your MGC ratio will work well too.

The only downside to the SD1 2-pot brakes is that with the earlier master cylinder on the MGB, pedal travel will be increased. If you use the later master, it's not much of an issue.

Mike Howlett


Go ahead and get it on the road, you can always get round to tweeking bits during the long winter nights when the telly's lousy,

Michael barnfather

Further to Mike's comment, SD1 2-pot calipers have a piston surface area 11% greater than standard MGB. This of course equates to 11% extra pedal travel. (The figure is +15% for SD1 4-pot). You'll find info and discussion in the achives. I'll email you my comparison table for MGB/SD1/Wilwood/Princess.
Pete Green

This thread was discussed between 21/09/2002 and 23/09/2002

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