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MG MGB GT V8 Factory Originals Technical - another driveline angle question


Before I go any further with the welder I wanted to run my angles by you to see if I'm on the right track. I'm installing a 302 in a '74 gt. I have my motor mounts tacked in resulting in the engine being offset 1" to the passenger side, and the engine is sitting at 3 degrees down in the rear. Am I okay so far? The engine is fuel injected so I think the 3 degrees should be okay?

I am having an 8.8 ford rear narrowed, is it okay to have the pinion centered, or does it need to be offset 1" to match the engine? Also, the pinion angle on the rearend should be 3 degrees up to be parallel with the tranny output? I've read everything I can find in the archives, but I figure now is the time to get this right!

Thanks for any help.

Ryan Reis


Setting the engine 1" off to the passenger side is not a problem. The important thing with respect to the engine/pinion angle is that the centerlines of the two need to be parallel. The pinion centerline can be up, down, right, or left of the engine centerline, but they must be parallel to each other.

3 degrees down on the engine should be ok with FI; if it were a carb, you would want to have the carb mounting surface on the manifold level, which is usually around 2 - 2.5 - 3 degrees, depending on the engine and the manifold make.

I think you would want the pinion centered in the drivshaft tunnel to ease installation, eliminating modifications being required for driveshaft clearance.

Think of it this way: remembering from solid geometry, any two parallel lines form a plane. Any line connecting these two lines lies within that plane. The two parallel lines of the engine and pinion centerlines form a plane. The driveshaft will then be in that plane, regardless of the relative locations (up, down, right, left) of the two centerlines.
Dan Masters

Thanks Dan,

I was pretty sure that I would be okay with having the pinion centered in the driveshaft tunnel, but I panicked a little last night as I was laying under the car and realized just how little room there is for the driveshaft. Especially with the engine offset to the passenger side. Any opinion on the smallest diameter of driveshaft tube that is acceptable? This is a stock '94 mustang motor rated at 215 horsepower by the factory, not sure about the torque. Probably will need more power in the future, but it'll be stock for a while. I would think that traction limitations will make twisting a driveshaft pretty unlikely?

Ryan Reis

Also consider the working angle of the driveshaft. Target 1 to 3 degrees between the trans output shaft and the driveshaft to keep the u-joint bearings moving. If they were concentric, the bearing wouldn't last very long. The same applies to the pinion joint but you seem to be on the right track to get parallel and the offset may take care of this anyway.

It's a great milestone when everything is welded and bolted down.


A large diameter shaft made of thin material will have the same strength as a smaller diameter shaft made from thick material. As a reference point, the axle shafts in a Jag IRS are solid steel, about 1 in in diameter. OTOH, a hollow shaft of 4 inches in diameter can be made of relatively thin material.

This does't really answer your question but it should point you in the right direction. There are links to some driveshaft specialists on the web site that you might want to check with.
Dan Masters

Ryan, the drive shaft with the small dia. should be .065 or.095 wall thickness, your drive line is going to be about 30 to 32 inches long which it would be plenty strong for your application.
Angles should be a s Dan wrote. Keep in mind that if you have 3 degrees on one direction you should have the same 3 degree in the opposite direction to keep them paralell.

Bill Guzman

Thanks for the advice guys. Now I can proceed knowing that I'm not screwing something up. Sometimes you think you know, but it's nice to get a second opinion.

Ryan Reis

This thread was discussed on 03/05/2005

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