9" Rear Questions
 

Apologies if this is in the wrong forum...

First off, some info on my car….1970 Mustang bracket car, 3400lbs., small block 351 Windsor, automatic leaving off a footbrake, Caltracs & 29.5x9” slicks. It runs 10.50’s with average 60’ times in the low 1.40’s with nice wheelstands.

So I am upgrading my 9” rear to 35 or possibly 40 spline axles and I need to buy a new larger bore case.
First question, is a Mark Williams Aluminum Thru-Bolt 9” center section a good idea? The rear end is braced and straight and I will be using a light weight steel spool and Pro Gears.
Concerned about deflection and longevity, mostly. And how much weight is really saved?
Stick with a nodular iron case?

Secondly, regarding 35 vs. 40 spline axles, obviously the price difference is significant, would 35’s be sufficient or are 40’s overkill for my application? I must say I like the peace of mind overkill can provide sometimes!
Are there any details I am overlooking or is this a straight swap into my housing? Housing ends, bearings, seals etc.?

Re: 9" Rear Questions
 

35 spline would be more than strong enough for that combo. I would look at Strange instead of MW. MW uses a oddball spline angle and is not compatible with any other manufactures parts. Strange makes a great product and supports sportsman racing with their Perfectly Strange program. I have had their axles and spool in my super stocker for 20+ years. Get them with the 5/8 studs too.

Re: 9" Rear Questions
 

FWIW MW will cut either spline angle.

Also the through bolt case can take a load bolt which has a brass tip that is adjusted so when the ring gear deflects it touches the bolt and can't deflect further.

Re: 9" Rear Questions
 

I think the difference in cost between a new nodular and aluminum center section is minimal, so I would choose the aluminum. I would also like the 40 spline axles, gun drilled and lightened, aluminum spool , and lightened gears. Are we changing the ratio too?

Re: 9" Rear Questions
 

I have some 33 spline moser axles in a 66 Fastback with a 4 speed. When I bought them in 1997 they said they guaranteed them against breakage for 10 years. So far so good. They are lighter than 35 or 40 spline and at your power level I think they will be fine. As for the case, if you want bullet proof my preference would be a strange nodular pro case. An S case is supposed to be rated to 850 horsepower and it is lighter than the pro case. The S case would work, but the pro case is the ultimate in my opinion. Derek

Re: 9" Rear Questions
 

Hey Pat, is this for me or for you?

Re: 9" Rear Questions
 

Thanks for the replies....

I shouldn't have muddied the waters with the 35 vs. 40 spline debate. Probably just going with 35's.

My real question is if an aluminum center section is a good idea for such a heavy car.

Re: 9" Rear Questions
 

I would think that the aluminum center would sacrifice gear life at some point. A large pinion support and an iron case from either Strange or Mark Williams would be bulletproof.

Re: 9" Rear Questions
 

Of course that is a wish list for you that I would love to have too. Just trying to lighten up your car to compensate for the wheelie bars you might need. Can't wait to see it leave the starting line with some new 5.57 gears in it.