If I were to have a Moser 9" rearend and a standard 28 spline centre section how much horsepower could I put through it.I know the Moser axles would take more than I'll throw at it but what about the standard diff,gears casing etc,whats the weak link? Any info would be greatly appreciated.

 

the factory guv loc is very weak (from my experience). I suggest trying to find a 9 bolt. I just found one today with rear discs and 3.45 gears for $250.

I think you need to call around local parts places and yards to see if you can find a 9 bolt. Most yards are ignorant to the fact a 9 bolt exists, so look for one with rear discs first, then check it yourself, it may be a 9 bolt. Count the bolts on the gear cover.

BTW, don't mention how valuable a 9 bolt is to the seller, I almost did that today.

I didn't really answer your question very well, but maybe you have another alternative.

good luck

 

foney he said 9" not 9 bolt, big differance. don't think you'll find 9" with 28 spline axles, more like 31 i beleive. for street and most strip applications you won't find a weakness with a 9". if any i'd say axles

 

I was only suggesting that he should consider the 9 bolt. It is lighter than a 9 inch and half the cost. It is just as strong and can be beefed up to be stronger too.

 

I've already looked at the 9 bolt option and because of where I live,getting one let alone performance upgrades for one would be difficult.It's just that someone is selling a complete 28 spline centre section at the right price so I don't really want to pass up the chance.Any 9" centre section in this country is not that common.Granted ede, a 31 spline is a better bet (my friend has one and he was very lucky to get it as they are as rare as rocking horse sh*t.).I just thought that I heard of some people putting big numbers through a 28 spline,just how much is the question.


Ps.are 10 bolts really that bad they come apart when abused?

 

Oh sorry, I didn't realize you lived across the pond. 10 bolts can be made to last, but I personally hate them. I have had my trans am for a year and a month and I am on my fourth rear. I was lucky enough to find a 9bolt.

Good luck on your search.

 

It isn't really the HP but the torque that kills them. The nine inch with 28 splines should have no problem with 500 hp. This gives to a factor of safety of 2 assuming 550 ft lbs of engine torque and a 3 first gear ratio and a 3.73 rear. some people claim the stock case deflects but I have yet to see this proved.

 

The maximum amount of torque the engine produces mutiplies by the first gear ratio mutiplied by the rear end gear ratio mutiplied by .9 for an efficiency factor.

Lets say you have a good engine producing 400 pounds of torque. Your TH350's first gear is 2.51. You didn't say the diff gearing so we'll assume 3.73

400 x 2.51 x 3.73 x .9 = 3370 foot pounds of torque.

Aftermarket axles are roughly all the same in strength unless you start talking about gun drilled axles etc.

I see no listing for a small 28 spline axle but..

30 spline can handle 6200 ft lbs per axle
31 spline = 7000
33 spline = 8200
35 spline = 9600

One axle should be able to take the maximum torque that a car can produce. That gives you a 200% saftey factor.

I'd take a guess and say 28 spline axles could handle 5000 ft lbs so you'd need a lot more engine torque or more gearing to get close to that.

Case deflection or pinion support will fail long before you break an axle. Getting an N (Nodular) case and a Daytona pinion support will help. I don't even have either one of these on my car and I'll put more abuse to the diff than you ever will.

 

The biggest weakness with a Ford 9" rear, is the stock center section...

If your only running a little smallblock and radial tires, you'll be fine with the stock 28 spline stuff...

I ran a bone stock 9" in a '67 Camaro (years ago) with a real mild 427 BBC and 4-speed...
Never had a problem with it...

My '70 Camaro is another story...
With a mild 427, TH400, and slicks, it spit two center sections out in less than 20 passes down the track...

"Case deflection" as earlier mentioned, isn't the word for what happens when these things break.

They always let go on the starting line, or if you experience a nasty wheel-hop burnout...

Both times when I broke mine, it blew the whole pinion & pinion support assy right out the side of the case, and out from under the car with the driveshaft still attached....

I stepped up to the Strange Engineering Iron center section & aluminum pinion support, and never had a problem again...

Also pushed a bunch more power through it...

Went to a 513 BBC roller motor, and a healthy dose of nitrous...

The car weighed 3050lbs with me in it, and was running easy 8.40's at 158-159mph...

Last runs down the track were with 1.21 60-ft times...



I think you'll be fine with the stock 9" as long as you don't hang slicks on it...

 

How hard is it to change a 28 spline third member to a 31 spline one? Thanks

 

Just unbolt the 28 spline one and install the 31 spline center section. Easy enough.