Rear Diff broke, decision time. Wisdom?

[TStark]

Drat, broke Pinion gear the other day.

Only had the car for four weeks got lots of little things fixed, just starting to enjoy the car

I think a pop start I had to do when it stalled bringing it home, and then a slipped clutch pedal (in loose ¾” stone) did it in.

This 75 appears to have the 1978.5+ style rear axle, so I have no idea its actual build year.
It seems R&P sets and bearings are awfully expensive.

I have an inquiry into a reputable axle house within an hour of me about rebuilding it.

However, I see lots of chatter about putting 8.8” fords that ‘bolt right up’ but I think that’s sugar coated.
Seems that narrowing, bracket fab, and bolt circle mods are unavoidable.

That being said, the 8.8” ford seems really overkill. It’s a 500hp axle and is quite heavy.

Yeas ago I kept alive a ford 6.75” axle after switching my 81 mustang to a 68 302, then upgraded to a ’85 7.5” from a GT.

The 7.5” is a 300hp axle, and given that we are not drag launching , and the tire diameter is always going to be modest,
Seems a 7.5” ford would be a preferable swap, plus they weigh 120# instead of 175#, for saving 55# of unsprung weight.
This way 10% of the car’s weight is not the rear axle.

If my case is grenade (I’ll have it out soon), i'm hesitant to put a weak, high priced junkyard axle in.

Given my experience, the 6.75” ford is strong enough for this car, and is really attractive weight wise. However a high ratio is scarce, and disc brakes could be a problem figuring out.
the 7.5 is insurance at a modest weight penalty, lots of cheap upgrades available.
I can’t wrap my head around putting a 8.8 behind a high revving low torque engine

If I have to have something fabbed, im thinking 7.5” ford.

I’m concerned the mustang rear disk disk brakes won’t fit the 13” minilites I have. That means new wheels/tires. Then front brake upgraded to match the braking power in the rear. This is mushrooming real fast. Then should i bother changing the bolt pattern and just abandon 98mm?

Any wisdom out there you can share? I'm early in the project

[narfire]

Not sure where you hang your hat, but out on the west coast try Auto Italia for a rear end. They are in Windsor CA.
East coast....not sure as to the go-to for used parts like that.

I'd try to source a used rear end from someone reputable and bolt it on. Takes about an hour and a bit to change a rear end on these cars.(depending on the brake calipers etc.)

Chris

[Exit98]

When I blew the rear on my 76 i popped in a used one with a 3.90 from a later year. I'm happy with the higher ratio and it was an easy swap (I had good help). Granted it could have been a bad one but it isn't. If it should ever go I'd just replace it again. We have access to plenty of used parts here in NJ through NJFiats.org and particularly through the generosity of George K. (NJFIAT1981). John Erskine and the Maryland/DC group are also a good source.

Having a support group is so helpful. I don't know where I'd be without them. Probably with an old broken Spider in the garage.

Where do you hail from?

Fiat rears aren't particularly weak unless abused. If you have the skills to fabricate a complicated swap my hat's off to you. But unless you have a big build motor I'm not sure what you'll gain by it.

[TStark]

Now thats the wisdom i'm after.

I'd have to be reliant on a fab house to make an axle, its beyond my abilities so cost is going to be up there.

Yes, the bolt off/bolt on is quite advantageous!

Ok then, i'll put more effort into locating an axle,

I'm in NE CT btw.

And thank you for the prompt replies!

[aj81spider]

If you're in CT check with Danny at Fun Imported Automotive Toys in Vernon. He may have something, or may be able to direct you to someone who does.

[TX82FIAT]

Depending on what you want to spend there are a few reputable vendors in Texas that could ship you parts. While the entire rear end is heavy, it is not as expensive if you ground ship and do not need it in a hurry. If you are going to do the upgrade consider a later model automatic diff to gain some crusing speed with a better ratio. Finding the automatic diff may be a little harder.

[htchevyii]

Maybe check with Mathews in Alabama.
https://www.google.com/search?q=matthew ... ent=safari
http://stores.ebay.com/MATTHEWSPARTS?_rdc=1
Also, check here, the first two say housing only, but maybe the others?
http://www.car-part.com/cgi-bin/search.cgi
Also might check with FLU. https://www.fiatclubamerica.com/

[Daniel]

if your not drag racing or going to abuse it buying a new ring & pinion would make the most sense vs all
the time,cost plus fab work to fit a ford rear end in the fiat. I used to go street drag racing many many years
ago in a Fiat and broke Ring & Pinions U joints and a Top Link but i was launching the car hard with a well
built engine. on the stock fiats never had an issue.

[TStark]

Thanks men!

Awaiting a call back or email from Fun Imported Automotive Toys,

and CT Axle is working of some numbers and part availability

Thats some good leads within an hour drive, so far so good!

[divace73]

I have done this and have spend the money with new items (I actually installed the earlier style diff in my car with a 3.9 ratio and torsion diff centre).
I was considering re-using the 4.3 pinion and ring gear and lucky I didn't, there were hairline fractures in the back end of the pinion. It may have lasted for year or 2 weeks???

If I were you I'd get my hand on the earlier style diff that should be in your car and put a new 3.9 ratio pinion and ring gear to get decent free way driving, if that is what you are after. It may cost a bit to get done but then at least you know it will be right for another 20 years....

[TStark]

Good to know!

If i read you right, the earlier 3rd member/banjo housing unit may be superior to the later salisbury type?

It appears available on an exchange basis for a good price, 250 vs 450 for the later!

Yes, gears in the high 3's would be superior, 4krpm was kinda noisy and fatiguing, speed limit was 55 when this thing hit the roads!

Now, are they dimensionally the same? 4-link the same? Input flange the same, or require a different driveshaft also?

My brakes are in good shape, what swaps over and what can't? backing plates/brackets?I want to make sure i come home with everything i need

Its good to have options, much appreciated

[Exit98]

Here's what you need from the donor along with the axle assembly.

The brake backing plates (they are different)
The brake line that runs from the rear soft line and onto the axle
The panhard rod. The new one will look like its bend and dented but that's correct.

The driveshaft is just a little longer or shorter, I forget which. Some people say you don't need to switch them.

There's a link here somewhere with all this info. I'll see if I can find it.

I dropped about 350 RPM at 70 MPH. From 4000 to about 3750 on 185-70-13"s.

[Exit98]

Here's a link:

http://www.fiatspider.com/f08/viewtopic ... driveshaft

[TStark]

Thank you all for your help with this.

Got a 79 rear from Danny yesterday.
I would have prefered to come home with a early style if he had one, but would have been a decent wait for one to come in.

Started yesterday morning, had it out and on the trailer by 10, drove an hour to get the replacement, went to my kids game,
later wire brushed and painted the new parts. By 11 Sunday morning it was being test driven, later we went out for a nice drive.

RPMS are way down, I miss the raciness, but its quite a pleasure on the highway now. About 3400 at 65, with same tires as you Exit98
The gear howl is gone also, now i hear some new creaks to remedy.

Thanks men

[Exit98]

I miss the raciness, but its quite a pleasure on the highway now

Easy fix if you still have the stock 75/76 restrictive exhaust header on the car. Get an earlier 4-2-1 header and downpipe set-up and you'll get all the "raciness" back. Huge improvement with minimal effort. After that you can go to a little bigger carb.