strength of a 7.5 rear to a 8.8(help please)

85-302 · Mar 25, 2004

i was getting my 3.73's installed today and he called meand told me that i had a 7.5 in place of a 8.8. this was expected with an 85. he can still put the gears in but wanted to know if i wanted a 8.8 instead that he had. i really dont want to replace it if i dont have to. the only thing that discourages me is he said it was a 4 cylender rear end type. is the 7.5 really a lot weaker than the later.

thanks for the help

rd · Mar 25, 2004

Unless you are planning to go immediately to an 8.8 I would just put the gears in the 7.5, and run them until you change or they actually fail.

I did this 8 years ago, and I am still running the 7.5, with an SVO traction lok and gear set that I bought new. It runs 13.40 quarters and 8.2/87 eighths on Drag Radials. My 8.8 is in the garage awaiting gears.

fordman54935 · Mar 25, 2004

rd said:
Unless you are planning to go immediately to an 8.8 I would just put the gears in the 7.5, and run them until you change or they actually fail.

I did this 8 years ago, and I am still running the 7.5, with an SVO traction lok and gear set that I bought new. It runs 13.40 quarters and 8.2/87 eighths on Drag Radials. My 8.8 is in the garage awaiting gears.

8 years is pretty impressive for a 7.5" rear in a car as quick as yours

I've already had to rebuild the 7.5 in my 93 2.3 LX because it started to make growling death noises at about 120,000 miles.

I'm sure you'll be set for a while with the 7.5 provided that you aren't making repeated 5000 RPM lauches with sticky tires. The 7.5" rear was used in all Mustangs from '79-'86, and in 1987 they switched to the 8.8. I would kinda keep an eye out for an 8.8 though in case yours does go south though.

moonenn3186 · Mar 25, 2004

Just a correction I noticed.

THe 8.8 came standard in 86 and up V8 cars. 85 was the last year for the 7.5" GT

One more thought - this I am not sure of...

will 7.5 gears fit in an 8.8? I don't think so...

Depending on how much he wants for the 8.8 - I would do it. Peace of mind goes along way!

Gearbanger 101 · Mar 25, 2004

moonenn3186 said:
will 7.5 gears fit in an 8.8? I don't think so...

Nope, apples and oranges....although the axles are the same.

The 7.5 should hold up for the time being. What really kills these rear ends is excessive abuse and traction. If you were planning on running it at the track with D/R's or Slicks, I wouldn't expect it to hold up for very long, but it should last quite a while otherwise.

My '85 Ranger lasted a year and a half before giving up. And it was a 4x4 with a 5.0 HO and 30' tires.....and Ohhhh, did I pound it!!!

PURESTREET5006 · Mar 25, 2004

7.5 just don't use any kind of sticky tire period...with the 8.8 you have guys running in the 7's with 8.8 rearend housings.

85-302 · Mar 25, 2004

i got the gears installed in the 7.5. and all i can say is dear god!!! what a change.

PURESTREET5006 · Mar 25, 2004

85-302 said:
i got the gears installed in the 7.5. and all i can say is dear god!!! what a change.

Gears are a MOFO aren't they... feels like you got a new power plant in the car now.

85GTlover · Mar 25, 2004

So you are saying stick better gears in my 7.5 and use it until it %$^#& up?

SmockDoiley · Mar 25, 2004

I just yanked my 7.5 out of my 85 because Im making too much power, but its not a bad rearend. It had no problems with the 13.8s I ran, and then when I drove around with the supercharged 342. They are actually pretty strong, and in fact they are still used today in all the V6 and 4 cyl. cars. Your rearend should be just fine especially now that its been rebuilt.

SuperStang83 · Mar 25, 2004

They aren't as weak as everyone thinks, but I would swap to an 8.8 just for peace of mind!

Jakob

maverick0716 · Mar 25, 2004

I yanked mine out before problems arose. I didn't want to take a chance. 7.5 rears are weird, some will last for a long long time, others will just break driving around normally with a stock car.

85-302 · Mar 26, 2004

what will happen when thre rear m %$^&^'s up like almost everyone thinks it will. i mean will there be a danger to me or will it just start makeing noise and then stop working.....

SmockDoiley · Mar 26, 2004

worse case is when it breaks it locks up on you. It would be worse than locking the brakes because the rearend is going to lock and skid. Youll really have no control of the car until it stops. I crapped my tranny and had to deal with this. There was nothing I could do till it stopped and then we couldnt move it either until the tow truck came. He had to soap down his bed to pull me up and back me off.

Gearbanger 101 · Mar 26, 2004

SmockDoiley said:
worse case is when it breaks it locks up on you.

That would be ABSOLUTLEY worst case scenario. Transmission locking up, yes, but I've never actually heard of a rear-end locking. They usually just grenade everything in the cluster, but I suppose anything’s possible. When mine finally went, it sheered a couple of teeth off of the crown and forced them through the inspection cover. It sounded like I was driving with gravel in the rear end until I limped it home. Gear lube everywhere!!!

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