Help! Rear End Decode

[1988_Mustang_GT]

I just purchased a used rear end (positive traction) that was apparently taken from a 1988 LX 5.)L Mustang. I am going to use it in my 1988 GT 5.0L.

My old rear end was an 8.8. I think this one is smaller. Is there anyway to decode the info on the door panels from the car that I got this rear end from to check and see if it is a 8.8? How do I tell what gears are in it? It came out of an auto, so it has to be 2.73's or 3.27's I guess. Any particular way to tell right off hand? I only have the rear end and the doors from the car. I am going to check the sticker on the door for VIN, etc. Any tips/advice would be appreciated.

 

[1988_Mustang_GT]

I just ran the VIN code from the door and it says that it is a 1990 Ford Mustang LX 2.3L!! I bet the rear end is a 4 cylinder!! Damn! The guy said he took the engine from the same car though. He used it in his own car. It is a 5.0L H.O. Maybe the guy with the scrapped car changed his car over to a 5.0L. If so, I hope he canged the rear end as well. He did say it was rebuilt. Probably because it is a 4 cylinder rear end and couldn't take the strain! What do you guys think? If it is a 4 cylinder rear end, what gears are in it? Will it last in my close to stock 5.0L?

 

[Bladez5_0]

The 8.8 should definitly be bigger than the 7.5. I think that the pumpkin may be offset on the 7.5 also but I may be wrong. If you are going to do hard launches on it and it is a 7.5 it won't last very long. If it is a 8.8 from an auto it most likely has 3.08's. They were optional with 2.73's standard equipment.

 

[1988_Mustang_GT]

Ok, I looked at pics on the net and it looks like I have the 7.5 rear end. Did this come in any V8 equipped Mustangs? Or is it a 4 cylinder rear end?

 

[Bladez5_0]

I'm not sure when they stopped putting the 7.5 in the 5.0's but I know that all the 5.0's that were fuel injected(87+) came with the 8.8. They may have put 7.5's in the turbo 4cyls but don't quote me on that.

 

[1988_Mustang_GT]

Damn! This rear end must be out of a 4 cylinder car for sure then! What a waste of money. I could have got a 4 cylinder rear end off a friend for free! Paid $400 Canadaian for this rear end + 2 doors. What gear options are in a 1990 4 cylinder 7.5" rear end? It is out of an auto.

 

[rel3rd]

The 7.5" rear was in all V8 Mustangs up until 1985.
In 1986 ALL V8 Mustangs came from Ford factory with 8.8 rears...
No Exceptions.

FWIW, I had an 82GT with a 86 5.0 engine with a swapped in T-5 and a 150hp nitrous kit. As long as I kept REGULAR Street Tires on it, I never had any issues. Whenever I had any tire even resembling being stickier than stock, I broke the rear. I finally upgraded to a 8.8 and was good to go.

That being said...for a cruiser on the streets, chances are you'll be fine, but it is no doubt much weaker than the 8.8 your car came with...

I must ask...Why are you changing rears anyway?

 

[1988_Mustang_GT]

Thanks for all the info. I am changing rears becuase my borther just sold me the car. Reason for selling: he welded the differntial when he knew the rear end was gettin' bad. A few months later, he destroyed the gears and rear end. The guy who sold me the 7.5 rear end (he didn't own the car the rear end came out of: he bought it for parts) has the same type in his 5.0. However, it is a 1984 GT. So, I guess he didn't know it was a four cylinder rear. The guy he bought the scrap car off must have done a 4 cyl. to 5.0 conversion. I ran vin codes on the doors and it was a 1990 4 cyl. LX.

 

[89MustangGX]

The 7.5" rear was in all V8 Mustangs up until 1985.
In 1986 ALL V8 Mustangs came from Ford factory with 8.8 rears...
No Exceptions.

The post 86 4-cylinder cars still had 7.5's -- so it very well could be from an 88.

 

[1988_Mustang_GT]

Yeah, I think it is definately a 1990 LX 4 cylinder rear end. That's what showed up when I ran the VIN. The quote from rel3rd was regarding V8's. All V8's after 1985 had 8.8's.

I hope this rear end is going to hold up. I will install it in the next few days and be on the lookout for a good 8.8 rear end. How much would a new 8.8 rear end cost? How about a new 9? Probably would cost more than my car is worth.

 

[maverick0716]

I don't know if you know this, but......if that 7.5 is out of a 4 cylinder it is an open diff, meaning no trac-lok unit. The 7.5's that came out of the earlier V8 stangs (85 and older) had a trac-lok unit.

 

[1988_Mustang_GT]

So it is not a posi traction rear end? Yeah it is out of a 1990 lx 4 cylinder.

 

[maverick0716]

So it is not a posi traction rear end? Yeah it is out of a 1990 lx 4 cylinder.

Nope, no posi. One wheel peel!

 

[1988_Mustang_GT]

If a rear end is posi, when u turn one side, does the other side turn? That is what happens in this rear end. My brother said if it was not posi the other side would spin the opposite way when I turn the other side.

 

[maverick0716]

If they both turn one way and its kinda hard to turn (if the trac lok is in good shape), then its posi.....so, if it is, then it didn't come out of a 4 cylinder car

 

[89MustangGX]

The quote from rel3rd was regarding V8's. All V8's after 1985 had 8.8's.

Wrong quote -- sorry. Meant to quote earlier post.

Sounds like you have more info now anyway. My own opinion, I wouldn't want to go backwards -- get the right rear and do it right the first time.

 

[1988_Mustang_GT]

Since I can install the rear end with the help of my brother in my own garage, I don't mind putting in this rear for now...until I find an 8.8. I agree, backwards is not the way to go, but in this case it will have to do.. for now. Thanks for the info guys.