THS_Steed06

Hi all,

I've been searching forums and the web for a few days on this but I can't seem to find any definitive information on 7.5" rear ends failing on S197's. I'm looking to upgrade my driveshaft (to aluminum) and rear end from 3.31 to 3.73 t-lock among other mod considerations (among other steps to try and get into the 13 second range).

One thing I can't follow is that everybody seems to ditch the 7.5" for an 8.8", and I get it the 8.8 is a stronger rear end no question, but I'm not looking to push much past 300HP anyway. So I'm thinking upgrading to 8.8 would be overkill for me and an unecessary PITA.

Isn't the T-5 manual and 7.5" rear end the same ones used on Fox body and Modular steeds with V8's for nearly 20 years? Why does everyone ditch 'em so quickly? It should be able to hold that power/torque no problem...unless the s197 generation parts are weaker for some reason. Anyone know?

Besides that I could blow my gears like three times before I approach the cost and hassle of an 8.8 swap. Am I wrong here? I'm not racing this car a ton, but it will see its share of hard stoplight launches and I'm thinking it can hold up based on the above.

Looking forward to any definitive evidence you guys are aware of.

Thanks,

Tom

2007StangV6

So you want to push 300HP, but want to stick with the 7.5"? Do yourself a favor, and get the 8.8". Why would you want to build the 7.5" 3 times when you could just buy the 8.8/gears once and never worry about it? It's going to save you time/money/hassle in the long run.

Did a quick Google search on JimC, another member here, and in every thread that mentions someone building up the 7.5", he tells them to steer clear of it. Look HERE, HERE, and HERE

Jim only had a CAI/Tune/Drag Radials and his axle blew, even after he rebuilt it. You're talking about putting more power down than he did, so I would imagine that yours would go out too.

I have the 8.8" w/3.73's and it is by far the most fun mod i've done as of yet. I have plans for mine in the future, so I just went ahead to save money in the long run.

Derf00

Never heard of any V8 Mustangs coming with a 7.5" rear (at least from 79 on). All are 8.8" IIRC.

The reason most people ditch the 7.5 for a 8.8 is that the 7.5 are ALL factory open diff meaning, one-wheel-spin. By the time you upgrade the gears and get a t-lok for 7.5, you may as well pony up a few more bucks and get a complete rebuilt 8.8 axle and do a swap.

It's easier to do the swap yourself than a T-lok and gear install.

THS_Steed06

Hey Derf, thanks.

I stand corrected on my original post, the last v8's to use the 7.5" rear were the 79-85 cars, but that said an 85 5.0 put out 210 HP and 270 ft. lbs of torque. Then even up to 93 they were still putting out 225HP/285 ft lbs. So they really didn't push the 8.8 rear ends all that hard until the mid to late 90's when they got over teh 300 ft. lb level.

American Muscle sells 7.5" gear sets for the V8 cars from 79-85, then 8.8's come into play in 86 up.

Apparently a member named "JimC" blew his 7.5 with drag radials and CAI/Tune only so he was probably pushing well over 320 HP on a 3.7L. I'll talk to him about it and see what's what. If the chances I'll blow it are that high, I may want to do the 8.8 swap afterall but I don't know if he blew it with limited slip or just the open standard diff.

Tom

THS_Steed06

Hi Satin Silver,

Thanks for the relay 411 on Jim C. I'll contact him and see what happened. I'm wondering based on his car how this went down. Did he blow the open diff or did he blow limited slip one?

On your end what did you spend to swap to your 8.8? How hard was it?

Thanks,

Tom

2007StangV6

HERE

He didn't bust the 7.5" on a 3.7L. IIRC, the 3.7L come with 8.8" already. He had a '06 4.0L before his current '13.

According to the post that I linked to, all he did to the car was "only a tune, CAI, aluminum driveshaft, 3.73 and Tlok and the LPW low profile girdle on the rear, and a set of drag radials at the track."

Pretty sure that didn't put him over the 300RWHP mark, so, I would just save for the 8.8".

As for me, it took me awhile to buy all the parts, but once I did, it was a breeze. Had a local Mustang shop install the gears, tlok, and everything else. I just had them install the axle itself while they had it. According to everyone here that has done it themselves, it's a pretty simple bolt off/bolt on process. I do, however, highly recommend having a shop install the gears unless you are experienced in doing stuff like that.

LilRoush

It's not the power that blows them, it's the abuse. A couple of hard lauches on drag radials with a stock 7.5" with an old 3.8L pushrod V6 from an 160 rwhp SN95 car could break a rear.

I ran a 7.5" rear in my 2000 V6. It put down over 500 hp to the wheels and the Eaton 7.5" took it just fine and kept going. Never had an issue. Just don't abuse it, and it will last.

capri debris

A stock '85 Mustang with a 7.5 rear has 210 hp and can spin the tires at will... so all it takes is 210 hp to lose traction with street tires. Now if you'd take the same car and add another 200 hp, it'll still lose traction at the same point. The tires losing traction acts as a safety margin and is what keeps things from breaking. So pretty much any amount of hp with a 7.5 is safe.... UNTIL you do something to hook up, like put slicks on and make a hard, high RPM clutch drop at a well prepped track.

So it really doesn't matter if you're pushing 300 hp with a 7.5 and stock street tires, your tires will spin before anything breaks... just don't make the mistake of thinking that same 7.5 will hold up at the track with slicks. Over at Four Eyed Pride.com plenty of guys are still running their 7.5 with over 300 hp and not breaking anything... but they are only driving them on the street without drag radials or slicks.

THS_Steed06

Thanks LilRoush & Capri!

I needed to hear some good news! I plan to run Pirelli P-zeros 235/55/17 or move up to Bullitt 18's this summer. So it sounds like I can upgrade to the t-lock and go 3.73 without too much worry at the power levels I'm planning on the 7.5. That is as long as I don't come across a cheap used 8.8 since it will cost me $600 to upgrade the current rear end. If I found a used 8.8 for like $500 it would probably be worth doing for the "insurance factor".

I just sholdn't be surprised if I cook it someday when the pirellis happen to hook hard!

kzonts

I haven't exactly babied my 7.5 with my ProCharger setup. I'm running Nittos which hookup much better than the stock Pirellis. See video link below:

http://s1195.beta.photobucket.com/us...nvsSS.mp4.html