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Topic: 7.5 vs 8.8 (Read 48139 times) previous topic - next topic

7.5 vs 8.8

Reply #15
so WTH actually goes in the 7.5? alot of them sound like bad setup, or maybe defective gears...or is the carrier walking?
'83 Cougar *the never ending project* warmed over 306 v8,c4,8.8 posi with 5 lug conversion
'91 mustang strictly street-in progress
'00 f150 7700-Mean Green: jet stage 1 chip,ported upper intake with 1" spacer,'04 Super Duty intake with injectors,summit racing short tube headers with true 2.5" duals with smithy's glasspacks!

7.5 vs 8.8

Reply #16
Quote from: blu84302
If you wanted True Posi just weld up the spider gears in your 7.5... that way you don't have to take a chance on getting the backlash perfect because you can weld it up with the axle still in one piece.  I could never put in a carrier assembly without it later ripping to shreads.  I tried carbon paper and lip stick to make sure the tolerances were correct but no matter what the 5 times i changed the gears they all went to puppies!

That's a fine solution for a drag-only car, though if you ever plan on deviating from a straight line you might wanna second think it. It's called a differential for a reason - it's designed to allow the two wheels to travel at different speeds while turning. Welding up the spider gears creates a "spool", eliminating differential action and making cornering dangerous.

BTW, if you REALLY want "True Posi" your only option is to install a GM rear end. "Posi Trac" is simply GM's brand name for the same setup Ford has (Ford calls it "Traction lock"), and the actual method of "Limited slip" (which is what all Posi and Trac-lock rears are) can vary even within the manufacturer - anything from the simple clutches like our rears have, to cones (Chrysler), to a mechanical ratcheting locker (GM Trucks), to an electronic locker (Toyota TRD package) and many others.
2015 Mustang GT Premium - 5.0, 6-speed, Guard Green - too much awesome for one car

1988 5.0 Thunderbird :birdsmily: SOLD SEPT 11 2010: TC front clip/hood ♣ Body & paint completed Oct 2007 ♣ 3.55 TC rear end and front brakes ♣ TC interior ♣ CHE rear control arms (adjustable lowers) ♣ 2001 Bullitt springs ♣ Energy suspension poly busings ♣ Kenne Brown subframe connectors ♣ CWE engine mounts ♣ Thundercat sequential turn signals ♣ Explorer overhead console (temp/compass display) ♣ 2.25" off-road dual exhaust ♣ T-5 transmission swap completed Jan 2009 ♣

7.5 vs 8.8

Reply #17
I've lifted both a 7.5 and an 8.8 and I can say that 80lb figure does seem a little high.  I only repeated it because I've heard it from 2 or 3 reliable sources.


7.5 vs 8.8

Reply #19
Maybe this fits here, maybe it doesn't, but I had 3.73's installed in my 7.5 and found it to provide plenty of off-the-line go.  I never abuse the car or mash the throttle, so hopefully I never have to worry about the rear failing. 

Chris
"I put my foot in my tank and I began to roll." Chuck Berry

7.5 vs 8.8

Reply #20
In my experience, (I have GRENADED 4, 7.5" rears. one behind a 4.2L V8, and the others behind stock 5.0L's)  It is the spider gears and the main carrier caps that let go.  The last one I wrecked, I never did find all the pieces of the spider gears, and the caps both broke into 3 seperate pieces EACH.  spend your money wisely.  go 8.8"  or waste your money and blow up a 7.5

And the weight isn't that much more, maybe 20lbs.

7.5 vs 8.8

Reply #21
A properly built 7.5" rear will withstand quite a bit of abuse. The key is to get a rear end girdle cover (yes, they exist for 7.5" rears) and a good locking center section. After that, thrash away.

So the weight thing...let me explain. I pulled the 80 lb. difference info from two different sources: my mechanic, and a magazine article. The mag--meh, not so sure about them as they've had errors in the past, but still, it felt correct to me. My mechanic--very trustworthy as he's the driveline specialist at the Ford dealership where he works. I think since he works on FWD and RWD vehicles, Focuses to F-350's, and also races Mustangs on the weekends, he can give a very good idea of weight differences between components.

A standard Cougar/T-Bird 7.5" open rear end with 2.73 gears and 9" drum brakes is the baseline. The top-of-the-line, I suppose, would be a 1987-88 Turbo Coupe 8.8" locking rear end with 3.73 gears, 10" discs and quad shock brackets. Fully loaded with brakes and gear oil, the difference in weight between those two rear ends is quite dramatic. Is it exactly 80 lbs.? Never said that. Is it realistically more like 40-50 lbs.? Possibly. I do know that I can carry a basic, loaded 7.5" rear around by myself but need help with a loaded 8.8" rear. And I'm not that big of a pu$$y...I can lift some fairly serious weight around. So it the real difference between 7.5" and 8.8" rear ends a mere 10 lbs.? I don't think so. Bare, possibly. Not fully loaded. No way. I think it's funny how everyone jumps to conclusions about "only a 10 lb. difference" when there aren't even any brakes attached. Isn't that how you, um, you know...USE a rear end in the real world?!

In the near future I will have the opportunity to weigh both, fully loaded to fully loaded, and will report actual numbers when I get them. I also have separate components (gears, center sections, 9" and 10" drums, etc.) that I'll throw into the mix, just for solid numbers. That should help smooth things out.

7.5 vs 8.8

Reply #22
I know of several 7.5 that have been used and abused that are still in working order.
84 Turbo coupe 2.3T Modded with 88 upper and lower intake, 88 injectors, E6 manifold, T3-4 AR.60 turbo, 31X12X3 FMIC, Homemade MBC , Greddy knock off BPV.
4 eyes see better than 2! 
Da Bird!

FreeBird

7.5 vs 8.8

Reply #23
buddy of mine had a Dominator Mustang that had a 7.5 under it-withstood a bunch of high-13 second 1/4 runs...
I pulled my TC's 8.8 just last week, and I will say that there IS more than 10 pounds of weight difference between it and a 7.5, and this was the complete rear, even the quad shocks :D
I could barely lift it into the back of my truck, and I ain't no wimp! :giggle:
I can pack around a 7.5 by myself, but I sure as hell can't an 8.8..
'84, '87 Mustangs ('87 is a 5.0, the '84 is TBD)
'98 Explorer 5.0
'03 Focus, because, you know...Brandon. Let's fckin' GO.
'06 Explorer EB 4.6 (wants cam phasers)
'11 Expedition EL (it's huge-that's what she said)

7.5 vs 8.8

Reply #24
The mustang 8.8" dont seem to be that much heavier the the 7.5"ers  I will be pulling the differential out of my '88 stang this week and I will weigh it when I do so we have numbers on those as well.

7.5 vs 8.8

Reply #25
I believe that the 8.8 axle tubes are only marginally larger as well. I changed the 7.5 trac-loc in my 86' for a 90' Lincoln 8.8 trac-loc w/rear discs and didn't notice much of a weight difference with the exception that I had left in the stock gears. BIG mistake!! I have since pulled the 8.8 and swapped in a 03' Cobra IRS. Now that does weigh 80# more than even the 8.8 live axle. But the trade off is worth it for me as I too will be autocross/road racing my car


86' T/C 4.6L DOHC
16' Chebby Cruze 1.4L Turbo
17’ Peterbilt 389 600hp 1850ftlb Trq 18spd

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7.5 vs 8.8

Reply #26
The axle tubes on the 7.5 are 2.75" and on the 8.8 they are 3.00"
Long live the 4-eyes!  - '83 Tbird Turbo

7.5 vs 8.8

Reply #27
so rangers come with a 7.5? would a tc rear bolt in the ranger, cause if so ill have a posi unit to go with the 2.3t swap once i find a decent ranger.
RIP 1988 and 1990 Lincoln Mark VII LSC
I welcomed the dark side and currently am driving a 2000 Dodge Durango SLT plus, with a 5.9, Code named project "Night Runner"
Shes black on black, fully loaded, with headers, 180 tstat, e fan, straight exhaust into a cherry bomb vortex muffler, full tune up, ported intake and T/B, MSD coil, and round aircleaner.
Mods to come: Fully rebuilt and heavily modded 46RE, and a richmond rachet locker.
my $300 beater ;)
R.I.P Kayleigh Raposa 12/18/90 - 2/24/07

7.5 vs 8.8

Reply #28
Some Rangers came with 7.5's some came with 8.8's. TC rears will not bolt into a Ranger - the Ranger has leaf springs (and brackets necessary to install them), while the TC rear is setup for four link/coil spring (again, with brackets to install 'em)
2015 Mustang GT Premium - 5.0, 6-speed, Guard Green - too much awesome for one car

1988 5.0 Thunderbird :birdsmily: SOLD SEPT 11 2010: TC front clip/hood ♣ Body & paint completed Oct 2007 ♣ 3.55 TC rear end and front brakes ♣ TC interior ♣ CHE rear control arms (adjustable lowers) ♣ 2001 Bullitt springs ♣ Energy suspension poly busings ♣ Kenne Brown subframe connectors ♣ CWE engine mounts ♣ Thundercat sequential turn signals ♣ Explorer overhead console (temp/compass display) ♣ 2.25" off-road dual exhaust ♣ T-5 transmission swap completed Jan 2009 ♣

7.5 vs 8.8

Reply #29
puppies, ill find a way to make it work, thats one thing im good at, making things into stuff its not ment to be, like a roll cage into a go cart intake and exhaust lol
RIP 1988 and 1990 Lincoln Mark VII LSC
I welcomed the dark side and currently am driving a 2000 Dodge Durango SLT plus, with a 5.9, Code named project "Night Runner"
Shes black on black, fully loaded, with headers, 180 tstat, e fan, straight exhaust into a cherry bomb vortex muffler, full tune up, ported intake and T/B, MSD coil, and round aircleaner.
Mods to come: Fully rebuilt and heavily modded 46RE, and a richmond rachet locker.
my $300 beater ;)
R.I.P Kayleigh Raposa 12/18/90 - 2/24/07