7.5 build up!!!!! where do i start?

[wizardofuz]

Well guys my friend is running a 84 Buick Regal with a 525 hp 355 and he is using the 7.5 rear. This is a drag car and runs 6.70's in the 1/8th. He has changed the ring and pinion gear to a 4.56 and replaced the axles with Moser 28 spline units. He has also welding the spider gears. The car has been running this combination for the last 3 seasons. Now his car only weighs 2700 lbs. and he is only launching it at 2500 rpms but the 7.5 is holding it's owe. He is planning to upgrade next season to a stronger one like a 9" or 12 bolt so he can use his trans brake. Good luck with build.

 

[pontiacgp]

Well guys my friend is running a 84 Buick Regal with a 525 hp 355 and he is using the 7.5 rear. This is a drag car and runs 6.70's in the 1/8th. He has changed the ring and pinion gear to a 4.56 and replaced the axles with Moser 28 spline units. He has also welding the spider gears. The car has been running this combination for the last 3 seasons. Now his car only weighs 2700 lbs. and he is only launching it at 2500 rpms but the 7.5 is holding it's owe. He is planning to upgrade next season to a stronger one like a 9" or 12 bolt so he can use his trans brake. Good luck with build.

the reason why the rear in your friends car is holding up he's bypassed all the weak points of the 7.5. For street use that rear doesn't work

 

[Clone TIE Pilot]

For a street car the 7.5 will be okay as long as you don't run slicks on it. If you are making enough power to to need an 8.5 upgrade, then you probably will also need gussets welded to your LCA mounts. In stock form the LCA mounts on the frame can't handle more than 400 HP safely.

 

[Intragration]

I've been running a 7.5" behind a 455 for a year and haven't had any problems. Having said this, I still wouldn't spend a dime building one. Not because it's going to instantly blow up when you step on the gas, but because there's no sense throwing good cash at a rear end that's still going to be questionable when you're done. Save your money for an 8.5" or a 9" if that's your thing and run the 7.5" in the meantime.

 

[monte olrac]

Here's some info if you want to step it up a bit. http://www.thirdgen.org/beefinguprear

 

[L92 OLDS]

I've been running a 7.5" behind a 455 for a year and haven't had any problems. Having said this, I still wouldn't spend a dime building one. Not because it's going to instantly blow up when you step on the gas, but because there's no sense throwing good cash at a rear end that's still going to be questionable when you're done. Save your money for an 8.5" or a 9" if that's your thing and run the 7.5" in the meantime.

Good advice. The 8.5" is definitely the way to go. A lot of guys underestimate the 7.5" though. I abused one in a 82' Cutlass when I was in high school and never had an issue with it. I see them running at the track on a regular basis with no issues. How many of you guys know someone that has destroyed one?

 

[pontiacgp]

I blew the pinion gears in an Auburn 7.5. The pinion gears in a 7.5 posi are alot smaller than the pinions in an open carrier. I have an 8.2 now with an Eaton posi. We ran the 7.5 in a circle track car with the side gears welded and the only problem we had was with the axles

 

[85GPLef41]

I've killed three stock 7.5 rears doing neutral drops.... That's when i was younger and and crazy aka "dumb"..... :lol: and the ring and pinion gear seem to be the weak link. I had the axle slide out of my Astro and the gears shred the cover out! That was behind the stock 4.3... Now i remember a 3rd gen Camaro and a TA running the streets back in the day and they were running the TPI with no problems.

 

[Intragration]

I've killed three stock 7.5 rears doing neutral drops.... That's when i was younger and and crazy aka "dumb"..... :lol:

As I think you're alluding to, this would be considered abusive treatment, versus aggressive but normal usage. Lots of things are prone to break quickly when abused, which might otherwise last a great deal longer.

I blew the pinion gears in an Auburn 7.5. The pinion gears in a 7.5 posi are alot smaller than the pinions in an open carrier.

This is an interesting point. Some might be more apt to seek out or keep a limited slip 7.5" because it's limited slip, where the 7.5" open is potentially more durable. From this angle, I guess I would add to my statement, you shouldn't spend money to upgrade your 7.5", AND you shouldn't spend money on a different 7.5" just because it's limited slip, since this might make it more failure-prone.

The 7.5" is not necessarily a ticking time bomb, but it doesn't have as much margin for abuse as a properly sized axle. If you're fairly careful with it like I am, it could potentially last for a long time even behind a bigger engine. I got a good deal on a 3.42 limited slip 8.5", so I'm switching to that next week. If axle work was cheap or I had the desire to do it myself, I'd probably upgrade the 7.5", but axle work ISN'T cheap, so having gambled potential tow truck money on my 7.5" and broken even, I'm putting my axle upgrade money on an 8.5".

 

[NY87SS]

First up do some research on the subject!
You'll find 10's of thousand or more people running sub 550 H.P. and 500 Ft lbs of torque have been running the popular easy to find and buy GM 10 bolts both on the street and strip with not one problem ever occurring.
Enemies of these 10 bolts are stiffened rear suspensions, raking the car, boxed control arms or aftermarket replacements. They don't allow any flex which then gets loaded onto the rear ends instead. Too sticky a tire versus more a street strip tire also is a problem.
Welding the tubes to the center section adds alot of strength verus a girdle cover which is more for look than anything else.
Also takeoff posi units can be found to replace the 7.5 and 26 spine axles to 7.625 and 28 spline axles for less than $300 total cost. But I know alot of Malibu owners that run stock 10 bolts with just a Auburn posi and report no problem.
If a setup will break a 10 bolt it more than likely damage a 8.5 unit hence the reason you'll find people will skip the 8.5's all together and go to a Ford 8.8 or 9 inch if worried are there!