Traction is what breaks 7.5" rears, I had a 7.5" with an Auburn carrier and 373 gears behind a healthy 496 BBC in my Monte and I never ran slicks and I also never had traction but it didn't break.
Quick performance 9" question
- Thread starter Drkuhar
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The only issue i have is the emergency brake is not what i expected. I went with the rear disc. Still playing with and i will make it work
Do the 9" so I can watch. It'll be my next major Cutlass purchase.
QP are good people to deal with, each and every question I had, Brydon not only answered in layman terms, but also ventured other options if he thought I had not considered them.....take into account the lower control arm brackets do not have the same angled mounting point for the shock bolt (they didn't make them back when I bought mine), a wedge washer from McMaster Carr will fix that issue though....
Thanks for the tip. This is the type of information i was looking for. What works and what doesnt.
Save your money is my advice. You don’t need a 9” unless your putting real wood in the stove. Sounds like you’re throwing in some pine lol.
A properly setup 7.5 will withstand 350-400 hp if you don’t run sticky tires and launch it hard. Street (hard) tired that spin easily and a 7.5 will live forever in proper conditions. Of course a 40 year old diff needs ‘proper’ attention.
There are some super cheap upgrades to a 7.5 that will make it live over 450 hp without issue as well.
A properly setup 7.5 will withstand 350-400 hp if you don’t run sticky tires and launch it hard. Street (hard) tired that spin easily and a 7.5 will live forever in proper conditions. Of course a 40 year old diff needs ‘proper’ attention.
There are some super cheap upgrades to a 7.5 that will make it live over 450 hp without issue as well.
I am definitely taking a second thought after seeing some of the post about a 7.5 holding up. I dont run slicks,i mostly run errands, go to a few local car shows and light em up at a stop sign once in a while. Its a large amount of money for no more than i do.
Plus if you try to "budget build" the 9" you could be sacrificing strength which is the whole reason to buy one in the first place.
I’ve referenced this in the past, and I’m sure you can find posts identifying this - I have a spare rear in the basement that is a stock factory Torsten diff from a 3rd Gen with 2wd S10 axles - both 28 spline. You have to space the stock brakes 3/16” via a homemade spacer to get the S10 axles to work properly. The rear I described we ran for a year at 500whp (not crank) burnt through multiple sets of tires. All junkyard parts other than the bearing kit. Never ran sticky tires on that rear, but did run 275/40R17’s that were aggressive.
A NA build that makes 400 crank hp will never break that setup. We bought the Torsen off eBay for less than $200 and it was a 3 series that would take 3.08’s and up - we used 3.73’s(from the junkyard of course) 😉
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