Lets talk Rear Ends

[Blown73]

In the basic sense of the rear end, what works best for the pro-touring scene/application? I am currently underway with building the car, I already have the rear end I am going to use, but I am thinking about what kind of carrier to run. What seems to work best for everyone?

[Ron Sutton]

Jeff a few questions to help provide clarity to everyone who may chime in ...

1. How much power are you building?
2. What type of transmission are you running?
3. How will you use the car "most" of the time?
4. What type of driving do you expect to abuse the car most?

[Schwartz Performance]

We use full floating Ford 9 inch style rear end housings, truetrac differential. Wavetrac diffs are great but expensive .
But yes it depends on use and power definitely!

[Blown73]

Well I left out engine power just for S&G's. I am looking at 600-650, with a 5 speed TKO. I was thinking true-trac diff, but I just wasn't sure if that was as applicable as I thought it would be.

The car will be a driver, but will hold its own on the track. I haven't given it much thought to "abuse" the car, but that is probably something that should be brought into the conversation. I am thinking there are track days in the future of this car, but ideally, it is a driver. I want to be able to jump in the car and take it anywhere, if that's to the grocery store or across the country.

Here's the build thread, if you want to see what I am working with:

https://www.pro-touring.com/showthre...S-Build-Thread

Thanks
-jeff

[Ron Sutton]

I run Detroit lockers, because they will handle 600-900 hp, hard launches & aggressive shifting ... live ... and completely disconnect the the inside tire in the roll through zone of a corner ... then re-engage like a spool on corner exit. BUT most people find the loud clunking noise very distracting & annoying for everyday street driving.

For a more civilized approach on the street, especially with daily drivers, many people like the Detroit Truetrac for 9" Ford rears ... and many use the Truetrac or typical clutch style Eaton Posi with Ford 8.8" or GM 10/12 bolt rear ends. The cone style positractions are designed different, but still behave like a clutch posi.

But both the Truetrac & Posi's can have durability issues when driven HARD, with lots of power. Hard launches (high torque, high rpm, heavy car, good tires, etc) like at the drag strip will break either of these with repeated use. Clutches & spider gears break in the posi's. The small helical gears break in the Truetracs. More power = breaks sooner.

For cornering (track days & AutoX) breakage is less of an issue. Getting the posi clutch pack happy ... so it slips enough to free up the car in the mid-corner roll through zone & re-engages strong for traction on corner exit ... requires some "tuning" with springs & oils, which is why you don't see posi units used much in racing. "Most" of the small helical gear type differentials use a method of pre-loading the unit which affects how the power is distributed under throttle on corner exit. And unfortunately they wear ... and the power distribution changes.

Not so with the Eaton/Detroit Truetrac. It doesn't wear, acts as an open diff when power is off & engages pretty consistently when power is applied. It is a good all-around differential

For your application, as a true pro touring car ... high performance daily driver with occasional track days ... I recommend the Eaton/Detroit Truetrac. Just know, if you start driving it hard (as in race conditions at the track) ... often ... with 650 hp, you should not expect it to last forever.

[parsonsj]

I run Detroit lockers, because they will handle 600-900 hp, hard launches & aggressive shifting ... live ... and completely disconnect the the inside tire in the roll through zone of a corner ... then re-engage like a spool on corner exit. BUT most people find the loud clunking noise very distracting & annoying for everyday street driving.

I ran a Locker in my Nova for a couple years, got bored, and switched to a TrueTrac just for fun. Mistake. The Locker is better in all respects except for turning while backing up (like out of a driveway). I wish I had never changed the car. Their reputation as noisy and clunky is overstated I think.

You can't go wrong with a Locker.

[Ron Sutton]

I ran a Locker in my Nova for a couple years, got bored, and switched to a TrueTrac just for fun. Mistake. The Locker is better in all respects except for turning while backing up (like out of a driveway). I wish I had never changed the car. Their reputation as noisy and clunky is overstated I think.

You can't go wrong with a Locker.

I'm with you John ... the noise doesn't bother me. But many people want their hotrod to be as civilized as a production car.

Backing up & turning with a locker does make a LOT of noise. People say, "Hey! You hear that? I think your rear end is broke!"


John, since you have ran both ... I think everyone (me included) would learn a lot, if you would share specifically what the differences are, that you experienced, from running the locker & Truetrac.

[parsonsj]

John, since you have ran both ... I think everyone (me included) would learn a lot, if you would share specifically what the differences are, that you experienced, from running the locker & Truetrac.

Sure thing, but it's important to know that most of my track experience is in my Z06 -- I only got the Nova (II Much) on the track a few times. And all of the track time with II Much was done with the Locker. I sold the car a few months after switching to the TrueTrac.

So in terms of how the car behaved on the street, I noticed Locker noise (as I mentioned above) mostly when backing out of my driveway. It wasn't that bad, and you couldn't hear it over the exhaust note anyway. I could feel the clunks as the car didn't turn smoothly (Locker's ratcheting release mechanism is designed for forward motion, not reverse). I never felt anything odd or strange or jerky when driving the car on the street, even in tight turns (since that was low speed). On an autoX, the car handled fine -- I could modulate throttle to induce oversteer if I wanted, and I didn't ever feel any non-linear effects. On a big track, there was no drama at all, and I was limited by talent and experience, not the car, and the Locker never even entered my consciousness. II Much had an awesome turn-in (better than my highly modified Z06), and felt flat and neutral. The Locker was a feature on paper, not practice.

The thing I noticed right away when I swapped to the TrueTrac was that I could feel the differential working. Maybe I had a bad one or something, but it squealed on left hand U-turns (though not right-hand ones, but you only need those in England, Japan, and Australia, lol). It was quiet backing up, and I never got to an autoX with it.

Hope that's useful... but it's not really a back-to-back comparison.

[Ron Sutton]

Thanks !

[Blown73]

Thanks Ron & John, that helps out a lot!

[sam 74]

i'm useing a fab9 rear, with a strange nod. iron center, 35 spline axles and a detroit locker, makeing 600hp with a big block.

[Skip Fix]

"Posi's can have durability issues when driven HARD, with lots of power. Hard launches (high torque, high rpm, heavy car, good tires, etc) like at the drag strip will break either of these with repeated use. "

I'll disagree Eaton posis can handle a lot of abuse if you have good spiders in them. Handle as much as the tranny can. Plenty of guys in the 9s with them in 12 bolts or even 8.5 10 bolts. Now the 9" "posi" is not as well made-ie clutches only on one side, although some of the aftermarkets have billet cases the factory style are cast iron. My local rear end shop felt confident using one for my 600 HP 409 Impala project.