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View Full Version : which rear diff do you prefer?


MOTOWN
03-16-2011, 07:32 AM
thinking of my next mod, building the rear end, which posi unit do you prefer?
i have the stock trac loc, which i just rebuilt, also considering an auburn pro which ive used in the past with great results, (not sure if it can be rebuilt), and the theres the eaton which i know can be rebuilt.
ctrlraven
03-16-2011, 07:46 AM
FRPP 31-spline unit with cobra clutches.
M-4204-F318C

DOOM just had his installed.
MOTOWN
03-16-2011, 07:49 AM
thats basically what we have from the factory ,only in a 31 spline set up right?

ive got some 31 spline spider gears some where if i can find em
Fosters
03-16-2011, 08:17 AM
I haven't done anything with the marauder yet, but with the mach I've been thru a few rear ends.

If you're gonna race it hard, spool. I put a 31 spline moser spool in the mustang after destroying an FRPP 31 spline trak loc, and it was awesome. Never had to worry about spinning both slicks or not at the track, never had to worry about chewing up spider gears, or clutches or whatever. The main expense/PITA with it was putting C clip eliminators in.

On the other hand, depending on where you live it might be a pain on the street. Back in Phoenix, I couldn't even tell the spool was in there. Up here in Minneapolis, the asphalt must be different or something because the thing hopped and skipped around corners like crazy, I ended up taking it out. For around town, the FRPP 31 spline is pretty nice; it's one of the few rebuildable diffs out there, and it's fairly cheap. The carbon fiber clutches available, i found, will outlast the spider gears at the track.

Ideally, I'd get an electronic or air locker, but those are $$$... My vote goes FRPP 31 spline if you don't race it; spool if it's mostly a track car, locker if you have a lot of money to blow... I don't particularly like the mechanical lockers as they seem to always like to lock and unlock in the corners on the street... For the expense, a spool seems a better option to those.
MOTOWN
03-16-2011, 08:28 AM
my car is a daily driver in the summer months, so a spool isnt an option, neither is a detroit locker (dont like babying it around corners), im pretty much focusing on the three mentioned
ctrlraven
03-16-2011, 08:29 AM
thats basically what we have from the factory ,only in a 31 spline set up right?

ive got some 31 spline spider gears some where if i can find em
Yes and no it has the carbon fiber clutch pak already in it. Standard on the 03/04 Cobra and 2007 and up GT500 Cobra.
Dragcity
03-16-2011, 08:55 AM
I grabbed a Tru-Trac. Still need to install it though. Been too damn cold up here.
MCAT
03-16-2011, 10:04 AM
Tru-Trac:bows:
computertech
03-16-2011, 10:51 AM
I grabbed a Tru-Trac. Still need to install it though. Been too damn cold up here.

what is the cost on the Tru-Trac ??? link ? thanks

:burnout:
MOTOWN
03-16-2011, 10:54 AM
what is the cost on the Tru-Trac ??? link ? thanks

:burnout:
$279 from summit w/carbon clutches
$259 from summit w/regular clutches

just noticed you said tru-trac, these prices are for a trac-loc
ctrlraven
03-16-2011, 11:19 AM
what is the cost on the Tru-Trac ??? link ? thanks

:burnout:


$279 from summit w/carbon clutches
$259 from summit w/regular clutches

just noticed you said tru-trac, these prices are for a trac-loc

M-4204-F318C (with carbon clutches, 31-spline)
Upgrade to the 31-spline CVPI axles while you're at it.
Dragcity
03-16-2011, 12:31 PM
I have to look up where I got it from. Was over $400....... Just make SURE you go to 31 spline axles, 28's will surely break.

Detroit/Eaton part number 913A561 Never pay for shipping and certainly ... (no tax)

Am I allowed to name where I got mine...? If you search, it is not on the first few pages. It is burried several back. Should find it for under $450
Fosters
03-16-2011, 02:56 PM
M-4204-F318C (with carbon clutches, 31-spline)
Upgrade to the 31-spline CVPI axles while you're at it.

Ohh, that is good to know about the cvpi axles. We need 03 and up, right? Earlier years are diff length, correct?

I vote FRPP 31 spline trak lok :)
ctrlraven
03-16-2011, 03:00 PM
Ohh, that is good to know about the cvpi axles. We need 03 and up, right? Earlier years are diff length, correct?

That I'm not sure. I believe it might be 2005 or 2006 and up. There is some info on them on here if you search.
DOOM
03-16-2011, 03:38 PM
05 and up for the 31 splines.
MCAT
03-16-2011, 03:49 PM
$400+ for a tru-trac is money well spent, & you don't have to keep replacing clutches.
DOOM
03-16-2011, 03:57 PM
Question:

What happens if you're at the track with a "SPOOL" type diff and you launch your car and snap an axle???
yjmud
03-16-2011, 04:04 PM
a very fast turn towards the wall
LANDY
03-16-2011, 04:59 PM
^+ i personally think spools are a thing of the past on any registered car
Joe Walsh
03-16-2011, 05:18 PM
It's always fun making turns in a street car with a Spool.
Even a Detroit Locker is a noisy sum-a-beatch.

True-Trac 'Torsen' FTW!

:banana2:
DOOM
03-16-2011, 05:46 PM
a very fast turn towards the wall

exactly!!!
05crownsport
03-16-2011, 06:17 PM
I have a 31 spline Auburn Pro in my '86 Mustang and am very happy with its performance.
fastblackmerc
03-16-2011, 06:23 PM
^+ i personally think spools are a thing of the past on any registered car

Not only a thing of the past, but most spool manufacture's do not recommend a spool for a street car.
FormulaMarauder
03-16-2011, 08:44 PM
I have a Detroit(Earon) Tru-Trac that my dyno guy installed this past fall, but I still have 28spline axles. Can I upgrade to 31spline, or do I need to replace the whole unit?

I have a centrifigual blower, so my torque is much lower than a roots blower, and the launches arent as violent.
Joe Walsh
03-17-2011, 04:51 AM
I have a Detroit(Earon) Tru-Trac that my dyno guy installed this past fall, but I still have 28spline axles. Can I upgrade to 31spline, or do I need to replace the whole unit?

I have a centrifigual blower, so my torque is much lower than a roots blower, and the launches arent as violent.

Entire unit + axles must be replaced to go to 31 spline.

Hard launches, and especially really sticky drag tires, are what trash most axles.
Dragcity
03-17-2011, 05:57 AM
I think rearch has found more drive components break from street use. The fact being.... You take off hard from a light, your rear wheels are on blacktop... You then hit the smooth surface of the thick white stop line and spin, then hit the balcktop after that an grab again, then hit the first smooth white stripe of the crosswalk, then the blacktop between the second white stripe, then the second white stripe......Grab, slip, grab, slip, grab slip, grab. = Hop.

All that grabing and slipping relates to a LOT of jarring on axles, gears, driveshafts and transmissions. Our cars are not generally prone to wheel hop, but that is a recipe for disaster on drive parts. IN effect, that is what ocurs on the street.

Now, granted, take a 475 RWHP roots Marauder with Mickey Thompson slicks to a well prepped track, and anything goes, first clutch packs, then axles. Then maybe Ring/pinion. (My best guess)

I am doing the Tru-Trac, 31 spline axles and having a 4" steel driveshaft made. I am guessing the transmission will be the first to go. But who knows. Maybe the ring/pinion will give it up.
Fosters
03-17-2011, 07:46 AM
Question:

What happens if you're at the track with a "SPOOL" type diff and you launch your car and snap an axle???

being that you will have c clip eliminators, you will be able to drive home.


a very fast turn towards the wall

wrong, it'll be just like running an open differential.


exactly!!!

What exactly makes you think that?