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Author Topic:   suggestions for best diff., please...
goldenbob
Journeyman

Posts: 30
From: medford, or., United States
Registered: Jun 2002

posted 07-27-2002 04:37 PM     Click Here to See the Profile for goldenbob     Edit/Delete Message   Reply w/Quote
67 coupe, mild 302, 4spd, 9" limitted slip differential.

Problem: keep smoking one tire off the line...(best 60ft time-2.1 secs, 1/4 mile-13.9s @100mph)

need to be able to road race on local course so spool is out of the question. would like something that can corner, but still hook up for friday night at the drags...(the limmited slip used to hook up, what gives?)

thanks...all suggestions appreciated

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67 coupe (my first car in '78)
10:1 302, 4spd, 9" (lsd)posi
windsor jr heads*
*(tweaked by Lindvig mach.)
crane rollers
performer rpm (match ported)
holley 750 (#4160)
hooker super comp.
full msd
drag radials (oops, ran out of $$$)

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SteveLaRiviere
Administrator

Posts: 31026
From: Saco, Maine
Registered: May 99

posted 07-27-2002 05:58 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
You probably just fried the clutches in it. You can either rebuild it, or swap it for a Detroit Locker.

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My Wild Oats have turned to Shredded Wheat.

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[email protected]
Gearhead

Posts: 307
From: Lakewood, CO, USA
Registered: Jun 2001

posted 07-27-2002 06:18 PM     Click Here to See the Profile for JCQuinn@work   Click Here to Email JCQuinn@work     Edit/Delete Message   Reply w/Quote
Nobody will like this but it is what I do with my race cars.

I always start out with an open rear end, traction bars and an air bag or air shocks with independant air lines. Go somewhere that I can do a lot of burnouts and see the tire marks. Then I do burnouts, adjust the bars and the air pressure until I have two equal tire marks on all of the burnouts. Then I know the chassis is set up to go straight and I replace the open rear with just about any locking rear.

When the rear is set up this way you don't put a lot of stress on the locking center section most of the time and the car will launch straight under normal conditions.

John

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Fastymz
Moderator

Posts: 9095
From: Reno Nv USA MEM#1240
Registered: Apr 2001

posted 07-27-2002 06:22 PM     Click Here to See the Profile for Fastymz   Click Here to Email Fastymz     Edit/Delete Message   Reply w/Quote
How do you rebuild a posi unit?
And whats the cost to have one rebuilt.

SCOOP

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65 coupe,351w,C4,Big Boss 429 hood scoop,8"3.40 TracLoc,Cragar SS,Black Suede.

https://mustangsandmore.com/ubb/Fastymz.html

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SteveLaRiviere
Administrator

Posts: 31026
From: Saco, Maine
Registered: May 99

posted 07-27-2002 06:33 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
You remove the ring gear, then the differential comes off the ring gear, and the differential splits in two. Inside the differential there are clutches and steels you replace.

It's probably about a $300 job. It's mostly labor, the parts are only about $50.

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My Wild Oats have turned to Shredded Wheat.

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SundanceKid
Gearhead

Posts: 861
From: UT
Registered: Feb 2001

posted 08-05-2002 03:39 PM     Click Here to See the Profile for SundanceKid   Click Here to Email SundanceKid     Edit/Delete Message   Reply w/Quote
Get a Truetrac. The are like a torsen or quaife differential in the BMW's and Miatas. They will last as long as the car no clutches to go out and will actualy make the car corner better (full traction in turn) unlike a LSD or locker that either slips or locks.

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jkilroy
Gearhead

Posts: 1636
From: Vicksburg, MS
Registered: Dec 99

posted 08-05-2002 05:31 PM     Click Here to See the Profile for jkilroy   Click Here to Email jkilroy     Edit/Delete Message   Reply w/Quote
The problem with TrueTrac's is that they don't hold up well under shock loading, which pretty much puts them out for serious drag race use. If you ask the makers of that unit they will tell you that.

------------------
Jay Kilroy
68' Fastback GT 390
"No such thing as a cam thats too big"

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jsracingbbf
Gearhead

Posts: 1217
From: Batesville,MS. , U.S.A.
Registered: Mar 2002

posted 08-05-2002 09:42 PM     Click Here to See the Profile for jsracingbbf   Click Here to Email jsracingbbf     Edit/Delete Message   Reply w/Quote
I'd buy a spool if your going to race it much. If not I'd talk to Tom of Tom's Differentials in Paramount, Ca. He has run some limited slip 9in rearends behind some serious horsepower with good results. He uses more clutches than is required in the Posi unit. Good Luck!

------------------
Jerry Smith
69 Mustang Pro ET Drag
"Even a blind hog can find an acorn every now and then "

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cpmaverick
Moderator

Posts: 1541
From: Auburn, AL.
Registered: Jan 2000

posted 08-05-2002 10:32 PM     Click Here to See the Profile for cpmaverick   Click Here to Email cpmaverick     Edit/Delete Message   Reply w/Quote
For Auto-X the torsen diff is a great choice and you can buy it for the 9". It's very popular in the SCCA divisions. It is plenty strong for 100 MPH traps, however seems like your combo is mor capable than that. It shoudl still hold up well.

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-Charlie Ping
1970 Maverick Grabber
[email protected] with AC and overdrive.
http://www.maverickgrabber.com

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SteveLaRiviere
Administrator

Posts: 31026
From: Saco, Maine
Registered: May 99

posted 08-06-2002 05:51 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by jsracingbbf:
He uses more clutches than is required in the Posi unit.

I've heard that makes them crack and fail. Those cases are real thin. Do you know how long he makes them last?

------------------
All Fords since 1977!

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bluestreek
Gearhead

Posts: 1086
From: Athens,GA
Registered: Jul 2001

posted 08-06-2002 06:49 PM     Click Here to See the Profile for bluestreek   Click Here to Email bluestreek     Edit/Delete Message   Reply w/Quote
I don't see how you could fit more clutches in without machining the case. I've tried to fit spacers or xtra clutches in, but the case wouldn't go back together. It's real tight in there with new clutches.

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SteveLaRiviere
Administrator

Posts: 31026
From: Saco, Maine
Registered: May 99

posted 08-06-2002 07:22 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
Unless you use thinner steels.

------------------
All Fords since 1977!

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pthornton
Gearhead

Posts: 577
From: Austin, TX USA
Registered: Jun 99

posted 08-06-2002 11:06 PM     Click Here to See the Profile for pthornton   Click Here to Email pthornton     Edit/Delete Message   Reply w/Quote
What about an Auburn Pro 9" unit? That's what i'm running in my boss and it works great from a standing start. Always spins both back tires evenly. Clicks some if I get down on it in a turn, but generally very quiet. Not sure of the maximum power it will take. It is a cone type diff and can't be rebuilt is the downside, but it only cost about $300 so not very expensive.

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bluestreek
Gearhead

Posts: 1086
From: Athens,GA
Registered: Jul 2001

posted 08-06-2002 11:30 PM     Click Here to See the Profile for bluestreek   Click Here to Email bluestreek     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by SteveLaRiviere:
Unless you use thinner steels.


I thought about that, but after looking at how bad the original steels were warped and worn in the last unit , I decided to try some .060" shims under the springs and just use the new HD clutch kit. I haven't put it back in the rear yet, but it felt really tight going back together.

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SundanceKid
Gearhead

Posts: 861
From: UT
Registered: Feb 2001

posted 08-11-2002 02:22 PM     Click Here to See the Profile for SundanceKid   Click Here to Email SundanceKid     Edit/Delete Message   Reply w/Quote
JKilroy, if you read the original post he says he needs a differential for roadracing, not Dragracing.
I have spoken to Tractec and they said unless you have ALOT of horsepower and do high RPM drops with slicks you should be fine using the Truetrac for dragracing. The differential I ordered was a 28 spline and they said I would break axles before the Truetrac. I use the Truetrac for roadracing anyway, I can switch out the rear to a spool if I wanted to go dragracing.

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jkilroy
Gearhead

Posts: 1636
From: Vicksburg, MS
Registered: Dec 99

posted 08-11-2002 09:53 PM     Click Here to See the Profile for jkilroy   Click Here to Email jkilroy     Edit/Delete Message   Reply w/Quote
I don't want to be switching anything if possible, those center sections are heavy! A detroit will work on the road track and on the drag strip, and it will not break, issue solved.

------------------
Jay Kilroy
68' Fastback GT 390
"No such thing as a cam thats too big"

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Rustang
Gearhead

Posts: 403
From: Clarion PA
Registered: Nov 2000

posted 08-11-2002 10:03 PM     Click Here to See the Profile for Rustang   Click Here to Email Rustang     Edit/Delete Message   Reply w/Quote
I machined the case in the trac-loc for extra clutches in my '67. It went several hundred passes and street miles with no problems.
Personally, I like JCQuin's suggestion of playing with the rear springs or installing air shocks. Theoretically if you can get close to equal traction to both tires, then power will go to both just like a posi.
You'd be amazed how playing with air pressure from one side to the other can make the rear act like a posi! Another option would be installing an extra leaf or two in the right, then play with spring clamps on each side until you get the car to leave.

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'68 mustang 351 clevor- [email protected]
'67 Stang, 351W [email protected]
'69 351C [email protected]
'78 Pickup [email protected]
'79 Pickup 460 ET=??

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SundanceKid
Gearhead

Posts: 861
From: UT
Registered: Feb 2001

posted 08-14-2002 04:59 AM     Click Here to See the Profile for SundanceKid   Click Here to Email SundanceKid     Edit/Delete Message   Reply w/Quote
Um,...guys...he's ROAD RACING!! not drag racing???
One tracked minds I guess??

Jkilroy, Lift weights and eat right you can do it!

Off topic, and not related to you Jkilroy (I don't know what you look like) When I watch Drag racing on TV...why are all the drivers overweight? Seems to me you'd want a jockie driving the car when weight matters so much?

I always wondered that?

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