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post #1 of 39 (permalink) Old 08-24-2005, 05:23 AM Thread Starter
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Stock iron pumpkin vs aluminum pumpkin

Is there any other differences, besides the weight, when picking between an 8.8 pumpkin with posi?

I am wanting to convert my open iron 8.8 pumpkin to posi and I have found an 8.8 out of an manual Super Coupe that I am considering purchasing

or

Should I keep on looking for an aluminum unit instead?

Suggestions?

Thanks,

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post #2 of 39 (permalink) Old 08-24-2005, 07:41 AM
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Quote:
Originally Posted by doug
Is there any other differences, besides the weight, when picking between an 8.8 pumpkin with posi?

I am wanting to convert my open iron 8.8 pumpkin to posi and I have found an 8.8 out of an manual Super Coupe that I am considering purchasing

or

Should I keep on looking for an aluminum unit instead?

Suggestions?

Thanks,

Doug
The only real difference is weight and even that is slight. If you already have a cast iron pumpkin and you are going to have a limited slip differential put in then that's just fine. The iron pumpkin still has an aluminum cover.

There are a lot of threads about this topic. You may want to do a search and see some of the specifics.

BTW, Ford uses the name of "Trac Lock" and GM uses "Posi-trac" for their respective limited slip differentials.
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post #3 of 39 (permalink) Old 08-24-2005, 09:17 AM
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I don't think that the small diffrence in weight is worth it. It is only about 7-8 pounds from what I have been told.
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post #4 of 39 (permalink) Old 08-24-2005, 09:55 AM
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the aluminum one doesn't get rusty though.

I like it.
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post #5 of 39 (permalink) Old 08-24-2005, 04:55 PM
 
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I'd prefer an aluminum, but I wouldn't turn down a good deal on an iron one. You can always have it painted or powdercoated if the rust really bothers you.
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post #6 of 39 (permalink) Old 08-25-2005, 01:35 PM
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The weight difference is actually closer to 15 pounds. Probably not a noticeable difference. I don't think you'd want a pumpkin out of a manual SC unless you're just using it as a core for a rebuild and gear swap. they only came with 2.72s or 3.08s if you're lucky.
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post #7 of 39 (permalink) Old 08-25-2005, 09:37 PM
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but if you plan on upgrading the gears anyway, getting a supercoupe unit with the trac-lock from the factory would be easier than buying one and the gears.

wether the weight difference is 6 or 15 it's still weight lost. It's all part of the weigh losing project Im undergoing. Every little thing adds up very quickly. Aluminum pumpkin, aluminum control arms, aluminum driveshaft, skinny front tires, etc.

I have the iron and the aluminum sitting in my garage, I think I'll go weigh them and report back

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post #8 of 39 (permalink) Old 08-25-2005, 10:02 PM
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k weighed them both just a few minutes ago.

Cast Iron 3.08 open differential - 81lbs
Aluminum 3.08 open differential - 62lbs

So it weighed in at just under 20lbs lighter than the cast iron. I can lift the aluminum with a little effort, but I had to drag that damn cast iron POS across the floor.

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post #9 of 39 (permalink) Old 08-26-2005, 02:23 AM
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Quote:
Originally Posted by Thomas
Cast Iron 3.08 open differential - 81lbs

...but I had to drag that damn cast iron POS across the floor.
Time to hit the gym.




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post #10 of 39 (permalink) Old 08-26-2005, 03:27 AM
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yeah no kiddin. At the first of the year I weighed 220lbs and now Im down to 185lbs I dont know what happened but hey, more weight loss for the car I guess

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post #11 of 39 (permalink) Old 08-26-2005, 03:38 AM
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I used to be hard on the trail for one of those aluminum ones. Then I started seeing the way that the cover flexes and thought...I would be willing to bet if you have 400 hp and sticky tires that you will crack the aluminum one. Now, I will be happy with the cast one and make the cover brace.

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post #12 of 39 (permalink) Old 08-26-2005, 03:51 AM
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the aluminum case should really have no reason to crack, the cover would be the only problem, which can be solved with the conver brace and poly mount bushings. I also invested in the poly bushings, cover brace, and the reinforced rear mount, along with the pinion brace, which all combined, should make the differential virtually indestructible.

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post #13 of 39 (permalink) Old 08-26-2005, 10:22 PM
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When I weighed my FRPP 3.73 rearend it came in at around 80 lbs.

Trac-lok adds to weight possibly?

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post #14 of 39 (permalink) Old 08-26-2005, 10:55 PM
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Quote:
Originally Posted by Thomas
the aluminum case should really have no reason to crack, the cover would be the only problem, which can be solved with the conver brace and poly mount bushings. I also invested in the poly bushings, cover brace, and the reinforced rear mount, along with the pinion brace, which all combined, should make the differential virtually indestructible.
I agree with that. When I broke the cover on my FRPP centersection (aluminum case, 3.73's, and T-Loc), no damage at all occured to the case. The chances of breaking the case itself are pretty slim, the cover and halfshafts are usually the weak links.


Quote:
Originally Posted by RichardM
When I weighed my FRPP 3.73 rearend it came in at around 80 lbs.

Trac-lok adds to weight possibly?
Definitely. Thomas, were both of the diffs that you weighed equipped (or not equipped) with a Trac-Loc?

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post #15 of 39 (permalink) Old 08-27-2005, 12:11 AM
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Quote:
Originally Posted by racecougar
I agree with that. When I broke the cover on my FRPP centersection (aluminum case, 3.73's, and T-Loc), no damage at all occured to the case. The chances of breaking the case itself are pretty slim, the cover and halfshafts are usually the weak links.




Definitely. Thomas, were both of the diffs that you weighed equipped (or not equipped) with a Trac-Loc?

-Rod

Both are open diffs. well at least I was told...by you Remember the 8.8 you sold me? You told your dad it was an open 3.08, so Id assume thats what it is. Cast iron is naturally much heavier than aluminum, so 20lbs seems about right for the same internals.

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post #16 of 39 (permalink) Old 09-06-2005, 08:56 PM
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Go to a junk yard and get the pumpkin out of a Lincoln Mark VIII. It's aluminum and limited slip. But I put a Auburn Pro in mine.


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post #17 of 39 (permalink) Old 09-06-2005, 09:18 PM
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Go to a junk yard and get the pumpkin out of a Lincoln Mark VIII. It's aluminum and limited slip. But I put a Auburn Pro in mine.


Rude
All Mark VIIIs have traction control, which means none of them have limited slip. Still a good pumpkin though...if you put a TL in it yourself.

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post #18 of 39 (permalink) Old 09-24-2005, 12:28 PM
 
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The lighter weight is significant. It's unsprung weight. I'd ditch the iron pumpkin.
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post #19 of 39 (permalink) Old 09-24-2005, 12:34 PM
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Quote:
Originally Posted by Decy
The weight difference is actually closer to 15 pounds. Probably not a noticeable difference. I don't think you'd want a pumpkin out of a manual SC unless you're just using it as a core for a rebuild and gear swap. they only came with 2.72s or 3.08s if you're lucky.
Not necessarily true. I purchased a Trac-Loc pumpkin out of a SuperCoupe and it has 3.27 gears, which is what I wanted.

I would love to have an aluminum case, but don't want to pay anyone to swap internals from my cast Iron case. And its a little higher on the mechanics scale of difficulty than I am currently at right now.


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post #20 of 39 (permalink) Old 09-24-2005, 01:21 PM
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Quote:
Originally Posted by ND4SPDLSC
The lighter weight is significant. It's unsprung weight. I'd ditch the iron pumpkin.

reduce your sig to ten lines please.




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post #21 of 39 (permalink) Old 09-24-2005, 01:35 PM
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I hate iron pumpkins with the flaky rust... drives me nutz, the carrier is equally as heavy in either case

I prefer the AL.

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post #22 of 39 (permalink) Old 09-24-2005, 01:59 PM
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Quote:
Originally Posted by ND4SPDLSC
It's unsprung weight.
How do you figure that it's unsprung weight? (It isn't).

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post #23 of 39 (permalink) Old 09-24-2005, 05:30 PM
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I was going to ask that too. Unsprung weight is weight that is directly effected by the forces of the road vs the car. Wheels, tires, brakes, Controll arms etc. The pumpkin is sprung weight that is controlled by the springs. Make sence?

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post #24 of 39 (permalink) Old 09-25-2005, 12:26 AM
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no kiddin.. i moved the pumpkin w/ some fluid in it by the mount holes with my thumbs


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post #25 of 39 (permalink) Old 10-27-2009, 09:16 AM
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An old bump for a good thread.. So, to make it clear to me, the Mark VIII pumpkin is a bolt on with no modification. I plan on getting trac-lock, 3.73s mounted into the Mark pumpkin. I just want to make sure mounting won't be an issue.

-=James
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post #26 of 39 (permalink) Old 10-27-2009, 10:02 AM
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At least it's weight at the rear, can't hurt traction.

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post #27 of 39 (permalink) Old 10-27-2009, 06:58 PM
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An old bump for a good thread.. So, to make it clear to me, the Mark VIII pumpkin is a bolt on with no modification. I plan on getting trac-lock, 3.73s mounted into the Mark pumpkin. I just want to make sure mounting won't be an issue.
Correct. It is a direct bolt in.

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post #28 of 39 (permalink) Old 10-28-2009, 07:02 AM
 
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since this old thread has been revivied, perhaps I could ask a few questions and become a little more educated.

what does the 96 cougar 4.6 come with? what gearing I mean, and what would adding the MKVIII rear end do for me. what differences would I notice with changed gear sizes and trac-loc?
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post #29 of 39 (permalink) Old 10-28-2009, 07:13 AM
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Thanks guys!

The 1996 Cougar has 3.27 gears and may or may not have Trac Loc. You can change the gears like I am doing (I have 3.08, going to 3.73) and add Trac Loc to do a little better off the line. Most people get Mark VIII 1993 one piece driveshafts and a SCT Tune after. You don't really add a "Mark VIII rear end" to your Cougar, just some componets from the Mark. I didn't know much about this until I started a few threads and did some searching.

I think I might stay with the iron pumpkin to get a little more weight on the rear wheels for better traction.

-=James
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post #30 of 39 (permalink) Old 10-28-2009, 07:30 AM
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think about this for those who want a little more weight on the rear.....just add 2 gallons of gas to the car....damn near the same weight.

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