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Old 02-22-2007, 22:50   #1 (permalink)
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Question Wanting posi...Which is easiest?

Hey all,
just out of curiosity, say I wanted to convert my open diff rear end to a posi.('88 crown vic with the stock 3.08) Which would be the simplest/cheapest way? (W/O welding my gears) I know its kind of a stupid question, but I'd really like to have a posi rear end. Would I just pull my gearing out and replace them with new, or replace my entire rear end with say the rear end out of a P71? Any suggestions would be great. Thanks.

P.S.
Would any of these Ford 9" posi trac rear ends I keep seeing on ebay work for me? This whole 8.8 or 9" thing is kind of confusing to me, as well as 31 spline axels and such, I know I'll research it. Thanks.
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5.0 FI - K&N, Accel 8.8mm wires
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Old 02-23-2007, 09:06   #2 (permalink)
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Re: Wanting posi...Which is easiest?

your car has an 8.8" diff with 28 spline axles. 9" diff is completely different and parts will NOT interchange.

you have several options for traction lock depending how much you want to spend and how much work you want to do.

1) find a limited slip diff assembly from a CV/GM or Town Car in the junk yard and swap it in.
2) buy a traction lock unit, new or used, and install it. this requires pulling the diff cover, pulling the axles, pulling the ring gear carrier out, swapping the ring gear to the traction lock carrier, installing new bearings, then shimming the traction lock carrier to get the proper back lash.
3) get an aftermarket unit by richmond gear (powertrax or lockright) it basically replaces the spider gear section in the stock ring gear carrier. you still gotta pull the cover and the axles, but dont have to swap the carrier or re-shim stuff. the down side is they are fairly expensive ($300-$500)

WELCOME TO POWERTRAX« BY RICHMOND GEAR
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Old 02-23-2007, 09:09   #3 (permalink)
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Re: Wanting posi...Which is easiest?

btw.... here are the axle codes

Axle codes are found on the drivers door info sticker.


2.73 open: 8
2.73 locker: M
3.08 open: Y
3.08 locker: Z
3.27 open: 5
3.27 locker: E
3.55 open: 2
3.55 locker: K
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Old 02-27-2007, 17:17   #4 (permalink)
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Re: Wanting posi...Which is easiest?

Quote:
Originally Posted by 88grandmarq
your car has an 8.8" diff with 28 spline axles. 9" diff is completely different and parts will NOT interchange.

you have several options for traction lock depending how much you want to spend and how much work you want to do.

1) find a limited slip diff assembly from a CV/GM or Town Car in the junk yard and swap it in.
2) buy a traction lock unit, new or used, and install it. this requires pulling the diff cover, pulling the axles, pulling the ring gear carrier out, swapping the ring gear to the traction lock carrier, installing new bearings, then shimming the traction lock carrier to get the proper back lash.
3) get an aftermarket unit by richmond gear (powertrax or lockright) it basically replaces the spider gear section in the stock ring gear carrier. you still gotta pull the cover and the axles, but dont have to swap the carrier or re-shim stuff. the down side is they are fairly expensive ($300-$500)

WELCOME TO POWERTRAX´┐Ż BY RICHMOND GEAR

I think i'll go with one of the 8.8 28 spline trac-locs ive been finding on ebay out of later 90s mustangs. Thanks.
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1988 Crown Vic LTD LX
5.0 FI - K&N, Accel 8.8mm wires
3.08 open diff :(
2.5% tint
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Old 03-01-2007, 12:16   #5 (permalink)
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Re: Wanting posi...Which is easiest?

probably by the time get a factory style trac-loc in$talled it'll co$t more than the powertrax alternative. then you have to wonder if the trac-loc unit you get is any good, no way to tell (unless you rebuild it) until it's installed. if it is no good, you pay again to get it rebuilt and re-installed. the powertrax unit is brand new and you can install it yourself, cha-ching!
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Old 03-08-2007, 19:56   #6 (permalink)
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Re: Wanting posi...Which is easiest?

I think this fits your crown vic. This is a pretty good price.

Ford Racing Traction-Lok Differentials: FMS-M-4204-F288 - summitracing.com
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Old 03-13-2007, 08:54   #7 (permalink)
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Re: Wanting posi...Which is easiest?

Quote:
Originally Posted by tinman351
probably by the time get a factory style trac-loc in$talled it'll co$t more than the powertrax alternative. then you have to wonder if the trac-loc unit you get is any good, no way to tell (unless you rebuild it) until it's installed. if it is no good, you pay again to get it rebuilt and re-installed. the powertrax unit is brand new and you can install it yourself, cha-ching!
You can rebuild the trac-loc unit yourself, and the kits are a whopping 45 bucks.
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Old 03-14-2007, 15:49   #8 (permalink)
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Re: Wanting posi...Which is easiest?

Cheapest decent alternative is to do as you are planning. Get a used 8.8 28 spline limited slip diff off eBay, and a rebuild kit. Rebuild it yourself, it's really easy since there are so few parts involved. Installing you self does take some time playing with painting the gear and judging the pattern (a piece of paper should come with the carrier bearings you buy that will tell you how to do this). However, you won't have any spacers on hand, nor in the kit. Which is why you will probably end up taking the rebuilt diff to a shop and telling them to install it. It's not a huge job, so they should do it for about 100 or so ish. If you decide to change the gears (very recommended for performance increase) then you will definitely want to take it to a shop and then it will cost upwards of $200 labor.

For any kind of street use vehicle I would NOT recommend the PowerTrax. It's a locker style setup, so what it will do it perform as an open diff when it starts slipping and then work like a welded diff when it's not. Great for off roading and strait line racing, not for street use.

If you want to spend the money on a good diff for daily use get a TruTrac, or a Torsen. Both of these style diffs are limited slip, but instead of being clutch based unit, it is a gear based unit, or a hybrid of both. The TruTrac is purely a torsion differential. It uses helical and worm gears instead of clutches so that when 1 wheel begins to spin it instantly reduces the torque on that wheel and transfers it to the other.

As an example of the real life difference from a conventional limited slip, suppose one wheel goes off in the gravel as you are accelerating around a road block while running from the entire police force.

In the case of a torsion differential it balances power to each wheel to maintain the same RPM at each wheel. So as the right wheel goes off into the gravel, the differential will sense the right wheel beginning to spin which will result in a reduction of power to that wheel, this power is then transfered added to the left wheel. So let's say that you put down 300 ft*lbs of torque. With both wheels on pavement without they can handle 500 ft*lbs before spinning. So one wheel can only handle 250ft*lbs be it self. So you put down 150tf*lbs to each wheel. But a wheel in gravel can only handle 75ft*lbs. As you put one wheel in the pavement, the diff transfers the excess 75ft*lbs to the other wheel. Now you are putting down 225ft*lbs on the left wheel, and 75ft*lbs on the right wheel. That means you are still at full acceleration with no wheel spin. But because the torsion differential does not try to hold the wheels together, but instead only balances the power, this means that in a turn the inside wheel is free to rotate slower than the outside as it is required to do.

In the case of a full locker (or spool, IE welded diff), both wheels are forced to spin together no matter what. So with one wheel in gravel you get the same result as the torsion differential. However, in a turn the wheels are not able to spin independently. So the result is pone of two things, either the wheels spin as a result of the tires losing grip because of a twist in the axle, or the axle breaks. This twist in the axle results in force at each wheel in opposite directions, it keeps building until one wheel slips and relieves the tress.

In the case of the clutch based (conventional) there is a % difference in which the wheels will still spin at the same rate. In most cases this percentage on street or mild track use differentials is less than 40%. This means that if the traction of the right wheel is less than 40% different from the traction of the left wheel, they will still keep spinning the same RPMs. However, in the case of one wheel on gravel and the other on pavement, the difference is significantly greater than 40%. In this case the clutches reach their limit and one wheel begins to spin, this spinning result in relatively all your power going to forcing a wheel to spin, and not accelerating. However in the case of a turn, this % difference allows the wheels to spin independently with only some interference. This interference is equal to that % difference. So you now see that as you increase the strength of the diff (ie increase the % difference) you become more and more like a locked differential. Something else to note, is that the clutches can, and do, eventually wear out. This means that periodically (not that often) you do have to service them with new clutches. The other two only wear out if you manage to wear a gear down to nothing.


So why do people not chose the torsion differentials all the time? For the most part, price. A conventional limited slip is less than half the price. The cheapest torsional diff is over $400 for just the part, not installation. Spooled diffs are good for people that go off-roading or need to handle massive HP numbers (ie. full time dragsters). Off roaders like it because if you have one wheel in the air, you still get 100% power to the wheel on the ground, pretty much a must have for rock crawlers. In this case a torsional diff would not work as good, as it depends on that wheel being able to handle at least some force.


So now you know. Informed decisions make good decisions....this thing turned out good, I'm going to have to post this on GMN.
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Old 03-14-2007, 17:17   #9 (permalink)
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Re: Wanting posi...Which is easiest?

Good stuff, Blaze! Definitely put that up on GMN too if you haven't already.
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Old 03-14-2007, 17:49   #10 (permalink)
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Re: Wanting posi...Which is easiest?

Already done, and with some major improvements for general info.
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