rear end question?

Topic: rear end question? (Read 1993 times) previous topic - next topic

rear end question?

March 29, 2007, 08:52:17 AM

i was wondering if a posi trac is the same as traction lok differential? if so how much is a good one?

rear end question?

Reply #1 – March 29, 2007, 09:38:13 AM

Posi Trac and Traction Lok are nothing but brand names. GM owns Posi, Ford owns Traction Lok. Both are limited slip differentials

rear end question?

Reply #2 – March 29, 2007, 11:52:34 AM

As for how much.. I don't know about new, but I purchased a used 8.8 rear assembly with posi for $150 and then about $45 to put new clutches into the Posi. There are several more on our local craigslist for the same price with varying gear ratios.
This $150. does not actually put the posi in the car however. This depends a lot on what you have to start with and what you want to end up with.
I don't believe the Posi's from an 8.8 will go into a 7.5 also don't know what your car has to start with.

My 88 Bird has a 7.5 ring gear, I'm changing to 8.8, 5 Lug, Disk Brake Posi, Poly Bushings, and new shocks. I'll be into the swap about $600+
Oh... and since I'll be 5 lug, my 4 lug wheels won't fit so add $350 for my new wheels.
And I'll need tires to fit the new wheels so add another $300 for just the back.

So as for “how much?” you can pick up a Posi unit for a ford real reasonable ($100). but think it through first because it could require much more than that to actually install it into your car.

p.s
If your car is a 71 cougar as your name implies then you possibly have a 9” or 8” rear and all the info above is null and void.

rear end question?

Reply #3 – March 29, 2007, 04:30:27 PM

Well,I just bought an 8.8 with 3.55 gears for $66.00 on E-Bay (I went and picked it up).I think you could do it all for a lot cheaper.That seems like a ton of money for that work you're doing.I'm cheap,though.

rear end question?

Reply #4 – March 29, 2007, 06:24:25 PM

to jim miller i have a 84 cougar with 7.5 rear end w/ 4 lug. so do just install it if i was going to just keep the same rear end and 4lug.also what is the best gear ratio like 4.10 stuff like that?

rear end question?

Reply #5 – March 29, 2007, 06:54:17 PM

i have an 84 t bird with 7.5 rear and 3.08 gears,aod transmission. I put in a trac lock main carrier from a ranger and 3.73 richmond gears,master rebuild kit and new clutches. It made a big difference in the car on the bottom end . But yet you can still drive 70 mph not reving the car to death.

rear end question?

Reply #6 – March 30, 2007, 02:03:21 AM

Blackcougar71
To ADD posi in the rear would require the diff to be set back up, (I believe, please correct me if I'm wrong people)
Thats going to cost around $250 above whatever you pay for a Posi Unit. I say "about" because you would need to check your local area, I have heard of prices for this ranging from a case of beer (my buddy Ron works for me for beer Ron's Camaro ) all the way up to $600 and that I think is WAY to high, I think $250 is about the norm.

IF you do this then that IS indeed the time to do a gear change as gears also require this same set up procedure, so do it at the same time and only have to pay for setup once.

As for WHAT Gears you would like, sorry Blackcougar I have no experience here. My 88 TBird has 2.73's and I am staying with 2.73's at this time. I would suggest talking with JrP seems he may have the same set up you have and has experience with different gear ratios.

Where I would start if I were you would be to crawl under the car and there should be a small metal tag on your rear diff cover. Assuming the rear has never been tampered with then this tag will tell you what gears you have now.

Knowing where your AT always helps in figuring out where you want to go.

rear end question?

Reply #7 – March 30, 2007, 09:53:12 AM

With a stock 3.8 or 5.0 SO I'd say 3.55 or 3.73 would be the best gears - anything higher and your engine will run out of breath too quickly. Higher gears make the engine rev, and these engines don't like to rev. If you're going with an HO or something wilder 3.73 or 4.10 gears might be better. A looser converter will help as well.

rear end question?

Reply #8 – March 30, 2007, 04:00:11 PM

Jim, you are right adding a trac loc takes all the set up work as just changing the ring and pinion, it is quite mechanically involved and you will need special tools such as magnetic base dial indicator and tools for removing/installing seals and bearings. If you are going in to do a repair or change, it is a good time to do all the work that is needed at once. The gear ratio can also be found out by looking at the axle code on the drivers door jam sticker.
There are a number of gear ratio / rpm calculators out there for figuring out what the new gears will do to your car. Do a search on this site for
7.5 traction-loc and you will find a rpm calculator that can be used if you know your original rpm at a certain speed.

rear end question?

Reply #9 – March 30, 2007, 04:27:43 PM

Another way for finding out your gear ratio is to remove the rear cover and count the teeth on the ring gear then pinion and divide.
example ,41/11=3.73 or 37 / 12=3.08