I am thinking of buying a rebuilt trac lock to go in my 8 inch. It is actually an entire 3rd member and has new bearings too. The gears are a 3.25 ratio. My question is; how does a trac loc compare to a modern day Auburn or TruTrac? I mean, I want it to leave 2 black marks when I stand in it, and actually hook at the track instead of spinning one tire. Will the trac loc still spin one tire on occasion? I just don't want to buy this thing and pay good money for it if it isn't going to be almost as good as a modern posi.

 

Trac-loc is the Ford style limited-slip differential. Nothing wrong with the design, and I think it would work fine for you. It's not as nice of a design as an Auburn (which uses cone clutches instead of flat clutch plates), and doesn't even come close to a TrueTrac, but it's still a solid design for a limited-slip.

What I'm concerned about is the gear ratio. I've got 3.25's in my car, but I do a reasonable amount of freeway cruising at 70mph and I have short (24") tires. If you're planning on being able to drive this thing on the freeway, the 3.25's will work well for you. But if it's just an around-town car and will spend time on the strip, you may want to consider something more aggressive, like 3.50's or 3.73's.

 

I have a trac-loc and if you accelerate at all in a turn it chirps the wheels. It leaves two even marks from the start. I like it fine. I was told by Moser that the Auburns are not rebuildable. They recomended the trac-loc.That is why I chose the trac-loc.

 

tyler

how much did they want for that setup?

-Gun

 

Well, its at an auction, so im not sure what it will go for. I currently have a 3.00 gear, but with all the motor I have and the 3000 stall converter, it really isn't that bad. The lowest I would go is a 3.55 because it would be an all around good gear for cruising or back roads. If I can get a completely rebuilt 3rd member with the 3.25 for around $500, I would be willing to compromise some. I should be able to get it for close that because the gears are not new, but they look good so they should be fine. Right now, my tires are roughly 28 inches tall in the back, and the drag radials I have are only about 24 inches tall, so if I want to take it to the strip, the tries themselves would help gear the car down for a faster launch. With the street tires on (28 inches tall) I am running at about 3000 rpm cruising on level ground at 70 MPH, so I dont want to go a lot lower than what I have right now. I am also curious if I am wasting my time with the 8 inch. I have heard nothing bad about them as long as they have the 4 pinion posi (the one I am looking at does) because the 2 pinion open carriers are weaker. Im not sure though. I mean, it is the same basic design as a nine inch but just a smaller ring gear. The axle shafts are exactly the same. I do plan on some strip time, but it wont be every weekend. Probably just once a month. So I think it should be fine.

 

Mmmm.....if you're planning on doing drag launches with sticky tires, I might still be skeptical about the 8". If you get the tires to bite, that engine has enough torque to do some damage. Not saying it won't work, but if you plan on long-term strip use, you might want to consider a 9" upgrade.

 

OK, im not against that at all, but before I go spending that kind of money, I want to know the advantages of a 9 inch over the 8? The ring gearand pinion shouldn't be a weak link. I know people who are running 7.5 inch chevy rears in camaros that are running 6's in the eighth mile and they seem to hold up just fine (and you can't convince me that a Ford 8 inch is weaker than these things). I don't know, like I said, I am not against the idea, but I just want to know what the advantages are. I know they way more and also having to buy one would be two major dissadvantages, but it may be worth it in the long run.

 

The 9" is very similar in design to the 8" but uses stronger components throughout. Figure an 8" with a 4-pinion diff will probably hold up to ~400hp on the street. But if you start taking it to the track and running sticky tires, as soon as those tires bite, you start putting lots of stress on the drivetrain. Clutch, u-joints, and the rear end are the weak points. Personally, I'd rather break a u-joint than grenade a rear end. And if I'm going to put that much money into a rear end, I'm not going to leave it as a possible weak point. That means a9".

I'm not saying the 8" won't hold up, but it's possible it might not with the abuseyou're going to throw at it. I was always taught to do things right the first time and not have to worry about it after the fact.

 

But what parts are the weaker parts? Specifically? The thing is, I don't have any moneyto buy a 9inch housing and then buy the internals for itlol. Everybodyaround here wants an arm and a leg for a nine inch, and then you stillhave to go through it and change the gears, add a posi, install new bearings,ect.Thats why I want to upgrade the 8 if I can, its open and sucks because it will only spin one tire. The owner of a local classic mustang shop/store told me that the 9 is no more durable than an 8 in stock form. He also said that with the aftermarket support of the 9, it can be built up alot stronger. I agree with doing it right the first time, but upgrading what I got is still better than just leaving it alone.It would give me better piece of mind.Like I said, it will rarely see the track.

 

Basically, everything inside the differential carrier is stronger, as well as the carrier itself. The diff, gears, bearigs, everything's slightly larger than the 8", and can therefore take more load.

If it's not going to see the track often, you can probably get away with a 4-pinion 8". I just get worried when you start saying 'drag radials.'