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jpaz

jpaz

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1972 Mach 1 Q Code
Has anyone ever installed one of these units? I am wanting to change my open differential. Was thinking about putting a Detroit True Trac in & changing my gears from a 3.25 to 3.50 while I'm at it.

I know its not a big change in gears, but I do have factory a/c and with 15" tires instead of the stock 14" I shouldn't have to worry about the compressor spinning to fast.

Anyway, if I go with the entire 3rd member, I can install myself & will be a bit cheaper. If I go with the True Trac I would have to get it installed & will cost more. http://www.speedwaymotors.com/Ford-9-Inch-Posi-Traction-Third-Member-Assembly,6788.html

 
Has anyone ever installed one of these units? I am wanting to change my open differential. Was thinking about putting a Detroit True Trac in & changing my gears from a 3.25 to 3.50 while I'm at it.

I know its not a big change in gears, but I do have factory a/c and with 15" tires instead of the stock 14" I shouldn't have to worry about the compressor spinning to fast.

Anyway, if I go with the entire 3rd member, I can install myself & will be a bit cheaper. If I go with the True Trac I would have to get it installed & will cost more. http://www.speedwaymotors.com/Ford-9-Inch-Posi-Traction-Third-Member-Assembly,6788.html
Click to expand...
I am running the 3.89 version and I like it. I did not install it myself so I can't help here.

 
Install is pretty straight forward. You can find a hundred write ups on how to do it. Nothing terribly complicated about it. Before you proceed, there is one thing to note. Some housings have drain plugs and some do not. If the new chunk doesn't have a fill plug you'll want to add one to the housing at the same level as the existing one. You can weld a bung in or just tap the housing if you prefer not to weld.

 
I have a 3.55 True Trak in my 69 vert and I love it. Quiet, nice gear setup (with my AOD). I had a local speed shop do the set-up for about $450 labor. The first thing they checked was the cut of the gears since at the time there were some issues with sloppy machining which in turn caused rear end noise.. They liked the machining on the unit I had purchased so went ahead with the build.

 
Should not make a sound if done right the only sound will be the engine rpms running higher. I run a 4:10 rear gear and it makes no noise at all. To change the 3rd member out the only big thing you have to worry about is the axle spline then its super easy. Take the wheels and Drums off and there is a hole in the axle turn it till the bolt lines up, unbolt it 4X and the axle slides out be careful not to damage the spline on the axle when you remove it. Repeat on the opposite side, unbolt the drive shaft, 3rd member (leave a couple of loose bolts in at the top to be safe) remove all the rest pry the 3rd member loose, remove the loose bolts (so it did not fall on you) and your golden. Its not going to be light when you remove the gear set from the Housing so eat your wheaties...lol I would replace the axle bearings since you have them out as well...

Remember when you replace it if you put a limited slip in it you need to add friction modifier (super stinky crap) or it will burn up. fresh gear oil and your good to go do burnouts.

Mike

 
Last edited by a moderator:
MT91106 Mike you are right about if its setup correctly just having the good luck of finding a good supplier was really the nature of my inquiry. Its not a bad price as motive gears are 240, bearings 104, tracloc unit usually 375 to 550 they are not marking these up hardly at all considering the cost of labor and the used case.

 
My car was recently restored, so I was going to just pull axles out just far enough to get 3rd member out & the new one in. Wasn't planning on replacing seals. I only have 2500 miles on car since restoration. I would replace if I felt that I damaged one.

I liked the idea of this cause its about the same price as taking it somewhere to have the new diff & gears installed. This way, I can easily put it back to stock if I want to, & I can do myself(with some help)at home. :)

 
Should not make a sound if done right the only sound will be the engine rpms running higher. I run a 4:10 rear gear and it makes no noise at all. To change the 3rd member out the only big thing you have to worry about is the axle spline then its super easy. Take the wheels and Drums off and there is a hole in the axle turn it till the bolt lines up, unbolt it 4X and the axle slides out be careful not to damage the spline on the axle when you remove it. Repeat on the opposite side, unbolt the drive shaft, 3rd member (leave a couple of loose bolts in at the top to be safe) remove all the rest pry the 3rd member loose, remove the loose bolts (so it did not fall on you) and your golden. Its not going to be light when you remove the gear set from the Housing so eat your wheaties...lol I would replace the axle bearings since you have them out as well...

Remember when you replace it if you put a limited slip in it you need to add friction modifier (super stinky crap) or it will burn up. fresh gear oil and your good to go do burnouts.

Mike
Click to expand...
That's about the size of it. I got a 3rd member with a Detroit locker for about $50 from a guy at the dragstrip who had broken some teeth, ordered gears and had a racing buddy rebuild it for another $50. I bumped up to 31 spline axles in the process, which required new axle seals. The installation of the 3rd member went just as MT91106 describes. It's an easy swap.

 

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