9" diff, differential, rearend tech

[Gatorac]

At my last event I had a failure with the rear in my GTRA. This gave me an opportunity to get to know this part of the car much better. Here are a few details specific to my GTRA. Yours may differ as we all know these cars are not always consistent.

9" Ford built by Tex Racing
3.50 gears
True trac differential
2.891 carrier bearings (there are 3 different size carrier bearings available). I would suggest disassembling the carrier and measure these bearings prior to ordering a bearing kit. My replacement carrier took a larger bearing.
"Daytona" style pinion bearing. The standard 9" pinion support has the same size bearings on both sides of the pinion support. The "Daytona" style has a larger inner bearing. This is supposed to be good. When ordering a bearing kit be sure to ask for the "Daytona" style. If not available, the timken part numbers for the bearing and race are;
bearing HM89443
Race HM89410
The typical differential uses a crush sleeve to set the pinion bearing preload. With a crush sleeve you torque down the nut until you measure the correct in/lb torque when turning the pinion. Our pinion support uses a solid spacer. This is a better method but takes more time to set up. For one, we can remove the pinion nut to replace the seal and not have to worry about getting a new crush sleeve.

This rear end is very easy to work on. It is not voodoo or magic. You can rebuild it or change the ring and pinion yourself. There are several internet pages to help you. By far the most informative is here. http://www.ford-trucks.com/article/i...ear_Setup.html

Bad Shoe Productions has a 3 hour video on rebuilding the Ford 9". A YouTube sample is here. It also covers an important step in setting up your rear.

You will need a couple of tools. A dial indicator and stand. These can be had for very little money from Harbor freight. An in/lb torque wrench with a dial scale. These are a little harder to find. If you have a friend that is a Snap On tool distributor, perhaps he'll loan you one. You will need one. A shop press for pressing on and off the bearings and races. Again, not too expensive from Harbor Freight and a handy tool to have around. You could take it to a shop for that part but setting up the pinion preload my require you to press the pinion out of the housing several times. I would recommend going ahead and buying the bracket to hold the carrier. They aren't expensive and boy would it have saved my back from rolling the dang thing around the work bench. If ever do this again, I'm getting one.

One thing the Fordtrucks.com site doesn't help with is setting up the pinion preload with a solid spacer. It is not difficult. It's trial and error. Assemble the pinion with the spacer and a few shims and torque the pinion nut to 150 ft/lbs. Measure the pinion preload with your borrowed wrench. Too much preload, add shims. Not enough, subtract shims. I ran into a little problem when doing mine. The existing spacer and a .010 shim was not enough preload. The existing spacer alone was too much. The .010 was the smallest shim that came in the kit. I took my existing spacer to a machine shop and had them mill .020 off of it. This way with the shims I had, I could go from the existing size all the way to +.010 in .002 increments to get the correct preload.

If something doesn't seem right, it probably isn't. I had an issue when using my stock carrier. The carrier bearing preload would go way up when torquing the bearing caps down. After beating my head against the wall for several days and thinking I must be retarded, I ordered a new carrier. Everything went together smoothly. My old carrier was F'd up.

Tex Racing makes the internal pump that the GTS cars use for the diff cooler. The carrier needs to be machined to accept this pump. The pump is driven off of the pinion gear. The pinion also needs to be machined to accept the drive shaft for the pump. If you don't already have the internal pump, I don't see the cost advantage of going this route over an electric pump.

The oil seals are in the axle tubes right by the pumpkin. This is not like your standard rear that uses diff oil to lubricate the wheel bearings. There are 2 different types of seals used in these. Mine had the seals made by Seals-it. The red ones were the correct size and the rubber parts are replaceable. They are available from Speedway Motors. Here's a pic.

Not sure what the other type of seal looks like as I've only heard rumors that they exist. Those same rumors say they suck too.

Good luck with your project.

[Blue Streak 21]

Thanks for pulling all this info together. Very helpful. A seal replacement is in the cards for my rear end this off-season. Don't know if I'll change gear ratios, as I'm pretty happy with the shift points at my home track and the way it pulls out of the corners.
I'm going to be visiting all the sites you mention for DIY.
Thanks again.

[Panoz Paul]

Greetings ... Why not pull the seals & let the diff lube out to the bearings ??? We turn left & right for distribution ; I know the circle track guys need pack their bearings because the inner will starve dry ... Any thoughts ... Thanks / Paul W.

[NZGTRA17]

Originally Posted by Panoz Paul

Greetings ... Why not pull the seals & let the diff lube out to the bearings ??? We turn left & right for distribution ; I know the circle track guys need pack their bearings because the inner will starve dry ... Any thoughts ... Thanks / Paul W.

Would seem the plan is to keep as much lube in and around the crown wheel and pinion as possible to keep it cool and prevent wear. I have run a full floater 9" rear in a previous car that did not have seals in the tubes but had baffles. In that application the hub bearings were lubed by the diff oil. This did not cause any problems but the car was used for sprint racing with only 6 - 8 lap races. May well have been an issue over extended operation.

At present my GTRA is a combi lube set up as the axle seals are letting some oil out to the hub bearings and this did not cause us any issues in our 6 hour race. I did set the oil level up to account for some loss outboard of the seal when filling the diff.