Precision Trans

Just wanted to post this to clear up any confusion. The other day following a post of mine regarding the "9 Bolt" axle in which I mentioned we had made and marketed a cover/girdle for this axle, Redbird 87 replied and said that this part was in big demand. Not wanting to sound skeptical, but his was the only reply to my post in this regard. (Thanks Redbird for your comments.)

Presently, it looks as though T/A Performance is still only at the casting pattern stage with their cover. If there is any update, I'd love to hear. It's quite possible, they are finding the same as we did when we made a run of this cover, that the demand is just not there.

If you go to T/A Performance web site and read about the history of the Geise Girdle http://www.taperformance.com/tagirdle.htm ,you will find some very interesting reading. I find somewhat amusing the story about testing with a hydraulic press. Lots of psi, but no mention of the ram size. We'll assume a 30 ton press. Quite admirable that no deflection occurred. The engineer is to be congratulated on his ribbing, and wall thickness along with the material spec and the heat treatment & aging of the aluminum. The only thing is, at these load levels, the cover retaining bolts would have torn completely out of the carrier casting. The point I am trying to make, is that this method of stiffening the carrier is only as strong as the weakest link.

So now, with that out of the way, I like to make a few comments about what we observed with the development of our cover from days gone by. Some of the things we tried were billet steel bearing caps and ARP studs to replace the stock ductile iron. This met with some degree of success, but failures cropped up that were related to carrier flex. Not all this flex is caused by the ring and pinion, a goodly portion is caused by forces transmitted from the tires through the axle tubes. This force tries to bend the outer ends of the axle tubes forward. That is why you see Pro cars running axle braces of 9 inch Fords, Chev 12 bolts, Dana 60's etc. A cover/girdle will help prevent some of this deflection if properly designed and executed. However, it is asking alot to require the girdle to handle this bending force along with the loads imposed upon it by the bearing cap pre-load bolts. We found that best gear life resulted from the use of billet bearing caps, top quality cap retaining studs, and a girdle held in place using grade 8 studs with washers and nuts as opposed to bolts. Further, in most cases it was necessary to increase the thread size of the cover retaining bolts to give even more retention strength, and to keep bearing cap preload bolt preload to a lesser value. At this point we reached the strength limit of differential cases and bearings, axle shafts, etc. There was even one instance of the main drive pinion head breaking clean off.

The afore mentioned mods are applicable to not only the "9 Bolt", but also the Corporate 7.50/7.625 axle, and the 12 Bolt conversions.

As always, should anyone have any questions, please do not hesitate to contact. Thank you for your time.