Does anyone have an experiance with the 9.375 3rd member? I bought one off a kid last weekend for $40 that he thought was a 9 inch. I didn't open the box to verify it before I left his house 102 miles away. I thought about cutting my loses but it has me thinking that it would be a good in between 3rd member to use in the meantime the other one is rebuilt the way I want it with 31 spline axles. So anyways, I posted the same question to the diff forum and no one had any info other then I can grind the 9 inch housing to fit it in there. I do know it is out of a 67 or 68 car. C6AW is found on everything but one case that has a C7AW. I measured the carrier bearings and they are 3.250. I've read on another website that the internals where the side gears mount are the same as a normal 9 inch so I can use a few aftermarket parts like a mini-spool or EZ Locker. The gear ratio is 2.80-1, nice tall freeway gears that the 460 can push around without screaming at 3200 rpm @ 65mph. I plan on hitting the library for the reference materials they have on hand from that time period. Does anyone else have an opinion on this 3rd member?

 

Mark, If you are turning 3200 at 65 you either have 5.?? ratio or your speedo is way off. With a 3.00 gear I am turning 2050 at 55 mph with 235 75 15 tires. I have run a 2.75 gear and liked it but it sucked the life out of the truck when trying to tow with it in there.

Running an overdrive tranny will give you grunt on take off and economy on the road. My truck doesn't have any take off grunt and starts waking up at around 2600 rpms.

There might be better ways of achieving what you are looking for without reinventing the wheel. IMHO

John

 

1968/72 F100 390 Camper Specials used this same setup with the 9 3/8 R&P (passenger cars: 1966-70 with a 428) and 31 spline axles. Even though the R&P is a 9 3/8" the rear axle is still considered a 9 inch, and the parts are listed as such (list #91).

 

If you are looking at the 3rd member, facing the pinion yoke, the ribbing that is right about at 1 o'clock, should have a rounded corner, as opposed to a 90 degree angle.
I have a 9 3/8" in my 72 Sport Custom. It came stock with 3.50:1 limited slip, 31 spline.

 

Morning everyone. The "new" 3rd member is bent down on the top right side of the upper horizontal rib. I've been told the 9.375 3rd member casting isn't as strong as the similar WAR case. I find that hard to believe to be honest. I'm still in the tear down process with the gears and case to clean it out and measure all the bearings. The side gear splines were counted once and I came up with 28 actual teeth with 4 evenly spaced gaps. Once the side gears come out I will reverify the spline counts. Bill thanks for the years that this rear came in trucks. It will help while gathering parts together. So far I have been lucky to find Timken bearing P/N's. Hopefully I find all the P/N's and don't have to receive the blank drooling stare from the part counter kid, I really hate that. Looking at the inside of the case I am going to be doing some casting flash removal. I don't like the sharp edges that can lead to stress risers. Lord knows the engine will be punishing it if I lay into the gas.

My rearend currently has a set of 3.89 gears with 235/70-15 tires, hence 3200 rpm @ 65-70 mph. I've replaced the speedo gear to find the right one after verifying my actual speed. I thought long and hard about the high cruising rpm vurse fast take off for racing. This truck is more cruised then anything else. The tranny when I go through it will have a wide ratio planitary kit installed to lower first and second gear. Third will still be a 1-1 ratio which will also help with moving from a dead stop. The forward drum will be modified to accept an extra clutch plate for more holding power. And a few of the bushings will be replaced with needle bearings to add a little more strength over all.

 

You can get OD trans with wide ratio. Best of both worlds.

http://www.transmissioncenter.net/AOD.htm

You have to scroll down to see the wide ratio stuff and adaptor to 460.

 

I thought of the OD tranny but don't want the headaches adapting it over. By the time I buy all the parts I am looking at $3000 in just the adapter and transmission. The wide ratio kit, http://www.broaderperformance.com/c6...sion_parts.htm and the rebuild kit with taller gears will do just fine.