Topic: 3:50 Trac Lok came from factory with 31 spline axles? - 1970 M Code

[BlockadeRunner91]

70 NJ January built Mach 1 M code 4 speed with original 3:50 posi. Trying to find out if anyone here knows what gear came with (got standard) 31 spline axles. I know the 3:91 and 4:30 cars got em..I have 31’s in my car and don’t know if they are original. I don’t have any reason to believe they aren’t. The original diff still has the tag on it and it still has the 3:50 locking gear. Did ford put 31’s in 3:25 locking and higher? 3:50 locking and higher? Looks like the axles say FOMOCO or Ford but don’t see any PNs or date codes. Pics attached.

Thanks fellas!

[J_Speegle]

Just looked at a couple of 3.50 traction lok rearend pictures from the second half of 69 production (both CJ's) and both had/have 31 spline.

[warwick]

If you decode the axle tag in the MPL/Master Parts List.  WFD-A is a 31 spline, 9", traction Lok-4 pinion, 3.50, medium wheel bearing, Large Diff Bear/cup

[BlockadeRunner91]

So maybe just slightly off topic but..Have either of you ever replaced the axle seals with NOS seals? I bought a NOS seal from the local ford dealer (been on the shelf since 67) and it looks and feels identical to a aftermarket federated (Mexico) seal so I thought I would try it first. The collar on the axle does not seem to stretch the seal out very tight. I am getting diff fluid inside the drum and it is saturating the shoes (same problem as before). There is a small tool mark on the axle collar where a novice attempted to service the axle at some point long ago. It looks like the tip of a pair of pliers about 3mm long. I VERY carefully filed the burrs down with a tiny file (size of a fingernail clipper file) so as to not distort the shape of the collar inside the seal for a good fit.

Is it a bad idea to use 50+ year old NOS seals? I can’t see that little tiny mark causing the fluid to get past the seal?? It’s smooth now so I know it isn’t wearing the inner rubber edge of the seal. I’ve only driven the car about 10 miles since replacement.

Should I have a shop or the ford dealer replace the collar? It should Ben the same size so I can’t see that changing anything. Appreciate any suggestions. Very frustrating. The one I took out looked like it had been knocked in with punch 🥴

[BlockadeRunner91]

Seal PN

[dieseldave]

If the 2nd picture is your axle then it is a 31 spline. If you used the 31 spline axle seal and don't have the axle sleeve for the seal to run on then it will leak. The 28 spline seal will work on a 31 spline axle if NO sleeve is present. Be very careful installing the axle thru the 28 spline seal, splines can damage the lip.
https://www.deadnutson.com/31-spline-axle-seal-sleeve/
Link to the axle sleeve... Dave

[BlockadeRunner91]

Thanks for the link, Dave. The axle still has the original collar/sleeve on it, I should have taken a picture but I didn’t and now it’s back in the car.  And I have the correct 31 spline seal, installed correctly. The sleeve rides about half way inside the seal like it should. I guess my main concern is how tight the seal should be around the sleeve. There is no other way for the fluid to get past it..if I replace the sleeve and it is the same diameter as the original I don’t see it preventing the leak. Probably making too big a deal out of this but I don’t want to keep driving the car with fluid all in the rear drum and running out of options for a fix.

Do you think the tool mark in the sleeve I mentioned could be causing the leak and I should replace it just to be safe? It didn’t even seem to be contacting the inner edge of the rubber seal.

[67350#1242]

You might try sliding the aftermarket seal down on the axle to see how tight that one is.

[warwick]

Are you using synthetic fluid in the diff? In that case I would use a newer synth compatible seal.

[BlockadeRunner91]

Brad Penn 80W90 conventional gear oil.

[cobrajet_carl]

70 NJ January built Mach 1 M code 4 speed with original 3:50 posi. Trying to find out if anyone here knows what gear came with (got standard) 31 spline axles. I know the 3:91 and 4:30 cars got em..I have 31’s in my car and don’t know if they are original. I don’t have any reason to believe they aren’t. The original diff still has the tag on it and it still has the 3:50 locking gear. Did ford put 31’s in 3:25 locking and higher? 3:50 locking and higher? Looks like the axles say FOMOCO or Ford but don’t see any PNs or date codes. Pics attached.

Thanks fellas!

My March DB 70 M code 4 speed 3.50 Traction-Lok mach has a 31 spline but not an N case axle. Pretty sure it's original but not 100% sure.