I have a 9 inch ford axle with 3.88 gears. When purchased i was told the dif has been broken twice. I got the engine running and placed into gear, the driveshft turned but not the wheels. So i thougt the differential was shot. Well i opened it up and the pinion and ring gear are fine. My thought is that one of the axles must not be the correct length. Is there a short axle and a long axle? i have two axles the same length.

 

Welcome to FTE

1957/67, the axle shafts are the same length, same part number.

1968/72's are 1/4 of an inch or so longer, because these years F100's have wider brakes (2 1/4" vs 1 /3/4").

You checked the R&P, how about the axle and spider gears?

You opened the rear end up how? By removing the carrier from the housing?

To remove the carrier, the axle shafts have to be removed first, is that what you did?

Foolish questions? Besides the 9 inch, Ford offered two other rear ends for 1961/66 F100's, the Dana 44 and Dana 60. Both have a removable inspection cover.

btw: there's no such thing as 3.88-1 gears. Ford never offered that ratio with the 9 incher.

 

I removed both axles and removed the center chunk. The 3.88 gear ratio came from the 35 teeth on the ring and 9 teeth off of the pinion gear. I have not checked the spider gears. I have been trying to see how many parts may try to pop out before i take the carrier assembly totally apart. I did notice that clutch like material was all crammed into the teeth of the driverside spider gear axle hole.

 

And. I know its a 9 inch axle without a doubt. Visually and by the casting numbers. I know 3.88 doesnt seem right. But, that doesnt mean that an aftermarket set was not installed.

 

k, got some serious cleaning done today. I totally dissembled the differential. After a complete inspection, and double checking with machinist blue-ing, the rearend is fine. I did a thorough cleaning. No actual metal was in the case. The spider gears were fine. The clutch like material turned out to be just really old dried up differential fluid.

Reason for no axle movement...

Someone had recently changed one of the axle bearing and did not fully seat the bearing. They definitly did not know what they were doing. They only made it flush with the first part of the final taper on the axle. There was still bout 3 inches of travel left till the bearing was fully seated. I over looked the axle bearings while removing due to my fear of total differential failure. I know better as a working tech, but thats how it goes sometimes.

Triple check of the ring gear teeth and pinion gear teeth show... 35 = 3.88:1 gear ratio.

I asked a ford part dealer here, they said that a lot of older gears actually are not the same as the mathematic gear. He said this gear was more than like listed as a 3.74:1 gear. Sounds even wierder to me but oh well.

 

Thanks for the info bout the same length axles. This oldie should be rollin real soon. dont know bout stoppin yet, i have two brake line that have 3 in long holes.

 

The axle code doesn't always jive with the ring and pinons part number, but only in a few cases.

For example, Ford lists 3-55's, but the ratio is actually 3.54, 4.11's can be 4.09's or 4.10's. But there is no spread that reaches farther than two or three digits.

I have the R&P charts which give the tooth count on both.

There's no ratio of 3.88, no ratio of 3.74, 3.75, 3.76, whatever. There are 3.70's and 3.73's listed, but the part number isn't the same for these two R&P gear kits.

B7AZ-4209-N = 3.89-1 ~ Used 1957/67 cars/trucks / replaced by C8OZ-4209-A (3.91-1) in 1968. Used on 1968/71 passenger cars.

 

lol, I have a feeling you might be taking this personal. Dont. I think that the 3.89:1 is definetly the right gear. 35/9 is 3.8888889 So rounding up. its right. I'll post the part number on the ring gear tomorrow. When i showed my the ford parts guy the ring gear he showed me a casting that said 374, but the rest of the castings were actual ford part numbers.

I have the diff assembled and the whole housing clean. I will be able to reinstall thursday. What is the torque-ing technique to tighten the load bearings? I have them snug by using a pair of 45* needle nose pliers. I know that this will make some noise, but i'd like to be close to spec as possible.

Thank you again!

 

OK setting up a 9" is pretty easy. Get a book that covers the procedure thats my best advice for you. From memory it goes like this. If the pinion preload is OK (10-20 in/lb to maintain rotation IIRC) you can install the carrier and snug up the bearing caps. Tighten both bearing adjusters until there is 0 end play and some backlash between R&P. Now move the carrier into or away from the pinion by adjusting the bearing adjusters evenly until you have .008" - .012" backlash. Use some impression paste to see the tooth contact pattern. The book will help interpit what you see. If the pattern looks good it shouldn't howl. If I've forgotten anything somebody will be along to correct me but I think you get the jist.

 

Thanks for the advice. I've set up like you've listed before. I just didnt know what the proper tightening technique on the bearing caps. I have some blue grease i used to check the gear meshing earlier. Im really afraid i might be messing up the locking cap/nut with the pliers i've been using.

 

As long as your not tearing chunks of metal out of them your fine. Just remember slight preload on the pinion, 0 endplay on the carrier, .008-.012 backlash, good contact pattern. Carrier bearing cap bolt torque is around 65-75 ft/lb IIRC.

 

sweet, thanks! I did just that and i have a great mesh pattern! So, it should be decently quiet, and the differential should last. Well, as far as proper installation goes.

kudos to you Cobraguy