39 pinion issue

[3739ford]

Seeking advice and lot's of opinions. I am building 276 cu.in. and putting AOD behind it. I separated the housing on the 3.78 rear end to find the ring gear good condition, but pinion has 4 or 5 teeth pitted terrible.

I have another rear end that is 4.11 that I took apart this afternoon and ring gear and pinion are in real good condition just needs cleaning up, but threads are an issue.

I really wanted to put the 3.78 in the pickup thinking it would get better gas mileage and overall good gearing to knock around in. What are the pitfalls in mating the pinion from the 4.11 to the 3.78? Would this work or do I need to stay with matched set of gears?

Also, the threads on the axles of the 4.11 are not that great starting out, but the ones on the 3.78 are in real good condition. Would I be better off to run the 4.11 with the engine I'm building? What is involved in taking the two apart and matching up good axles with other gears? I have included a picture of the axle threads on the 4.11 rear end, both axles look like this.

I would appreciate any advice, and all opinions.

[JSeery]

Originally Posted by 3739ford

What are the pitfalls in mating the pinion from the 4.11 to the 3.78? Would this work or do I need to stay with matched set of gears?

Also, the threads on the axles of the 4.11 are not that great starting out, but the ones on the 3.78 are in real good condition. Would I be better off to run the 4.11 with the engine I'm building? What is involved in taking the two apart and matching up good axles with other gears? I have included a picture of the axle threads on the 4.11 rear end, both axles look like this.

I would appreciate any advice, and all opinions.

You can not mix ring gears and pinions of different ratios!! You really can not even use a different pinion of the same ratio. They are matched pairs that are factory lapped to match. Are these stock rear axles? How are you mating them to the AOD? Are they open driveshaft conversions?

Depending on the years of the axles, you should be able to switch the axles around.

[3739ford]

Yes, I'm going to use open driveshaft just got the trans conversion kit and rear open drive kit today.

[ford38v8]

Ring/pinion come in matched sets. They do not mix and match. Complete axle sets including bell housings and spiders are interchangeable with each other. Individual parts of same can be replaced with like units. Pitting on pinion gears may appear "terrible" as stated, but will have no real effect on the useful life of the set, unless extreme pitting has already caused significant wear patterns.

You are correct as to the desirability of the 3.78 set, and also correct as to the very poor condition of the axle threads. While reassembling the desired parts, do follow all recommended procedure without guesswork.

[JSeery]

Originally Posted by 3739ford

Yes, I'm going to use open driveshaft just got the trans conversion kit and rear open drive kit today.

Ok, now I have a question on how you are going to control axle rotation?

[JM 35 Sedan]

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I'd suggest going with 3.78 gears. The 4.11 gears would be okay for racing, hill climbing, or use in a Columbia 2spd rear, but not the best choice for today's open road driving. Post some pictures of your 3.78 gears, with a closeup shot of the pitted pinion gear. I'm having difficulties understanding how a pinion gear gets pitted, and ring gear did not get pitted in a properly matched set of gears. It's possible someone mixed that set years ago. A quick check of the gear numbers would tell the story. Also, its been my experience when mixing and matching questionable parts, I usually had to do the job again.

[rotorwrench]

As JSeery questioned, what is your plan for replacing the torque tube? Are you going with a torque arm set up like The Hot Rod Works sells? https://www.hotrodworks.com/product-...is-components/

An AOD might be OK with the 4.11:1 ratio. It could be better for highway speeds with a 3.78:1 but I don't know. The Mercs with OD in the 50s had 3.92:1 and they worked OK. Some of the shoe boxes had 4.10:1 gears and they did OK.

[Kahuna]

If it were me, I'd factor my selection of rear axle ratio depending on the AOD ratios.
I run a 4.11 axle with a .78 O/D ratio. Makes my final drive 3.21 or so.
What is the O/D ratio on the AOD?

[3739ford]

Here are a few pictures of the pinion. I counted the teeth and it is a 3.78 gear set.

I do plan on adding a torque arm, I have not decided which brand yet, but have seen some pictures of homemade ones also. The center X member from the 39 frame I am using has been cut out already before I acquired it. I am reworking the rear end and front end first to get back under the frame so I will be able to move with tires on.

My AOD is mid to late 80's with O/D ratio of 0.67:1.

Thanks for the comments I need all the advice, and opinions I can get.

[russcc]

The rust on the pinion looks to me like it has been in water.

[3739ford]

It surprised me when I first saw it. I removed it from the pickup with original closed driveshaft. The 4 speed transmission had the cover still on and when I looked inside no rust there. I drained the black very thick crude oil out of the rear end into open container and there was more than I thought came out.

The bearings on the right side are still in great condition, but half the bearing on left side are rusted and pitted. The ring gear teeth are all bright and shiny with no signs of rust.

[Ken/Alabama]

I've got a 9-34 open drive ring & pinion. PM me if your interested.

[JSeery]

AOD OD is .67. So 4:11 ends up 2:75 & 3:78 ends up 2:53.

[alanwoodieman]

either of jseery's gear ratios for final drive would move you down the road real well, I believe I would go with the 4:11 even to LA (lower alabama) for those not in the south

[3739ford]

Thanks for the ratios I had no idea what final outcome would be.

I would be taking apart both rear ends to use pinion/ring gear from 4.11 and using axles from 3.78.

Who sells real good bearings I plan on replacing them all don't want to pull this rascal out again.

[Ken/Alabama]

Use Timken bearings

[JM 35 Sedan]

Originally Posted by 3739ford

Here are a few pictures of the pinion. I counted the teeth and it is a 3.78 gear set.

I do plan on adding a torque arm, I have not decided which brand yet, but have seen some pictures of homemade ones also. The center X member from the 39 frame I am using has been cut out already before I acquired it. I am reworking the rear end and front end first to get back under the frame so I will be able to move with tires on.

My AOD is mid to late 80's with O/D ratio of 0.67:1.

Thanks for the comments I need all the advice, and opinions I can get.

Some of the pinion gear teeth do look rough, as if they have been in water for a good while. I would press the pinion and bearings out of the banjo housing, then press the bearings off the pinion, and bead blast the gear teeth to clean off the rust crud and determine the extent of actual damage. Does the pinion have 6 or 10 splines?
I still don't understand why there is no rust/pitting on some of the ring gear teeth.
Speedway sells a open drive conversion kit that works with the closed drive pinion.

[JM 35 Sedan]

Originally Posted by 3739ford

Thanks for the ratios I had no idea what final outcome would be.

I would be taking apart both rear ends to use pinion/ring gear from 4.11 and using axles from 3.78.

Who sells real good bearings I plan on replacing them all don't want to pull this rascal out again.

You might want to check with barnfind08 on some good quality nos bearings. The quality level of some of the new off shore bearings is not that good.

[Kahuna]

Use the 4.11

[3739ford]

I'm curious Kahuna, your post to use 4.11 because I already have one, or because it will suit my build better?