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08-01-2018, 07:11 PM | #1 |
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Location: Dothan, AL
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39 pinion issue
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. |
08-01-2018, 07:16 PM | #2 | |
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Re: 39 pinion issue
Quote:
Depending on the years of the axles, you should be able to switch the axles around. Last edited by JSeery; 08-01-2018 at 07:27 PM. |
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08-01-2018, 07:28 PM | #3 |
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Re: 39 pinion issue
Yes, I'm going to use open driveshaft just got the trans conversion kit and rear open drive kit today.
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08-01-2018, 09:53 PM | #4 |
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Re: 39 pinion issue
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.
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08-01-2018, 11:05 PM | #5 |
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Re: 39 pinion issue
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08-02-2018, 08:15 AM | #6 |
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Re: 39 pinion issue
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John "Never give up on what you really want to do. The person with big dreams is more powerful than one with all the facts". Albert Einstein Last edited by JM 35 Sedan; 08-02-2018 at 08:14 PM. Reason: Removed 3.54 gears as a recommendation. Forgot about plans for AOD trans. |
08-02-2018, 08:54 AM | #7 |
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Re: 39 pinion issue
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. |
08-02-2018, 08:54 AM | #8 |
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Re: 39 pinion issue
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? |
08-02-2018, 10:02 AM | #9 |
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Re: 39 pinion issue
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. |
08-02-2018, 11:16 AM | #10 |
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Re: 39 pinion issue
The rust on the pinion looks to me like it has been in water.
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08-02-2018, 11:37 AM | #11 |
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Re: 39 pinion issue
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. |
08-02-2018, 06:41 PM | #12 |
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Re: 39 pinion issue
I've got a 9-34 open drive ring & pinion. PM me if your interested.
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08-02-2018, 07:46 PM | #13 |
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Re: 39 pinion issue
AOD OD is .67. So 4:11 ends up 2:75 & 3:78 ends up 2:53.
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08-02-2018, 08:22 PM | #14 |
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Re: 39 pinion issue
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
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08-02-2018, 08:55 PM | #15 |
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Re: 39 pinion issue
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. |
08-02-2018, 09:16 PM | #16 |
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Re: 39 pinion issue
Use Timken bearings
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08-02-2018, 09:45 PM | #17 | |
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Re: 39 pinion issue
Quote:
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.
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08-02-2018, 09:54 PM | #18 | |
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Re: 39 pinion issue
Quote:
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John "Never give up on what you really want to do. The person with big dreams is more powerful than one with all the facts". Albert Einstein Last edited by JM 35 Sedan; 08-03-2018 at 04:00 PM. |
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08-03-2018, 11:12 AM | #19 |
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Re: 39 pinion issue
Use the 4.11
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08-03-2018, 01:28 PM | #20 |
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Re: 39 pinion issue
I'm curious Kahuna, your post to use 4.11 because I already have one, or because it will suit my build better?
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