Mysterious Drive Train Problem

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slumley1
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Mysterious Drive Train Problem

Post by slumley1 » Sun Mar 18, 2012 12:21 pm

I have an 85 cj7 that I bought last October. It has a Chevy 350, TH350, and Dana 300. Dana 30 front axle and AMC 20 rear. Since I bought it, I always felt like something wasn't right with the transmission/transfer case. The transmission would take a few second for the gear to engage and would go in to 1st or reverse really hard once it did engage. The transfer case seemed to make a loud humming sound when I'd let off the gas a 30+ mph. Everything else seemed ok.

About a month or so ago I started having problems intermittently with what I thought was the transmission. I'd have to really ease slowing on to the gas when it drive or reverse whenever I was starting up from a complete stop or slow roll. Otherwise I'd get this metal against metal sound and wouldn't move. It I let off the gas and very slowly applied the gas again it'd be ok. Once it was going it had no problem shifting or staying in gear. It got progressively worse so I picked up a rebuilt transmission (TH350) and had a buddy help me put it in. We put the same old transfer case back in which I've been told plenty since then was a big mistake.

It worked ok at first. After a few days it started doing the exact same thing again. Then the other night I stopped at a light and then it just wouldn't move. I had to have it towed home and now it won't move at all.

I got under it and had my wive go through the gears. It seems to click right in to gear. While in 2hi and in gear, when she gave it gas while in gear I heard a grinding coming from the transfer case and neither drive shaft moves. When I put it in 4hi it makes a terrible grinding sound in the rear axle and the rear wheel wobbles badly. The rear drive shaft spins and the front does nothing.

Does anyone have a clue what this might be? Or what else I can try to help diagnose what it is?

Thanks in advance for any help.

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Re: Mysterious Drive Train Problem

Post by slumley1 » Sun Mar 18, 2012 5:18 pm

I put it in 4lo and then pushed it all the way back to 4hi and the front end works. It'll move by the front axle pulling it and when it's in 4hi/lo the rear noise and rear wheel wobble stops.

Assuming it's the rear axle, what would be the best/easiest solution? Rebuild the AMC 20 rear or replace with another like a dana 44 or otherwise?

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Re: Mysterious Drive Train Problem

Post by bigbirdcj » Sun Mar 18, 2012 7:35 pm

Does your rear Model 20 still have the 2-piece axle shafts in it? Sounds like maybe you stripped one. A V8 Chevy will do that. You can buy the one piece shaft kit for around $300.
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slumley1
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Re: Mysterious Drive Train Problem

Post by slumley1 » Sun Mar 18, 2012 8:36 pm

Yeah it's the stock 2 piece axle. How difficult is the swap? I have a buddy down the street who has a garage, lift, tools and will charge me $40/hour. He doesn't know jeeps since he's a bmw mechanic but he helped me swap my th350 in about 4 hours. Is this an easier solution or would it be easier to swap the whole rear? I can't find the '86 dana 44 near here so I'll either swap for another AMC 20 or swap the axle on mine.

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Re: Mysterious Drive Train Problem

Post by wesleypipesyo » Sun Mar 18, 2012 8:48 pm

If it is a rear axle shaft, it should not be too hard to do. You could probably do it in your driveway with a jack stand.
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Re: Mysterious Drive Train Problem

Post by bigbirdcj » Sun Mar 18, 2012 8:50 pm

I haven't done the install personnally but it can't be that difficult.
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slumley1
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Re: Mysterious Drive Train Problem

Post by slumley1 » Sun Mar 18, 2012 9:09 pm

What else can it be other than an axle shaft based on what it's doing?

What can I do to determine what it is?

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Re: Mysterious Drive Train Problem

Post by thezman » Mon Mar 19, 2012 12:32 am

I had a similar issue with the rear Amc 20 the hub spun off the axle. I eventually did the one piece conversion and it was fine. Without looking at it I have no idea what it is or where to start. Finding a 44 would be best but it's very costly and rare. I gave away a Amc 20 wide trac today. I bought the 44. The best thing I could say is jack it up take the wheels off and start at the rear moving forward to eliminate all possibilities. If I can find time I'd take a look at it. Could be your rear bearings are binding up and bad as well. Maybe take the pan off the transfer case and check out the gears. I have a good transfer case in my Cj that's coming out if you need one I'm currently building a low max one and getting rid of the stock one would make me speed up the process.
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Re: Mysterious Drive Train Problem

Post by thezman » Mon Mar 19, 2012 12:37 am

Oh and the one piece axle swap is very easy just remember to pre grease the bearings or the axle may walk out going down the road. Not like that happened to me or anything oh wait it did cause I was in a rush. Moser makes a good kit with timken bearings for $275 I think from 4wd.com
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Re: Mysterious Drive Train Problem

Post by Brent Borgaard » Tue Mar 20, 2012 11:11 am

If it`s the axle? You can see it spinning in the hub. It` would`nt have gone away, for a short time. After swapping the tranny. I`m wondering if your input shaft. In the transfer case , is stripping. It`s splines.
How did i spend four grand on parts in one month?

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Re: Mysterious Drive Train Problem

Post by slumley1 » Wed Mar 21, 2012 11:23 pm

So I was pretty sure it was the rear driver side axle shaft. I found someone near me who had a stock 2 piece axle for $30. I know it's not a part that anyone likes but for what I do in the jeep, I think it'll be ok. If not, I only wasted $30. I pulled off the rear wheel and the brake drum and immediately knew that was the problem. All the splines came out in the form of dust. I put a picture below of the old axle shaft.

The new axle shaft went in perfectly and it all runs great.

Image

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Re: Mysterious Drive Train Problem

Post by thezman » Thu Mar 22, 2012 2:57 pm

Yeah I had the same thing happen. Make sure you torque the new one down
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Re: Mysterious Drive Train Problem

Post by wesleypipesyo » Thu Mar 22, 2012 5:54 pm

I think I found your problem. If you replace the part that looks all messed up you will be fine.
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