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Thread: Can I put too much fluid in my Dana 20 t-case?

  1. #1
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    Jul 2008
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    Default Can I put too much fluid in my Dana 20 t-case?

    I decided to top off the fluids in my T-150 and Dana 20. I thought it would be easier to just take off the shifter on the T-150 and fill it until fluid started coming out the fill plug. Check. After that, I went to the t-case and took off the fill nut (to top it off) and fluid started flowing out. I let most of it out thinking it would not be good for the t-case to be overfilled. It sure looks like the two components share fluid but it might be allowing the tranny to run a little low. Can/should I refill the tranny and keep the t-case a little over full?
    1978 CJ5; I-6, bored 30 over; Holley 4bbl Truck Avenger; Offy intake; aluminum rad; elec pusher fan; Dana 30 front - 4.88; AMC 20 rear - 4.88 - Moser 1pc axles; OX locker in rear, Detroit locker in front; T-150 3spd; Dana 20 case - Teralow gears and Don's twin stick; 33in MT's; Line-X all over; full roll cage; JYG ignition upgrade

  2. #2

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    They don't share fluid. However, I have recently read on this forum that there were two different rear seals offered between the Dana 20 and tranny. I know mine do not share fluid. You don't want to over fill either the tranny or the t-case.
    '79 CJ5 with not much '79 left to it

    SOA on Wagoneer Dana 44s locked
    T18/D18 with OD drive train
    258 with HO 4L head and OBD1 Fuel Injection
    Still fixing and building after almost 20 years

  3. #3
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    Oct 2010
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    New Port Richey, Fl
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    There should be seals between the two, of course if it leaks, they will share fluid. I had a 71' chevy with auto trans and np 205 t-case that leaked atf from the rear output shaft, I drove it like that for a couple of years adding some atf to the trans every month or so. They shared the atf. Moral of the story: if it concerns you, you will have to drop the t-case to swap in new seals.
    Last edited by nprjason; 11-24-2010 at 10:55 PM. Reason: wording
    98' ZJ 5.9 Limited (mine)
    98' ZJ 4.0 2wd (wife's)

  4. #4

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    Usually that is a sign of bad seals I just replaced mine on a d300, not much of a job.

  5. #5
    Senior Moderator CJSIXER's Avatar
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    Mar 2002
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    Salem, OH
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    8,485

    Default

    I would probably fix the problem. When I first put my CJ together I had a similar problem that ended in disaster. It seems that a seal had been installed backwards in the adapter between my NV4500 and Model 18 transfercase. It was allowing the fluid to flow into the transfercase but not back into the transmission. I noticed that the T-case was over filled and was bleeding fluid out the vent tube but I couldn't figure out why. I never bothered to check the transmission because I knew I had filled it and I knew there was a seal between the two. I ended up frying the front input bearing in the tranny because it got starved for oil. Luckily there was enough in the trans that the rest of the bearings and gears were no worse for wear but it was a valuable lesson!

    1970 CJ-6: 305 TPI V8, NV4500, Dana 18 w/Teralow 3:15 gears, Dana 44 rear w/Detroit, 4:88s and custom Moser Alloy shafts, Dana 30 front w/4:88s and Bid Daddy OR HD Tierod kit flipped on top of the knuckles, full cage tied in with Saginaw power steering conversion and power brake conversion. 35 inch Super Swamper SSRs on 17x9 Procomp Steel Wheels. Kilby On Board Air---
    2000 XJ Cherokee Sport - Traded the old girl in on a 2011 Dodge Ram 1500 so I could tow the CJ to and from the trail. Only one Jeep in the family these days.

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