Farm Equipment - 7020/40 Oil Transfer

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7020/40 Oil Transfer

Printed From: Unofficial Allis
Category: Allis Chalmers
Forum Name: Farm Equipment
Forum Description: everything about Allis-Chalmers farm equipment
URL: https://www.allischalmers.com/forum/forum_posts.asp?TID=208446
Printed Date: 29 Nov 2025 at 7:29am
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Topic: 7020/40 Oil Transfer

Posted By: joe
Subject: 7020/40 Oil Transfer
Date Posted: 07 Oct 2025 at 8:32am

Good morning. Have a 7020 and 7040 that were transferring oil from rear end to trans. 1 PD, the other PS. Replaced pump driveshaft seal and seal between gerotor and gear pumps. Spring facing the rear end and gear pump, respectively. Used retaining compound on both.

Both continue on exactly the same. Seal direction would fight against this direction of transfer. Kind of at a loss, as PTO seal transfer is unlikely, and pinion seal transfer should occur only at higher speeds, but these both failed near immediately after repair. I realize that this topic has been covered at length, but I just can't make sense of this. Any thoughts are appreciated.

Replies:

Posted By: DrAllis
Date Posted: 07 Oct 2025 at 8:59am

I know Mack talked about the seal on the hydraulic pumps drive shaft as pretty much always his fix. I myself don't ever remember fighting a rear end to tranny oil transfer situation. Mine have always been transmission disappearing into the rear end and that was always related to the gerotor pump to gear pump seal or bad pump bushings/bad pump. I did have one 7080 back in 1979 that another dealer had just recently been in the rear end and had that upper PTO seal in backwards. It would transfer oil when running it down the road and didn't seem to bother in the field. Do you think your transfer occurs only when using the tractor?? or might it slowly transfer sitting in a level shed?? I guess if you drained the tranny completely and left a clean 5 gallon pail under the trans suction screen for a week, you'd know if the rear end was going down and the 5 gallon pail was gaining. That would then get down to the pump drive shaft seal and bushing (you could actually see it) or the pinion seal or the large core plug inside the range transmission floor. A plugged breather to the rear end (the fill cap) I suppose is a possibility, so I'd leave it removed for this gravity test. If the fill cap was plugged I could see it allowing pressure to build in the rear end maybe forcing oil to push thru the pinion seal ?? especially when in the field and hot. EDIT: I know on the gerotor pump seal, I always had to wrap the splines with a thin spirol layer of black tape and oil it, to slide the new seal over the splines to not damage the seal. I don't remember the pumps drive shaft design if it is also prone to seal damage when sliding it on over the splines or not. You kind of made mention that repairs had just been made to each of these tractors and then they started transferring oil????? I know for a fact there have been times when black belly tractors have had hoses and lines crossed up ahead of the radiator causing this.

Posted By: tbran
Date Posted: 07 Oct 2025 at 9:35am

That back seal on the drive shaft really needs a special made seal driver to install. We use to have one a tech made. We made it because of an error installing seal resulting in multiple teardowns ...

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When told "it's not the money,it's the principle", remember, it's always the money..

Posted By: joe
Date Posted: 08 Oct 2025 at 9:09am

The 7020 was mainly in for this and for general fluids and filters. The 7040 was much more involved, but no cooler lines were disconnected. The transfer was a very ongoing problem with the 7020. I'm less sure on the 7040. We bought the tractor and did a bunch of work. I thought I'd start fresh with these seals, given it's been really annoying to have oil transfer on the 7020. I may need to check whether leaking is only when sitting still or running. I know initially, the 7040 did not leak when sitting still. I did wrap both shafts with a single layer of black tape, grease the seal, and I'm very sure I oiled the pump(driven) shaft, though maybe not the pump drive shaft. On the 7040, I've added a 1/4 hose from where the pressure switch is on the PD filter head, to near the rear end fill port with a 1/4 turn valve to make transferring oil easy, clean, and no dirt. We need to keep running, it's been in the shop long enough.

Posted By: joe
Date Posted: 09 Oct 2025 at 5:29pm

Just a further question. If it is a bushing problem, I'm not seeing any parts listing for the bushing. Is it available separately?

Posted By: DrAllis
Date Posted: 09 Oct 2025 at 7:44pm

70269992 bushing.

Posted By: joe
Date Posted: 10 Oct 2025 at 11:32am

Thank you so much!