Farm Equipment - 7020/40 Oil Transfer

Print Page | Close Window

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: 07 Oct 2025 at 4:45pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com

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 ...

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