Allis Chalmers 7080 Hydraulic issues
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=205433
Printed Date: 22 Feb 2025 at 2:49pm
Software Version: Web Wiz Forums 11.10 - http://www.webwizforums.com
Topic: Allis Chalmers 7080 Hydraulic issues
Posted By: cumsmk6
Subject: Allis Chalmers 7080 Hydraulic issues
Date Posted: 13 Feb 2025 at 4:52pm
The 7080 I have is having surging issue that you can feel in the remote lever. It has the correct low stand by pressure and the correct remote output pressure sometimes. Sometimes when you pull remote lever in cab, it works fine.
Other times you can pull remote lever and you can hear it surging/pulsating and almost feel basically in the lever.
Usually after the surging happens, you can pull remote lever and nothing happens then.
I’ve torn apart piston pump and it all looks well inside. I removed the priority valve in the rear by the remote valves in hopes to find something in there but nothing looks out of place.
Where can I look next for what’s causing my issues?
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Replies:
Posted By: DrAllis
Date Posted: 13 Feb 2025 at 5:16pm
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Power steering always perfect ??? Until you unscrew the top sight glass (with the tractor on the level and been sitting for a time) you don't really KNOW if the hydraulic system is full of oil. Also, the stand-by pressure makes the hydraulic system work much better if it is at 600-650 psi, not 300-350 psi. Lastly, with the engine OFF, do all the remote levers "detent" into the raise position?? and also the "float" position ?? They must or you aren't getting full stroke on the spools.
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Posted By: cumsmk6
Date Posted: 13 Feb 2025 at 5:48pm
Dr allis, yes power steering always works the way it should. To increase stand by pressure, add more shims?
Also I’m gonna put remote assembly back together and look more into checking levers with tractor shut off.
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Posted By: DrAllis
Date Posted: 13 Feb 2025 at 5:50pm
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Add more SMALL shims to the main pumps compensator. And check those remote valve detents.
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Posted By: cumsmk6
Date Posted: 15 Feb 2025 at 3:31pm
Dr. Allis, Ok I’ve got my remote detents working correctly and I added small shims to get 600 psi on stand by pressure. Remotes also have proper pressure now also.
I believe what has been happening all along is the hydraulic reservoir is being pumped into the transmission reservoir because after doing my testing/ adjustments on compensator, the hydraulic reservoir is low and the transmission is overfull.
I just had piston/ gear pump apart and replaced that internal pump seal so I don’t believe that’s where it is transferring.
Are there any quick fixes that you know of that don’t require pulling transmission to fix possible internal leaking seal?
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Posted By: DrAllis
Date Posted: 15 Feb 2025 at 7:14pm
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The last tractor I heard of that transferred rear end (hydraulic) oil into the transmission had the radiator and oil coolers ahead of the radiator worked on and hoses got crossed up. If it wasn't transferring oil like that, (or that quickly) before you had the gear pump apart, something is wrong in that shaft seal area.
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Posted By: cumsmk6
Date Posted: 18 Feb 2025 at 7:09am
Update on my situation for anyone interested. To solve my problem of hydraulic reservoir filling into my transmission reservoir. This is happening due to some internal shaft seals passing through the housings. Currently at this time, I’m not devoting that much time to a tractor I don’t use anymore.
So I drilled and tapped (1/4”NPT) the transmission and rear end drain plugs and connected the two together.
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Posted By: DrAllis
Date Posted: 18 Feb 2025 at 9:00am
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You didn't know you had an oil transfer issue before removing the hydraulic pumps?? I'd still drain the transmission oil and remove the suction screen underneath and watch and see if the oil seal on the pumps drive shaft is leaking ?? That's not a terrible hard fix.
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Posted By: cumsmk6
Date Posted: 18 Feb 2025 at 7:27pm
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No I didn’t know I had a transfer issue prior to tearing into this winter. Last summer when I attempted to use tractor, it was pulsating in the remote lever ( kinda making noise from pump). So instead of properly diagnosing the problem, I assumed it was in piston pump. I was wrong, nothing was wrong in the pump. I’ll have to check that shaft seal.
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