8070 powershift jerky
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=130532
Printed Date: 23 May 2025 at 7:26pm
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Topic: 8070 powershift jerky
Posted By: Transaxial
Subject: 8070 powershift jerky
Date Posted: 27 Oct 2016 at 7:10pm
I have a 1983 8070 with the 6 speed PS and it is very jerky when letting the clutch out and fairly abrupt shifting when changing speeds while under way. It seems to work ok other than that. It has 6200 hrs and has had regular oil and filter changes. I have had the local dealer work on it 4 times now and the pressure checks and little adjustments they did have not helped any amount. I just borrowed their service manual and am just getting into some pressure checks. The modulating valve pressure seems to be very erratic and does not drop smoothly when stepping on the clutch. The mv spool seems free. The system pressure is 235 psi and 245 with clutch pedal pushed. I would like some help as to where I might look for things that might make this transmission shift better.
Thanks,Barry.
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Replies:
Posted By: DrAllis
Date Posted: 28 Oct 2016 at 1:39pm
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There is a port on the side of the power shift valve for monitoring inching pressure. Usually 80 to 100 psi will make the tractor move. You should be able to easily control clutch inching pressure from zero up to the maximum pressure number. Third gear should require the inching pedal to come up higher to get the tractor to move and that is normal.
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Posted By: Transaxial
Date Posted: 31 Oct 2016 at 2:53pm
So should I grind down the spring in the inching valve to get down to 90 psi? or is there a part no. for the right spring? Outer inching valve spring is listed as 70268277 or inner inching valve spring 70275929. There are no shims under this spring. I was getting 50 psi at idle and room temp and 100 psi at 2000 rpm. Is that too high, enough to make it so jerky?
Thanks Dr Allis
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Posted By: DrAllis
Date Posted: 31 Oct 2016 at 10:01pm
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Inching pressure should be that 200+ number when the inching pedal is clear up. You should be able to control inching pressure from near zero up to the 200 plus figure. If your pressure is as low as you say, it would make things delayed and jerky. Are you sure your clutch pedal comes all the way up to the top?? When clutch inching pedal is clear up the inching spool should be almost clear pushed in. Like a .030" feeler gauge from clear in. Maybe you have a bad cable from the pedal to the inching valve ??
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