hjelmsd
Member
My 727 has had a slipping reverse gear for some time. I finally started diagnostics. I get only 180-190 psi when checking the reverse servo line pressure. Service manual indicated 240-270 psi. So I have low pressure, which I assume is consistent with my reverse problem. I also checked the low/reverse port pressure while in Low 1 gear. Measured 55 psi, just about right per the manual. I did these checks while transmission was relatively cold, wheel spinning around 1600 - 2000 rpm.
Based on my research and manual, I am thinking there are 2 possible causes to diagnose: low pump pressure (failing pump) or valve body issue. I found another valve body that I will swap in and test to rule out valve body. If I still have low reverse line pressure with the other VB, I will concluded the issue is the pump.
I haven't bothered to check line pressure on the other ports yet, but can if it's likely to be helpful. 2-3 shift and operation in 3rd gear (1:1) has been fine I think. All forward operation has been fine, but I just cruise around.
Any other likely root causes to further diagnose?
Data: Engine is 383, 2400 stall converter, transmission is 1968 727, valve body is factory style for this year. The issue first appeared after my rooster comb assembly loosened and I jammed the rooster comb against the valve body casting - jammed into park. I fixed the comb assembly, but think maybe the comb arm had the manual valve loaded/jammed up and maybe damaged the VB (it wasn't obvious)
I made sure I am in the reverse detent location, ruled out shifter linkage variation.
Thanks for your help,
Scott
Based on my research and manual, I am thinking there are 2 possible causes to diagnose: low pump pressure (failing pump) or valve body issue. I found another valve body that I will swap in and test to rule out valve body. If I still have low reverse line pressure with the other VB, I will concluded the issue is the pump.
I haven't bothered to check line pressure on the other ports yet, but can if it's likely to be helpful. 2-3 shift and operation in 3rd gear (1:1) has been fine I think. All forward operation has been fine, but I just cruise around.
Any other likely root causes to further diagnose?
Data: Engine is 383, 2400 stall converter, transmission is 1968 727, valve body is factory style for this year. The issue first appeared after my rooster comb assembly loosened and I jammed the rooster comb against the valve body casting - jammed into park. I fixed the comb assembly, but think maybe the comb arm had the manual valve loaded/jammed up and maybe damaged the VB (it wasn't obvious)
I made sure I am in the reverse detent location, ruled out shifter linkage variation.
Thanks for your help,
Scott
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