700R4 no pressure when cold - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Consaka · 03-19-2014, 08:06 PM

I have a 1984 diesel van with the 700r4 transmission. This rig suddenly started not moving when cold. No gear did anything till it was allowed to warm up. I put a gauge on it and it literally has zero pressure when running cold. After 15 minutes or so when it starts warming up the transmission will gradually start showing an increase in pressure. At about 30 lbs you can move it and I believe all gears will work. If allowed to get hot you might see as high as 60psi. needle on the gauge jumps around a lot. I pulled the pan off but could find nothing obviously amiss. I figured maybe the pressure regulating spring had broken but it seems fine.
Thoughts?

**hatzie** · 03-20-2014, 10:14 AM

30 PSI is low. It sounds like something in the Pressure regulation system failed. You're on the right track.
Besides the pressure regulator valve there's a spring loaded relief valve and the TV cable valving. Is the TV cable working?

Consaka · 03-21-2014, 07:15 AM

Quote:

Originally Posted by hatzie

30 PSI is low. It sounds like something in the Pressure regulation system failed. You're on the right track.
Besides the pressure regulator valve there's a spring loaded relief valve and the TV cable valving. Is the TV cable working?

TV cable is working fine. The part that's throwing me is the no pressure cold part. Usually if a transmission gets worn it will have pressure cold but not hot. The gauge needle jumping like it does seems like another clue I'm missing. I suppose there is nothing for it but to pull the transmission and take it apart on the bench. ugh. Not looking forward to that.
Oh and another thing TV cable position does not seem to have any affect on pressure. I mean even in Neutral I should have some pressure right?

beamn7 · 03-23-2014, 07:21 PM

Pump rotor vane seal maybe? Had plenty of autos that slip and won't engage when cold. Warm em up and the lip seals start holding pressure.. Usually only effects one clutch pack, maybe 2. I would look more at the pump considering you have zero pressure. If your gonna pull it apart, might as well overhaul it.

Consaka · 03-25-2014, 12:45 PM

Yep I think that's what I'm going to have to do. Thanks for the advice.

Quote:

Originally Posted by beamn7

Pump rotor vane seal maybe? Had plenty of autos that slip and won't engage when cold. Warm em up and the lip seals start holding pressure.. Usually only effects one clutch pack, maybe 2. I would look more at the pump considering you have zero pressure. If your gonna pull it apart, might as well overhaul it.

03-19-2014, 08:06 PM	#1
Consaka Registered User Join Date: Mar 2014 Location: Vancouver, WA Posts: 5	700R4 no pressure when cold I have a 1984 diesel van with the 700r4 transmission. This rig suddenly started not moving when cold. No gear did anything till it was allowed to warm up. I put a gauge on it and it literally has zero pressure when running cold. After 15 minutes or so when it starts warming up the transmission will gradually start showing an increase in pressure. At about 30 lbs you can move it and I believe all gears will work. If allowed to get hot you might see as high as 60psi. needle on the gauge jumps around a lot. I pulled the pan off but could find nothing obviously amiss. I figured maybe the pressure regulating spring had broken but it seems fine. Thoughts?

03-20-2014, 10:14 AM	#2
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: 700R4 no pressure when cold 30 PSI is low. It sounds like something in the Pressure regulation system failed. You're on the right track. Besides the pressure regulator valve there's a spring loaded relief valve and the TV cable valving. Is the TV cable working? __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

03-23-2014, 07:21 PM	#4
beamn7 Registered User Join Date: Oct 2011 Location: Wildomar, CA Posts: 466	Re: 700R4 no pressure when cold Pump rotor vane seal maybe? Had plenty of autos that slip and won't engage when cold. Warm em up and the lip seals start holding pressure.. Usually only effects one clutch pack, maybe 2. I would look more at the pump considering you have zero pressure. If your gonna pull it apart, might as well overhaul it.



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