TH350 in a '71 Chevy truck. Less than 20k miles on rebuilt transmission. Worked fine for 15k or so. Started to take a while to go into any gear on cold starts. Then started to slip out of gear on the steep uphill stretch of the driveway (again, on cold starts). Wait a second, or blip the throttle, it drops back into gear and off you go.
Lately, this has progressed to won't move in any gear for several minutes on cold starts, and when it does, it almost always slips out again within 30 seconds of driving. Where blipping the throttle used to work, now it wants sustained 1500-2k rpms for 10 seconds or so before it goes back into gear, and often that doesn't do the trick.
Just tried to go to lunch, went into gear perfectly, but dropped out of gear before I made it out of the parking lot and wouldn't go back in for anything. Tried draining a bit of fluid, tried adding a little more fluid, nada. Currently stranded at work.
Fluid level is good, doesn't smell burnt, doesn't look dirty or frothy. Doesn't get as warm as I remember it used to, but it is cold (30's and 40's) and I've got an external cooler.
Any thoughts appreciated, this is my DD and I can't really be without it.
Sounds like a pump/converter issue.
Talked to a couple of the other car nuts at work, one suggested o-rings in the valve body could be bypassing. I didn't see any such o-rings on the exploded diagrams I've looked at, but maybe the valve body gasket is kaput?
What kind of rig do I need to test line pressure? Simple pressure gauge (0-200psi) and a fitting to match the port in the transmission case?
JohnInKansas wrote:
What kind of rig do I need to test line pressure? Simple pressure gauge (0-200psi) and a fitting to match the port in the transmission case?
In the past I have used regular parts store 0-200psi pressure gauges and fittings to make it work. Just make sure you are testing the right port(s).
I really think the pressure relief spring in the pump is broke.
got the same problem with 81 Corvette, last time I had this issue it was worn o rings that bypassed when cold, expanded hot and then it would go.
As a quick get home and wait till the weekend try, you could add one of those snake oil transmission fixers, they've helped me buy some time before.
When is the last time the filter was changed ?
And of course, there always is Mystery Oil.
Haven't changed or checked the filter since the rebuild (18 months, about 20k miles). That'll be the first thing I check.
o rings/ seals whatever you wish to refer them as, they are on the main shaft between the clutch packs, IIRC. I personally only rebuilt my Ford AOD trans and had the t350 down by a speed shop.
