Dead Reckon

So I've had this issue for a while, I'm not sure what causes it, I know the leak that I have back around the speedometer cable doesn't help. But sometimes, regardless if the transmission is hot or cold, it hesitates coming out of park. Though it usually does it more in the cold, I'm thinking it's the filter blocking fluid flow, but I am not sure. Some sources I've read say it's the modulator, some say it's the filter.

So basically, I'll get in the car, fire it up, throw it in any gear except neutral and it won't go for up too 15 seconds. It comes out of park and goes into neutral until it catches. Sometimes if I rev the the engine a couple times in park (up to maybe 2,500RPM) then put it back into gear it goes. I've of course never done this in gear as I don't want to kill my transmission.

Here's what I've done to try to fix the issue:

Soft vacuum lines replaced at the transmission and carburetor, I have it on manifold vacuum as it should be. The hard line that runs past the exhaust seems to be in tact, though I'm tempted to pull it off again and check it.

Fluid is full, haven't changed the filter, but I may if that's what it comes down too.

Linkage all seems tight enough to function, I do need to replace a plastic grommet up on the shift linkage where it makes a 90 degree turn downwards. But I do not think that is causing the problem.

I do have a few leaks so I keep having to add fluid, I need to fix those soon, but it does it not matter if it's full or a pint low, it still behaves the same.

Also, I should note it's done the same thing through four carburetors, two quadrajets, a Summit 600 4 barrel, and a Holley 750 4160, so I'm not entirely convinced it's a vacuum issue unless the modulator its self can cause this. Once it's in gear it shifts fine 1st at about 20, 2nd at about 30, and 3rd whenever I stop flogging it.

joe_padavano

The modulator has absolutely nothing to do with this. It is a sort of throttle position sensor (engine vacuum is roughly related to throttle position) and has no effect when shifting from Park to Drive.

The two most likely causes are low fluid and clogged filter. Did you check fluid level under the correct conditions (hot fluid with the engine running and trans in Park)? If so, then change the filter.

ThePackRat

Do this SOONER rather than later.

Years ago my father cooked not one but TWO TH350's on a couple of OldsmoBuicks that had run low on fluid.

Cooked the first one & still didn't take my advice to never ever again keep trying to force a car to move if it was thought to be low on fluid ......

And proceeded to cook a second one in the other OldsmoBuick that had taken over daily driver duties of the other one with the cooked trans.

Dead Reckon

Thought that's what it would be, I'll have to get a new filter when I get paid Thursday, shouldn't take much fluid since most of it is in the converter. I knew the modulator controlled shift points, but I wasn't sure if it did anything else, kind of hard to find clear answers sometimes.

Edit:

O'reily's carrys a WIX or AC Delco, prices being $7.99 or $25.99 respectively, they also carry a cheaper "PowerTorque" brand for $5.99 but I ain't interested in that. I don't like AC Delco's oil filters, they're garbage, I run WIX filters so I guess when I get paid I'll get one. Comes with the gasket either way, so it's a good deal. Time to bathe in transmission fluid, fun times.