tranny help
 

Me and my father-in-law placed a built 350 and a rebuilt turbo 350 in his 72. I'll have to post pics it is an awesome truck. The tranny shop is reliable, and I had a master overhaul kit with a shift kit installed. We thought the old tranny was bad b/c we couldn't get it to shift. When we put this one in it won't shift either. However, both will shift through all gears if I shift manually from 1st-2nd-3rd. All three gears work great and it shifts fast and hard like it is supposed to. He replaced mod valve, replaced rubber vacuum hose with copper, and nothing works. How much vacuum does this require? It is not a real strong vacuum due to being plugged in to a small nipple on the carb. The next step is putting the line on a bigger nipple to get more vacuum. Any ideas? I am racking my brain here. I don't know a whole lot about auto trannys.

Mine is plugged into a fitting in the manifold between the carb and dizzy. Probably not getting enough vacuum from the carb (ported vacuum fitting maybe?).

It will either be the wrong vac fitting, or a bum vac modulator. Did you by chance take the modulator off the old tranny and install it on the new one?

no bought a new mod valve for 10.99 at autozone

anybody else know anything I could try?

You can try putting a vacuum gage on your line and see how much vacuum your getting. Did you switch the fitting it was connected to?

It was same one the old tranny was connected to, however the old tranny didn't shift right either. I am sure the fitting has a little less vacuum due to the bigger cam, and am going to try the intake fitting next.

Ok now I have great vacuum going to new mod valve, and still does not shift on its own. Any other ideas? What else would make it not shift? It shifts great manualy just not on its own

anybody?

Just a shot, was the tranny built with a manual valve body -- one that requires shifting into each gear. I know they do this in race cars. Could also be somethig with the rebuild. Have you talked to the tranny shop yet?

Rob

1972. Does the TH350 have a kickdown-cable from the tranny to the carb? While this may not root of your problems, it something that should be in adjustment.
You wrote that you installed a new vacuum modulator. Is is the "adjustable" type? Pull the line of the Vac.Mod and see if there is a slotted set screw that could be adjusted. If so, get a small tip (slot) screwdriver and adjust accordingly. I don't recall if turning inward lengthens or shortens the shift point. Best of luck.

stiffler has a good point, many (even stock replacements) are adjustable. Turing it in will raise the shift point, unscrewing it will lower it.
The only way the kickdown cable would do this is if it is pulled out and stuck in that position.

Vac. should be hooked directly to the intake manifold and do check adj. screw.

Take the kickdown cable loose at the carburetor and see if the inner cable slides back into the outer housing. If it does then try driving it and see if it will shift.

Have done all of that, replaced and adjusted mod valve, and installed new kickdown cable but still does not shift. Tranny is out and going to trans shop tomorrow

I'm wondering if it had a manual valve body all along, even before the trans work and it still does. Maybe that's the problem as Hart Rob said.

started as a stock 350 tranny that was slipping and had it built no manual valve body, but the trans shop did say he thought it was in the valvebody...will know for sure soon and will update