Thread: Turbo 350 Shifts

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I started driving my truck with the new motor today, and it runs strong. But, after a while the transmission started acting up some. The more gas I give it, the sooner it shifts. I have messed with the detent but that had no effect. If I am just cruising, everything works perfectly.

Ok, thats wierd. Sounds like a governor problem.To tell the truth, im not sure how to diagnose for that. You may want to call up your tranny shop.

do you have a passing gear?

I'm not sure. I think it did downshift once. There is probably something wrong with the detent, but I am not sure. I have it set right now to do the downshift way early but it doesn't.

Originally posted by 76GMC1500
I'm not sure. I think it did downshift once. There is probably something wrong with the detent, but I am not sure. I have it set right now to do the downshift way early but it doesn't.

at "light throttle" the detent dont have any thing to do with the shifting, from around 1/2 to full WOT then it will effect the shift. sounds like to me your detent ant working. at lower speeds the modul. and gov. would reg. the shift.

I'll have to do some research on the module. I forgot to hook up the vacuum line to the module once so the module saw 0 vacuum, interpereted it as WOT and wouldn't shift out of 1st. It's almost like the vacuum signal to the module is high. Maybe there is a kink in the line and as I go to WOT vacuum at the module isn't dropping as quickly as vacuum at the manifold ? I'll look into that one tommorow.

Oh, I did notice the transmission ins't shifting as hard as normal, too.

Originally posted by 76GMC1500
I'll have to do some research on the module. I forgot to hook up the vacuum line to the module once so the module saw 0 vacuum, interpereted it as WOT and wouldn't shift out of 1st. It's almost like the vacuum signal to the module is high. Maybe there is a kink in the line and as I go to WOT vacuum at the module isn't dropping as quickly as vacuum at the manifold ? I'll look into that one tommorow.

you are saying 2 dif things. at first you said it was to soon, if you had 0 vac. that would make it not shift at all or it would be real late hard shift.

I was trying to say something along the lines that a pinched hose is delaying the drop in manifold vacuum from reaching the modulator, so the modulator is still under vacuum while the manifold is not, causing an early shift.

I may also pop the cover on the governor to check for broken springs on the flyweights. It's just an o-ring seal and there are no gaskets that I have to replace? I don't have time to open it up and then have to make a bunch of runs to the parts store replacing consumeables.

you say: that a pinched hose is delaying the drop in manifold vacuum from reaching the modulator, so the modulator is still under vacuum while the manifold is not, causing an early shift.

i say thats not true, if you pinch off a vac. line that would be the same as unpluging it. if the line was pinched then there would be no shift or late shift. i cant see the gov. making a early shift either. want hurt to check it though. if it works ok at light throttle, and you dont have a pass gear id be fixing the passing gear before i did anything else.

I took it down a freeway onramp today, and the passing gear is there alright. It may have dropped all of the way to first, but the thing really took off. My mom was in the truck and she started yelling.

sound like it might be internal. see if you can adj. the modulator, i've never fixed a trans by doing that, but it wouldn't hurt to try. screw the screw in a little, should make it shift later.

I do have plans to rebuild it, but I have only $14 right now and I need to buy books for school. I don't mind manual shifting on hills for a while.

a man has to do what a man has to do.

I think you will find that you hooked you modulator to a ported vacumn source If you have no vacumn at idle but vacumn as you open the throttle your on ported vacumn You need manifold vacumn to the modulator.If you un plug the modulator you should get a hard late shift.

"My mom was in the truck and she started yelling"