Thread: Passing gear problems

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Ok, here is my problem. I purchased a car ( 1940 Ford convert) with an 85 Corvette TPI in it. Upon looking at the brake system. I found the previous owner had hooked the trans vacuum into the brake booster line. This caused the brake pedal to be hard as a rock. So, I found another vacuum line to hook the trans to. This line ran to a plastic canister under the dash. I just ran a tee off it. Well brakes are good but, now I have no passing gear. Could moving the vacuum line be the problem? I checked the kick down adjustment and it's fine. This TPI system is new to me. Couldn't find a schematic on what vacuum lines on it go to. Appreciate the help. Thanks!

It sounds like the trans needs a vacuum source which is equivalent to what it had previously.
The strength of vacuum will vary depending on where it is sourced.

Thanks, I will look at the vacuum on the lines. But I really haven't a clue where to go for more vacuum on this engine. My first with a TPI and computer. Tried looking on line for a source for more vacuum but couldn't fine a schematic on the lines. Found videos on some on original motors but, this is anything but original. Was built by Street & Performance even they couldn't help. Thanks for the fast info.

Thanks for the info. My only thing is this motor does not have a big cam in it. I know when it was in the original car it had to be hooked up to the auto trans and the booster through two separate lines. I'm trying to find where the other line would be. I really don't want to have to buy a pump. Any way thanks for the help. I figured maybe I'll look in the junk yard. Maybe someone will have a 85 Corvette TPI in it. Then I can try and locate the lines. It's a chance I guess? Thanks again the vacuum pump is a good alternative. Just hate the fact about not knowing this motor. Should of kept my carb motor new that one very well. Thanks again!

try tapping into the PVC line .. more vacuum there than needed .. and check to see if you have an adjustable modulator .. if so you can play with that .. on another note isn`t the passing gear on GM cars controlled by a cable ?

Thanks for the info. I checked the kick down cable and it's adjusted perfectly. The only other thing I did was swap the vacuum lines around. He had the booster and trans running on one line making the brakes not so good. So I found another line and ran the trans to that and the booster separately. Now brakes good down shift not so good. LOL Seems like every thing on this car turns into a project. Thanks

Sounds to me like the modulator is leaking.
And reviewing the schematics Denny posted, I don't see a tranny connection and I was already wondering if that trans used a "kickdown" or a throttle valve in the trans.?.?.?

Originally Posted by 34_40

Sounds to me like the modulator is leaking.
And reviewing the schematics Denny posted, I don't see a tranny connection and I was already wondering if that trans used a "kickdown" or a throttle valve in the trans.?.?.?

I agree. It really shouldn't matter how many things you hook to a vacuum source as long as none are leaking. What you've described points to a bad vacuum modulator. Just my $0.02.