Transmission shifting to soon....

[Hart_Rod]

My TH350 will shift first through third prior to getting up to 15 mph. Even if you get on it with mild throttle, it shifts really quick and then seems like it's lugging the motor (if you manually shift it, everything works great). I've checked and double checked the vacuum and I have no fluid coming out of the modulator. It has been working fine and just recently started doing this. Could the modulator be stuck or bad? It's a Sid Neal built transmission with less than 2K miles. Thoughts? TIA.

[red69ss]

some modulator valves are adjustable so you can adjust shifts if memory serves me correctly, I think it adjusts with an allen wrench. but if it just started doing it the valve may be bad. hopefully someone with more knowledge will chime in .

[beebster]

I replace my bad t350 with another (junkyard) turbo 350 and it wouldn't shift at all.
I replaced the vacuum modulator (new at napa for $10 bucks) and then it shifted way too soon just like yours.
so i took off the original vacuum modulator from the bad t350 and it shifted fine.
If not i would have tried another vacuum modulator or gone to the junkyard and pulled a couple to try the different shift points.
seems like the different vacuum modulators all give different shift points

[cparman]

pull the vacuum hose off of the modulator. See if it is adjustable. Remove the governor cover from the drivers side of the trans. I cannot remember ( old fart ) it the cover has a bell wire ( hoop ) or if it has four 1/4 bolts to hold it on. Anyway, after removing the cover, remove the governor. There will be an assembly that is about 3-4 inches long. At the end nearest the cover will be two ' wings' and at the other end will be a nylon gear. The gear can become ' apple cored " thin in the middle. If the gear is that way replace it. it is held on with a roll pin. Should be able to get one from a trans shop, don't know if NAPA carries them. After replacing the gear wash the governor assy, very well with brake clean and work the wings back and forth as you do it.

As for the modulator, IF I REMEMBER, if there is a straight slot screw inside of the vacuum nipple turning it in will make the shifts later.

Do you have the kickdown cable connected to the throttle linkage? needs to be. IIR this will also delay shifts with 1/2 + throttle.

WELL GET TO WORK!!!!!

[Longhorn Man]

check to see if the kickdown cable came disconnected from the carb. If it has not, then try adjusting it. Make sure it hasn't snapped.
Odds are the modulator is fine. If anything would have changed, it would have gone from shifting fine to not shifting at all.
After inspecting the cable I'd pull the govener and see if it is working properly.

[gonzo6869]

Kick down Cables x2. I adjusted my cables a few weeks ago because it shifted to early and hardly kick down when I stood on it. Know it does not shift till about 2000 RPM and it kicks down with less than half throttle, it will also hold a gear longer if I am going up hill.

[Hart_Rod]

Originally Posted by gonzo6869

Kick down Cables x2. I adjusted my cables a few weeks ago because it shifted to early and hardly kick down when I stood on it. Know it does not shift till about 2000 RPM and it kicks down with less than half throttle, it will also hold a gear longer if I am going up hill.

The kickdown is not hooked up. It hasn't been the entire time that I've had the truck and it just started doing this....

[clinebarger]

Pull the governor cover and inspect the governor for broken springs.

[JPCY72]

wow I guess im not the only one with this problem i dont have the kick down hooked up either.... mines shifting really early...

[davebloomer]

mine shifts early too with kickdown hooked up. I don't care though as I'm looking for a 700r4

[Longhorn Man]

with no kickdown, it will shift early.

[BarryB]

I'll also say check the governor, easy as pie to replace. I had one go bad on me but that was along time ago, can't remember the symptoms though. Oh it was also on a trans that was recently rebuild, sometimes the governors don't get replaced during a rebuild.

[Hart_Rod]

OK, I figured out the problem and yes, it turned out to be me.... I kinda over thought myself on this one. I was worried about pressurizing the modulator when the motor is boosting. So me being the engineering, pocket protector wearing geek that I can sometimes be (no snide comments required here, ), I installed a one way check valve in the vacuum line. Eureka!!! Problem solved on the boost part. Anyone want guess what new problem this created????

EDIT: I spoke to a very knowledgable tranny guy and he said the kickdown has NO effect on the normal operation of the transmission. He said the only purpose was to drop the transmission down into 2nd. I will however get this connected as soon as I gain a little room underneath the carb enclosure. More to come on that later, .

[Longhorn Man]

the kickdown does in fact hold the tranny in first and second when you are at wide open throttle, and even at medium throttle to a much lesser extent.
Drive a vehicle around the block with a properly adjusted one, then disconnect it and go for a drive. It will be obviouse.

[Hart_Rod]

Originally Posted by Longhorn Man

the kickdown does in fact hold the tranny in first and second when you are at wide open throttle, and even at medium throttle to a much lesser extent.
Drive a vehicle around the block with a properly adjusted one, then disconnect it and go for a drive. It will be obviouse.

350 or 400? I'm know transmission expert, I'm just telling you what the man who does it for a living said, .

[gonzo6869]

I have a TH350 and I can Tell you, when I adjusted, it held the grear longer then it did when it was out of adjustment. I can really notice it in second gear. Oh yeah, it will hold third till the engine blows

[Hart_Rod]

Originally Posted by gonzo6869

I have a TH350 and I can Tell you, when I adjusted, it held the grear longer then it did when it was out of adjustment. I can really notice it in second gear. Oh yeah, it will hold third till the engine blows

What did you adjust? The kickdown or the modulator?

[Longhorn Man]

the 400 doesn't have a kickdown cable on it.
I've had a tranny rebuild guy tell me the same thing. Had another one tell me that the modulator wouldn't keep a trans from shifting. (while it won't technicly keep it from shifting, if disconnected it'll make it 'hold' the gear till 4500 - 5500 RPM)
We no longer use that guy for obviouse reasons... he was a parts swapper and didn't know how the trans actually worked.
The guy you are talking to may be like him too, or he may be too familiar with late model stuff and has forgotten old school 3 speed GM trannys. They have been out dated for a long time, so it is a possibility.
With the kickdown disconnected, you'll only get 4000 or so RPMs out of first, and then second will only hold on for a moment before going into third. Some call this 'stacked shifting' The kickdown will hold each of the lower 2 gears untill the govonor tells it to shift.

[Hart_Rod]

Originally Posted by Longhorn Man

the 400 doesn't have a kickdown cable on it.
I've had a tranny rebuild guy tell me the same thing. Had another one tell me that the modulator wouldn't keep a trans from shifting. (while it won't technicly keep it from shifting, if disconnected it'll make it 'hold' the gear till 4500 - 5500 RPM)
We no longer use that guy for obviouse reasons... he was a parts swapper and didn't know how the trans actually worked.
The guy you are talking to may be like him too, or he may be too familiar with late model stuff and has forgotten old school 3 speed GM trannys. They have been out dated for a long time, so it is a possibility.
With the kickdown disconnected, you'll only get 4000 or so RPMs out of first, and then second will only hold on for a moment before going into third. Some call this 'stacked shifting' The kickdown will hold each of the lower 2 gears untill the govonor tells it to shift.

Sounds good to me. As soon as I can figure out a way to hook it up, I'll git R done, .