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Discussion Starter #1
I would appreciate any links/etc. to information on adjusting TH350 modulator/governor or whatever it's called.
Thanks!
Ed
 

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sabino56 said:
I would appreciate any links/etc. to information on adjusting TH350 modulator/governor or whatever it's called.
Thanks!
Ed

they are two separate items. Which are you working on?

:cool:
 

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Discussion Starter #3
As you can tell, I am new to automatic transmissions. I have rebuilt engines but never messed with automatic transmissions. I bought a used TH350 for our 65 Belair w/ sbc 350. I've had trouble getting it setup w.r.t. shifting where I want it. I adjusted the screw in the vacuum port to get shift points at WOT close but not exactly where I want them. At normal low driving, I'd like to move the shift points up a bit also. I can't get it to downshift like I'd want (I'm pretty sure I have cable adjusted correctly). It will occasionally downshift when crusing around 20mph (it's in third gear then - which is why I'd like to adjust shift at low throttle acceleration) but I can't get it to downshift from around 40mph like you'd like it when accelerating up a freeway onramp. The speedo gearing was way off when I got the transmission - almost 2x too high. I got that close by changing gears on both output shaft and speedo cable input. The bell housing has bolt pattern for both Chevy and what I'm told is "other GM".
All this makes me wonder if the transmission was orginally in something like a truck or something.
A previous post suggested it was the governor and I should check the springs. I wanted to look into that possibility and whether it might be setup wrong for my application.
Thanks for any advice!
Ed
 

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sabino56 said:
As you can tell, I am new to automatic transmissions. I have rebuilt engines but never messed with automatic transmissions. I bought a used TH350 for our 65 Belair w/ sbc 350. I've had trouble getting it setup w.r.t. shifting where I want it. I adjusted the screw in the vacuum port to get shift points at WOT close but not exactly where I want them. At normal low driving, I'd like to move the shift points up a bit also. I can't get it to downshift like I'd want (I'm pretty sure I have cable adjusted correctly). It will occasionally downshift when crusing around 20mph (it's in third gear then - which is why I'd like to adjust shift at low throttle acceleration) but I can't get it to downshift from around 40mph like you'd like it when accelerating up a freeway onramp. The speedo gearing was way off when I got the transmission - almost 2x too high. I got that close by changing gears on both output shaft and speedo cable input. The bell housing has bolt pattern for both Chevy and what I'm told is "other GM".
All this makes me wonder if the transmission was orginally in something like a truck or something.
A previous post suggested it was the governor and I should check the springs. I wanted to look into that possibility and whether it might be setup wrong for my application.
Thanks for any advice!
Ed
Springs in the governor have little effect on a wide open throttle shift. The inner weights have more to do with WOT shifts.

Modulator has little effect on WOT shift points. The vacuum mod has the most effect on light throttle shifts.

Down shifts; if the speed-O was reading that high (2x) .... What is the rear end gear & tire size of the vehicle? Lower gears ( higher numerically) will cause the tranny to not down shift as easily with the throttle at WOT.

You can trim the outer weights to achive a downshift at higher speeds.
 

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Discussion Starter #6
[/QUOTE=jakeshoe]http://www.nastyz28.com/forum/showt...overnor+weights[/QUOTE]
Thanks for link, nice info. Do you know if TH350 came with different springs, weights from factor for different applications?


Crosley said:
Down shifts; if the speed-O was reading that high (2x) .... What is the rear end gear & tire size of the vehicle? Lower gears ( higher numerically) will cause the tranny to not down shift as easily with the throttle at WOT.
Before I put transmission in car I counted wheel revs/drive shaft - I came up with 3.37 . The original engine in car was a 6 cyl with 2sp powerglide automatic. I have wheels very close to stock in diameter on car.

[/QUOTE=Crosley]Modulator has little effect on WOT shift points. The vacuum mod has the most effect on light throttle shifts.[/QUOTE] Thanks - I was underimpression that vacuum shift was for WOT. So I guess that higher vacuum levels on modulator delays shift point? and turning the adjustment screw how much of that vacuum gets to modulator? In this case, if I don't like the shift point between 2nd and 3rd at WOT - the only thing I can check, mess with is the governor?

I also found that shift from 2nd to 3rd was very close until I got a kickdown cable and put it on. Then spead between 2nd and 3rd increased at WOT. I didn't really check it at light throttle - I will check that when I go out later today.
 

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Yes the transmissions were calibrated differently depending on application.

You can modify the governor to overcome most of the differences, sometimes playing with the shift valve springs is necessary to get it exactly how you want it, but usually this isn't necessary.
 

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modulator / detent / governor adjustments

[/QUOTE]
> I bought a used TH350 for our 65 Belair w/ sbc 350. I've had trouble getting it setup w.r.t. shifting where I want it. I adjusted the screw in the vacuum port to get shift points at WOT close but not exactly where I want them. At normal low driving, I'd like to move the shift points up a bit also. I can't get it to downshift like I'd want (I'm pretty sure I have cable adjusted correctly). It will occasionally downshift when crusing around 20mph (it's in third gear then - which is why I'd like to adjust shift at low throttle acceleration) but I can't get it to downshift from around 40mph like you'd like it when accelerating up a freeway onramp.
> A previous post suggested it was the governor and I should check the springs. I wanted to look into that possibility and whether it might be setup wrong for my application.
Thanks for any advice!
Ed[/QUOTE]

Ed.. you are going about this all the wrong way. If you want your trans to work correctly, then you need to pay attention carefully to this post. I will teach you how i train transmission professionals, especially hi performance rebuilders to adjust the mod.

1. MODULATOR ADJUSTMENT.. is not about setting the shift timing (especially max throttle) where you want it. Modulator is for LINE PRESSURE BOOST, and here's how it works.

The modulator is a spring loaded vacuum canister. At hi vacuum, the force of vacuum opposes / cancels out spring force. As vacuum drops, the spring exerts an increasingly greater force against the modulator valve, until at zero vacuum maximum boost is achieved. Now, boost is needed when torque is increased, so that clutches and bands won't slip. but we don't need boost sitting in park or neutral idling in the parking lot. This just causes premature pump gear and sealing ring wear). Therefore, line pressure should not be boosted at idle. If you use your car as the daily driver, the most intelligent setting is that which provides maximum boost during acceleration without unnecessarily hi line when it is not needed. That is.. NO BOOST AT IDLE, BUT AS SOON AS YOU BEGIN TO ACCELERATE (that is, you drop 1" of vaccuum off idle) you want RAPID / RESPONSIVE BOOST.
Here's what you need to know..
WHAT IS THE VACCUUM READING AT IDLE IN DRIVE? ________
[[ the following work is most easily done on a lift with all 4 wheels off the ground and the emergency brake firmly locked!]] We want the engine HOT for this test, and take the reading at the TRANS end of the vaccuum line. Unplug the modulator hose. Attach a vaccuum guage to the hose. Start the engine, TURN ON THE AIR CONDITIONER, put the shifter in DRIVE, and take the vaccuum reading on the guage. WRITE IT DOWN ON PAPER!

next, Get yourself a pocket screwdriver and a new modulator "elbow" (keep the elbow in your pocket). INSTALL PRESSURE GUAGE ON MAIN LINE PORT. PLUG the engine side of the vaccuum line (so you won't have a vac leak). Get your vaccuum pump and attach it to the modulator. Get your little screwdriver and punch it thru the rubber hose (yes thats right!) about 1/2" behind the modulator stem. This way you can adjust your modulator inside the hose with it attached and the engine running!
Now.. what was the vaccuum reading you wrote down? Lets say your engine pulls 16" in D, HOT, with AC on. we want to drop ONE inch of vaccuum, then start boost. So, start the engine (neutral is ok for this part), raise idle to 800-1000rpm, and pump up 15" on your vaccuum pump. (you may need someone to help maintain a steady 15" on the pump with the screwdriver punched thru the hose due to very minor leakage). Typically a 350 will run about 60-65 psi at idle, but there are variations in PR spring. If it is much higher, back the modulator adjustment out until there is no more "drop" on the guage. Now, start to screw IN on the modulator adjuster until you see
the pressure guage start to lift and STOP right there. To check this, pump up 20", watch guage and start to bleed vaccuum off very slowly and the guage should start to increase exactly at 15".

If you took your initial readings correctly, you now have a perfectly adjusted modulator. For a slightly steeper boost rate with higher max line, use a 2" modulator instead of the 1 9/16" can size and adjust it exactly as described here. Once you have set it this way YOU ARE FINISHED WITH MODULATOR! DO NOT CHANGE THE ADJUSTMENT!!

DETENT CABLE ADJUSTMENT... is real simple.
Floorboard the gas peddle and the detent cable should just pull tight as throttle reaches wide open. THATS IT! if it doesn't pull tight, readjust, bend bracket, or whatever is necessary to achieve this. if it doesn't pull tight
you will not have full detent at wide open throttle. If it pulls tight BEFORE full throttle, you'll break the cable end.

NOW THAT DETENT AND MODULATOR ARE SET CORRECTLY, >>NOW<< and only now, are we ready to think about shift scheduling. ROADTEST THE CAR. I want to know minimum and maximum throttle shift speeds for 1-2 & 2-3, the RPM for the max throttle shifts, and the highest speed you can get a 3-1 and a 3-2 kickdown. Also, what is the axle ratio.

from this point we work with governor weights, springs, and shift valve springs.

Dean Mason
TransLab engineering
 

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Discussion Starter #9
Thanks, I really appreciate your response and willingness to share your knowledge. I will go through this and post results. It may be this weekend as I have to go back to work this week....
I counted revs on axle with transmission out - I got a 3.37 - the car was a stock 65 Belair w/ 6 cyl and has been in the family since purchased so I know it wasn't modified. I haven't found the stock info for the car yet. I'm using wheels which are almost same as stock. 77.75in unloaded circumference which is about 3% smaller than what was on car.
Thanks again
Ed
 
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