3 burns, 3 adjustments, my turbo 350 still shifts the same

[mikey531]

My turbo 350 shifts into second before I even get out of my driveway. I read that turning in the screw behind the vacuum modulator will increase the shift point between first and second. I turned it in 1/2 turn each time and it is in 1 1/2 from where it started. Did I turn it the correct way or should I have turned it out? After my arm heals or the exhaust cools I will try any suggestions. It is behind a almost stock 350, it is getting plenty of vacuum, the line is steel with rubber connections, am I forgetting anything other info?

THANKS !!!

Mike

[Longhorn Man]

turn it all the way in and see what it does.
You can also hook to ported vac instead of manifold.
You don't have a working kickdown cable, do you?

[mikey531]

It seemed to stop at 1 1/2 turns I didn't want to force it. Yes the kickdown works fine, The truck has 4.10's and I want it to stay in first at part throttle, I would think until 20 mph? It shifts fine at wot. I have an edelbrock carb I assume one of the vacuum ports on the front would be ported?

[texanidiot25]

I can hit into third with a light light foot at 25... Do about 20-25 at about 900 RPM, just perfect for testing car alarms.

But with normal driving it hits 2nd at 15 or so. This is with either 3.9x or 4.1x gears on a 31" tire

[dwcsr]

Vacuum to the modulator should not be ported it should be mainifold.
Have you tested the modulator to see if its good? New can also be bad. Check your GM manual on testing it.
Remove it and see if any fluid comes out of the vacuum line port.
Check the governor to see if you have any busted springs or weights.
Did this truck have 373 gears before the 410's? if so get a Gov kit and change the weights.
You should only have to make 1 turn IN to change the shift by 1500 rpm or more.

[clinebarger]

The modulator valve and kick down are not the only things that affect shifting.
The governor plays a major role in what rpm the trans will shift. In fact you have to order governors by gear ratio. or buy a spring kit from B&M,Transgo, etc. Lets say the tranny you have is out of a car with 2.41:1 and your using 4.10:1 gears. The output rpm of the trans whould be way higher than with the 2.41:1 causing early shifts. Your governor springs need to tighter to delay the shift.

[Dustydog]

I have been fighting a similar problem with my truck. It was leaking from the modulator, especially after hard accelerations. It was leaking a LOT! and spraying onto the right side exhaust pipe.

So I got a new modulator today. It did not come with an "o" ring but I put a new one in anyway.
With the new modulator installed, it still leaks a lot and smokes a lot on acceleration.

#1 Does the modulator require an "O" ring?
The modulator does not seem to fit in very "tightly".

#2 I do not have a working kickdown cable.

#3 The vacumn is from the modulator is routed to the manifold.

Truck is a 1970 GMC with 396 and turbo 400

Any suggestions would be greatly appreciated!!

[texanidiot25]

If it had an O-ring to start, I'd wager it needs one now.

TH400s don't use a kick down cable. They have a wired switch

#3 is setup proper

[texanidiot25]

If it had an O-ring to start, I'd wager it needs one now.

TH400s don't use a kick down cable. They have a wired switch

#3 is setup proper

[dwcsr]

The modulator requires an O ring

TH400 does not have a kickdown cable. Its done with a switch on the pedal linkage and a solenoid in the pan.

Look and see if the lines are leaking. The modulator should not leak under acceleration.

[Dustydog]

Thanks Tex,
Do you know where I could find a diagram for the kick down wiring? I actually ordered a shop manual last night for the truck but it wont be in until later next week.

Based on your info I seem to be on the right track. Maybe it will just take a little more work, tomorrow is another day!

[Green Machine]

Modulator only can change chnage shift points a litte, the governor is where the tuning happens.

[mikey531]

dwcsr, clinebarger, Green Machine The governor seems to be where my problem is. I don't know what the transmission came out of so it could think it still has 2.73's or something! I tried to get the cover off the governor but it seemed to be stuck. I didn't pry too hard as I have a tendency to break stuff. I guess it just is a press fit? I will order a kit and try that.

Now about those burns....

[mclairmo]

Originally Posted by Dustydog

Thanks Tex,
Do you know where I could find a diagram for the kick down wiring? I actually ordered a shop manual last night for the truck but it wont be in until later next week.

Based on your info I seem to be on the right track. Maybe it will just take a little more work, tomorrow is another day!

I just replaced the modulator on my TH400 and it came with a new o-ring and hose in the box, I think it was a FRAM. It should not leak at all. Also, you can use a nitrous full throttle micro switch to wire in the kickdown. It's easy, just mount the micro switch on the carb so that it is activated upon full throttle. Wire it up to the kickdown switch on the trans. Should work fine and cost about $15-$20. B&M also sells a more expensive switch that looks worse. Lokar sells a really expensive switch that mounts directly to the trans pan and is cable actuated. OEM switch is not available new.

[mikey531]

dwcsr, clinebarger, Green Machine, Is this what I need to do ?

http://www.dragracingonline.com/tech...vi_9-bm-1.html

[Green Machine]

Yes, that looks like a complete kit, might be good to get a spare governor from a tranny place or a junk yard to play with. I use a long screwdriver and a hammer to remove the cover.

When we did our C20, I did not buy a kit. We installed a shift kit too. The shift kit came with 2 springs which were too heavy. I had a spare governor here. Both governors had the same weights, but each had a heavy and a light spring in it. I was able to use the two 2 lightest springs and got really close on the shift points and did not have to take the govenor apart to change weights, got lucky I guess.

It now shifts at about 5600 into 2nd and about 5400 into 3rd which hits the cam in our 383 just about right. It also took care of the stacked shifts where it hit 3rd right after 2nd. Light throttle shifts are good now, it stays in 2nd a while before shifting to 3rd.

Do not hook the vac line to ported vacuum, it needs full manifold vacuum to sense engine load, I would also put the modulater back to about where it was before tuning the governor. Cranking the modulator screw just raises line pressure for everything, and may firm up the shifts a little, but higher line pressure at idle and cruise is not really needed.

[racin69z]

If you need it to shift higher, drill an 1/8" hole in each weight, or pull 1 of the springs out to start. If that don't work drill a 1/4 hole. But, you will also change the full throttle shift point as well. It may take a few tries, but its free.

I wouldn't have figured that the governers would be matched with gear ratio, because the engine wants to shift at a certain RPM reguardless of how fast your going.

Lynn

[dwcsr]

Originally Posted by racin69z

I wouldn't have figured that the governers would be matched with gear ratio, because the engine wants to shift at a certain RPM reguardless of how fast your going.

Lynn

Thats some what correct, but with lower or higher gears and shorter or taller tires the final ratio changes there for the speed at which it shifts also changes higher or lower

[texanidiot25]

Originally Posted by Green Machine

It now shifts at about 5600 into 2nd and about 5400 into 3rd which hits the cam in our 383 just about right. It also took care of the stacked shifts where it hit 3rd right after 2nd. Light throttle shifts are good now, it stays in 2nd a while before shifting to 3rd.

Jeez! What were the stock shift points by chance? 4500 is my WOT shift points, which of course suits the engine well for me..

[Green Machine]

Stock shift points were around 4500, thats true. But with the new 383, and we dont have a huge cam, 218-224, the shift points were too low. With the stock weights in drive, it would light the tires all the way through low gear, get to about 4500, shift while still spinning the tires, bog, downshift back into low, get traction and then shift again into second, not real good shifting action there.

Now shifting at about 5600, it hits the power band where it should be. The tires quit spinning at the top of low gear and it grabs second and just keeps on pulling like a train, smaller cam equals torque, its a blast to drive now.

[texanidiot25]

Originally Posted by Green Machine

With the stock weights in drive, it would light the tires all the way through low gear, get to about 4500, shift while still spinning the tires, bog, downshift back into low, get traction and then shift again into second, not real good shifting action there.

And I call that the peg leg peel! Except it keeps on going threw 2nd gear

[Green Machine]

Originally Posted by texanidiot25

And I call that the peg leg peel! Except it keeps on going threw 2nd gear

Yeah, but we have posi !!! I can ruin 2 tires at once !

[texanidiot25]

Originally Posted by Green Machine

Yeah, but we have posi !!! I can ruin 2 tires at once !

I have a semi-posi-trac. I guess it's seen better days, but it never locks when I want, but will not hesitate to toss the rear out when I don't want it.