Transmission help!! 350 turbo shifts 2-3 too fast - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Brently · 10-06-2003, 10:33 AM

i am not a transmission expert but in my 71 with a 350 turbo, newly rebuilt, first to second is a fine shift but from second to third is too quick if at all - i have changed the modulator valve and adjusted it as well but no dice - help please - is this an adjustment or a take it out problem? oh did i mention i cannot find the guy that rebuilt it for me? any help would be appreciated - thanks, Brent

BLACK AND BLUE 67-72 · 10-06-2003, 11:11 AM

Well it could be a number of things: Incorrect Oil Pressure, due to a defective vacuum modulator, leaking vacuum lines, or a stuck modulator valve (Not the canister with the vacuum line, but the actual valve that is inside the trans, accessed by removing the modulator canister. Governor Malfunction: Remove the governor. Invert governor and move weights up and down, to check for stuck governor valve. If valve is stuck, disassemble and clean governor. Governor Circuit Oil Blockage: Remove the transmission pan and valve body. Check for blocked or leaking feed holes. Check screens for blockage. Faulty Detent-Cable Operation: Check for stuck, disconnected or broken detent cable. Check cable adjustment. Valve-Body Malfunction: Remove pan. Remove valve body and shake. Check for stuck detent valve, 2-3 shift valve or 1-2 shift valve. Valves should drop of their own weight. Disassemble valve body and free up valves as necessary. I hope this gives you an idea of what it could be.

And good luck!!

O'l Buck · 10-06-2003, 01:01 PM

I've never had a th350 apart, but most transmissions have adjustable shift points, my guess is that when it was rebuilt, it got a new valve body, and the shift point is incorrectly adjusted. I've only worked on Allison transmissions, all that is required to set the shift points on them is to drop the pan and turn a shaft with a needle nose pair of pliers which has a pin in it to drop into a detent plate. some transmissions are shim adjusted.

Brently · 10-06-2003, 01:46 PM

good grief what problems i may have - oh well i sure do appreciate your ideas for what the problem could be - i have already replaced the modulator valve once (hopefully it was a good one i put on - it was new but you never know) you can adjust the mod valve and it will shift much later but still very little shift takes place - you have to listen carefully to even hear a shift to third you cannot feel one - oh well thanks, can all this be checked in the truck? i sure hope so - Brent

tom hand · 10-06-2003, 06:32 PM

I would think that if the modulator or the govenor was the problem it would affect the 1-2 shift also

BLACK AND BLUE 67-72 · 10-06-2003, 06:45 PM

Yes all of these things can be checked while the transmission is in the truck. Does it feel like it is slipping in the 2-3 gear shift? Or just softly shifting. Possibily a shift improver kit would fix this, I know that they will help your transmission last longer. I have one in mine and I am missing a friction plate, It has been this way for about 15,000 miles and I am still driving with the same transmission.

Brently · 10-07-2003, 01:10 PM

thanks for the replies to my problem - i will try and fix with a process of elimination - i also have a 350 that was in good shape when i bought the truck with a shift kit in it - i just pulled it out with the motor and replaced because i had this rebuilt 350 turbo just sitting in the garage - should i replace it with the one that was in it or try and fix this one by a process of elimination? thanks, Brent

Longhorn Man · 10-07-2003, 11:08 PM

Do you have the kick down cable hooked up? On a TH350, it will do exactly as you indicate witht eh kickdown cable disconnected.

Brently · 10-08-2003, 06:31 AM

if you are talking about the passing gear cable, i do have it hooked to the carburator but it does not engage - there is too much slack in the cable for the carb to engage it - is this the problem? if so how can i adjust the cable to engage when the motor is at medium to full throttle? help - thanks, brent

Brently · 10-08-2003, 07:13 AM

if you are talking about the passing gear cable, i do have it hooked to the carburator but it does not engage - there is too much slack in the cable for the carb to engage it - is this the problem? if so how can i adjust the cable to engage when the motor is at medium to full throttle? help - thanks, brent

tom hand · 10-08-2003, 08:40 AM

To adjust the cable, look on the back of the bracket that holds it. There are two little half moon shaped plastic clips that you pop out with a screwdriver. Once the clips are loose the spring will take up the slack in the cable. Now have someone push the trottle to the floor while you push the clips back in. It is much harder to desribe than it is to do.

tom hand · 10-08-2003, 08:50 AM

Found a pic on the board in another post. The kickdown cable is laying on top of the trans but it might help a little

Brently · 10-08-2003, 09:00 AM

so do you think this will fix my problem? i can do this easily - and thanks for the information - i sure hope this fixes it - man this message board sure is a big help - imagine if i had never stumbled onto it! yikes! thanks, Brent

Longhorn Man · 10-08-2003, 10:45 PM

I am 99% sure it'll fix you up.

70c10 · 10-08-2003, 11:06 PM

I have the exact same problem. I tried adjusting mine like Tom said but it didn't work. I think my cable is shot.

Longhorn Man · 10-08-2003, 11:10 PM

I may be disconnected on the other end then.

67cst · 10-09-2003, 12:02 AM

dont mean to steal the post but im the opposite, my truck winds out too far before it shifts, its also a th350, could it be the kick down cable also?

BLACK AND BLUE 67-72 · 10-09-2003, 12:06 AM

67cst in what gear or gears does it shift late? Also when it does shift is it a rough shift or a smooth shift ? Also you can check out my first post it is the same symptoms for early or late shifting. But it could be something different depending on my two questions.

Longhorn Man · 10-09-2003, 08:16 PM

It could be your shift cable being too tight, or it could be the hose disconnected/leaking on the vac modulator.

10-06-2003, 10:33 AM	#1
Brently Registered User Join Date: Feb 2002 Location: Chattanooga Posts: 151	Transmission help!! 350 turbo shifts 2-3 too fast i am not a transmission expert but in my 71 with a 350 turbo, newly rebuilt, first to second is a fine shift but from second to third is too quick if at all - i have changed the modulator valve and adjusted it as well but no dice - help please - is this an adjustment or a take it out problem? oh did i mention i cannot find the guy that rebuilt it for me? any help would be appreciated - thanks, Brent

10-06-2003, 11:11 AM	#2
BLACK AND BLUE 67-72 Firefighter Join Date: Feb 2001 Location: Yellville, Ar, USA Posts: 1,943	Well it could be a number of things: Incorrect Oil Pressure, due to a defective vacuum modulator, leaking vacuum lines, or a stuck modulator valve (Not the canister with the vacuum line, but the actual valve that is inside the trans, accessed by removing the modulator canister. Governor Malfunction: Remove the governor. Invert governor and move weights up and down, to check for stuck governor valve. If valve is stuck, disassemble and clean governor. Governor Circuit Oil Blockage: Remove the transmission pan and valve body. Check for blocked or leaking feed holes. Check screens for blockage. Faulty Detent-Cable Operation: Check for stuck, disconnected or broken detent cable. Check cable adjustment. Valve-Body Malfunction: Remove pan. Remove valve body and shake. Check for stuck detent valve, 2-3 shift valve or 1-2 shift valve. Valves should drop of their own weight. Disassemble valve body and free up valves as necessary. I hope this gives you an idea of what it could be. And good luck!! __________________ '72 Chevy SWB 350 Auto '67 GMC LWB 350 4 speed '70 Chevy 4x4 Stepside 350 Auto Yellville, Ar. USA

10-06-2003, 01:01 PM	#3
O'l Buck Recovering Truck Driver Join Date: Mar 2002 Location: Orleans, NE USA Posts: 1,883	I've never had a th350 apart, but most transmissions have adjustable shift points, my guess is that when it was rebuilt, it got a new valve body, and the shift point is incorrectly adjusted. I've only worked on Allison transmissions, all that is required to set the shift points on them is to drop the pan and turn a shaft with a needle nose pair of pliers which has a pin in it to drop into a detent plate. some transmissions are shim adjusted. __________________ 67 K-20 350, SM465, Eaton rear, 4.56 no spin option 00 Dodge 2500 4x4, 24V cummins, 5 speed Chad South Central Nebraska

10-06-2003, 01:46 PM	#4
Brently Registered User Join Date: Feb 2002 Location: Chattanooga Posts: 151	trans problems good grief what problems i may have - oh well i sure do appreciate your ideas for what the problem could be - i have already replaced the modulator valve once (hopefully it was a good one i put on - it was new but you never know) you can adjust the mod valve and it will shift much later but still very little shift takes place - you have to listen carefully to even hear a shift to third you cannot feel one - oh well thanks, can all this be checked in the truck? i sure hope so - Brent

10-06-2003, 06:32 PM	#5
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	I would think that if the modulator or the govenor was the problem it would affect the 1-2 shift also __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

10-06-2003, 06:45 PM	#6
BLACK AND BLUE 67-72 Firefighter Join Date: Feb 2001 Location: Yellville, Ar, USA Posts: 1,943	Yes all of these things can be checked while the transmission is in the truck. Does it feel like it is slipping in the 2-3 gear shift? Or just softly shifting. Possibily a shift improver kit would fix this, I know that they will help your transmission last longer. I have one in mine and I am missing a friction plate, It has been this way for about 15,000 miles and I am still driving with the same transmission. __________________ '72 Chevy SWB 350 Auto '67 GMC LWB 350 4 speed '70 Chevy 4x4 Stepside 350 Auto Yellville, Ar. USA

10-07-2003, 01:10 PM	#7
Brently Registered User Join Date: Feb 2002 Location: Chattanooga Posts: 151	trans problems thanks for the replies to my problem - i will try and fix with a process of elimination - i also have a 350 that was in good shape when i bought the truck with a shift kit in it - i just pulled it out with the motor and replaced because i had this rebuilt 350 turbo just sitting in the garage - should i replace it with the one that was in it or try and fix this one by a process of elimination? thanks, Brent

10-07-2003, 11:08 PM	#8
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Do you have the kick down cable hooked up? On a TH350, it will do exactly as you indicate witht eh kickdown cable disconnected.

10-08-2003, 06:31 AM	#9
Brently Registered User Join Date: Feb 2002 Location: Chattanooga Posts: 151	trans problems if you are talking about the passing gear cable, i do have it hooked to the carburator but it does not engage - there is too much slack in the cable for the carb to engage it - is this the problem? if so how can i adjust the cable to engage when the motor is at medium to full throttle? help - thanks, brent

10-08-2003, 07:13 AM	#10
Brently Registered User Join Date: Feb 2002 Location: Chattanooga Posts: 151	trans problems if you are talking about the passing gear cable, i do have it hooked to the carburator but it does not engage - there is too much slack in the cable for the carb to engage it - is this the problem? if so how can i adjust the cable to engage when the motor is at medium to full throttle? help - thanks, brent

10-08-2003, 08:40 AM	#11
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	To adjust the cable, look on the back of the bracket that holds it. There are two little half moon shaped plastic clips that you pop out with a screwdriver. Once the clips are loose the spring will take up the slack in the cable. Now have someone push the trottle to the floor while you push the clips back in. It is much harder to desribe than it is to do. __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

10-08-2003, 08:50 AM	#12
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	Found a pic on the board in another post. The kickdown cable is laying on top of the trans but it might help a little Attached Images __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

10-08-2003, 09:00 AM	#13
Brently Registered User Join Date: Feb 2002 Location: Chattanooga Posts: 151	trans problems so do you think this will fix my problem? i can do this easily - and thanks for the information - i sure hope this fixes it - man this message board sure is a big help - imagine if i had never stumbled onto it! yikes! thanks, Brent

10-08-2003, 10:45 PM	#14
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	I am 99% sure it'll fix you up.

10-08-2003, 11:06 PM	#15
70c10 67-72 Addict! Join Date: Feb 2002 Location: The TAX State! Posts: 7,857	I have the exact same problem. I tried adjusting mine like Tom said but it didn't work. I think my cable is shot. __________________ Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads



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10-08-2003, 11:10 PM	#16
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	I may be disconnected on the other end then.

10-09-2003, 12:02 AM	#17
67cst i love summertime Join Date: Jul 2002 Location: Kelowna BC Posts: 4,303	dont mean to steal the post but im the opposite, my truck winds out too far before it shifts, its also a th350, could it be the kick down cable also? __________________ 1967 shortbox stepside Chevy, 365 hp 327, th400. GLOVE BOX LIGHTS FORSALE, click link for info http://67-72chevytrucks.com/vboard/s...d.php?t=273724

10-09-2003, 12:06 AM	#18
BLACK AND BLUE 67-72 Firefighter Join Date: Feb 2001 Location: Yellville, Ar, USA Posts: 1,943	67cst in what gear or gears does it shift late? Also when it does shift is it a rough shift or a smooth shift ? Also you can check out my first post it is the same symptoms for early or late shifting. But it could be something different depending on my two questions. __________________ '72 Chevy SWB 350 Auto '67 GMC LWB 350 4 speed '70 Chevy 4x4 Stepside 350 Auto Yellville, Ar. USA Last edited by BLACK AND BLUE 67-72; 10-09-2003 at 12:22 AM.

10-09-2003, 08:16 PM	#19
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	It could be your shift cable being too tight, or it could be the hose disconnected/leaking on the vac modulator.

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