Turbo 400 Issues - The 1947 - Present Chevrolet & GMC Truck Message Board Network

gmc1969custom · 12-04-2008, 03:45 PM

Here's what its doing. Reverse is perfect, when you put in in 1st its fine, put it in second it shifts from 1st to second fine the first time but when you come to a stop and take off it starts in second. When you put it in drive it does the same thing, the first time it shifts butter smooth, but from then on when you come to a stop it wants to start out in 2nd instead of 1st. Fluid looks good. One sidenote. I did just have the carb rebuilt b4 this started. Thanks in advance

sneakysnake · 12-04-2008, 04:06 PM

I know if the vac line is leaking or unhooked it will cause it to not shift "up" but it might be something to check.

big_al_71 · 12-04-2008, 04:17 PM

Check the kickdown cable where it connects to the carburator...

Longhorn Man · 12-04-2008, 04:33 PM

there is no kick down cable on a TH400, and even if it did, it would not do this... same with the vac modulator... it would be staying in first till about 5000 RPM till is would slam into 2nd.
However... I don't even have a good theory on what it could be though.

2bits · 12-04-2008, 05:12 PM

Quote:

Originally Posted by Longhorn Man

there is no kick down cable on a TH400, and even if it did, it would not do this... same with the vac modulator... it would be staying in first till about 5000 RPM till is would slam into 2nd.
However... I don't even have a good theory on what it could be though.

Second everything said.

Yes the kickdown is electronic and wouldn't affect this. If the modulator is disconnected, it wouldn't shift right, but I am wondering if the modulator is conneced but somehow messing up since the modulator does affect the upshifting? Possibly a small vaccum leak?

JimKshortstep4x4 · 12-04-2008, 08:35 PM

I have had a problem like this with a TH 400 and it turned out to be a sticky governor valve. The spool valve would stick and not return. A good burnishing and cleaning of the spool fixed the problem. ( I used 1500 grit paper to polish the spool).

Jim

71big block · 12-04-2008, 10:03 PM

I agree with JimK, I've seen this problem a couple of times

crazy longhorn · 12-04-2008, 10:28 PM

3rd that.....it sounds like the govenor is hangin. crazyL

gmc1969custom · 12-05-2008, 10:16 AM

Ok, I will check the governor out and see what I can figure out. Thanks for the help so far.

12-04-2008, 03:45 PM	#1
gmc1969custom Registered User Join Date: Jan 2007 Location: Canton, TX Posts: 210	Turbo 400 Issues Here's what its doing. Reverse is perfect, when you put in in 1st its fine, put it in second it shifts from 1st to second fine the first time but when you come to a stop and take off it starts in second. When you put it in drive it does the same thing, the first time it shifts butter smooth, but from then on when you come to a stop it wants to start out in 2nd instead of 1st. Fluid looks good. One sidenote. I did just have the carb rebuilt b4 this started. Thanks in advance __________________ 1969 Custom w/Turquoise Interior. 75k miles, 350 Auto, (Almost) All Original Last edited by gmc1969custom; 12-04-2008 at 03:48 PM.

12-04-2008, 04:06 PM	#2
sneakysnake It's a catastrophic success. Join Date: Jan 2003 Location: Oklahoma Posts: 2,077	Re: Turbo 400 Issues I know if the vac line is leaking or unhooked it will cause it to not shift "up" but it might be something to check.

12-04-2008, 04:17 PM	#3
big_al_71 Registered User Join Date: Jun 2008 Location: South Florida Posts: 11,375	Re: Turbo 400 Issues Check the kickdown cable where it connects to the carburator... __________________ Get your facts first, and then you can distort them as much as you please!!!!!. Sylvester's build thread >>>http://67-72chevytrucks.com/vboard/s...ht=big+rebuild

12-04-2008, 04:33 PM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Turbo 400 Issues there is no kick down cable on a TH400, and even if it did, it would not do this... same with the vac modulator... it would be staying in first till about 5000 RPM till is would slam into 2nd. However... I don't even have a good theory on what it could be though. Last edited by Longhorn Man; 12-04-2008 at 04:34 PM.

12-04-2008, 08:35 PM	#6
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: Turbo 400 Issues I have had a problem like this with a TH 400 and it turned out to be a sticky governor valve. The spool valve would stick and not return. A good burnishing and cleaning of the spool fixed the problem. ( I used 1500 grit paper to polish the spool). Jim __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC

12-04-2008, 10:03 PM	#7
71big block 1971 GMC 3/4 ton, 572 CID Join Date: Aug 2007 Location: Green Bay, WI Posts: 293	Re: Turbo 400 Issues I agree with JimK, I've seen this problem a couple of times __________________ 71 GMC 3/4 572 CID, 1988 GMC 1/2 2006 Saturn Vue "We always have parts left over on a job this size"

12-04-2008, 10:28 PM	#8
crazy longhorn Fabricate till you "puke" Join Date: Jun 2002 Location: Ill Posts: 9,403	Re: Turbo 400 Issues 3rd that.....it sounds like the govenor is hangin. crazyL __________________ 69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears....

12-05-2008, 10:16 AM	#9
gmc1969custom Registered User Join Date: Jan 2007 Location: Canton, TX Posts: 210	Re: Turbo 400 Issues Ok, I will check the governor out and see what I can figure out. Thanks for the help so far. __________________ 1969 Custom w/Turquoise Interior. 75k miles, 350 Auto, (Almost) All Original Last edited by gmc1969custom; 12-05-2008 at 10:18 AM.



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