The 1947 - Present Chevrolet & GMC Truck Message Board Network

The 1947 - Present Chevrolet & GMC Truck Message Board Network (https://67-72chevytrucks.com/vboard/index.php)
-   Engine & Drivetrain (https://67-72chevytrucks.com/vboard/forumdisplay.php?f=24)
-   -   no 3rd gear in a th 400 (https://67-72chevytrucks.com/vboard/showthread.php?t=250306)

chadfowler 07-19-2007 10:53 PM

no 3rd gear in a th 400
 
i have a th 400 that will not shift into 3rd gear. it shifts from 1st to 2nd
nice and quick but when its time to go into 3rd it will not. have checked the
vacuum line,vacuum modulator , and the governer, all seam to be ok.
i have tried 3 vacuum modulators with no help. trans sat for 3 or 4 months
while i changed engines but worked fine after i got it all hooked up for a while.
when i went out one day it would not shift into 3rd.any ideas on what the problem could be. thanks

shadetree 07-20-2007 12:55 AM

Re: no 3rd gear in a th 400
 
Have you changed the trans filter? Sometimes that clears up shifting problems.

chadfowler 07-20-2007 04:31 PM

Re: no 3rd gear in a th 400
 
no i have not took the pan off yet, but when i take the modulator out all the fluid comes out should that happen

performabuilt2 07-21-2007 12:56 AM

Re: no 3rd gear in a th 400
 
the modualtor tries to keep the tanny downshifted it fights against governor pressure and yes a little fluid will come out of the modualor bore when its removed......you may have a stuck valve though.......you have reverse right so that means that the direct drum is working. the tranny uses the direct drum to turn reverse. take the modulator valve out and look for any burrs and see if it moves freely lets start there.

chadfowler 07-21-2007 10:09 AM

Re: no 3rd gear in a th 400
 
2 or 3 quarts came out when i took out the modulator. i have took out the
modulator valve, looks good also the governer looks good and the vale moves. could it be the 2-3 vales in the vale body? tranny has strong reverse,
1st and 2nd but not 3rd.

chadfowler 07-21-2007 12:00 PM

Re: no 3rd gear in a th 400
 
are there any thing else i should be looking for besides the vale body when i drop the cover? what does the front servo do? thanks

performabuilt2 07-21-2007 06:38 PM

Re: no 3rd gear in a th 400
 
well anything is possible....the front servo controls the band which is only on in manual 2 or on a force downshift ot during engine braking it holds for second gear....really has nothing to do with 3rd......you can pull the VB and see if the 2-3 shift valve is stuck. like i said the 3rd clutches apply to give reverse so they should be working for drive also if you have reverse. i would look into the VB to start off

454HO 07-21-2007 10:06 PM

Re: no 3rd gear in a th 400
 
It's been a while, but I thought the vacuum modulator was only for the 1-2 shift. Maybe check the kickdown switch wiring. If it is shorted to ground it may try and hold 2nd gear too long.

chadfowler 07-21-2007 10:59 PM

Re: no 3rd gear in a th 400
 
some one told me (it has always been the clutchpack every time I've run into this problem. hope your luck differs from mine.)

but it pulls and works to good to have a clutch problem in r 1 and 2. pulled the cover of and looked clean and great, also took the vale body off and did not see a problem or no stickin vales.did not have time to try it out.

also it seemed like it worked a little better when it is cold and got a little worse as it got a little hotter before i took the vale body off.
will try it in the morning.

performabuilt2 07-22-2007 09:57 AM

Re: no 3rd gear in a th 400
 
as i have said before i dont think you have a clutch failure becuse it doesnt act up in reverse unless you have insane boosted line pressure in reverse and its making the clutches hold in reverse that is possible but not having any material in the pan leads me to belive there is a hydraulic problem somwhere other than the direct drum I do not belive there is a mechanical problem with the clutches

chadfowler 07-22-2007 04:01 PM

Re: no 3rd gear in a th 400
 
drove it about 8 miles today and at first still no 3rd gear, so i got up to about 40 and let off and had no gears. i could rev up a little ad it would catch alittle
so i through it in neutral and then back into drive, i had 3rd gear. it done this several times until the last 3 miles, started working good,i could drop it into
2nd and go back 3rd and it would shift great, did this several times, all worked great. it acted like something in the vb was sticking and taking a minuate to release. yesterday the regulator vale in the vb was sticking.
i hope this was the problem.

performabuilt2 07-22-2007 08:26 PM

Re: no 3rd gear in a th 400
 
sounds to me you have a sticky valve in the VB


All times are GMT -4. The time now is 02:26 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com