TH400 Problems
Greg Hanauska
I just recently had my TH400 rebuilt. I have a problem now that I didn't
ever have before. The 1-2 shift was occuring too late, so the guy adjusted
that to happen at the right time, but now the 2-3 shift happens almost at
the same time! It seems like it doesn't want to stay in 2nd gear. It is
reluctant to downshift from 3rd to 2nd also. I really have to get on it for
it to downshift.
Any suggestions would be great.
Unfortunately the guy who rebuilt it doesn't know what is wrong.
Thanks.
Greg Hanauska
eb7...@goodnet.com
Don Kuhlman
Unfortunately Greg, you'll find a lot of people out there rebuilding automatics
these days who don't know what they're doing. Don't ask me how I know!
With the TH400, there are three major things that control the shift points. There
is the kickdown linkage, the vacuum modulator, and the road speed governor. There
are also things you can do within the valve body, but we'll assume you have a
basically stock rebuild. We'll also assume you didn't change the governor.
This leaves the kick down linkage and the vacuum modulator. From what you're
saying, it sounds like the kick down linkage is a bit late for your tastes. In
other words, you have to use more throttle than you did before to get it to
down shift. This is usually an easy adjustment of the cable or rod mechanism.
Basically, you want the throttle/carb linkage to pull the kick down out sooner.
Make a small adjustment and then road test until you have it where you want it.
The vacuum modulator is the main control on how soon the transmission upshifts
in full automatic mode. It will be overridden by the shift position and kick down
linkages. There are two types of vacuum modulators; a fixed type and an adjustable
one. The adjustable ones are only a bit more money than the fixed type and I've
had good results with them. If it is adjustable, be sure to not back the screw
adjustment all the way out or it will come apart. You may or may not be able to
put it back together.
The vacuum modulator should get its signal from manifold vacuum, not a ported
source. It sounds like you may have the vacuum line connected to the wrong
port on the carb. Make sure the port it is connected to gets a full vacuum
signal at idle. If you have an adjustable modulator, adjust and road test it
as well. No more than a 1/2 turn at a time.
If these adjustments don't fix the problem, you most likely have something wrong
with the valve body, or possibly the governor, but it doesn't sound like it. The
transmission seems to be basically working from what you've described. You
probably have a bad or misadjusted modulator, or it isn't hooked up properly.
Hope this helps,
Don Kuhlman
Hampton Virginia
--
(Spam Stopper: when replying, remove the ! from my e-mail address)
Terry Nixon
Hey, Don: Sure you're not thinking of a TH350? TH400s have electric
kickdown switches.
Terry
phillip patterson
Don Kuhlman <!dc...@erols.com> wrote:
>With the TH400, there are three major things that control the shift points. There
>is the kickdown linkage, the vacuum modulator, and the road speed governor. There
>are also things you can do within the valve body, but we'll assume you have a
>basically stock rebuild. We'll also assume you didn't change the governor.
>This leaves the kick down linkage and the vacuum modulator. From what you're
>saying, it sounds like the kick down linkage is a bit late for your tastes. In
>other words, you have to use more throttle than you did before to get it to
>down shift. This is usually an easy adjustment of the cable or rod mechanism.
>Basically, you want the throttle/carb linkage to pull the kick down out sooner.
>Make a small adjustment and then road test until you have it where you want it.
This is incorrect for the Turbo 400's. They have an electric
kickdown mechanism. There should be a switch that is "shorted" during
full throttle. it mounts on or near the carb and sends 12V to an
eletrical connector on the drivers side (I think, can't remember, mine
is at the transmission shop getting a rebuild at this time) of the
tranny.
Phillip Patterson
Don Kuhlman
As Terry said, I'm probably thinking of the TH350. I'm not sure going
from memory if any of the TH400s had a manual kickdown linkage. The
Powerglides and TH350s have a kickdown and vacuum modulator. The
TH200-R4 and TH700-R4 use a "TV" or throttle valve cable that performs
both functions; throttle position and kickdown. I don't remember what
the TH200 uses.
In any event, the drill is basically the same. You adjust the kickdown
switch or linkage, and then make sure the modulator is doing it's job.
On transmissions with just a TV cable, the adjustment is critical for
proper operation. Too little and it upshifts too soon and may or may
not downshift properly. Too much and it shifts late and too hard.
I ain't even going to get into the new E model computer controlled
trannies!
Unknown
Don Kuhlman wrote:
>
> "Greg Hanauska" <eb7...@goodnet.com> wrote:
> >I just recently had my TH400 rebuilt. I have a problem now that I didn't
> >ever have before. The 1-2 shift was occuring too late, so the guy adjusted
> >that to happen at the right time, but now the 2-3 shift happens almost at
> >the same time! It seems like it doesn't want to stay in 2nd gear. It is
> >reluctant to downshift from 3rd to 2nd also. I really have to get on it for
> >it to downshift.
> >Any suggestions would be great.
> >Unfortunately the guy who rebuilt it doesn't know what is wrong.
> >Thanks.
> >Greg Hanauska
> >eb7...@goodnet.com
>
> Unfortunately Greg, you'll find a lot of people out there rebuilding automatics
> these days who don't know what they're doing. Don't ask me how I know!
>
> is the kickdown linkage, the vacuum modulator, and the road speed governor. There
> are also things you can do within the valve body, but we'll assume you have a
> basically stock rebuild. We'll also assume you didn't change the governor.
>
> This leaves the kick down linkage and the vacuum modulator. From what you're
> saying, it sounds like the kick down linkage is a bit late for your tastes. In
> other words, you have to use more throttle than you did before to get it to
> down shift. This is usually an easy adjustment of the cable or rod mechanism.
> Basically, you want the throttle/carb linkage to pull the kick down out sooner.
> Make a small adjustment and then road test until you have it where you want it.
>
linkage (at least on my GTO it was).
The TH350 and newer hand the cable kickdown - those are usally
autoadjusting (assuming you have the right brackets) simply adjust all
the way "in" and floor the gas pedal, adjusts itself.
Without the kickdown switch, the trans will only down shift at very low
speeds, and rapidly upshift (at least from 1st to 2nd) if you leave very
light on the throttle.
Dirk