TH400 wont shift to drive

Some details: 69 chevy c20 with a 350 sbc and a th400. Neither the
motor nor the transmission are original.

Problem: when starting the truck everything shifts fine from 1st to
drive. Say I drive a few miles to home depot. If I spend about 30
minutes or so, and come back to the truck and start it up, it will not
shift from 2nd to drive. If I play with the shifter a bunch I can
eventually get it to shift into drive, but as soon as I slow down
enough for it to down shift again (say a stop light) it will not shift
back into drive.

I have checked the fluid levels and they seem to be fine. I know
quite a bit about engines and other mechanical stuff, but not as much
about transmissions. I am thinking that this may have to do with a
vacuum modulator or perhaps the solenoid. But I do not know how to
check these, or even if these could be the problem. I would hate to
waste the money on parts that were not needed.

Does anyone think it may be one of the two parts I mentioned? If so
how would I verify they are broken. Any help would be appreciated.

Thanks
Andrew

"Andrew" > wrote in message
...
> Some details: 69 chevy c20 with a 350 sbc and a th400. Neither the
> motor nor the transmission are original.
>
> Problem: when starting the truck everything shifts fine from 1st to
> drive. Say I drive a few miles to home depot. If I spend about 30
> minutes or so, and come back to the truck and start it up, it will not
> shift from 2nd to drive. If I play with the shifter a bunch I can
> eventually get it to shift into drive, but as soon as I slow down
> enough for it to down shift again (say a stop light) it will not shift
> back into drive.
>
> I have checked the fluid levels and they seem to be fine. I know
> quite a bit about engines and other mechanical stuff, but not as much
> about transmissions. I am thinking that this may have to do with a
> vacuum modulator or perhaps the solenoid. But I do not know how to
> check these, or even if these could be the problem. I would hate to
> waste the money on parts that were not needed.
>
> Does anyone think it may be one of the two parts I mentioned? If so
> how would I verify they are broken. Any help would be appreciated.
>
> Thanks
> Andrew

It won't cost much to replace the mod. valve. I'd get an adjustable
one--easy to adjust, and this may solve problem; no need to buy high-priced
branded mods. BTW: if you pull the flexible vac line hose-connector off the
mod valve and fluid seeps out this hose, that indicates it's bad. If no
fluid, still may be bad. Ensure no holes/leaks in vacuum line from source,
near carb, to the connector hose. If no go, then change fluid and filter.
All this is driveway mechanics and won't break the bank. About covers
simple service, fixes, testing. That's a good tranny. Easy to make a
homemade 'shift kit' while changing fluid and filter--plus this increases
fluid-flow to clutches to help it shift into high (and into 2nd) gear much
crisper. Do a google search to find how to do this shift kit (where to
drill a hole or 2 and finish off job with fluid a quart low), and you just
might have a crisp-changing tranny. HTH, sam

"sdlomi2" > wrote in message
.. .
>
> "Andrew" > wrote in message
> ...
>> Some details: 69 chevy c20 with a 350 sbc and a th400. Neither the
>> motor nor the transmission are original.
>>
>> Problem: when starting the truck everything shifts fine from 1st to
>> drive. Say I drive a few miles to home depot. If I spend about 30
>> minutes or so, and come back to the truck and start it up, it will not
>> shift from 2nd to drive. If I play with the shifter a bunch I can
>> eventually get it to shift into drive, but as soon as I slow down
>> enough for it to down shift again (say a stop light) it will not shift
>> back into drive.
>>
>> I have checked the fluid levels and they seem to be fine. I know
>> quite a bit about engines and other mechanical stuff, but not as much
>> about transmissions. I am thinking that this may have to do with a
>> vacuum modulator or perhaps the solenoid. But I do not know how to
>> check these, or even if these could be the problem. I would hate to
>> waste the money on parts that were not needed.
>>
>> Does anyone think it may be one of the two parts I mentioned? If so
>> how would I verify they are broken. Any help would be appreciated.
>>
>> Thanks
>> Andrew
>
> It won't cost much to replace the mod. valve. I'd get an adjustable
> one--easy to adjust, and this may solve problem; no need to buy
> high-priced branded mods. BTW: if you pull the flexible vac line
> hose-connector off the mod valve and fluid seeps out this hose, that
> indicates it's bad. If no fluid, still may be bad. Ensure no
> holes/leaks in vacuum line from source, near carb, to the connector hose.
> If no go, then change fluid and filter. All this is driveway mechanics and
> won't break the bank. About covers simple service, fixes, testing.
> That's a good tranny. Easy to make a homemade 'shift kit' while changing
> fluid and filter--plus this increases fluid-flow to clutches to help it
> shift into high (and into 2nd) gear much crisper. Do a google search to
> find how to do this shift kit (where to drill a hole or 2 and finish off
> job with fluid a quart low), and you just might have a crisp-changing
> tranny. HTH, sam
>

You think it's easy to make a shift kit for a TH-400? (Or any tranny?) We
tried that back in college with a B&M kit for my friend's 1977 Cadillac
Coupe De Ville. That was the last time the car moved until the tow truck
picked it up and took it to the garage. Ha!

Craig wrote:
>
> "sdlomi2" > wrote in message
> .. .
>
>>
>> "Andrew" > wrote in message
>> ...
>>
>>> Some details: 69 chevy c20 with a 350 sbc and a th400. Neither the
>>> motor nor the transmission are original.
>>>
>>> Problem: when starting the truck everything shifts fine from 1st to
>>> drive. Say I drive a few miles to home depot. If I spend about 30
>>> minutes or so, and come back to the truck and start it up, it will not
>>> shift from 2nd to drive. If I play with the shifter a bunch I can
>>> eventually get it to shift into drive, but as soon as I slow down
>>> enough for it to down shift again (say a stop light) it will not shift
>>> back into drive.
>>>
>>> I have checked the fluid levels and they seem to be fine. I know
>>> quite a bit about engines and other mechanical stuff, but not as much
>>> about transmissions. I am thinking that this may have to do with a
>>> vacuum modulator or perhaps the solenoid. But I do not know how to
>>> check these, or even if these could be the problem. I would hate to
>>> waste the money on parts that were not needed.
>>>
>>> Does anyone think it may be one of the two parts I mentioned? If so
>>> how would I verify they are broken. Any help would be appreciated.
>>>
>>> Thanks
>>> Andrew
>>
>>
>> It won't cost much to replace the mod. valve. I'd get an
>> adjustable one--easy to adjust, and this may solve problem; no need to
>> buy high-priced branded mods. BTW: if you pull the flexible vac line
>> hose-connector off the mod valve and fluid seeps out this hose, that
>> indicates it's bad. If no fluid, still may be bad. Ensure no
>> holes/leaks in vacuum line from source, near carb, to the connector
>> hose. If no go, then change fluid and filter. All this is driveway
>> mechanics and won't break the bank. About covers simple service,
>> fixes, testing. That's a good tranny. Easy to make a homemade 'shift
>> kit' while changing fluid and filter--plus this increases fluid-flow
>> to clutches to help it shift into high (and into 2nd) gear much
>> crisper. Do a google search to find how to do this shift kit (where
>> to drill a hole or 2 and finish off job with fluid a quart low), and
>> you just might have a crisp-changing tranny. HTH, sam
>>
>
> You think it's easy to make a shift kit for a TH-400? (Or any tranny?)
> We tried that back in college with a B&M kit for my friend's 1977
> Cadillac Coupe De Ville. That was the last time the car moved until the
> tow truck picked it up and took it to the garage. Ha!

Well, then you didn't follow the instructions. The B&M kits came with
clear instructions and adequate explanation to guide most people.

Once you know what ports to enlarge, the "kit" is largely superfluous.

It's not that hard but you do have to pay attention to detail.

Check the vacuum line for the shift module. (from the intake to
module) If no leaks, pull the line off at the module. You might see
tranny fluid. (alot of times the module will leak when bad) I’ve had a
“frozen” governor do this also.

"anumber1" > wrote in message
...
> Craig wrote:
>>
>> "sdlomi2" > wrote in message
>> .. .
>>
>>>
>>> "Andrew" > wrote in message
>>> ...
>>>
>>>> Some details: 69 chevy c20 with a 350 sbc and a th400. Neither the
>>>> motor nor the transmission are original.
>>>>
>>>> Problem: when starting the truck everything shifts fine from 1st to
>>>> drive. Say I drive a few miles to home depot. If I spend about 30
>>>> minutes or so, and come back to the truck and start it up, it will not
>>>> shift from 2nd to drive. If I play with the shifter a bunch I can
>>>> eventually get it to shift into drive, but as soon as I slow down
>>>> enough for it to down shift again (say a stop light) it will not shift
>>>> back into drive.
>>>>
>>>> I have checked the fluid levels and they seem to be fine. I know
>>>> quite a bit about engines and other mechanical stuff, but not as much
>>>> about transmissions. I am thinking that this may have to do with a
>>>> vacuum modulator or perhaps the solenoid. But I do not know how to
>>>> check these, or even if these could be the problem. I would hate to
>>>> waste the money on parts that were not needed.
>>>>
>>>> Does anyone think it may be one of the two parts I mentioned? If so
>>>> how would I verify they are broken. Any help would be appreciated.
>>>>
>>>> Thanks
>>>> Andrew
>>>
>>>
>>> It won't cost much to replace the mod. valve. I'd get an adjustable
>>> one--easy to adjust, and this may solve problem; no need to buy
>>> high-priced branded mods. BTW: if you pull the flexible vac line
>>> hose-connector off the mod valve and fluid seeps out this hose, that
>>> indicates it's bad. If no fluid, still may be bad. Ensure no
>>> holes/leaks in vacuum line from source, near carb, to the connector
>>> hose. If no go, then change fluid and filter. All this is driveway
>>> mechanics and won't break the bank. About covers simple service, fixes,
>>> testing. That's a good tranny. Easy to make a homemade 'shift kit'
>>> while changing fluid and filter--plus this increases fluid-flow to
>>> clutches to help it shift into high (and into 2nd) gear much crisper.
>>> Do a google search to find how to do this shift kit (where to drill a
>>> hole or 2 and finish off job with fluid a quart low), and you just might
>>> have a crisp-changing tranny. HTH, sam
>>>
>>
>> You think it's easy to make a shift kit for a TH-400? (Or any tranny?)
>> We tried that back in college with a B&M kit for my friend's 1977
>> Cadillac Coupe De Ville. That was the last time the car moved until the
>> tow truck picked it up and took it to the garage. Ha!
>
> Well, then you didn't follow the instructions. The B&M kits came with
> clear instructions and adequate explanation to guide most people.
>
> Once you know what ports to enlarge, the "kit" is largely superfluous.
>
> It's not that hard but you do have to pay attention to detail.

Riiiiiiiiiiiiiiiiiiight. Remove this and that ball, do this and that,
drill here and there. The instructions were about as easy to follow as a
Chinese fire drill.

When I had my C-4 build it was done totally professionally, for dirt cheap,
and I was stress free.

"Craig" > wrote in message ...

>
> When I had my C-4 build it was done totally professionally, for dirt
> cheap, and I was stress free.

I did it on a Fiero and it worked out fine. Nervewracking to take some of
those
valves to the grinder, but if you work slowly and carefully, I found it went
quite easily.