THM400 2-3 shift hesitation; G-05 coolant and intake mfld gasket

Two questions today:


1. Tranny problem -

My 3 speed THM 400 (1985 Chevy pickup) hesitates during the 2 - 3
shift. It seems like it stays in both gears until I lift my foot a
little to "baby" it thru the shift. I have a tranny temp gage and the
problem does not vary with tranny temp.

Tranny has 175K miles on it, majority of which is city driving. I just
got through changing the filter, and that did not improve or worsen the
problem. My tranny oil is 80% Mobil synthetic (Every 20K or so I drain 4
quarts and replace with synthetic.)

I would like to avoid a complete rebuild. Would a shift kit (like
TransGo) help?


2. Intake manifold gasket problem -

'85 pickup again. I originally used green coolant, for 16 years. It
tended to clog the radiator a lot, so I switched to DexCool (red) for a
while. Heard horror stories about it so two years ago switched to G-05
coolant (yellow color). Starting a year ago I have slow seep from
intake manifold gaskets, foward end, both sides of engine (big block
with aluminum intake manifold). Need to replace the gaskets, but want
to do the job only once and have heard that many people have repeated
gasket failures when using DexCool in late 90's and up pickups. DexCool
is very similar to the G-05. So, it boils down to question of whether
G-05 is just as bad on gaskets as DexCool. Anyone know?

Henry

Henry wrote:
> Two questions today:
>
>
> 1. Tranny problem -
>
> My 3 speed THM 400 (1985 Chevy pickup) hesitates during the 2 - 3
> shift. It seems like it stays in both gears until I lift my foot a
> little to "baby" it thru the shift. I have a tranny temp gage and the

> problem does not vary with tranny temp.
>
> Tranny has 175K miles on it, majority of which is city driving. I
just
> got through changing the filter, and that did not improve or worsen
the
> problem. My tranny oil is 80% Mobil synthetic (Every 20K or so I
drain 4
> quarts and replace with synthetic.)
>
> I would like to avoid a complete rebuild. Would a shift kit (like
> TransGo) help?


>From experience, you may have brittle seals (three of them) around what
*I think* is the High / Reverse piston -- its the one all the way at
the back of the case. It can cause other symptoms involving 2-3
shifts, but any problem with third not engaging properly would make me
think of that on a high mileage TH350. You may also have a valve
sticking in the valve body. All of this can be corrected with a proper
overhaul. A shift kit will do nothing for you now, but I would suggest
a shift improvement kit during overhaul (unless something's previously
been done to the valvebody). And whats with the multiple fluid use?
Just stick to Dextron III.


> 2. Intake manifold gasket problem -
>
> '85 pickup again. I originally used green coolant, for 16 years. It

> tended to clog the radiator a lot, so I switched to DexCool (red) for
a
> while. Heard horror stories about it so two years ago switched to
G-05
> coolant (yellow color). Starting a year ago I have slow seep from
> intake manifold gaskets, foward end, both sides of engine (big block
> with aluminum intake manifold). Need to replace the gaskets, but
want
> to do the job only once and have heard that many people have repeated

> gasket failures when using DexCool in late 90's and up pickups.
DexCool
> is very similar to the G-05. So, it boils down to question of
whether
> G-05 is just as bad on gaskets as DexCool. Anyone know?


There's no reason why you should need to use anything other than 50%
green coolant in that truck. Changing to three different formulas
(ones that aren't fully compatible with each other) is only worsening
the situation. A complete flush of the yellow/red/green slurry,
including removing the Tstat from the system and running the engine
with water through the radiator as it pumps through and out the engine
is recommended. Do this til water runs clear. Then fix the manifold
leak with quality gaskets and torque the bolts properly. Use pipe dope
or threadlocker as suggested by the gasket manufacturer or repair
manual.

The additive package found in Dexcool will destroy gaskets not made for
it. I don't know about the yellow long-life but would suspect it may
be damaging to gaskets as well. Green coolant changed every few years
in a system that never is allowed to run low is near fool-proof
protection.

Toyota MDT in MO

Part of my first sentence got attached to the OP quote, even though I
typed it two lines below the quoted text. Is it still Monday??

Toyota MDT in MO

> 1. Tranny problem -
> I would like to avoid a complete rebuild. Would a shift kit (like
> TransGo) help?

You seem to have given the transmission better than normal care but
everything finally wears thin in time. I doubt that anything short of a
rebuild will help, but there are some exceptions. If the engine is not
running right, the transmission won't perform correctly. Are vacuum lines,
etc all in good shape? Have you replaced a vacuum modulator on this
transmission? (I assume it has one, haven't specifically checked)

You can always try an additive like Redline if all else fails, but a rebuild
may not be far away.

> 2. Intake manifold gasket problem -
So, it boils down to question of whether
> G-05 is just as bad on gaskets as DexCool. Anyone know?

I don't know. DexCool has a stained reputation and I don't know personally
whether it deserves it or not. Some GM engines have problems that no gasket
yet available and no coolant will alleviate totally. You don't say
specifically which engine you have.

The only problems I have ever seen with the old green antifreezes have to do
with the silicate corrosion inhibitor precipitation. As far as I am
concerned,
the DexCool stories are still anecdotal, until I see a dependable
evaluation.



> Henry

> 1. Tranny problem -
> I would like to avoid a complete rebuild. Would a shift kit (like
> TransGo) help?

A shift kit can be a good idea on a fresh transmission, but won't raise the
dead.
It can make a transmission work better and last longer.

You seem to have given the transmission better than normal care but
everything finally wears thin in time. I doubt that anything short of a
rebuild will help, but there are some exceptions. If the engine is not
running right, the transmission won't perform correctly. Are vacuum lines,
etc all in good shape? Have you replaced a vacuum modulator on this
transmission? (I assume it has one, haven't specifically checked)

You can always try an additive like Redline if all else fails, but a rebuild
may not be far away.

> 2. Intake manifold gasket problem -
So, it boils down to question of whether
> G-05 is just as bad on gaskets as DexCool. Anyone know?

I don't know. DexCool has a stained reputation and I don't know personally
whether it deserves it or not. Some GM engines have problems that no gasket
yet available and no coolant will alleviate totally. You don't say
specifically which engine you have.

The only problems I have ever seen with the old green antifreezes have to do
with the silicate corrosion inhibitor precipitation. As far as I am
concerned,
the DexCool stories are still anecdotal, until I see a dependable
evaluation.



> Henry

> 1. Tranny problem -
> I would like to avoid a complete rebuild. Would a shift kit (like
> TransGo) help?

A shift kit can be a good idea on a fresh transmission, but won't raise the
dead. It can make a transmission work better and last longer.

You seem to have given the transmission better than normal care but
everything finally wears thin in time. I doubt that anything short of a
rebuild will help, but there are some exceptions. If the engine is not
running right, the transmission won't perform correctly. Are vacuum lines,
etc all in good shape? Have you replaced a vacuum modulator on this
transmission? (I assume it has one, haven't specifically checked)

You can always try an additive like Redline if all else fails, but a rebuild
may not be far away.

> 2. Intake manifold gasket problem -
So, it boils down to question of whether
> G-05 is just as bad on gaskets as DexCool. Anyone know?

I don't know. DexCool has a stained reputation and I don't know personally
whether it deserves it or not. Some GM engines have problems that no gasket
yet available and no coolant will alleviate totally. You don't say
specifically which engine you have.

The only problems I have ever seen with the old green antifreezes have to do
with the silicate corrosion inhibitor precipitation. As far as I am
concerned,
the DexCool stories are still anecdotal, until I see a dependable
evaluation.



> Henry

I don't "speak" hydramatic, so I can't really be much help on the
transmission. If it were a Torqueflite, I'd say a sticky shuttle valve
in the valve body, stuck governor, or badly mal-adjusted band.

As for the G-05 versus DexCool debate, that's easy. G-05 is FAR "safer"
for old engines than DexCool. DexCool is an organic-acid technology
(OAT) coolant, whereas G-05 is a hybrid organic acid technology (HOAT)
coolant. That's a pretty fundamental difference in the corrosion
inhibitor package, even though it doesn't sound like that big a deal.
HOAT antifreezes protect all the same metals and combinations that old
silicone-silicate antifreezes protected, pure OAT packages like DexCool
don't, so they can only be used in engines that do not have certain
metals and materials in the engine, gaskets, heater core, and radiator.
DexCool is known to be incompatible with copper heater cores and the
solder used in them, for example.

Zerex has a pretty decent write-up on their page:

http://www.valvoline.com/pages/produ...10&section=404



Henry wrote:
> Two questions today:
>
>
> 1. Tranny problem -
>
> My 3 speed THM 400 (1985 Chevy pickup) hesitates during the 2 - 3
> shift. It seems like it stays in both gears until I lift my foot a
> little to "baby" it thru the shift. I have a tranny temp gage and the
> problem does not vary with tranny temp.
>
> Tranny has 175K miles on it, majority of which is city driving. I just
> got through changing the filter, and that did not improve or worsen the
> problem. My tranny oil is 80% Mobil synthetic (Every 20K or so I drain 4
> quarts and replace with synthetic.)
>
> I would like to avoid a complete rebuild. Would a shift kit (like
> TransGo) help?
>
>
> 2. Intake manifold gasket problem -
>
> '85 pickup again. I originally used green coolant, for 16 years. It
> tended to clog the radiator a lot, so I switched to DexCool (red) for a
> while. Heard horror stories about it so two years ago switched to G-05
> coolant (yellow color). Starting a year ago I have slow seep from
> intake manifold gaskets, foward end, both sides of engine (big block
> with aluminum intake manifold). Need to replace the gaskets, but want
> to do the job only once and have heard that many people have repeated
> gasket failures when using DexCool in late 90's and up pickups. DexCool
> is very similar to the G-05. So, it boils down to question of whether
> G-05 is just as bad on gaskets as DexCool. Anyone know?
>
> Henry

"Henry" > wrote in message
ink.net...
> Two questions today:
>
>
> 1. Tranny problem -
>
> My 3 speed THM 400 (1985 Chevy pickup) hesitates during the 2 - 3
> shift. It seems like it stays in both gears until I lift my foot a
> little to "baby" it thru the shift. I have a tranny temp gage and the
> problem does not vary with tranny temp.
>
> Tranny has 175K miles on it, majority of which is city driving. I just
> got through changing the filter, and that did not improve or worsen the
> problem. My tranny oil is 80% Mobil synthetic (Every 20K or so I drain 4
> quarts and replace with synthetic.)
>
> I would like to avoid a complete rebuild. Would a shift kit (like
> TransGo) help?
>
Henry, check in Google and/or with a friendly, knowledgeable tranny
tech. The 400 THM's were such that you could enlarge one certain hole in
the valve body PLATE, reassemble, run it a half quart low in fluid, and it'd
shift as well as any shift kit. No cost exc. gaskets.
You may wanna do it even if you do overhaul it. My 1-ton hauler with
135000 miles needed fresh rebuild, and I did the above and with 180000 it
was still pulling hard & shifting strong. Did same procedure to my '63
Nova--heated up, of course--& it'd get squirrely on both shifts.
HTH & good luck. s