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Th350 rebuild kit and converter

S

Sleblanc

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hey guys so took the blazer down the road yesterday and was letting it run and work out a few things well after the carb seemed to clear up. I noticed the trans was not shifting right at all it was sliding into the gears and revving up between shifts I would have to get out the throttle completely for it to get in third. Once in third max speed was about 45mph anything more then that it was just revving and slipping. Today I will check the modulator and vacuum tubes fluid and such. Anything else I need to look for before I just pull it and rebuild?

What is the best rebuild kit I can put in this thing being its stock now but will still hold up once I build the motor some. Also what torque converter do you guys recommend. Cam will be comp cams with about 262 lift I think the Rpms on it are about 1600-5000
 
Anyone know more about it not shifting to third because of the vacuum modulator issues? TC seems strong if I lock it in 1st or second.
 
thank you sir i for some reason such at the search on this site it never generates me the good results.
 
i went through and checked the line for the modulator its the original metal line it T's into the intake manifold between the carb and the Hei distributor. doesnt look like its collapsing. also i ran it when it was cold the other day and it seems to shift through the gears fine but very softly and seems to be early in the RPMs compared to the hard shifts it had last year. SO its leading me to think the modulator is the correct issue. I still will drop the pan being it has a small leak around the gasket and i will inspect the clutches.
Thanks,
 
Other question since i have it down how do you guys feel about the B&M shift kits in these trans?
 
I don't know that I would want to install any mods to a trans of unknown condition. It may be strong enough to keep going a while for you but who knows if it is strong enough to take the added strain of additional pressure and altered shift timing/firmness. A cheap easy upgrade is a red stripe adjustable vacuum modulator with the screw turned 3 turns clockwise.
 
was just a thought while i had it down and looking over everything. i am already getting the red stripe adjustable modulator.
 
You know you wont be able to see any clutch packs with the pan removed right? You will have to pull the trans out and apart for that kind of visual inspection.
 
For some reason I thought I could see them but I just read over the book again that is correct.
 
Sleblanc said:
For some reason I thought I could see them but I just read over the book again that is correct.
Click to expand...

Greg can comment if I'm wrong, but I am pretty sure the modulator cannot prevent a shift. They firm up the shift under load, it's what was used before the TV cable later on, but they can't physically stop the shift.

I ran with a TH400 for years that the modulator line would just fall off (too dumb to just replace the hose I suppose) and due to the gears in the car apparently, I could barely tell that it had come off. The shifts should be firmer with no modulator vacuum, and most of the time I didn't even notice.
 
My modulator is ran with a steel tube. I started looking tonight it looks like my kick down cable connected to the carb is stuck. Would it be possible for the kick down cable to be stuck in between second and third.
 
If the cable is bound in the kickdown position it can delay upshifts. The vacuum modulator regulates pressure according to throttle demand. This pressure acts against the shift valves governor pressure to help determine shift points and firmness. On a gas engine, having no vacuum to the modulator almost always results in no upshift. A diesel on the other hand, can sometimes upshift without a modulator vacuum signal due to its very low rpm governor.
 
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Greg that cable runs down to the governor ? What is the Governor responsible for controling?
 
That cable runs down to a lever inside the trans which pushes a valve in the valve body upon throttle demand. The Governor is located at the rear of the trans behind a baseball sized round cover on the driver side. The governor ultimately controls shift points
 
Well been out of town and super busy for a while no time with the k5 grabbed new modulator valve today which turned out to be wrong size and won't fit how I need with the metal vacuum line. But I pulled modulator and got a gush of fluid I would guess about almost a quart so I am assuming the trans was overfilled a bit or is this normal. Also was expecting a rod to show itself behind the modulator and I did not see one doe they get stuck sometimes in the trans? Also what should I set the screw to for the new modulator I will put in?
 
Normal for trans to be full over the modulator point, especially if sitting a while. There is a valve in the case behind the modulator, you may be able to pull it out with a magnet or scribe. I would turn the modulator screw in one full turn to start. Turning clockwise makes shift points later and firmer.
 
Was kinda worried it isn't in there at all or it's stuck...... I am really leaning to the governor being the problem though I still need to get a kick down cable also
 
Also had to get a modulator for a th400 because all they had for the th350 was some long big modulator valves that didn't fit well or line up with my metal piping for the vacuum line
 
If there was no valve in the case there would be a huge loss of pressure, the 400 and 350 modulators interchange
 
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