Th350 has to warm up before moving and more

[Patrick Reeve]

1981 C10 with a 383 and th350
It has to warm up for at least a few minutes in 30-40 degree weather. not as bad in warmer weather but still takes some time.

It also seem to shift fast like it’s going about 25 and already in 3rd gear

And finally the trucks has 3.42s with 295/59/15s tires . At 5000 rpm it’s only doing 55 mph

I have a 700r4 but not ready to put it in yet just trying to fix what I got till I’m ready. Any help would be great it’s not cool to sound fast and go slow lol

 

[HotRodPC]

Fluid level is OK? Could be a filter that's got a little junk clogging it and has problems letting the cold thicker fluid through, or you may have dried up seals that shrink up when cold and swell enough when warm.

 

[gotyourgoat]

Also the th350 has an adjustable vacuum modulator. You can adjust to change shift points. I'd check that and the lines connecting it.

 

[77 K20]

You have stock heads on that 383, or vortec heads? Vortec heads cause some cold weather issues as there is no heat crossover tube capability. And if you have the old standard heads did you keep the heat crossover passage, or is it blocked off with plates? Heat in the intake will make it run better when cold. But then you lose power when its hot outside.

And your RPM at 55 mph sounds way off. A 295/50R15 tire is about 26" tall...

You must be registered for see images attach

So a 26" tire with 3.42 at 65 MPH shows 2874 RPM. Then you have some torque converter slip... so maybe 3000 RPM? 3100?

You'd have to have those 5.71 gears to get 5000 RPM at 55 mph. Or something is slipping bad. Or your tach is way off...

 

[Patrick Reeve]

Fluid level is fine and I’ve tried adjusting the modulator and still didn’t change anything

The motor has Bowtie phase 2 heads non vortex and a air gap intake

Is there any certain way to test for a bad torque converter ? Tach might be a light off but I don’t think it’s too bad

 

[Patrick Reeve]

Vortec* sorry lol

 

[QBuff02]

if the vacuum modulator isn't hooked to full manifold vacuum port on the intake or carb it will mimic a slipping issue and cause early shifts while driving. You didn't state whether you had worked on it recently or not? or just acquired the truck? Could be as simple as something like a mouse chewed on the hose or the modulator itself has failed as a place to start. Another thing to address is whether or not the tv cable is adjusted properly. Have you worked on the carb recently? unfortunately if it is one of the above symptoms that is the root cause and it's been driven very much, it's likely the trans may be toast or on its way out the door. When and how long ago did these problems start?

 

[Patrick Reeve]

Got the truck from a buddy engine was built by a local performance shop and trans was built in 2016 so I’m sure it out of warranty and I have adjusted the kick down . Before you could stomp on it and it wouldn’t kick down now I have it to where it will kick down . All vacuum lines look good it’s driven about 3 times a week

 

[Frankenchevy]

I recently pulled my vac mod line and it was packed solid. Might be worth a look.

 

[Patrick Reeve]

Ok I’ll check that

 

[77 K20]

Fluid level is fine and I’ve tried adjusting the modulator and still didn’t change anything

The motor has Bowtie phase 2 heads non vortex and a air gap intake

Is there any certain way to test for a bad torque converter ? Tach might be a light off but I don’t think it’s too bad

Ah- there you go. The air gap manifold is good for power but doesn't let the intake manifold warm up easily. A cold intake manifold will help fuel drop out of suspension and will make it idle rough and sputter a bit until there is a enough heat transfer to warm up the manifold a bit.

 

[Frankenchevy]

The 5000 rpm at 55 sounds like second gear though.

You’re positive it’s shifting 2-3?