TH350 shifting problem...Help

[onebig76k5]

My TH350 tranny is shifting late 1st to 2nd and 2nd to 3rd. I developed this problem after changing my engine from a mild 350 to a stroked 383. My tranny is about 2 yrs old and this problrm didn't exist prior to changing engine. My engine is generaing significant RPM before the tranny is changing gears. What I have beed told locaaly is it's either the modulator or kickdown cable. What I'm having trouble with is it was shifting fine before the engine rebuild. I removed the kickdown cable (detent) and I still had the problem. Do you think I need to adjust this cable?? If so how? what else do you suggest?

 

[greyhoundjc]

I had a similuar problam after I did the 1 ton axle swap with different gear ratios. I replaced the vaccum modulator and everything started working fine. The part was less than $12 from Autozone and took about 5 minutes to install. The modulators are also adjustable (mine was anyway). Pull the vaccum line and there is a small set screw where the line plugs in.

 

[roadnotca]

Vaccuum check the modulator. Draw a vaccuum on it and see if it holds.

 

[4X4HIGH]

You probably knocked a vacuum hose off the modulator valve. The modulator valve is what controls upshift points. The tranny will still shift without it hooked up but the RPM's will be around 4500 or so before it will shift.

 

[onebig76k5]

Thanks for the help. It was the modulator. I went to A-Zone picked one up for $10.75, took me about 45 minutes and she is shifting like new.