Can a vacuum modulator cause this: Starts off fine and normal, and then won't shift up til way too many RPM's (at least 3000). When it shifts, it continues to run fine. Fluid is full and new. Vacuum lines are in good shape. Kickdown is installed and works properly. Problem occured suddenly. It's either that or tear it down... Frank
Frank, Modulators usually go bad when the vacuum diaphram inside goes bad and leaks vacuum. When that happens, trans fluid can be pulled into the intake manifold and burned. Pull the modulator out, and point the vacuum nipple down. If any trans fluid comes out, the modulator is bad. If you have a vacuum tester, like a mityvac, you can see if it holds vacuum. A bad modulator can cause delayed upshifts.
The hose at the intake manifold end is DRY as a bone. Confession: Remember, this is the original TH350 from my car that was in it before I swapped in the 70 model 455, (only a month or so ago) which has a ton of power more than the 350 engine did. And I took it racing at Temple 2 weeks ago... it drove fine back to Austin-- 60 miles-- but who knows? BTW-- I had water on my tires and spun til the 1/8th mark and let up. Traction didn't hurt it, but high RPM's might have... While I had it out, I saw it had been signed when rebuilt-- in 1989. The sudden stress of dealing with a 455 could have been hard on it... :ball: ou: Is rebuilding this thing something I should tackle myself? I found rebuild kits from driveline.com, Summitt and others for around 150.00... Frank
I removed the old modulator, and turned it facing downwards, and voila, ATF! So I replaced it. It still does the same thing, which is: starts off fine, and then at 20 or so, I can feel it try to shift and it starts slipping. So, I seem to have lost 2nd and maybe 3rd gears. Are there any other external things to check? o No: Or is it rebuild time? ou: Thanks guys Frank
