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I have a 65, with a 250 and powerglide, manual steering and brakes.
Tranny downshifts harsh most of the time. I can vary (somewhat) how harsh it shifts through braking, etc. But under normal driving it's harsh. Modulator seems ok and holding vacuum. I pulled the modulator and checked the valve, etc. Seems allright, but if I were an expert, I wouldn't be seeking help.
It downshifts right at 10 mph every time. If I happen to be braking hard at 10 mph, it often downshifts smoothly. Also, sometimes the engine seems to slow down, sometimes almost dying, when I brake hard coming to a stop.
Tranny fliud looks and smells ok, level is good.
Upshift is smooth.
Haven't noticed any indication that clutches are going bad- fluid is reasonably clean.
Tranny doesn't seem to have any unusual vibrations, noises, smells, etc.
Carb isn't great, but I'd take it across the country tomorrow, so I wouldn't say it's a huge problem.

One thing that I wonder about: as I let off the gas and start coasting, it seems there is a little too much braking action from the trans. Could be I am just used to OD in trannys now and the old non-OD ones do that normally. Ideas on that and the harsh downshift?

Any help is appreciated.

John
 

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Rig up a vacuum gauge so you can read it while driving and see how much vacuum you have at the downshift point. Deceleration increases manifold vacuum and may affect the downshift. Braking hard uses vacuum and could smooth the downshift.

Some modulators are adjustable, there is a litle screw in the tube hole for the vacuum line. If yours has one you can change the setting and see what happens.

Welcome to the site, glad you stopped by. :waving:
 
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