Modulator Valve for a 1974 TH400

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Dec 29, 2013 | 07:52 PM

Paul L

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From: Ontario

Modulator Valve for a 1974 TH400

I would like to replace mine in the spring. Local NAPA version OK? I don't need adjustable or the like. Are there different versions for the stock TH400?

Dec 29, 2013 | 08:05 PM

lbzraptor

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Quote:

Originally Posted by paul 74

I would like to replace mine in the spring. Local NAPA version OK? I don't need adjustable or the like. Are there different versions for the stock TH400?

Napa one will be alright. I could be wrong but From what I remember they are not adjustable or different. What is wrong with yours? If the modulator valve is sticking or the vacuum from the carb is not getting to the valve then It will not change gears. From what I remember though the turbo 400 trans would still change after a certain rpm or maybe that was an old tale. lol

Dec 30, 2013 | 01:28 PM

7T1vette

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Modern-day replacements for the original vacuum modulator can look nothing like the original. They are much smaller and have a zinc chromate (gold) coating. They will work fine, but are not adjustable. You can get them at about any car parts place.

Dec 30, 2013 | 03:18 PM

lvmyvt76

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From: Springfield Missouri

my new modulator on my th350 is adjustable, and I did not know it.

Dec 30, 2013 | 03:26 PM

Paul L

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Quote:

Originally Posted by lbzraptor

The transmission shifts well although the shift points are "soft". But the TH400 was used in Cadillacs and Buicks as well and that crowd might like that kind of action. I figure for $25.00 or so it would not hurt to put a new modulator valve in. I might go even further and have a TransGo shift kit installed. But it's 0*F outside and I get all kinds of ideas this time of year while the Corvette is sleeping....

Dec 30, 2013 | 05:32 PM

diehrd

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When you do the modulator if you have not done a filter and gasket in the last several years do so . The filters are a cloth material and are known to plug or restrict fluid flow. And a shift kit at that point would be a good idea as well so long as when you drop the pan your fluid is not burnt and the pan is not full of a sludge material or brass filings.

Dec 30, 2013 | 05:38 PM

Paul L

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Quote:

Originally Posted by diehrd

Thanks for that suggestion. The transmission has not been serviced since at least 2008 when I bought the car. And who knows how many years before that? There is a good shop close by and I may just have them do a flush, filter, gasket, modulator job in the spring. The fluid is still pink but I do not know what resides in the pan.

Dec 30, 2013 | 11:55 PM

7T1vette

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There will be some clutch plate "silt" on the bottom of the pan. The clutch plates wear slowly, and particles sink to the bottom of the pan. If you don't find any metallic particles mixed in with the clutch silt, everything is still OK.