When my car is cold ('67 Thunderbird w/390) the C6 trans is taking longer and longer to engage in "D". But if I give some throttle it seems to speed up the process. Trans grabs firmly into gear (no slippage) once engaged, and doesn't seem to have the same hesitation when I've been driving it (when it's warmed up).

I know there's some vacuum modulator on the trans that controls some of this, which is connected to the engine intake. Does my engaging problem seem to be this modulator? And if so, is it an easy/cheap replacement? Thanks.

Possible that it is only just a vacuum line, linkage or low fluid level.

Modulator, if required is fairly simple to replace and cost is around $30.00

Here is a link to the Ford transmission forum: http://www.network54.com/Forum/260730/

Hope this helps.

I did check my fluid level today and that may be the culprit. It was lower than I thought it would be since the tranny isn't leaking (that I know of). I added most of a left-over quart of fluid and will top it off later today.

Thanks for that insight, Jim - especially the web link.

Well topping off the tranny fluid didn't help after all. I'll try a new modulator next. If anyone has any more suggestions regarding these symptoms, I'd love to hear 'em!

Thanks, guys.

Take the vacuum line off the car and inspect it. If there is much age to it, replace it even if there are no obvious leaks. This takes one more variable out of the equation. Good luck.

When was the last time the transmission was serviced? The filter may be at least partialy clogged. If the transmission upshifts normally, the vacuum modulator must be functioning.

You might want to try Lucas transmission treatment. This stuff is great.It helps restore some of the old seals and other parts in the trans. It won't help any kind of vacuum leak of course but, It can help other problems.

Thanks, guys. Did the Lucas treatment, but no change. I figure the filter is getting clogged and with the fluid cold, it's much more viscous. Therefore I'm dropping the pan tomorrow and replacing the filter and gasket. Can't hurt. Shop wanted over $100 for this but the filter and gasket are under $10.00. I'll report back with results. Hope I don't have to get the C6 serviced by a trans shop...

I had a friend from high school that I always took my transmissions to that eventually owned his own shop. He told me one time many years ago that the C-6 trans was one of the least expensive trans to rebuild. Back in the 70's early 80's he would only charge me $100 to rebuild it if I pulled it. I'm sure it's more now but it might not be that bad if you need a rebuild.

And I've rebuilt an AOD (twice, actually) for use in my Ranger 5.0 swap. Not too expensive for parts. It's the friggin' labor that kills you! Lol...

Actually, I was talking about the labor.

Another piece of FYI about the C-6 trans is that in the 70's I had four Ford's with this trans in them that gave out. They all went the same way, first I lost "D"rive, then 2nd, then 1st. One car I drove three blocks in reverse to my buddy's house that did the rebuilds.