brake booster check valve

[JimB66thunderbird]

I have a 1966 hardtop with disk brakes in the front and drum brakes in the rear. My question is should the brake booster check valve have one or two nipples? If two where should they be connected? Thank you.

[RedBird64]

If it has two, one goes to vacuum at the intake manifold and the other is a smaller line that goes down to the transmission modulator.

Scott

[losendos]

On my 1966. the smaller nipple is capped off. Why, I don't know, but it looks like it's meant to be that way.

[RedBird64]

On my 1966. the smaller nipple is capped off. Why, I don't know, but it looks like it's meant to be that way.

Is the modulator supplied by another line?
If your missing the the connection to it you will have very hard, slightly delayed shifts but that's about it. A little hard on the diff and U-joints but actually easier on the trans itself. It just isn't as refined feeling when it shifts.

Scott

[losendos]

Hmm, I always thought the car shifted nicely - firm and quick shifts. I've actually wondered if it has a shift kit installed,

Where is the transmission modulator located?

[RedBird64]

It's on the Dr. side of the trans down low if you have a COM. It's on the pass. side, below the tail housing and behind the pan on a C6.
You should see a small vacuum line heading down in that direction from the Dr. side of the eng bay. It will connect to rigid section of metal line that snakes down to the Modulator. The modulator is connected by a short section of rubber hose at the other end of the metal line.
I've found that the shift from 1st to 2nd is most telling when the line is missing. If you're going very slow underlight throttle, like through a neighborhood, it will be very harsh when it shifts.

S

[JimB66thunderbird]

Thanks to all who responded about the booster check valve. Since I have not had any problems I will not make any changes. The smaller valve on mine is capped off and I will leave it as is.

[Mike Tbird]

I have a 66. Smaller port on brake booster check valve has always been capped. Before and after a transmission rebuild. Transmission shifts very smoothly.
If it's not broke...... .

[RedBird64]

I have a 66. Smaller port on brake booster check valve has always been capped. Before and after a transmission rebuild. Transmission shifts very smoothly.
If it's not broke...... .

My guess is you modulator is connected to eng vacuum somewhere else. Otherwise it would shift hard into second (unless the trans is worn out and just can't do that anymore..). There's nothing special about the vacuum port at the check valve. It was just handy for Ford.