[1410]

Where do you get the vacum for modulator valve on the 400. Does it come off the manifold or the carb? please advise as I think it should come off the carb. Only fiting I have for vacum from the carb is vacum advance to the distributor.

Thanks in advance.

Sid Blumner

 

[dfjeepster]

Manifold vaccum is fine, there should be a fitting on the back passenger side.

 

[1410]

Thanks a bunch. A buddy said that would be to much vacum for the modulator. Glad I asked. Was concerned abou the hook up since I only had one vacum line off of the carb and it was going to the distributor.

Sid

 

[1591]

Isn't the fitting on the manifold a special one to limit the vacuum? (has a small orifice in a 3/8" or so 90 degree fitting?) Seems like it is, but I don't have Jeepster books at work.

Brad.

 

[090]

Most mods have an orofice built in.

 

[Guest]

It takes a special brass fitting that connects to the passenger side upper intake manifold. The fitting is a 90-degree "street elbow" type (has a male end and a female end), that most importantly has a tiny internal orifice to limit the vacuum to the modulator. Straight manifold vacuum IS too much. Mark Vilbert in St. Louis should have plenty of these fittings if you can't find one.

Those little orifices will carbon up --- a real "hidden problem" on TH400 Commandos. You need to take them off and open them up with a sewing needle or straight pin.

 

[Bonecruncher]

What will hapen with a bad vacum or vacum modulator? Seems my commando is holding 1st gear longer than it should with a hard shift to second, unless I really get into the throttle. Good for fun, but not so good for gas mileage or city driving.

A friend told me it could be the vacum modulator. Waddya think?

 

[1591]

Besides the clogged up manifold fitting, it could also just be a leaky vacuum line to the modulator. Make sure the rubber line on each end is new, connections are tight and see if that helps the shifting. (At least each end of a hard line on Ole Yeller has a piece of vacuum tubing on it, not sure if that is stock).

If the line comes off, it will still shift, but only at reallllllly high RPM (don't ask, chris has already tried this!) and a small leak will just delay the shift a little.

Easy & cheap to try before buying and replacing the modualtor.

Brad.