TH400 Modulator Adjustment

[gndoug]

So this last weekend I finished up the 400 swap. I decided to try a mechanical modulator to keep an automatic valve body. My TV cable was already set pretty tight for my 200... but on the modulator I had to loosen the cable to the MAX otherwise it didn't have enough slack to go WOT. Now, the other thing I noticed was that on my test drive it felt kinda sluggish, and seemed like it was shifting pretty early. I'm not sure of the RPM's because the car has no Tach right now. I guess this weekend I'm going to try the vacuum modulator with a check valve and air bleed on the modulator side and see if that makes it any better.

But my question is for any of the other guys with the mechanical modulator... Did you have to let the adjustment all the way out on the TV cable, or am I missing something. It just seemed kinda hokey, because with it adjusted for enough slack for the throttle plate to be able to open all the way, the wire cable does not spring back all the way into the plastic housing.
Just wondering if that is how other guys have it set up also.

Thanks,
Doug

 

[49-blues]

Subscribed.

 

[gndoug]

Ok so I figured out what was going on.
Mechanical Modulator = piece of crap.

What was happening was that the puck in the modulator was getting stuck all the way out ( or towards the transmission). I noticed that the transmission shifted ok until I made a WOT run, and after that it shifted like crap... being that the puck got stuck after the WOT run.

I took the modulator out and saw that this was what had happened, poked it with a screwdriver, and it sprung back to where it was supposed to be. I pulled up on the arm the the TV cable is hooked up to to manually check the actuation, and every time it would get stuck at the position it would go to at WOT.
So my solution was to throw the modulator in the box with the rest of the crap I just dont want to throw away yet, and put the vacuum modulator back in.

I ran line from a vacuum source, put in a check valve, then a T on the modulator side of the check valve. One side of the T went to the modulator, and the other side got a vacuum cap with a small hole poked in it to vent any residual vacuum that might be trapped when the valve "checks".

Went out and test drove it and it shifted like a champ. Nice firm mid throttle shifts, and health WOT shifts. I was taking pics along the way during the swap, so I'm going to try and get a thread up in the "how to" section on doing a 400 swap. But I would never waste my money on a mechanical modulator. The brand new vacuum modulator was 12 bucks from a local parts store, then throw in a couple bucks in vacuum line and check valve... worked WAY better than the mechanical modulator.

 

[kingots2004]

get those pics up i gearing up for the 400 swap myself.what length driveshaft?

 

[gndoug]

get those pics up i gearing up for the 400 swap myself.what length driveshaft?

I took my drive shaft to a local drive shaft shop and had 3/4 of an inch cut off, a nice 400 yoke installed with 1350 u-joints, and balanced. It was about 270 bucks.... I was thinking of getting a denny's d.s. but I called them and was told it was a 4-5 week turn around time on orders, and it was gonna run around 410-420 bucks.

 

[pajo]

tranny

Is this a short tail end or long tail end 400 tranny ..

 

[gndoug]

It is a short tail

 

[Scooter3800]

Here is another post about driveshaft length and TH400s
http://www.turbobuick.com/forums/general-turbo-buick-tech/279416-400-driveshaft-length.html

 

[kingots2004]

lol i started that thread i was just curious on his experance