TH400 vacuum actuator assembly and reinstall questions...I'm stuck

[shiner2001]

In replacing the vacuum actuator on my 73 Wag TH400, I seem to be at a stopping point. First of all, the replacement is a much, much tighter fit to slide in (the old one goes in and out no problem, the new one not so much). Also, after removing the old one, this guy was hanging out there in the hole and I'm not sure what to do with him:



Does it simply sit loosely in the hole on the shaft of the new actuator, like this?



For comparison, here is the old one and the new one. There is no perceptible difference in the size of the two, but the new one sure doesn't fit like the old one. I haven't measured with calipers yet. And I have read that the external portion of the actuator is smaller on the replacement parts, so that doesn't bother me, just the diameter of the part that slides inside the housing.



Also, with the actuator and the above pictured piece removed, if I stick my finger in the housing, I feel what feels like a roller bearing or something cylindrical that lies perpendicular to the opening laying in the bottom. Is that normal or did something else fall out when I took the old one out?

I'll have a beer and await someone more experienced than me to chime in...thanks as always, guys and gals.

[gsmikie]

do you still have the elbow that the modulator goes in ???? or does your modulator go right into the trans >????

[shiner2001]

The elbow is still there. All I did to take the old one out was remove the bolt that threads through the hold down clamp.

I got the new one in and have the "spring" for lack of a better term (first picture in the post) in there. However, I don't know if there is a way for it to go in right and a way for it to go in wrong. The actuator is "compressed" to seat all the way down. I don't know if at rest that is proper or not. Any ideas? I sure hate to try to try it out with a drive and fry the whole thing.

[shiner2001]

To clarify that, it slid in almost all the way pretty freely, but then I had to push and hold it down to get it to go far enough in to get the clamp over the shoulder on the actuator.

[Lambrewski]

Newer smaller modulator (your new one) are not made to be used with the elbow, "spring", and valve just inside your tranny case. And, I don't believe the large modulator (the one you took out) is available any more....or if it is I don't know where.

The smaller modulator (your new one) can be used by:
- replacing the valve inside the tranny case with the right length, and
- install the new modulator directly in to the side of the tranny case - no longer using the elbow, the "spring", or the old valve

The valve inside the tranny case should be just sitting in there - a magnet will get it out

A transmission shop should have the different valve you need (I think it's shorter but could be mistaken....can't recall which). If you explain what you're doing they should know which one you need.

Good luck!

[shiner2001]

So is it not possible at all to use the new modulator with the old elbow, or will it still work, even though it's made to do directly in the case?

As far as the valve, what's the full name for that part so that I can ask for it?

And when you talk about removing the valve and replacing it with another one of a different size, that is AFTER the elbow is off, correct?

[Lambrewski]

Here's a fuzzy pic of the two different valves. I would guess you have the long one (old modulator w/ elbow and spring) and need the short one (no elbow or spring, installed directly into tranny case).....but not positive



Maybe GSM will clarify....

[Lambrewski]

Can't use new modulator with elbow

Don't know the official name....would try calling it a modulator valve and see if they know what you're describing

Yes - valve is in the hole inside - have to have the elbow off to get to it

[Carnuck]

I pulled the elbow off mine, made sure there was a pin inside that was about teh size of a 1/8" drillbit (from memory) and it wasn't bent. That fit in the new modulator without the elbow and it cleared the front driveshaft

[shiner2001]

Thanks for the pics, good to see what you're talking about. At this point I'll be out of town for the week, so there's no rush for me to get it figured out. Maybe by the time I can get back to working on it I'll know what the heck I am doing. It's all so simple in reality that I'd hate to have to throw it on the trailer just to take it to a tranny shop just for this...

[shiner2001]

I pulled the elbow off mine, made sure there was a pin inside that was about teh size of a 1/8" drillbit (from memory) and it wasn't bent. That fit in the new modulator without the elbow and it cleared the front driveshaft

So were you able to just use a new modulator with the old valve and no elbow, no other new parts (namely the valve) required?

[Lambrewski]

You need the new valve. Maybe someone here has an extra lying around they would offer to send (?)

[Carnuck]

The old style valves with the elbow were slightly different than '75-79 seeing how the early trans was a Buick nailhead one circa 1964

[Lambrewski]

[Lambrewski]