Could you tell me if its possible or even desirable to adjust the Gearbox Modulator (unless you have to buy a Special one?)

So that you can have the Gearbox hold back longer before it changes gear, to enable faster acceleration.

Or is it best to keep with the Factory Setup and just drop down a gear with the stick when you need to.

 

Original Modulater = NO.

Replacement Compact adjustable - Yes.

I run the latter, and I like it. Some fiddling to get it where I wanted it, but tahts life.

I DO NOT run the electric kickdown, and the reasons are many, mostly coz I cannot get full throttle with the half leg, works for me.

Hence the adjustable Compact Modulator set to down change quicker, and hold just ever so slight for increased upshifts, BUT, I also modified the Governor, being the fiddler that I am.

 

The stock GM th/350 and th/400 modulators were always adjustable with a small straight slot put through the vacuum pipe. Companies sell an "adjustable" one but the stock ones also are adjustable, always have been. Turn the screw clockwise to firm/later shift points.

 

Hi Grant

Cheers!

Where would I find one of those adjustable Modulators?

Does it have a Special name to ask for.

 

Hi JT

Do you mean take the Vacuum Pipe off the Modulator and then put a small Screwdriver down the metal tube where the Vacuum pipe came off?

Not had any experience with modding one of these.

 

Yes, take the pipe off and shine a light in there, you will see a small flathead. Do a search on "adjusting a th400 vacuum modulator" lots of info out there. Mine is stock and has the adjustment screw.

 

 

Agree in principle.

That one in the snap is what we here call the Compact Adjustable Modulator.

The original on all my TH400 units was double the diameter, and nothing up the snout at all as far an adjuster.

 

Mine is a BW12 trans, but the new and old modulator have the screw to adjust shift. I thought it was normal.
Even the 1972 printed manual suggests adjusting a new modulator to make it shift the same as the old one.

 

Hi JT

Excellent!

But should I screw it in more or should I unscrew it?

What difference would I notice by screwing it in?

What difference would I notice by unscrewing it?

How many turns of the Screwdriver are required.

 

Hi Grant

OK Cheers!

 

Hi Clarke

Thanks, that is very interesting.

Perhaps I should tell 'Bro' Paul about this, as he is doing some stuff with the Transmission Oil.

 

You screw it clockwise to firm up the shifts and counter clock for opposite. I always run one up clockwise to "snug" then drive and if need be slacken a half turn at a time till I get what I want. AU must have gotten a different one, all the Jaguar ones I've seen are adjustable as well as every t/h 400/350 I've worked on/owned. Mine is the stock unit my XJS came with and its adjustable.

 

Hi JT

Many Thanks

When I get her off the ground, I will have a look and see if I have got the Adjustable type.