There is a guy in vic called Phill Soderstrum.
He is the power glide king of australia. He can manualise any valve body you want. But if you manualise the valve body you will get harsh shifts. You will have to ring TCE there a torque convertor company & ask them how to get on to him. 03 9879 8455. they send converetors all over australia so a valve body wont be a drama. You DONT have to pull the auto out to do the job but to do it properly you should reco the trans aswell. I think you will get more out of a manual gear box & more fun and cheaper. But theres nothing wrong with being differant. good luck if you have any dramas PM me
P.S I think phills a bit of a grump as he probably should be retired but drag racers wont let him. He is the best in the buisness.

How do I identify my box? where are the markings/ numbers?

I don't have a factory 1200 manual, & the aftermarket ones i have don't cover the autos. There was a Jatco trans in the '69 & '70 Datsun 1000's, but my factory manuals are for '67 models. I have another B10 manual coming, so perhaps this one will cover it.

The only comprehensive coverage i have is in my factory 120Y manual & it is a VERY good book to have, particularly if this is the same model of trans.

I got a factory manual chassi, body and an engine one but it covers only the 3 and 4 speed manuals (never knew there was a 3 speed manual) will go to the book store tomorow to see if a seperate auto book is available, thanks dodgeman

and thanks for the restriction tip on the vacuum hose.

Draw vacuum from both runners if you can. To stop the fluctuations in the guage, simply squeeze the line to restrict the flow of air. Use a fishtank air line clamp if you have one. Squeeze the line just enough to dampen out the pulses so that the guage reads smoothly.

It sounds like the adjustable unit is the way to go, but i highly recomend that you buy a factory manual & have a good read up on the parts that tell you what you should expect from this trans. It will also tell you how to fit the modulator.
Like I keep on saying, the manual should be the FIRST piece of performance equipment that one should get. It saves so much angst & grief.

Just hooked up a boost guage (also measures vacuum) to my manifold and at idol after the car has warmed up the vacuume fluxuates rapidly between 30 and 50 cm Hg I didnt get a chance to drive it with the guage hooked up (didnt have a long enough hose, will do it tomorow) but maybe because the way the vacuume is taken from the manifold (alternating throats) the signal is fluxuating too much for the modulator to pick up, Just a thought.

The manifold is the cross over type I think

The first throat supplys 1 and 4 cylenders

The 2nd trroat supplys 2 and 3 cylenders


I just rang the auto place that I rang earlier and an adjustable modulator is available $77 AUS, looks like this is the way to go (cheepest and easiest)

This shouldnt be too hard to fit should it?

Well it looks like you are trying to do the right thing with the carby. 1 carb & moderately sized internals should make the engine run well enough.

What sort of manifold is it? If it is the crossover type where 1 side of the carb feeds two cylinders only, then drawing vacuum from both sides would be a good thing. If it is of conventional design where one carb feeds all four cylinders [like the original did] then only one vacuum source would be needed.

About the only other thing that i can think of is to ensure that the engine is in a top state of tune. The more eficiently it runs, the more vacuum it makes.

I think that the modulator is a sealed unit. You may be able to get it apart, but i don't know about puting it back together.
If you have a spare modulator unit, then give it a go, but don't hack up your good one just yet.

Lucky i didnt get the canister then (was looking for 1 today)

Already running only 28mm ventiris 40mm throats and thats pretty small and only 1 carb dellerto DHLA 40 on stock a12 block and head with tuned headers.

So does this mean if i take vacuume from all 4 cylenders it proably wont make a differance?

Does the modulator have a diafram with a spring inside?
Could i just pull it apart and put a weaker spring in ? (so less vaccume is needed to give the same effect)

Quote:The vacuum signal available at the distributor vacuum port will not be any stronger than at any other point in the manifold, so this will not offer any advantage.
Using a vacuum storage tank will also help to confuse the trans as vacuum storage tanks normally use a one way valve to prevent the manifold gasses from entering the tank & lowering the vacuum value at higher throttle settings.
What this means is that when you floor it going up a hill, the engine works harder, but the vacuum modulator sees a high vacuum signal from the tank & hangs onto the higher gear for longer.

The vacuum modulator works like a TPS [throttle position sensor] or looked at another way, it acts as an engine load detector. This signal, combined with the rotational speed of the govornor produces a line pressure that controls the shift point.

With low vacuum [high load] the govornor needs to send a high pressure signal before it will upshift This means it needs a higher rotational speed at the output shaft of the gearbox. As you reach the top of the hill [or whatever] & the throttle setting it reduced, the vacuum signal increases & the upshift pressure requirement is reduced, so it upshifts.

A vacuum tank will screw this up even more than it is now. My suggestion is to do some research on your carb. If it is possible to use a slightly smaller venturi, then give it a try. The simple fact is that in its present state of tune, for street use, with this trans, the engine is over-carbureted.