other possable ways of "fixing" the problem without a lot of brain damage are to use the vacuum advance port for the distributor to also supply the trans. or get a vacuum canister like many of the GM and Ford cars use on thier cruise controll systems, these look something like a juice can with vacuum fittings on them, built into them is a one way valve to allow vacuum to be stored and allow enough to be there when it is needed,
you can probably get one at a local wrecker for next to nothing. that would save you the time and expense of modifying or changing the trans.

mate just put the SR in it! a lot more fun on the street and cause its an auto atleastyou wont have th cut the gear box tunnel just use a hammer problem solved

Dodge man u bring me hope!

Anyone know any auto specialists in syd aus preferably close to sutherland shire (south east syd)?
Pretty sure that any auto specialist will easily be able to manualise the valve body.

Its running only one carb (ie 2 cyl per throat)

Will look into the vaccume canister.

Thanks for this alternative info will have to wait till monday till i can ring an auto dude.

thanks again

uterous is this 4 sure about the tunnel (ie have u had 1st hand experiance with this?) Or have u just heard about this being the case. cause the tunel in my SR datto is alot bigger than the auto tunnel.

If it dont fit then it will be done properly no gentel persuasion with a hammer on my datto thanks.

Besides i would like to be able to seperate the gearbox from the engine in the car not like my current SR 1200

I rang a reputable auto place today and found out a few things.

1. The JATCO box is very comon in lots of cars from mazdas to nissans to holdens, even VL turbos run the jatco with an overdrive setup infront of the box but the first three gears are the same. So its a very strong box (proably unbreakable with an a12) there would be no problem running these boxes behind an a14 or a15.

2. Fully manualized valve bodies are purchaseable and they even reverse the order of the gears (ie instead of it being N D 2 1 it will be N 1 2 3(D) which is better for racing) But this is too expensive for me, I was quoted $1000 supplied and fitted so it looks like I will have to look into making more vaccume (with the canister thing first then if that dont help I will tap a thread and put a vaccume fitting into the other side of my manifold as well)

Cheers everyone so far.

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.

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)

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.

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?

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.