the the vacuum supply for the transmission vacuum modulator where does the supply come from do it come from the 3 port manifold on the firewall or does it come from the manifold underneath the carburetor if it comes from the manifold underneath the carburetor does it matter which one are any of them ported and last question does it need a ported supply for vacuum or not. 86 f150 300 6cyl auto

 

Line on the right side of the firewall vacuum splitter goes to the trans. Middle goes to the vac tree off the intake, so manifold vacuum. I feel like I read that manifold vacuum changes depending on maybe, engine RPM? And I assume that sends some kind of info the transmission via vacuum.

 

where does the left go and are they ported different...or does it make a differance

 

Left runs over,hits a t with a check valve, one goes the the actuator over the blower motor, and the other side goes to the vacuum reservoir. As far as I know there aren't any check valves, inside the 3 way connection on the firewall. I assume it's just a fancy t. I'll thumb through my book and see what it says. You having any particular issues or trying to figure out your vacuum routing?

 

just varifying the last piece of the puzzle and seeing if it made sence. I replaced a leaking vacuum module but when cold it had low vaccum issues for 2-3 shift. I remember on previous 81 truck a vacuum resivore so I made one and attached it here and solved the problem. I was just double checking to see if my 39 year old memory of my new 81 was correct...I got lucky...

 

I had a vacuum leak myself. Spent weeks studying the vac system. I'm like 80% clear on how it all goes together, but I do have documentation now.

 

Can you post a photo of your vacuum reservoir setup that you made?

 

You do not want a reservoir on the transmission vacuum line. Like someone mentioned, the trans monitors the load on the engine using that line, and that along with road speed decides what gear it should be in.

Low vacuum means you have the throttle open pretty good and the trans needs to hold on to the lower gears a little longer, and raise the pressure in the transmission.

High vacuum means the throttle is close to being closed, so you are just cruising down the road with no load. That tells the trans to go ahead and shift up the gears quicker, and no need for high pressure in the trans.

And like I mentioned, that is all juggled with the governor in the trans, which tells it the road speed.

 

this worked for or me even with new vacuum module when engine was cold I did have enough vacuum for 2-3 shiftI hook this up to passenger side of the fitting on fire wall and solved the problem...tomato juice can poke hole top (very small)and bottom to drain. Wash out solder 1/4 hose barb one side plug other side with solder. With juice way less than $5 and 1/2 hour

 

Very Nice, I was hoping you'd make it out of a juice can. The connection from my firewall splitter goes into a check valve then to the reservoir. Both the '82 and '85 are connected this way. So I assume that makes it so there isn't a reservoir hooked to the tranny, just the ac.

 

Do you guys know there is an adjustment for the shift points inside the modulator? You take the vacuum hose off and take a small flat screwdriver and insert it in the nipple and turn the adjustment for earlier or later shifts.

 

But that's just for replacement modulators isn't it? if I recall it was clockwise for earlier,firmer and counter clockwise for later,smoother shifts

 

I am not sure about the OEM modulators being adjustable. But he did say he replaced his modulator in a previous post, so I am safe on that part.

 

Kinda what I thought,that the OEM ones being non adjustable. I looked at the hose going into my modulator, and it is very mushy, so will replace that while I'm working on my ignition swap

 

Okay the whole problem if I change the timing up to about 23 deg before top dead center the transmission shifts fine I believe because it is getting more vacuum but at 23 degrees before top dead center it starts hard hard enough so I was breaking gears on the starter plus that is way too much timing I'm going to do damage to the engine if I try backing off on the timing down to say 16 degrees before top dead center it'll start fine but then the second to third gear shift especially when it's cold keep cycling back and forth until the engine warms up and it has to get all the way up to normal operating temperature so to me it sounded like I had a vacuum leak I did find a vacuum leak in the vacuum modular there was transmission fluid in the vacuum line which indicates a leak so I replace that. The shifting was a little bit better and I was able to bring the timing down a little but still not to 16 degrees so I figured I would add the juice can as a vacuum Reservoir so the transmission would see more vacuum so I could turn the timing down even more so far this is working. I now have the timing at 16 degrees before top dead center which is still higher the normal but I don't think I'll do damage to the engine, no pinging. I will see if the vacuum modular is adjustable.