Distributor Vacuum Advance

[ARCHINSTL]

AbusedJalopy - it looks like all of your posts were in February of this year, so I don't know if you are still looking - but THANKS for the color-coded vacuum diagram. That has really been a help.

3AC Vacuum Advance: I get a vacuum to hold on the bottom subdiaphragm and can feel the advance lever move, but the upper two pipes will not hold a vacuum at all, nor can I feel the lever move. Granted, I forgot to check this when the cap was off, but I figured I could feel it as well. Are they supposed to hold a vac? The FSM seems ambiguous on this (at least to me), and just says "check that the advance moves". This is quite a big-buck part, even from AZ or Advance, let alone a Toy dealer, and I wonder if it is vital to at least a partial solution to the dreaded hesitation?
Thanks,
Tom M.

[takza]

There is a specific method to test those...think you have to hold one closed while testing another.

[xirdneh]

3AC Vacuum Advance:

i bought a new vacuum advance at shucks for 96.00
the toyota dealer wants 150.00

[MootsMan]

I just had mine replaced. I didnt' feel competent enough to handle getting everything back correctly and get the timing set right, so I had a mechanic do it. He had to get the part from the dealer, and it was around the $150. I'm glad this guy only charges $25 an hour for his time !!

[2wagons]

Xirdneh, Mootsman, did you get the vac advance with three ports? My upper stage also will not hold vacuum even with the other port plugged off. I think the upper stage is for altitude adjustment where the timing is moved according to altitude. I just plugged both lines and my idle seems to have stabilized a bit. I’ll let you know if it affects performance or gas mileage.

[ARCHINSTL]

Interesting - -
I had not considered doing what 2wagons suggests.
One of the two top pipes does go to the HAC thing, and the other goes directly to the manifold port and nowhere else. So I guess these two guys must play against each other at times to micro-adjust the timing advance, depending on the manifold vacuum, and the "real/macro" advance is the bottom pipe which is hooked up to the TVSV and a number of other gizmos?
The way someone had it hooked up before had the bottom advance being controlled by the HAC which must not have given the proper amount of vacuum? St. Louis is not exactly a "high altitude" market - how about you guys in the Rockies, etc. - anyone have the HAC disconnected from the distributor?
I will try this tomorrow when the rain stops (no garage, alas).
Thanks.
Tom M.

[xirdneh]

Xirdneh, Mootsman, did you get the vac advance with three ports?

Mine have the three ports
I hook up the bottom one
And the top inboard one
It has a larger hole
The other top port has a small hole and I believe it is for the high altitude thing
Being at sea level I do not use it (plugged)

[xirdneh]

Xirdneh, Mootsman, did you get the vac advance with three ports? My upper stage also will not hold vacuum even with the

to whom it may concern
Removing the distributor to replace the vacuum advance
And getting it back together with the correct timing
Is not difficult if you take a few prep steps

Remove distributor cap

!!!!Manually!!!! with a ¾ or 19 mm socket (depending on model year)
Rotate crankshaft to get the number one cylinder to the top of its compression stroke
The crank pulley timing mark will be at zero degrees (degree mark on plastic shroud) (about 1 o’clock position)
The distributor rotor should be pointing nearly northwest (looking straight at distributor from drivers side)
It will actually be slightly below northwest
If it is pointing southeast you will have to rotate the crank pulley one complete revolution

I place a small piece of masking tape on the distributor to mark the rotor location

Remove distributor

Do not rotate engine crank until after distributor is reinstalled

When reinstalling you can shove the distributor in and out until the rotor lines up in that northwest position

If for some reason the crankshaft was rotated while you had the distributor out
You will have to get the number one piston back to the top of its compression stroke
Unfortunately you will not be able to tell very easily when this is so.
When the crank pulley timing mark is lined up at zero degrees the number one or number four piston
could be at the top of its compression stroke
I only know of two ways to determine which one is which

One method is to pull the valve cover and check the valve rockers
When the number one piston is at the top of its compression stroke the first two cam lobes will be pointing downward and the first two rockers will be loose
If one is tight rotate the crank one complete revolution and recheck

The other method is to remove the number one spark plug and plug the hole with toilet paper
When you !!manually!! rotate the crankshaft the compression will push the toilet paper out
You could also plug the hole with your finger while someone else rotates the crank
You will feel the air pushing your finger out

When you have it all back together check to see if you removed the tool that you used to rotate the crankshaft. Starting the engine with that tool down there may rip the bottom of your radiator apart.

My Tercel vacuum advances have the three ports
I hook up the bottom one
And the top inboard one
It has a larger hole
The other top port has a small hole and I believe it is for the high altitude thing
Being at sea level I do not use it (plugged)