Some questions about 85-95 cruise control not covered in the FAQ:

1. Anybody know how to test the vacuum pump operation on the '85 to '89 cruise control? ( See diagram at http://mikechaseleadership/Curise.jpg )

From the diagram it looks like current is applied to post #3 on vacuum pump through the cruise control switch (is that correct?). Which post is ground applied to on the vacuum pump (#1 or #2?)? And why is there a third post?

2. How many inches of vacuum should the pump be able to pull?

3. Anybody know if the orientation of the Control Unit is critical? If yes, it is to be horizontal or vertical?

4. The Control Unit is grounded through pin #8. What is the signal that is applied to #3 on the Control Unit from the air valve switch and brake switch? Seems like it may be ground too (and if air valve or brake open the curcuit then there is no ground?) Is that right?

Mike

http://mikechaseleadership/Cruise.jpg

As Rob said, there is no vacuum pump in the system. I installed a Volvo cruise control into my 1988 244 two years ago, works fine. I had the Volvo installation instructions for the job, without which I would have been DItW.

Vacuum is supplied from the intake manifold to two units mounted on the firewall in the engine bay. The unit from which a long hose goes into the cabin is the servo, the other is a vacuum reservoir. I installed no check valve in the vacuum supply line; it went to an additonal brass nipple I installed in a previously plugged hole in the I-manifold.

Are you perhaps considering one of those units to be a vacuum pump?

The instructions do not explain what part does what function. By following the vacuum diagram and wiring connections one can get some idea of what does what.

I know that some portion of the control unit gets its ground through the brake lights, so that closing the brake light switch drops the ground and CC shuts off. The vacuum switch on the brake (and clutch, if equipped) is another route to dropping out of cruise control quickly when circumstances seem to warrant that.

The control unit, when installed per instructins, is sort of flat, above the steering column and clamped to it. I can't imagine that another orientation would make any difference.

Hope this is helpful. Are you installing, troubleshooting?

Good Luck,

Bob

:>)

Bob & rhaire,

Thanks for the help. I think I am getting on the right track now.

I'm trouble shooting and was working from a diagram in the Haynes. Now I see that it doesn't correspond to my '88. I just checked the Bentley and got a different diagram for 1986 to 1989. I put up both diagrams on http://mikechaseleadership.com/Cruise.htm.

That two-part vacuum servo valve housing above and behind the engine head has three wires running to it. I assumed that it created vacuum because it had three wires running to it (motor or something). A short vacuum hose was missing when I got the car. I did put in a T so that there would be vacuum continuity between the nipple that says "Vacuum" on the smaller black canister (has three wires running to it from the control unit) and the nipple on the larger cannister (which seems to just be a small plastic air tank) and the intake manifold. Did you put the check valve in that long hose running from the two-part vacuum serve vale housing and intake manifold?

If yours is working, how many inches of vacuum do you have (indirect way of asking how much vacuum is needed)?

I can hear air being released when I step on the brake. Does this mean that the vacuum line is holding vacuum and that my hose system has continuity (no leaks)?

Mike

at the vacuum hose diagram for the engine bay components....

Vacuum source shows to be a Tee fitting spliced into the line that feeds the cabin air vent directors. The splice comes after the existng check valve.

From that point, the hose goes to the 2-unit area, and goes into another Tee.

From the tee, one line goes to the round-end vacuum reservoir, to the only nipple it has. The other line goes to the valve housing to a nipple marked "vacuum".

The valve housing has another nipple, marked "Servo" and the hose from it is the long one that goes into the cabin and connects up under the dash.


You asked how much vacuum is needed? That I never questioned. I just figured the system would work OK on the vacuum created by the engine. It works fine.

Hearing air released when you step on the brake pedal may mean nothing. I don't notice it, but my hearing isn't youthful anymore. There may be a sound like that from the brake booster, too.

If the cruise control works, then everything is OK. Otherwise, otherwise.

I use the CC pretty much every chance I get. Easier on the feet.

Good Luck,

Bob

:>)

There is no vacuum pump used on 86-89 cruise for 240s.