CRUISE CONTROL PROBLEM 1978 CADILLAC

[joecaristo]

It seems like its always the controller. ( The little red box ) I had a 77 Eldorado and the cruise never worked right. It would engage and then slow up and speed up. I put in a controller from a junk car and then it worked perfectly.  That was about 10 years ago. I also had a 78 where the controller went bad. Good luck.
Joe

[R Schroeder]

Joe, it is possible. I need to run a couple of more checks on the system.
Do you still have the Caddy you were parting out ?
Do you know if the cruise was working on that one ?
If so I might contact you.
Roy

[joecaristo]

Hi Roy,
The car did not have cruise.
Sorry,
Joe

[R Schroeder]

OK. Thanks

[TJ Hopland]

Is that module a 'potted' device?  Potted means that after they made it they filled the case with something like epoxy.  If its not I would imagine that it has few if any IC's (chips) on it so you could get lucky and repair it.  If its potted or had IC's on it it would likely be very difficult to repair.

[R Schroeder]

TJ - I got it working. Well almost.
I think the 3 wire plug coming down from the dash might have had a bad connection , at the controller.
I was checking for power on it this morning. Took it off and cleaned it, and it started working.
The problem I have now is that it will engage , but it drops 5 mph ,then holds steady.
There is an adjustment on the power solenoid, but I turned it both ways and it doesn't make a difference. Might need a new power solenoid. Still drops 5 mph once it is engaged turning it either way.
To answer your question about the board , it is inside a plastic holder, but it isn't sealed.
Seems you were right about bad connections.
Roy

If anyone has a solenoid for this cruise email me. Looking for new. Just missed one on Ebay.
Pt number 25031699  Group 3.885

rschroeder100@wi.rr.com

[TJ Hopland]

The power solenoid I presume is the one that adds vacuum?   

I have something that does that 5mph drop thing.  Thinking it may be my 73.

[R Schroeder]

The power solenoid controls the vacuum on the servo. It is the smaller of the two solenoids. The large solenoid just opens the vacuum line to the servo , and the power solenoid. It has a small screw on the top for adjustment of the set in speed. I turned the screw both ways on mine and it made no difference. Could be dirt in it from 34 years of sitting around.................ha
I don't think the 73 is the same as the 78 though.
Here is a picture of the power solenoid on my car. I just missed this one on Ebay. The screw in the picture is the mounting screw, not the adjusting screw.
Roy

[TJ Hopland]

That looks like what was on my 80.   Ya the 73 has that inline unit in the speedo cable and I believe that has the speed sensor and solenoids all in one unit.   

[R Schroeder]

It could be the same as mine on the 80, but if its diesel, I believe the parts book says its part of the servo.
This is a picture of the control solenoid on mine. It just opens the vacuum line to the servo and the power solenoid.
Roy