1970s 1975 vacuum cruise control not engaging

[_Cap_]

I'm having an issue getting my cruise control to work on my 75 Eldorado
When I click to engage it through the turn signal button the green light (engagement/cruise light) turns on showing that the transducer is functional, however nothing happens.
I got a fully functional vacuum servo, and have re-built the transducer about 3 times. and I've clamped every vacuum line
I presume power is properly getting to the transducer because of the light indicator. The amber light also turns on properly when I turn on the system
Any help with this would be greatly appreciated, I've been stuck on this for months

[Roger Zimmermann]

I cannot help directly, but have a look at this booklet.

1968-1982_Cruisemaster_Cruise_Control.pdf

[bcroe]

I believe you have the mechanical version CC with
a pair of speedo cables.  These pot metal units do
not last long, and probably must be replaced. 

I believe in 77 Cad went to an electronic CC,
photo pickup built into the speedometer.
good luck, Bruce Roe

[TJ Hopland]

The light coming on does seem like electrically its working.  You have rebuilt the transducer 3 times?  Its always been the same transducer?   I'm not knocking your rebuild skills, getting a 'professional' rebuilt unit is also a crap shoot.  Do you think you truly understand the unit?   I didn't quite get it till I took one apart and then I was like thats pretty neat now simple it actually is but the materials its made out if are not the best and once they wear there really is no easy repairing them.

Are you wanting to keep this original or just want working cruise?  If you just want it to work get a Rostra universal unit.

 

[_Cap_]

I understand how the transducer operates, and have taken apart another worn out one to make sure everything was set up properly.
However I don't have the experience to tell if parts are worn out enough to effect the function of the transducer

I'm going to try to keep the cruise control as original as I can

I was thinking of sending it off to a professional, but with the price I'm hoping there's a simpler fix to it

[TJ Hopland]

Have you tried setting it when going very slow?  Does the engage light still come on?  I forget where but below like 15 mph its not supposed to engage.  If it does engage that slow or stopped that kinda implies its not moving like it should. 

Basically its like a speedometer.  The gears and that magnet disc thing stuck to the one gear constantly turn when the car is moving.  The other side has that copper looking disc thing that is positioned very close to the magnet one.  The copper disc has a shaft on it and that would be where the speedometer needle was attached if it was a speedometer.  So we have the speedometer shaft but instead of a needle its got a small arm on it and a rubber drum.  The small arm is what operates that low speed cutout switch.  When you engage the system the solenoid does double duty of opening the housing to vacuum and clamping the slide valve mechanism to the drum.

The slide valve should center itself when its not clamped to the drum.  In the center position its blocking both the vacuum bleed port and the servo port.  If the speed slows down / needle drops it slides the valve to open the servo port to the housing which is now under vacuum so it pulls the throttle which increases the speed.  If the speed speeds up / needle raises it slides the valve to bleed pressure out of the servo so lets the throttle go.  In theory unless your are going up and down a bunch of hills it should find an equilibrium where its mostly in the neutral position and only making slight tweaks to the vacuum in the servo. 

What has killed most of them for me is the 'bearing' that holds the copper disc drum shaft in the main housing and that little stub shaft pilot bearing thing that sets the spacing between the discs.  I say bearing in quotes because there is no bearing its just the casting.  It seems to get lose or that stub shaft gets worn and rattles the disc around and that wears the bearing.  Basically you see evidence that the discs are rubbing and this is also what can be causing your speedometer to bounce.

The foam air filter rots and get sucked into the unit and other places and clog up ports. 

When you put them together that little low speed lever can be in the wrong place and mangle that clamp and or the switch. 

I have seen the drums both become petrified so they don't grip the clamp and I have seen them turn to goo so they don't ever let go.

I have got 'rebuilt' ones where the servo port thing was so far out of adjustment it didn't work at all as well as the slide thing being so loose fitting maybe worn that it didn't even slightly seal. 

[_Cap_]

Ill have to open it up again and check the fittings of everything, and see if it will clamp the drum, because it could be slipping. Ive checked all of the vacuum ports in it and they all seem to be fully clear. It also could be the whole thing out of adjustment. it dopes cut off below 10 or 15 mph
But i do experience alot of bouncing in my speedometer at low speeds so i wonder if thats what may be causing it.
Ill pull it apart soon and check it, thank you for the advice!

[TJ Hopland]

Was there any signs of wear on the copper looking disc which is the the one that the drum is connected to?   There should not be any signs that it was contacting the magnet disc on the other side.

[The Tassie Devil(le)]

Isn't it supposed to cut off below 30 MPH?

Bruce.

[TJ Hopland]

I have seen different cut off speeds listed for different years and in different places.

[Richf1966]

Cap, can you please update what are you found with this problem.  Thanks

[TJ Hopland]

Rich, having a similar issue?   

Mine on my 73 got to the point where it would work maybe 1 out of 10 tries.  Was sort of staring at all my projects in the garage trying to decide which one not to do and saw a box on the shelf, turns out to be the Rostra aftermarket system I took off my 80 diesel.  I got to get the manual and see if there is some tuning I can do, its not as smooth on the EFI 500 as it was on my whipped Olds diesel.