Repair or replace Cruise Control?

[D20T_73]

My '73 318 has, what i think, is an oem cruise control system.  I was looking at it the other day to see what it would take to get it up and running again.  My dad, who owned her back before i did, said that he replaced the magnets in the drive shaft (at least thats where i think they are). I don't know if i'll be able to get the old one working again but are there any good aftermarket units out there? These old engines are so basic that it shouldn't take much to retro fit one. Any ideas?

[ClydesdaleKevin]

Ours still doesn't work either on our 77.  It was factory installed but was made by "Perfect Circle."  I have the instruction and installation manual for it, as well as the troubleshooting guide, but haven't had time to completely troubleshoot it yet.

What I have done and discovered so far might help you:

First, I'm not sure what you mean by "magnets."  Yours may operated completely differently than ours, but our has an actual control box under the floor near the brake master cylinder.  The speedometer cable comes out of the transmission, into this control box, and then another speedo cable comes out of the control box and goes to the speedometer on your dash.  This box is the actual brains of the whole unit, and Perfect Circle calls it a Regulator.  This is how it picks up your speed signals from the vehicle.

The wiring works like this:  On your steering column, on the turn signal switch lever, is your "Engagement Switch."  This is where you turn the cruise control on or off, etc.  The wiring from this switch next goes to an inline fuse.  The next thing in line on this wiring harness is a relay under the dash.  After the relay, the wiring harness splits...a violet wire comes into the harness from a power source.  At this same junction, one wire goes off towards your brake light switch, with an inline fuse in the path before it gets to the switch, and another wire returns from the brake light switch.  From this junction, the whole harness goes down to the control box or Regulator.  Two more wires come out of the regulator and go to a Deceleration Switch, which is a mercury switch on the chassis.  That is it for the wiring...pretty simple.  So lets see if I can somehow type in a wiring diagram to make it more simple:

                          |-----------Violet Wire to Power Source
Regulator---------|
       |                  |----------Fuse--------Brake Light Switch----|
       |                  |-----------------------------------------------|
       |                  |
       |                  |----------Relay-------Fuse--------Engagement Switch
       |
       |------Deceleration Switch (two wires, too and from mercury switch)

Okay, that went well, so here is a diagram for your speedo cable routing:


Transmission---------------Regulator---------------------Speedometer


Alright...pretty simple so far.  Now for the vacuum system: 

You have a vacuum line that comes from a "Vacuum Source" that goes to the Regulator.  The manual says "For an adequate vacuum source, remove single outlet manifold fitting at rear of intake manifold that supplies the transmission modulator valve...install one of the dual fittings supplied in kit...Reconnect transmission line."  So the Perfect Circle cruise control unit relies entirely on intake manifold vacuum, so there isn't any kind of vacuum accumulator in the system like with some newer cruise control units.

Then you have a vacuum line that comes out of the Regulator and goes to the Servo Assembly.  That's it!  Just two directly attached vacuum lines.  The Servo Assembly is the big round can with a rubber diaphram that sits at the back of and on top of your engine, with a Throttle Linkage Assembly that goes directly to your carburator linkage.  Here is a diagram:


Regulator-----------Vacuum Source At Rear Of Manifold--------Transmission Modulator Valve
       |
       |
       |---------------Servo Assembly*********(Throttle Linkage bum.)********Carburator


So that's it in a nutshell! 

Check your fuses first.  Then check the relay.  If in doubt, bring the relay to an automotive shop and have them match it up with one they have and replace it.  Now check the mercury switch, also called the Deceleration Switch.  Is it still in one peice and not broken?  Unscrew/unbolt it carefully from its location once you find it, and hook up your voltmeter to it and check it for continuity.  Rock the switch back and forth...it should open and close the continuity as you move it back and forth.  If your switches are good, and your fuses are good, and the relay is good, then check to see if the Regulator is functioning properly. 

Chances are according to the manual that if your speedometer is working, then the Regulator is working, since it is mostly a system of gears, with very simple circuitry inside, just on/off transistors and whatnot.  If its the regulator that is bad, then your system is pretty much DOA unless you can find another one, either new or at a junkyard.

Check and/or replace your only two vacuum lines.  Again, chances are that if your transmission is shifting properly, then the vacuum line going from the splitter on the manifold to your transmission is good, which means the vacuum line going TO the Regulator is good.  Check the vacuum line going from the regulator to the Servo Assembly, and if that is good, you've isolated and cleared the vacuum system as a culprit.

Now check the Servo Assembly.  For this you'll need a decent vacuum source.  I tried testing mine by just sucking in on the vacuum line going to it, but couldn't generate enough vacuum.  I used my hand vacuum pump I bought for bleedling brakes and it showed my Servo Assembly as still good.  To test yours, disconnect the throttle linkage assembly from your carburator, disconnect the vacuum line going to the Servo Assembly, and then apply vacuum to the fitting on the Servo Assembly...the throttle linkage should move in and out as vacuum is applied and then released.  That's it for that!

The only thing left now is to make sure your Throttle Linkage Assembly is installed and adjusted correctly.  From the Manual:  "Step 10:  Attach servo linkage assembly to carburator throttle lever using the lever pin and cotter pin.  Step 11:  Feed bead chain and inner cover thru flared end of outer chain cover.  With carburator set at hot idle, pull bead chain tight between throttle linkage and servo clip.  Without moving the throttle linkage back off one (1) ball and then manually open throttle and attack chain to servo clip.  Squeeze clip tabs together to secure chain.  CAUTION:  Carburator must be in hot idle position (off the fast idle cam).  Step 12:  Slide outer chain cover against servo clip, push cotter pin thru hole, spread pin and press ends tightly against outer cover.  (Be sure bead chain assembly clears power brake line)."

Hope that helps!  I know just typing all this helped me with at least one thing I thought was good...the vacuum line on mine going from the Regulator to the Servo is messed up on mine.  When I first bought Excalibur the dash vacuum guage wasn't working, so I looked at the mess of disconnected vacuum lines in my engine compartment, and connected them together with T fittings...the dash guage now works, but I made the mistake of connecting the line going from the Servo into the rest of the vacuum lines, and ditto with the vacuum line going from the Regulator.  So now I know that I have to connect this directly to the regulator.  Don't know how I missed it before, but now I know!  I'll let you all know if it works on our next trip!

Hope this helps!

Kev

[D20T_73]

Thanks for all your help That should help me alot when i get into it a little more..i may even check it out this weekend. I have a good vaccum story for you...When i first brought the winne from my uncle's in texas she wasn't running quite right.  It idled fine but it would spit and backfire once it got warm.  Not haveing time to look at it (2 hours between getting off the train and hitting the road), i just left it alone.  We got home and i did a little work to it but once the winter came i just kinda let it go for a while.  I started thinkig about how it was running. I told my dad "I bet since it only spits when its warm that the vaccum advance on the distributer is stuck, since its so old". So the other day i went out to start her up and let her run i pulled off the doghouse to take a quick look...the guy that put the new carb on when my uncle owned it didn't even put the vaccum line that goes to the advance on a vaccum port! DUH!!!! So i reworked the vaccum lines a little bit and TADA!! she runs like a champ.  Its amazing how its the simple stuff...caused by morron people who claim to be mechanics.  Oh, and when they put a new air filter unit on the new carb they decided not to hook up the crankcase breather hose...so no filtration...not a good idea :/

[tiinytina]

Once upon a day I installed an after market cruise control into my Datsun 310GX. It did have a magnet type thing that I had to install on the front wheel drive shaft and a sensor that got located above it...
don't remember connecting anything to the spedometer... but then again I am blonde and the potential for senior moments seems to be growing exponentially some days....  Gone has cruise control and after a bit of jiggling found it works but I don't use it too often.
Tina

[D20T_73]

Yeah...really the only time I would use it would be on really long trips. We run about 230 miles down to missouri often and theres about a 3 hour stretch of constant speed...luckily the old 20 gallon fuel tank required a stop in between

[ClydesdaleKevin]

A lot of our trips are from 250 miles to 1200 miles on highways at constant speed.  I would LOVE if my cruise control worked!!!...lol!

Kev

[75Travco]

Couldn't get the old Perfect Circle unit to work, replaced it with an Audiovox Universal fit cruise control.  The new unit would not engage at first, contacted technical service and confirmed that the setup was OK, they suggested grounding the brake light sensing wire as the LED lights are not compatible with the control unit.  Worked great after that, now I need to figure out a permanent fix that will work with the LED tail lights.  Some of the motorcycle sites show a relay wired into the brake light circuit.

The new unit has a dash-mounted rocker switch.  The old turn signal stalk switch has the same type of electrical connector and same wiring convention, I might try using the old switch as it is much easier to operate than a rocker type switch.  The Audiovox has dip switch settings for both "open" and "closed" type switches, so it might work.

The old Perfect Circle parts are in the bottom of the garage trash can, don't know if they are functional.  Maybe if I had tried grounding the sensing wire?

[75Travco]

The old switch (turn signal stalk, part of the orginal "Perfect Circle" system) works fine with the new Audiovox CCS 100 universal cruise control system.  Just have to change the dip switch settings for a "closed" type control switch.  This is nice as the old switch is a lot easier to use than the dash-mounted rocker switch that came with the new unit. Same wiring convention, same 4-pin electrical connector.  Talk about backward compatible!  Or is that forward compatible?

Still have the old Perfect Circle control unit, wiring, and cables if anyone needs them.  They are in the garage trash can, so far nothing dirtier then sawdust has been thrown on top of the old parts.