M body cruise control adjustments?

[R.W.Dale]

The cruise control in my 88 fifth Ave actually works except for one issue

In order to set it to the speed I want I have to be going nearly 10mph faster than I want to set the cruise at and then press the button at which point it will take over after the speed drops off 10mph and hold there just fine.

it’s pretty annoying. Any ideas?

 

[Mikes5thAve]

There's a screw on the cruise unit to adjust it. I don't know which way you should turn it but I'm sure someone else will chime in. There are directions on it in the service manual. Which can be gotten pretty cheap on eBay if you don't have one.

 

[Aspen500]

If the speed drops after setting, turn the adjusting screw counterclockwise. 1/4 turn is about 1 mph but don't go more than 2 turns in either direction.

 

[R.W.Dale]

This little Allen head?

 

[Mikes5thAve]

Yes.

 

[R.W.Dale]

Thanks for the replies guys. I backed it out half a turn and I’ll give it a try during my commute tomorrow and see if that helped


EDIT

1/2 turn out seemed like it cut my pull in speed from being 8-10 below my set speed to around 6ish. Definitely much more useable. I’ll give it another half turn and if it does the same thing I’ll be golden.

 

[Aspen500]

Sounds about right. 1/4 turn is ABOUT 1 mph. Just remember, don't go more than 2 full turns in either direction. Not sure what would happen but the service manual has a caution that it may damage the servo.

 

[R.W.Dale]

1.5 turns got the drop to be just under 5mph which is completely workable now. I might try the other half turn later but I see no reason to push my luck.

 

[Mikes5thAve]

That's assuming the screw wasn't already adjusted at some point before in the last 30+ years and you're not going beyond the two turns now.

 

[R.W.Dale]

Or it wasn’t ran in two turns hence the problem and I still have 2 turns to go.

who knows

that’s why I’ll stop here

 

[Aspen500]

Yep, no reason to tempt fate, right?

 

[BudW]

It has been my experience the cruise cable adjustment fixes most of issues, more than the set-screw does.

If engine idle speed is set (and engine is hot), check to see how much play is here:

The bracket should not be holding the throttle open, yet still have a smidge of play (0.010-0.015”). If there is more play than that, then adjust the cruise cable and retest (which, as far as I know, might have already been done).
BudW

 

[Aspen500]

The manual says with the lost motion link held against the throttle stud, there should be 1/16" of clearance between the front of the cable slot and the stud. I didn't think of the adjustment but now recall fixing quite a few speed control systems "back in the day" where the speed would drop after hitting "set" by adjusting the servo cable (mostly on Ford's since I was a Ford dealer tech back then). An advantage of drive by wire, the speed always sets exactly where you want it to be.

 

[69-]

This thread came in pretty handy at the weekend.

Adjusted the set-screw 1/2 turn and now she plays along well.

So - thanks guys.

 

[Milezero]

Yep, no reason to tempt fate, right?

Never tempt fate with pieces made from "Unobtainuim".