How well does the stock Cruise work?

[C10Silverado79]

I got the vacuum leaks resolved and my CC seems to be working now.... sort of. The CC does ok on flat but steadily loses speed on any kind of hill or rise. Is this typical of CC of this era or do I maybe have a vacuum leak in the CC. (possibly in the brake switch?)

[iroc12valve]

It Depends on a few things,
1 how well does the truck climb hills out of cruise,
2 how sharp of a hill, and
3 when its slowing down if you wait long enough does the tranny down shift

on the older truck 1995 and prior its not uncommon for the cc to vary 2-4 mph

[78 Big10 454]

I've never used the cruise control in the 32 years I've owned my truck. Pretty sure it wouldn't work, anyhow.

[rblcori7]

i use mine all the time on my 84 and if i go up a steep hill i will lose about 3mph but other then that it works great

[C10Silverado79]

I'm not dealing with steep hills at this point. Just some rolling humps on the interstate. It's dropping 10-15 MPH before I kick it off and pick the speed back up. Sounds like I have a problem to work on.

[tucsonjwt]

Not very well - in my experience. The cc in my 83 C20 never worked very well, consistently. Many "good" mechanics have worked on it and have never been able to find a problem - works well in the shop, on a dyno, etc., - get it out on the road - cuts out when A/C is on high, cuts out on upgrades, cuts out whenever it wants to....
I, and others, suspect vacuum leak somewhere - but have never been able to find it. On the other hand, it seems to work OK at higher speeds on the highway. I like to use it in town to keep within the speed limit and conserve gas on my 454. I am ordering a rebuilt servo as a last attempt to get it working (GM/Delco discontinued making new servos - last price I saw for a new one was $750.)
I think vacuum controlled systems are the worst idea ever in the automotive industry. Makes me want to buy a new truck again.

[Keith Seymore]

Mine works great; like you would expect it to.

Holds the speed within a mph or two on rolling hills and on the flat; drops off significantly if you are going up a steep grade (my truck is a stick shift, btw).

I use it all the time and it functions just like a more "modern" set up - if yours is dropping 10 - 15 mph then it sounds like something is wrong.

K

[78 Chevyrado]

I have the old 1978 style... I bought a new transducer from rockauto.com and it works great! it's usually within +/-3MPH of the set speed. I use it all the time.

when the cruise started acting funny on my 87, I took apart the big servo on the back of the engine for an inspection and I found nothing wrong so i reassembled it... then after that it worked great! musta been a seal needed cleaning or something, cuz i didnt fix anything.

[gchemist]

The problem is vacuum loss. Does it have the big ball? Is the check valve in-line working?

[C10Silverado79]

Originally Posted by gchemist

The problem is vacuum loss. Does it have the big ball? Is the check valve in-line working?

Sorry, I'm not sure what 'big ball' or check valve your referring to. i check the line and switch on the brake pedal with a Mighty Vac today and they are held a vacuum without leaking. I did the same for the diaphram that holds the throttle open the other day and it worked fine. I was out for a little bit today and it seems the CC will hold speed on a hill if it's set there but won't compensate at all if it's set on flat before the truck starts up the hill. I'm thinking the transducer may have problems. I haven't checked on a replacement yet but someone mentioned a new one costing $700 or so. It that's the case I'll either forget it or find an aftermarket electronic system. Or maybe I'll look for one to take apart and play with from the junk yard.

[gchemist]

The cruise system should have a big black vacuum ball under the hood. It should also have a check valve. The check valve prevents vacuum loss. You really don't need the ball reserve. A check valve is enough. You can buy inline small check valves.
I have an aftermarket cruise. It still uses the stock vacuum lines.

[C10Silverado79]

gchemist,
Your 83 had a newer CC design than I have. Here is what my transducer looks like. There is no ball or check valve in my system.

[gchemist]

First try to install the check valve. The valve will reduce loss of vacuum on hill acceleration. Install the check valve between the servo and "gear reducer/cruise" unit.

[joe231]

Since you guys brought it up....
can anybody tell me or show me how the newer style (early-mid '80's and up) vacuum lines are routed?
I need to hook up the cruise on my crew with the '89 vacuum and electronics

[C10Silverado79]

Originally Posted by gchemist

First try to install the check valve. The valve will reduce loss of vacuum on hill acceleration. Install the check valve between the servo and "gear reducer/cruise" unit.

I don't think that would be such a good idea. This system works entirely on vacuum except for the transducer. If I put a check valve in I'd never be able to disable the cruise once it was set.

[78 Chevyrado]

It'll still disable... theres a release under the dash that breaks the vaccum when you depress the brake pedal... there should be a vaccum hose going through the firewall to under the dash.... Usually the transducers go bad. its extremely common to that type of unit....

Check the servo... its the black round thing behind the air cleaner in your pic. it has a rod going to your linkage. pull a vaccum straight on it and see if it holds the vaccum. if not, its bad. if it does hold vaccum, check all the lines. if the lines are bad its the transducer. The transducer is about $90 at rock auto. I dont know where you'd get another servo though.

[gchemist]

The unit releases vacuum through the other line. The check valve is between the engine and unit. Not unit and vacuum release hose.