Factory OEM Cruise Control

[stangeba]

Who has factory OEM style Cruise control in their 71 Monte Carlo?

When I set the speed the engine accelerates too much, then drops down too much then up too much again, over and over...

I added it to my 71 over 3 decades ago and did have some problems over the years.

I bought a backup, complete kit, and never tried it till today, but no luck.

I have repaired it in the past successfully but not today.

There is a air filter inside the unit but mine both fell apart like a dry old sponge so I need that also.

 

 

[stangeba]

[Scott S.]

The issue with the factory cruise control is that it's vacuum operated, not electrically or mechanically.

So not only will the filter have an effect, but any load on the engine will increase the vacuum, and it's harder to regulate vacuum than electricity. 

My '76 Silverado liked to take off up hills, but didn't want to slow down coming back down. 

[Rob Peters]

2 hours ago, Scott S. said:

So not only will the filter have an effect, but any load on the engine will increase the vacuum, and it's harder to regulate vacuum than electricity.

That is just the opposite of what I thought.  Not saying that is wrong but I am basing my thought on 2 things.  

One of those thoughts is my Model A Ford has a vacuum driven windshield wiper motor and the more load on the engine the less vacuum it produces.  When going up a hill or accelerating there is almost no vacuum produced and if it is raining and the wiper is turned on I have to let off the gas so the wiper arm can wipe.

The other reason I felt a load reduces the vacuum is the more things you add that causes a load has people adding a vacuum pump or a vacuum storage canister for extra vacuum.

Again,  I may be using reversed thinking.

rob

 

[Dtret]

1 hour ago, Rob Peters said:

That is just the opposite of what I thought.  Not saying that is wrong but I am basing my thought on 2 things.  

One of those thoughts is my Model A Ford has a vacuum driven windshield wiper motor and the more load on the engine the less vacuum it produces.  When going up a hill or accelerating there is almost no vacuum produced and if it is raining and the wiper is turned on I have to let off the gas so the wiper arm can wipe.

The other reason I felt a load reduces the vacuum is the more things you add that causes a load has people adding a vacuum pump or a vacuum storage canister for extra vacuum.

Again,  I may be using reversed thinking.

rob

 

I agree. WOT =  zero to little vacuum but I’m not an engine builder either. 

[stangeba]

I believe the problem may be with a moving part in the unit is sticking. I have in the past taken it apart and just cleaned the moving parts and perhaps added a bit of lube and the problem was gone for several years. I have been running without a filter (did you see the picture of that thing) and that may have added to the ? sticky movement of the area where vacuum is allowed to the diaphragm that controls the cable to the carb linkage. 

I just need to take it apart further and clean the moving parts. I watched two Facebook videos about this unit, that are helpful.

Time to take it apart again!!!!

I have had cruise control on every vehicle since my 1976 Ford Thunderbird, I miss it!!

Thanks everyone.

[420ponies]

On 5/27/2025 at 7:48 PM, stangeba said:

Is it possible you could use a shop vac defuser? Kinda looks like that filter. 

[Scott S.]

20 hours ago, Rob Peters said:

That is just the opposite of what I thought.  Not saying that is wrong but I am basing my thought on 2 things.  

One of those thoughts is my Model A Ford has a vacuum driven windshield wiper motor and the more load on the engine the less vacuum it produces.  When going up a hill or accelerating there is almost no vacuum produced and if it is raining and the wiper is turned on I have to let off the gas so the wiper arm can wipe.

The other reason I felt a load reduces the vacuum is the more things you add that causes a load has people adding a vacuum pump or a vacuum storage canister for extra vacuum.

Again,  I may be using reversed thinking.

rob

 

Which vacuum port you use can have an effect to.....

Years ago the second ex and I went camping with her friends, they had a "Blue Oval" mini van.

Every time we started up a hill, the van would take off like a rocket..... So much so that she hit the brakes every time.

But when we started downhill, the van wouldn't accelerate. It just coasted at what she'd set the cruise to. 

[Scott S.]

20 hours ago, Rob Peters said:

That is just the opposite of what I thought.  Not saying that is wrong but I am basing my thought on 2 things.  

One of those thoughts is my Model A Ford has a vacuum driven windshield wiper motor and the more load on the engine the less vacuum it produces.  When going up a hill or accelerating there is almost no vacuum produced and if it is raining and the wiper is turned on I have to let off the gas so the wiper arm can wipe.

The other reason I felt a load reduces the vacuum is the more things you add that causes a load has people adding a vacuum pump or a vacuum storage canister for extra vacuum.

Again,  I may be using reversed thinking.

rob

 

The cam you're using will also influence vacuum, turbos too.

My '86 T-Type's brake system was run off an independent vacuum pump. 

 Olds Vista Cruisers of that time also used the pump, as well as taxi cab versions of the Caprice. 

Something to do with the low RPMs/stop and go driving. 

[stangeba]

My 71 is all stock, runs great and only has 168,152 miles on it, so it's like new!! 🤣

I have had cruise control for many years (30+) and it always has returned to working fine after I tore it apart, cleaned up the inside parts and put it back together.

This time I didn't take it apart fully so I will work on it again and clean everything this time.

It has been missing the "Air Filter" since I repaired / cleaned it several years ago. I thought the particles of the filter got sucked in and caused the last surges but it did it even without any filter now also.

Thanks for the input!!!