Gizmo2

Hello,
I'm a new truck owner. I inherited my grandfather's 1977 F150 Ranger. The engine is a 351M. It has a motocraft 2150 carburetor. The truck runs good when in drive. However, when the truck is in park or neutral it sounds like I've got the gas pedal on the floor. When the truck is in gear the engine sound great. I have a few questions. #1 Is this issue only a carbutor issue? And suggestions for how to correct the issue?
#2 What is the part in my picture? And could it be contributing to the issue?
#3 Does anyone know of any good parts distributors for this era truck?
Thanks

ilovefords31

That kind of looks like a servo for cruise control. Does the truck have cruise? If that is for cruise, it could be stuck and holding the throttle open too far so it is not going back to its intended curb idle speed.

Gizmo2

Thanks for the response! The truck does have cruise control but it has never worked. Do you know if it will effect anything else if I disconnect the Servo chain from the Carburetor? Also, is their a way to test the Servo to see if it works or test the controls on the steering wheel?

ilovefords31

Being such an old truck, I would say that testing should be pretty straight forward. I would try pulling the chain it should move freely. If it does not, then the servo is probably in need of replacement. You could test the switch in the truck with an ohmmeter the specs should be somewhere online. Check for blown fuses. I really don't know much of how the cruise worked back then, but I believe the chain was used to set the cruise, and then vacuum from the engine was what kept the speed. When the vacuum changed from speed dropping, it would suck the diaphragm and the chain would pull the throttle open to speed up. So disconnecting the chain would cause no significant problems, but if you disconnect the vacuum line to the governor, then you will need to cap it off to prevent a vacuum leak. I could be wrong in the lingo, because I have not seen older cruise in a while, but a Haynes manual will give you all the info you need if you want to get it working again. It is a nice feature to have and probably is not a feature on many of the 70's trucks. Back then when it came to getting cruise as an option, Ford was priced much higher than any of the auto companies. So many did not take it as an option. Hope this helps.

Gizmo2

I disconnected the chain from the Servo cruise control to see if their would be any changes in the idle. Their is a very noticeable difference with the chain disconnected. The arm of the Servo that pulls the chain seems to move freely, so that doesn't seem to be the issue. I'm wondering if something is causing the Vacuum to pull the arm. Any ideas for what might cause this?

I've looked around and haven't found much information on these servo cruise controls from this era. My grandmother gave me the original bill of sale from 1977 and it looks like this truck has almost every option available. I'm happy I have all these options but it sucks finding parts for stuff like this.

ilovefords31

Gizmo, could you give some more pics of the system? I would like to see where the chain hooks up on both the servo, and the carb, and also look around the servo for anything that looks like an adjuster. It could be that the chain is too tight or too loose. Also the noticeable difference, is it engine idles higher, or lower? Being it has all these options, and the year of the truck, I wanted to tell you that I stumbled upon a Ford Service Manual for the 70's trucks. I haven't looked at it recently so I cant remember what it covers, but I believe it covers main things like engine, transmission and stuff. So I will look at it and if it could be of help to you I will send it to you.

Gizmo2

Here's a few extra pictures of the servo cruise control. As far as I can tell their are no adjustable parts of the servo externally. I have not attempted to take it apart as of yet to inspect the internal parts. With the chain connected, the truck idles very high. I would definitely be interested in checking out that manual if it has any information on the servo. Thanks!

ilovefords31

Hello again Gizmo. I know its been a while and if you have already figured this out, I apologize for not getting back sooner. The chain connected to the servo is what pulls the throttle when the cruise is engaged. So I would say the servo is probably bad if cruise is not working and if all other things have checked out. Fuses, switches, etc.