Diagnosing Speed Control

[Gary Lewis]

I'll slip an amplifier in the box with the servo.  If you have a good cable you should be able to make it work with some combo of those parts.  

[Gary Lewis]

Chris - This is going out today:

Servo: I can't test this one as I don't have a way to do so, but it does pull in with vacuum and doesn't appear to leak.  And you can see how the cable goes on, with the bullet on the end of the cable going into that clip in the middle.

Amplifier: I know this one works as it has the hole I drilled in the case, circled in red, in order to get to the potentiometer to adjust it.  That pot determines how close to the current speed the set point will be when you hit Set.  I have one that I've written on that says "Jumps 6 MPH", which means it works but is no fun. This one was adjusted to pick up ~1 MPH on Big Blue, but it may be different on your truck so you may want to adjust it.

Pickup: This one is from Dad's truck so I know it worked as I used it a bunch.  (Don't worry as I'm going with one of the tranny-mounted units when I build Dad's truck.)

Relay: I thought about not sending a relay, but having re-read this post where I tried a standard Bosch relay and found that the speed control didn't work I decided you might need this.  It is also from Dad's truck so I know it works.  But I couldn't find another one, although I should have one, so don't let it get away if you don't need it.

[ckuske]

Thank you Gary!  I'm looking forward to having some goodies when I come home from this work trip, although my wife and/or kids will ask "What truck parts did you order now?"

[Gary Lewis]

I'm hoping it'll be there when you get there, Chris.  Enjoy!

[ckuske]

So I have made some progress (which is good!)

I went to swap out the amplifier in the cab - and while under there, noticed there is nothing to actuate the vacuum dump valve!  I think it may be called a "brake pedal adapter" but can't find much yet in the parts catalog (I still have a hard time finding stuff there).  It looks like something was mounted to the pedal at one time but was broken off????

[Tarheel Blue]

Your assumption is correct. The pad that pushes the little white plunger is missing/ has been removed. I’ll send photos when my devices synch

[Gary Lewis]

Yep.  I may have an extra one of those, but you can at least get the thing working w/o it.  So maybe get a bit farther and see if there's anything else we missed and in the interim I'll see if I have one.

[ckuske]

Yep, agreed!  It was just a surprise to see it completely missing!  

The PO told me several things when I bought it back:

A/C didn't work... (worked when I sold it)
Cruise Control didn't work... (worked when I sold it)

I think he got amnesia about all the things that broke while he had it, or tried to fix...

[ckuske]

Well I hooked everything up, and did a road test.  It didn't hold speed, or accelerate. I'll start running more tests, hopefully tomorrow.

[Gary Lewis]

Make sure that vacuum line going to the valve on the brake pedal isn't open.  That's a dump valve and needs to be sealed for the system to work.

[ckuske]

The line is connected to the servo, and looks to be good all the way through the firewall to the dump valve in the cab.

But as a test, would capping the nipple for that hose at the servo work?

[Gary Lewis]

Yes, for a test you can cap it at the servo.  Just be aware that then the only way to turn it off is via the switches on the horn pad.  Or turn the key off.

[ckuske]

I capped the line that goes to the Vacuum Dump Valve at the servo and... Speed Control now works!!! .  On, Off, Set Accel and Coast all work - I didn't try Resume yet (it won't work without the dump valve working, anyway).

To determine if its the line or the dump valve itself, how would you guys go about testing it?  I was thinking to just pinch the line near the valve, and see if the line holds vacuum from the servo to where it is being pinched off.  Should I just buy a new valve as well since I'll be trying to put a new brake pedal adapter in too?

This one has been driving me crazy, I'm happy to have the end in sight.  Thank you again to Gary for the parts!

[Gary Lewis]

Yippee!!!  <smiley image="anim_claps.gif"/

As for testing the hose, I'd plug it inside the cab.  I wouldn't squeeze it for fear of cracking it since it is old.

I'm looking for another dump valve and the bracket for the pedal........

[Gary Lewis]

Found a dump valve, but I cannot find the bracket that goes on the brake pedal, officially known as ADAPTOR (SPEED CONTROL VACUUM VALVE ACTUATOR) and the one you need is PN E2TZ 9C962-B and has ID #'s of E0TA 9C962-AC or AD; E1TA 9C962-AA; or E2TA 9C962-DA.  I know I have the one that came off of Big Blue but cannot find it.

In the pic on the left you can see the right one in the middle, the black one.  And in the pic on the right you can see how it mounts.

I'll look more tomorrow and then if I find it I can send it along with the dump valve - if you need it.  Or you may be able to find the "adapter" online.  It is a very common part - that is good at hiding.  

[ckuske]

Hi Gary,

Thanks for the part numbers.  I did check the line - it didn't hold vacuum but of course after thinking about it and pulling the valve, the valve is supposed to hold vacuum when the button is pressed IN (which it seems to do).  

For some reason in my mind with the brake pedal I had the button being pressed in to release the vacuum, and not the other way around.  I think the valve I have is ok (it holds vacuum when the button is depressed).  Since I don't have the brake pedal adapter, the line is always "open" right now.

I am going to run a new line from the servo to the valve in the cab - the line was in good shape on the inside but I didn't like the way it looked/felt in the engine bay.  It seems to be 5/16" as well.

[Gary Lewis]

I think running a new line is a good idea.

As for the way the valve works, I was surprised how it worked as well until I thought about it.  So your valve is probably good, you just need the bracket.

I'll look again tomorrow, but if I can't find one and you don't find one online then you might consider gluing a piece of aluminum angle to the pedal.  I welded one on Big Blue's pedal since the hydroboost pedal is different and the old bracket wouldn't work.  So I know that approach works well.

[ckuske]

I've started looking on Google.  Not any hits yet, but I'll keep trying!

Maybe it'll be another part I end up getting 3D printed for myself and others?

[Gary Lewis]

That would be a good application of 3D printing. But you need one to measure.

Still, a piece of aluminum angle epoxied to the brake pedal would be easy. I can post a pic of what I did if it would help.

[ckuske]

Yes, agreed on the measuring.  I'd have to do some trial and error to get it right without a reference part, to be sure.

If you wouldn't mind posting a picture of what you came up with, I would appreciate it.