[Little]

Have a 1987 with 8v92, Williams throttle. Anyone know a place in AZ that knows about these? Throttle is  almost impossible to maintain in 1 position. Either 1000 rpm or 2200. Slow response and erratic at same time if that makes sense. Ideas?? Thanks in advance, Mark

[Fulltiming]

Does the pedal move smoothly with hand pressure or does it feel jerky? Sometimes the bottom hinge and spring unit can get some rust on them and affect smoothness.

[77newell]

The pedal controls the air pressure sent to the spring loaded air cylinder on the engine that moves the throttle lever on the governor.

There are three places things can go wrong; pedal movement not changing air pressure, the air cylinder not proportionately moving according to air pressue, or the governor not proportionally changing engine speed according to changes in throttle lever position. The first two are the most probable.

I would start by putting a pressure gauge in the air line to the cylinder, then watch the pressue as you move the pedal. If pressure changes appropriately, then I would watch the cylinder rod movement as pressure changes. These tests will make the part causing the problem show itself.

[Little]

Does the pedal move smoothly with hand pressure or does it feel jerky? Sometimes the bottom hinge and spring unit can get some rust on them and affect smoothness.

Pedal travel is easy, feels normal with 3-4 inches travel. I will get DW to run throttle while I watch travel at rear. Then put the gauge on both ends. Thanks.

[77newell]

You only need a gauge on whichever end is convenient

[MrE]

I'm having my Williams throttle replaced with the engine/transmission swap, the ZF transmission being installed has to talk to the throttle so the donor bus throttle is being used. My coach is in Missouri, PM me if you need parts.

[kyleb]

My '87 used the same actuator (at the engine) for the Bendix cruise control & the foot pedal. There were some check valves involved.

Any ways, when the cruise was on, it used a LOT of air, so much that the compressor was running more than it was off.
When using the foot pedal, I had to keep adding more pedal to get the motor to rev up. Once the motor started to rev, it continued to accelerate until I completely took my foot off the pedal. Quite aggravating to say the least!

The problem was the rear actuator. I replaced it with a WILLIAMS CONTROLS THROTTLE CONTROL CYLINDER that I got off Ebay. I made a custom mounting bracket & used a throttle cable (also from Ebay). I also modified the KING CRUISE throttle bracket to ensure everything works smoothly.

The results are that I now have predictable throttle response & cruise control that isn't an air hog.
I am very happy with the results.

[Little]

Sounds similar to whats happening here. We had a water leak today so didn't get any time to look at throttle issue. I may be pestering you in the future. Thanks for this, Mark

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I'm having my Williams throttle replaced with the engine/transmission swap, the ZF transmission being installed has to talk to the throttle so the donor bus throttle is being used. My coach is in Missouri, PM me if you need parts.

Will be in touch. Thanks

[superbirds]

On my 1975 the rear throttle valve linkage mover had leaks in the rubber seal. Sounds similar to your issue, I also had a continuous leak at the air manifold under the dash part for the parking brake. I found a couple new parts on EBay that fit. They were not both exact but worked great. I think I also bought a rebuild kit for the rear unit. Shortly before I found the new old stock unit. If you need the kit drop me a line I’ll try to find it. I read on a couple truck forums that a lot of truck shops used to keep these on the shelf. I think this in an older system that may not be true now.
Good luck on your project.

[Little]

So we have no air leaks, pressure seems ok but slow response. Take maybe 2 sec to open throttle and a full 3 to close. I pulled the return spring and will look for a replacement. Maybe the actuator at the drivers end may be restricted?? I will update when its figured out. Mark