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matts4290
Advanced Member

224 Posts

Posted - 04/26/2010 :  11:21:33 PM  Show Profile  Visit matts4290's Homepage  Reply with Quote
Hey all. I'm new to RE school buses, and I was wondering how the throttle linkage works on older buses. The only one I own and have been around is a 2002, which has an electronic throttle. Are the older ones air, or do they actually have a cable running that far?

78fordwayne
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USA
2868 Posts

Posted - 04/27/2010 :  10:56:02 AM  Show Profile  Visit 78fordwayne's Homepage  Send 78fordwayne an AOL message  Send 78fordwayne a Yahoo! Message  Reply with Quote
The older REs I have seen were all air throttles.

Robert B.

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Thomasbus24
Administrator

USA
4543 Posts

Posted - 05/12/2010 :  11:42:27 AM  Show Profile  Reply with Quote
More than you wanted to know about popular RE throttle controls, stated as to be clear as mud:

Williams Controls came out with the air throttle system in the 1950s but it didn't really catch on with the school bus world until around 1980.

Prior to 1980, many RE units did have mechanical long-link systems, which was just a cable from the pedal all the way back to the engine compartment. Thomas used the Morse Teleflex system which did the job, but let me tell you, when those linkages got worn, that bus became a real dog (see 1 minute 45 seconds to go from 0-55 on a straight, flat road---did that for years).

Another weakness was that the pedal linkage system would seize up after sitting for extended periods which made the first day back from summer break a real treat. Fast idle was accomplished by a locking cable device attached to the pedal itself.

Also, when an autoatic transmission was used, yet another cable was attached near the engine-end of the cable to run to the tranny to serve as a modulator.

In the 80s you'd find air systems that had two cylinders mounted at the engine. One served as the slave for the master (pedal up front) and was attached directly to the injector pump linkage, the other was for fast-idle. It would be charged with air via an electic solenoid upon switch activation by the driver, and would pull via a cable, the slave cylinder's linkage a predetermined distance to rev up the engine. Turning the switch off simply dumped the air to the thing

These systems were often VERY sensitive and took a while to get used to driving. A few complaints surfaced about speed control in heavy traffic, the best solution was to add a heavier spring to the pedal and the rear linkage!

90's models had one slave cylinder in back which had two inlet air lines. The cylinder's at-rest position was adjusted to keep the engine at fast idle, when one line had air applied to it (this happened when the bus air system reached around 70PSI, it would force the cylinder's linkage inward, reducing the engine speed to idle. This line was attached to a solenoid that upon activation by the driver would dump the air, thus putting the bus at fast idle when desired.

The other line was simply the feed from the pedal.

This system had one major downfall---cold starting a bus that had lost it's air, you instantly had an engine turning 1000-1300 RPMs! That's just not healthy boys and girls.

I've seen 3126 equipped Thomas ER's with air throttles also. Same setup as the other 90s units, except the rear cylinders were attached to an engine compartment mounted rheostat (just like the pedal would be on modern units). Seemed a bit overcomplicated for my taste.

Edited by - Thomasbus24 on 05/12/2010 11:44:30 AM
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bus724
Top Member

USA
1609 Posts

Posted - 05/12/2010 :  4:14:10 PM  Show Profile  Visit bus724's Homepage  Send bus724 an AOL message  Reply with Quote
quote:
Originally posted by Thomasbus24
[brThese systems were often VERY sensitive and took a while to get used to driving. A few complaints surfaced about speed control in heavy traffic, the best solution was to add a heavier spring to the pedal and the rear linkage!



I've heard it was even more fun in city transit buses with an air throttle and an un-synchronized manual transmission.
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matts4290
Advanced Member

224 Posts

Posted - 05/16/2010 :  09:02:57 AM  Show Profile  Visit matts4290's Homepage  Reply with Quote
Thanks for the replies. I was wondering. I kinda want to drive one with an air throttle now. I'm surprised that they used cable linkage. That would be a real long set up, and I would be concerned about it sticking that first day after summer!

We can't all be conventional!
http://www.youtube.com/user/matts4290
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