Installing a throttle cable in an MCI MC series bus

bevans6 · October 23, 2011, 06:02:46 AM

This is kind of for posterity, for the next guy that tries to find out how to do this. I installed a new throttle cable in my 1980 MC-5C yesterday, after struggling for some time with it, so here is the story.

The stock throttle cable is a Morse cable, and runs about dead straight front to back in the duct chase that all the plumbing runs in down the center of the bus. I could not find a stock replacement cable, so I pulled the old one out, pulling a pull-cord behind it, and sent it off to a control cable place to have it duplicated. I got the cable back and noticed immediately that the swaged on ends were larger than the ends on the stock cable. Maybe it won't matter, sez I. Yes, it matters.

The cable runs through a series of supports, which are grommeted holes in flanges or bulkheads that run across the duct. The holes are about .6" in diameter. The stock cable is about .510" in diameter at the swaged end, and can be pulled through. Anything larger cannot. The tightest part is at the heater core bay, where there is a section of tube that the cable runs through, and the entrance to that little bit of tube is a tight pull fit over the swaged end. Your replacement cable MUST have no larger than .51" diameter or it won't go through.

Next thing is pulling through. In my case I had removed my original cable to have a new one made to match. I tried to pull the new one, with the larger .65" ends, and it hung up about three feet in. I could tell that it was hanging up on the ends by the scuff marks. I tried pulling the original cable back in as a test, which is when I found the thing about the tight tube entrance in the heater bay. I had a few wraps of tape over the swaged end to hold the pull cord tight, and the wraps of tape and the pull cord were enough to hang up the cable and jam it. I had to pull it back out, take that tape off, trim the pull cord, lube the heck out of it and try again. Even then it was a tight pull past that bulkhead.

After I got the original cable back in and found that tight spot in the heater bay, I ground and filed the swaged end on the new cable to .5" diameter from it's original .65" diameter. I made up a coupling bolt and bolted the new cable to the end of the old cable, taped up the sharp transitions, lubed it up and pulled it through. Again quite hard to get the ends past that tight spot, but this is really the best way to do it.

So there you go. If you are having a new throttle cable made for your MCI, specify that the swaged ends and the cable itself can be .5" diameter, no larger. If you are pulling an air line through for an air throttle, same deal - pull it through but no larger than .5" OD. And if you ever pull the throttle cable out for any reason, pull a strong pull-cord through behind it - you could spend a month of Sunday's trying to fish a line through the twenty odd support bulkheads that it has to run through!

Hope this helps someone sometime! Pretty mundane, run of the mill, PITA project otherwise...

Brian

Van · October 23, 2011, 08:36:19 AM

Brian thanks for the post. For us non fly by wire folks, what did the cable set you back?

Thanks!
Van

TomC · October 23, 2011, 08:41:27 AM

I know a cable is direct, but I sure like my air throttle-nice, lite foot pressure. Would have been just as easy to run a 1/2" air hose. Good Luck, TomC

bevans6 · October 23, 2011, 10:16:40 AM

Tom, you as well as everyone else advised me to not use an air throttle with a spicer 4 speed. The word was that the delay in the throttle response made synchronizing the engine speed while shifting problematic. In the end, it's not an irreversible decision and it's only money...

One thing I might investigate is differences in throttle response with a 1/2" air line compared to what is probably the standard 3/8" line. But if I do it again it will probably be a true drive-by-wire electronic throttle, they have to be available but I never bothered to look.

The cable was around $300 and took about three days to get made. My race shop buddy got it done for me.

Brian

usbusin · October 23, 2011, 08:08:07 PM

I had an air throttle on my 4104 with a four-speed manual. No problem shifting up or down. After 150,000 miles I'd do it again. Like TomC says; sure is nice on the right leg!

eagle19952 · October 23, 2011, 08:15:27 PM

I do not own an MCI but it might help some to know HOW the new cable was specified,ie: total length,total throw/slide,thread dimension,etc.
this might help get the right cabe for this model.
Just a thought.
Glad you solved your problem.

RJ · October 23, 2011, 08:27:45 PM

Brian -

FYI, I've driven stick/air throttle and stick/cable all during my professional charter career.

The air throttle is much less fatiguing to drive.

The cable throttle is much more precise, thus easier to modulate while shifting.

Shifting with an air throttle just takes a little more practice, pile on the miles, it becomes second nature.

The real challenge is a wet-clutch, stick shift, air throttle GMC 4905 Buffalo!

"Stomp & Steer" automatic-only drivers whine forever when forced to drive one. . .

Glad you're project went well, you'll be pleased with the results after you spend some time on the road.

FWIW & HTH. . .

bevans6 · October 24, 2011, 05:18:58 AM

Eagle19952, the new cable was specified by shipping the old cable to the cable shop. I thought that was the easiest way to go about it.

Brian

longjohn · October 24, 2011, 05:58:21 AM

Brian,
Thanks for the detailed report, I filed it in my folder. The time you take to explain has helped me to visualize what the job entails. So when i find the"coach" and it turns out to be an MCI...............ahhh

eagle19952 · October 24, 2011, 11:08:08 AM

Quote from: bevans6 on October 24, 2011, 05:18:58 AM
Eagle19952, the new cable was specified by shipping the old cable to the cable shop. I thought that was the easiest way to go about it.

Brian

just thought it might help if you measured the old one..and made that info available.

bevans6 · October 24, 2011, 11:38:17 AM

Well you know, you are right!

I didn't do that, but I still have the old cable intact (mostly, cut off one end) so I went out and measured.

This is for a 35 ft bus, MC-5c. The outer is 32' long, and the inner is 13" longer than that so 33' 1" long. The outer is 1/2" OD nominal. The inner is .125" nominal multistrand stainless cable The ends are threaded 1/4" NF 2" long swaged onto the inner cable. The outer cable ends are 1/2" OD and have a locating groove approximately .1" deep located .5" from the end, the cable ends are mounted with machined aluminium split blocks that locate on the groove. The front connection is a clevis that screws onto the 1/4" threaded end. and the rear connection is a spring loaded rack that similarly screws onto the end. The spring loaded rack is designed to absorb operator foot motion when the engine is locked on fast idle. Actual throw of the cable in use is about 1.5".

Brian

Oonrahnjay · October 24, 2011, 01:04:31 PM

Thanks for posting your results and the data, Brian. It won't make much difference to me (I took the advice of people who said to go with an air throttle when the hydraulic system on my bus locked up from deterioration in the master and engine-end cylinders) but it's good to know that this is there for people who may be dealing with issues in their cable-operated systems.