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Author Topic: MC 8-Allison HT 740 hard to shift  (Read 2115 times)
Sam 4106
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« on: November 11, 2012, 12:03:10 PM »

Our transmission in our MC 8 has become increasingly harder to shift so I am guessing there is a problem with the shift cable. Anyone have any suggestion on where else to look for a problem other than the cable? If the cable is bad I think I would like to switch to a Stone Bennet shifter. Anyone have a good used 24 volt SB electric/air shifter for sale, or a source for one? Other than routing the control cable, a clean air supply and 24 volt power supply are there any impediments to installing an SB shifter? I already have several winter projects planned but the shift problem just went to the top of the list, because my wife, who does a lot of the driving, has complained long enough. Time for a solution!!

As always, thanks for your assistance. Sam
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1976 MCI-8TA with 8V92 DDEC II and Allison HT740
luvrbus
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« Reply #1 on: November 11, 2012, 12:27:03 PM »

Sam,  check with Gary at B&B Coach in Vegas,used Bennett shifters are getting hard to find but check the wrecking yards in old trash trucks also check www.utxchange.com they have rebuilt units from time to time they do have new ones also 

The 12v unit doesn't cost much to change to 24v about 50 bucks  just do not buy the hydraulic Bennett they are slow to shift,the Bennett is going to spoil you lol I could never see anybody a owning a 740 without a Bennett shifter

good luck

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Lin
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« Reply #2 on: November 11, 2012, 01:31:54 PM »

First though, disconnect the shift cable at the transmission.  If it is still hard to move the shifter, it is the cable.  If the shifter becomes easy, it is something else.  You should be able to move the shift lever on the transmission by hand too.
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buswarrior
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« Reply #3 on: November 11, 2012, 04:01:08 PM »

Interesting.

In my parts coach, which just sits around, but is still somewhat mobile, the shifter is getting quite stiff.

Didn't think much about it until this thread...

The coaches are remote to my location right now.

I'm wondering whether it is a corrosion or obscure lubrication issue of some kind?

happy coaching!
buswarrior



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lostagain
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« Reply #4 on: November 11, 2012, 04:18:08 PM »

I had the same issue with mine.

I took the hand lever off and lubricated everything as much as I could with silicone spray. Tried to get as much as I could into the cable sheath. It improved it somewhat. Still not as good as I would like. I think the cable wears into the sheath where it bends, and it might not be fixable.

I might be looking into a Stone Bennett shifter too.

JC
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JC
Invermere, BC
1977 MC5C, 6V92/HT740
buswarrior
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« Reply #5 on: November 11, 2012, 04:27:05 PM »

The throttle cables in the old GM's are reported to improve significantly with being pulled out of the sleeve, diesel or the solvent of your choice blown through it, re-lubed with a proper type lube and threaded back in.

Perhaps the time has come where the MCI auto shifter cables have simply reached that age where this will be required?

Remember, the first of the Allison cables, found in the last of the MC7, is only just reaching 40 years old...

happy coaching!
buswarrior

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junkman42
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« Reply #6 on: November 12, 2012, 03:45:52 AM »

I have a morse cable that is just like the shift cable that connects from the throttle belcrank on the engine to the HT70 in My MC7!  My throttle was getting impossible to use and after disconnecting the tranny cable figured out the throttle problem was the morse cable.  My shifter was also getting stiff as hell.  My solution was to wrap the tip of a pump oil can to the end of the cable with silicone tape and pump a can of auto tranny fluid into the cable.  Problem solved.  Easy to do and costs almost nothing.  John L
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Sam 4106
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« Reply #7 on: November 12, 2012, 07:14:09 PM »

Today I removed the shift cable from both the transmission and the shift tower. The transmission shifts fine using the lever on the side and the shift lever moves freely with the cable off. So, I conclude that the problem is in the cable. I tried pumping transmission fluid through the cable ,but so far it doesn't move any easier. I looked at both ends with the thought of pulling the center out of the sheath but the inner cable is 3/16" and the solid ends are 5/16" so no chance of pulling the inner cable out without cutting one end off, that would ruin the cable. I will see if the cable moves any better in the morning, after soaking all night.

I am thinking that the wrong cable was installed at some point because I can only shift from neutral into reverse or drive and third. There isn't enough travel of the cable to shift into second or first.

So, tomorrow I will begin looking for a Stone Bennet shifter. Waste Management has a local shop and there are two independent garbage haulers in the area too. Also a ready mix. Otherwise, I will extend my search.

Thanks for all the suggestions, Sam

P.S. Can the shift cable be easily pulled out of the bus? if it can I would pull in the wiring harness Stone Bennet shifter with the cable as it is being removed.
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1976 MCI-8TA with 8V92 DDEC II and Allison HT740
Lin
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« Reply #8 on: November 12, 2012, 07:23:20 PM »

There can be several issues that limit your ability to shift into the lower gears.  As you say, the cable itself may not have enough travel.  However, the shifter might be the wrong one, and there are even different length levers for the cable to connect to on the transmission that can effect travel.  I went through that problem when we installed our Allison 647.  We had a 740 shifter which was wrong, and the lever on the transmission was for a 740 transmission.  I had to replace the shifter and drill out another hole in the lever to get all the gears shifting right.

I think, though am not sure, that how you connect the cable in the shifter itself can change the throw also.
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luvrbus
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« Reply #9 on: November 12, 2012, 07:47:28 PM »

Sam, the wiring harness for the Bennett will be to large to pull through cable housing, I hope you find one it's the only way to go IMO sure makes a 740 shift smooth when down shifting or up shifting when needed 

good luck
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Sam 4106
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« Reply #10 on: November 19, 2012, 03:06:43 PM »

I finally got my shift cable to work smoothly. After forcing ATF through the full length by clamping a 5/8" reinforced plastic tube to the threaded shifter end of the housing, filling the tube 3/4 full of ATF, and applying 60 PSI of air pressure. The first day I started with 20 PSI and worked the cable back and forth and got easier movement. The second day my neighbor suggested twisting the inner cable with a drill and working it back and forth, with 40 PSI, resulting in easier movement, but still no oil at the transmission end. Today, I used 60 PSI, spun the inner cable some more, while moving the cable back and forth, and finally got some very black goo to come out at the transmission end. I kept working the cable back and forth, stopping 3 times to add oil to the plastic tube, and eventually got red ATF dripping out at a rate of 1 drop every 5 seconds. Now the cable works very freely by hand, and I can feel the transmission shift arm drop into the detents from the shifter at the front of the bus. Even though it took a lot of time, I am quite sure my wife won't complain any longer when she has to shift.

I posted this in the event that someone else can benefit from my tenacity. I only worked at this project between working on other things. I left the pressure on all the time and went back occasionally to check the level of the oil in the tube, adding as needed. NOW, the question is do I need to use some other lubricant or just leave the ATF in there? Thanks for all the advise. Sam
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1976 MCI-8TA with 8V92 DDEC II and Allison HT740
wg4t50
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« Reply #11 on: November 19, 2012, 04:56:41 PM »

Convert to the electric shift, got two kits from the DDC/Allison factory shop, push button or lever.

Me, I used the RTO910 Road Ranger, shifted with the Kenworth Cab Over Cable shift setup, worked great. 

Dave
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MCI7 20+ Yrs
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Lin
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« Reply #12 on: November 19, 2012, 05:19:55 PM »

Sam, glad you got it working.  If you ever have to do something like this in the future, I would not try twisting the cable though.  Since they are stranded, torquing the cable one way can cause the strands to loosen and torquing it the other way can break several strands.  Now, losing a strand or two will not seriously weaken the cable, but if the ends of broken strands begin to unravel, they can lodge in the housing, crumple up, and lock the cable.  I have managed to achieve that with very little torque.
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Sam 4106
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« Reply #13 on: November 19, 2012, 07:29:16 PM »

Dave,

How expensive is an electric shifter? When I mentioned that possibility to my wife she asked how much, and since I didn't know, she said a couple hundred would be ok, but a thousand would not. So for about $7.00 I fixed the cable.

Lin,

I knew there was a possibility of twisting off the cable, but what did I have to lose by trying? I thought I had twisted it off when I first tried spinning it so I asked my wife to watch the cable at the front while I spun it from the back. It was turning so I continued. The outside of the inner cable is spiral wrapped and I spun it in the direction that tightened the spiral, if it moved at all. My neighbor had suggested using a cordless drill to spin the cable, but the ends are threaded 5/16" rod and I didn't want to clamp the chuck onto the threads. So, I put 2 nuts on, tightened them together, and used my 1/2" slow speed drill. I am pleased with the result. How long the cable will last is anybodies guess.

Thanks, Sam
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1976 MCI-8TA with 8V92 DDEC II and Allison HT740
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