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Author Topic: 6 spd auto & jakes  (Read 1310 times)
jaybe_2
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« on: October 15, 2006, 05:44:52 PM »

An mci 8 that I am doing some work on has an 8v-71 w/ an allison 6 speed. The problem is that when you let off the gas the trans seems to coast when in high gear. This is a lot of fun for him because at times the jake will stall the engine and he looses power steering. This problem conserns me also as I just bought a truck for the engine and trans (8v-71t and 6 spd allison) and I would like to install a jake before I install the engine in my bus.Is this a common problem or does he have a problem with his trans?
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TomC
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« Reply #1 on: October 15, 2006, 10:33:24 PM »

First off, if it is a 8V-71 with a 6 speed Allison, then the only transmission would be the MT43 which is a cast iron case that is out of production with very few hard to find spare parts for it.  The shifter on the MT43 would read 1, 1-2, 3, 3-4, 3-5, 3-6, N, R.  What it actually was, was a 4 speed transmission with 2 deep lows. 

On the other hand, what may seem like a 6 speed transmission is a HT754CR, that is a 5 speed transmission.  Its' shifter would look like 1, 2, 3, 4, D, N, R.  Since it has a shift pattern of 1st converter, 2nd converter, 2nd lockup, 3rd lockup, 4th lockup, 5th lockup, it feels like it shifts 6 times, but the extra shift is just the torque converter locking up. 

The torque converter on both transmissions stay locked up in the higher gears continuously.  If it is dropping out of lockup (or maybe it isn't locking up at all?) it is definitely time for overhaul.  It is entirely possible that the lockup clutch is worn out. 

Also-if the Jake is stalling the engine, then the Jake is not hooked up correctly.  It sounds like it is wired through the switch, then through the accelerator pedal only.  It should also be wired through the engine governor so when the engine comes down to idle and the governor gives the engine fuel again for idle, it would shut the Jake brake off and not stall the engine.  Sounds like a couple of problems.  Let us know what you find.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
jaybe_2
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« Reply #2 on: October 16, 2006, 04:30:20 AM »

The shifter in the bus is marked  1, 1-2, 3, 3-4, 3-5, 3-6, N, R  I have not looked to see if it is cast iron. I looked at the truck and it looks like it is a 5 spd. The truck I bought seems to have some sort of elecktric motor brake on the trans. Turns out the truck was set up for a man that had only one arm, so it has a lot of neet stuff on it.
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TomCat
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« Reply #3 on: October 16, 2006, 06:57:30 AM »

I'm curious how many people are using a Jake and Automatic together...successfully?

Jay
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DrivingMissLazy
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« Reply #4 on: October 16, 2006, 07:09:39 AM »

Jay, they work great together. Probably better than with a manual. I traversed every major grade in the country, I believe, and the Jake/Allison combination was great.
The only disadvantage that I found was that the Allison would drop out of lockup at about 15 mph.
Richard

I'm curious how many people are using a Jake and Automatic together...successfully?

Jay
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Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming:  WOO HOO, what a ride
belfert
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« Reply #5 on: October 16, 2006, 07:11:31 AM »

I'm curious how many people are using a Jake and Automatic together...successfully?

I am, but I have a newer bus that is fully computerized.  The B500 automatically downshifts and turns on the Jakes as soon as the pedal is lifted, if the Jakes are turned on.

Brian Elfert
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H3Jim
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« Reply #6 on: October 16, 2006, 08:44:07 AM »

The jakes stop at 15 mph so it doesn't lug the engine.  Take a bit of getting used to coming to a stop. 

Bill, the fellow that used to work for Dick Wright had a nice Newell that he had done an engine tranplant in.  They way his new gears worked, it dropped out about 30 mph he said.  Going down a short steep narrow hill while towing, he lost control when the jake cut out and went over the edge of a ravine.  Totalled the bus.  A good reason to not try to drive a bus like a car, just beause you have jakes on it.

I too am very pleased with the way the Jake and B500 work together.  I don't use my brakes much.
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Jim Stewart
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DrivingMissLazy
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« Reply #7 on: October 16, 2006, 10:14:37 AM »

I believe there are two cutouts. My Jakes were set to cut out at 1000 rpm to allow the engine to idle properly. My tranny cut out at about 15 mph. This was, as far as I know, two entirely different actions.
Richard


The jakes stop at 15 mph so it doesn't lug the engine.  Take a bit of getting used to coming to a stop. 

Bill, the fellow that used to work for Dick Wright had a nice Newell that he had done an engine tranplant in.  They way his new gears worked, it dropped out about 30 mph he said.  Going down a short steep narrow hill while towing, he lost control when the jake cut out and went over the edge of a ravine.  Totalled the bus.  A good reason to not try to drive a bus like a car, just beause you have jakes on it.

I too am very pleased with the way the Jake and B500 work together.  I don't use my brakes much.
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Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body. But rather to skid in sideways, chocolate in one hand, a good Reisling in the other, body thoroughly used up, totally worn out and screaming:  WOO HOO, what a ride
TomC
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« Reply #8 on: October 16, 2006, 04:21:50 PM »

Jaybe_2- It sounds like you do have the old MT43 transmission which is the 6 speed with the first two being a deep reduction.  So when the bus starts in 3rd, it will feel like it is a 5 speed with the lockup of the torque converter feeling like another gear.  Personally, I wouldn't even fool with that transmission.  Look for a HT740 4 speed or a HT754 5 speed to replace it.  They are bigger transmissions, still have parts being made for them (even though they are not made anymore), and are plentiful in the used market.  What looks like a motor retarder at the end of the transmission is most likely a Telma electric retarder.  It looks like a big disc brake with about 6 electromagnets on either side.  If you do get rid of the 6 speed trans, by all means keep the Telma.  Installed, a brand new one is around $10,000!  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
jaybe_2
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« Reply #9 on: October 16, 2006, 04:58:50 PM »

My friend that owns the mci 8 w/6spdis fine with the trans, it has been this way sence he bought the bus several year ago. But we might check to see if the jake is tied into the govenor to keep the engine from stalling. Thank for the info. The info on this BB is top notch!!!!
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