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Author Topic: High & Low For Jakes or High Only?  (Read 4139 times)
JackConrad
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« on: April 10, 2009, 10:52:30 AM »

I am getting ready to wire a switch for the Jakes on our 8V71 NA engine. It is connected to an Allison HT740 Transmission. I would like first hand information from those of you that have jakes on an 8V71NA/Allison 740 combination in your bus (I want to compare apples to apples).  Do you use High only or do you use High & Low settings.  Thanks in advance, Jack
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« Reply #1 on: April 10, 2009, 11:03:00 AM »

Jack, I don't have a 8v71 but I use the low setting on my 8v92 with a 740 all the time living here in the west they work great for the long descending grades where the hi setting will slow you to much.
I like the low setting also because you won't be flipping the switch off and on to maintain the correct speed.
A friend of mine only has a hi setting and longs for a low setting.       good luck
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« Reply #2 on: April 10, 2009, 11:18:37 AM »

My drivetrain is 8-92 & 10 spd RR but I wouldn't like to be without the low setting either.  I don't use it a lot but I would miss it.  As Clifford said, sometimes the full Jakes is just too much for the hill.  I also use my low setting for less aggressive action in lower gears.  I'm not sure how that would translate to an auto trans.
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« Reply #3 on: April 10, 2009, 01:00:43 PM »

Jack, I have jakes with high only.  My tranny is an ht70 which is different than almost everyone else that has an auto.  My jakes are sometimes much to aggressive on long gentle downgrades.  I also have a retarder and use it instead of the jakes in that situation.  If I had a low position I would certainly use it.  I will probably modify Mine when I manage to get off My lazy backside.  I have held off because I am planning to pull My engine to upgrade to a turbo.  Your engine sure looks good.  John
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« Reply #4 on: April 10, 2009, 01:07:17 PM »

Jack, I have high only and its works great, cant imagine driveing the western states with out it. That said the high setting is VERY aggressive in the lower gears when I use it to slow for a stop or turn, sometimes good and sometimes not.>>>Dan
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« Reply #5 on: April 10, 2009, 01:16:02 PM »

I don't have an 8V71 but I do have a 740. I travel in the mountains a lot. It is nice to have different setting as the grades change when coming down a hill and it makes it very simple with the touch of a switch.

FWIW Wayne
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« Reply #6 on: April 10, 2009, 01:23:49 PM »

Jack,

On my MCI 8 with 8V71 and 740, I used high jake about 90-95% of the time.  On my current bus, I use high at about the same ratio.

Two ideas I had if I were going to modify it for easier operation.  First, install a foot activation like the high beam switch.  Second, I would consider having the jake operate whenever the stop lights activate.  There may be a negative to this, so I would ask some questions first.

Ed Roelle
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« Reply #7 on: April 10, 2009, 04:32:35 PM »

Hello:
   Just a few thoughts.  If you consider the relative cubic inches of the motors involved you can evaluate the difference between the jake brake systems. The 892 is 736 cu inches vs the 568 cu in of the 871. The ratio is about 30 %  difference between the engines.  Therefore the jakes will have a proportional response of at least 30% more for the larger engine.   Or looking at the % of the low side of the 892 engine its response is about 64% of the full or high 8V71.     368/568= 0.64
   SO be careful when you compare one engine to the other.  That being said the only difference  for wiring is another wire and a switch to the front.
   Having said all that I was advised when I had the jakes installed (On that engine )  that the response on high was probably the best choice I could make and low would probably not help much.  Therefore I wired the jakes so that they both always came on . This worked well for me. I did not find the jakes too aggressive but my experience is limited tothe mileage on the motor about 45K . 
      Now as far as the foot switch I used one all the time and still do with the retarder instead of the jake.
  THe control for the jakes with an air throttle requires a pressure switch in the line to the throttle which is a nc contact set at 1 psi   In other words when the throttle is off then the switch closes to pass voltage thru to the foot switch or other devices in the circuit. I still use the same circuit then pass it thru to the retarder enable wire to  the B400 computer.
     I recommend a pressure switch in the transmission which will cut the jakes off around 600 or so rpms.Jake brake has that info on their website.   If you keep the jakes on below 600 rpms or so the engine will stall..  I dont know if Allisons like turning without power. Now I did not have that switch installed so when the jake was on via the foot switch I watched the tack faithfully.
   Regards and hapy bussin   mike
   
« Last Edit: April 10, 2009, 05:20:02 PM by mikelutestanski » Logged

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« Reply #8 on: April 10, 2009, 04:41:51 PM »

Jack,

On my MCI 8 with 8V71 and 740, I used high jake about 90-95% of the time.  On my current bus, I use high at about the same ratio.

Two ideas I had if I were going to modify it for easier operation.  First, install a foot activation like the high beam switch.  Second, I would consider having the jake operate whenever the stop lights activate.  There may be a negative to this, so I would ask some questions first.

Ed Roelle

Hi Ed & Jack,

Jack, I only use high and most of the time the jake switch is off because I live in the flat lands of the Jersey coast. Low seems not so noticable.

Ed, The NJ Transit busses have a set of yellow lights that come on above the stop lights when the jakes are activated. This cautions the following
traffic that the bus is slowing. I think it's a great idea..

Nick-

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« Reply #9 on: April 10, 2009, 05:20:50 PM »

    Thanks for all the replies.  Looks like I will probably be using High most of the time. Since I have room for 2 switches in the panel next to the drivers seat, I will install 2 switches, one for each cylinder head.  This will not only allow running 1 or both banks, but give me the option of running either bank on Low (this might also be a good diagnostic tool, should I have a problem with the Jakes). 
    As far as Jake Brake control, I have a pressure switch on the air throttle actuator as well as a pressure switch on the lock up test port on the Allison transmission. When the Jakes are turned on at the driver's panel the Jakes will not activate unless the air throttle is at idle postion and the transmission is in lock up mode (Jakes would not be effective in converter mode). We have installed an indicator LED in the dash that is connected to the Jake Brake wire at the ouput from one of the Jake Brake relays in the rear panel to confirm Jakes will only activate as above.  Driver's switches and pressure switches only control Jake Brake relays in rear panel (to reduce load on switches).
    Thanks again for all the advice.  Jack
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« Reply #10 on: April 10, 2009, 07:21:57 PM »

[Jack, I only use high and most of the time the jake switch is off because I live in the flat lands of the Jersey coast. Low seems not so noticable.

Ed, The NJ Transit busses have a set of yellow lights that come on above the stop lights when the jakes are activated. This cautions the following
traffic that the bus is slowing. I think it's a great idea..

I think federal law now requires activation of the brakes lights whenever the engine brake is active.  I couldn't actually find anything on the web about this, but I swear I read it somewhere.
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« Reply #11 on: April 10, 2009, 10:33:49 PM »

Nobody mentioned the mod to the trans that forces it into lockup while in 1st gear.  I understand that 1st never goes into lockup so "feeling" your way down a curvey mtn road in 1st yields very hot or failing brakes unless you can use the jake and the trans will stay in lockup.  It is on the board and has diagrams and pics of the install and Allison approves....I think they said.  This seemed like a must do to me.

HTH,

John
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« Reply #12 on: April 11, 2009, 06:33:53 AM »

John Ed, I don't think Allison approved the lock up of the converter for transportion vehicles it was used to lock the converter when using the PTO mostly on fire trucks running the pumps.I was told by Cole that setup will rip the flexplate and do damage to the transmission if not careful      good luck
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« Reply #13 on: April 11, 2009, 11:52:24 AM »

Cliff,

I read all the comments and I think there were two sets of instructions on the board.  Rave reviews.....on how it slowed them down.  After reading all that and researching the posts you would have thought I would have come across the negative.  Color me the ten percent that never gets the word.  Thank you for cluing me in.  I won't send anybody else down that path.

It was mentioned in the "how to" post that you could stall the engine if you stopped with the lock up override engaged.  Now my imagination tells me that that would CERTAINLY stress the flex plate and other stuff in the TX.  How did the firemen keep from trashing their gear or was it a consumable to them?  Maybe the PTO never stalled the engine?  I think you could hit slower engine rpm in low than the other gears because they down shift at a higher rpm than you might grind out in low creeping.  Cliff, I don't expect that you will have all these answers, or might anybody else, but I hope they are discussed by those that do. 

Thanks again for the info,

John
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« Reply #14 on: April 11, 2009, 12:54:58 PM »

   The control for the jakes with an air throttle requires a pressure switch in the line to the throttle which is a nc contact set at 1 psi   In other words when the throttle is off then the switch closes to pass voltage thru to the foot switch or other devices in the circuit. I still use the same circuit then pass it thru to the retarder enable wire to  the B400 computer.
     I recommend a pressure switch in the transmission which will cut the jakes off around 600 or so rpms.Jake brake has that info on their website.   If you keep the jakes on below 600 rpms or so the engine will stall..  I dont know if Allisons like turning without power. Now I did not have that switch installed so when the jake was on via the foot switch I watched the tack faithfully.
   Regards and hapy bussin   mike
   

Jack

When you hook up your Jake, whether you use 1 switch or 2, you should put in the buffer switch in the governor (replacing the buffer screw). This buffer switch makes it impossible for the Jake to stall the engine. As soon as you touch the throttle or the engine rpm's drop to the preset idle speed, the Jake will automatically shut off. This makes all the other switches that have been suggested unnecessary and redundant. A simple on-off switch on the dash (or 2 if you wish) is all that is needed.

This is the way Detroit Diesel has been setting them up for years. You can run with the switch "on" all the time if you wish. That way, when you lift your foot off the throttle pedal, the Jake will be on right away without having to hunt for a switch. If you want to coast without having the Jake on, just hold a little throttle on because any amount of throttle will hold the buffer (Jake) switch off.

Hope this helps. . .
Jim
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« Reply #15 on: April 11, 2009, 02:04:29 PM »

Hello:
   The buffer switch idea is good one however I have discussed this with several detroit mechanics and the final disposition on the switch (for my experience)  is as follows: 
          The  micro switch is difficult to get right and stay adjusted for this application .  One mechanic was an allison dealer.
   Now is this true   dont know   is the right mechanic available and can he/she set this up in 30 minutes and have it work perfectly.   dont know.   
     Is this a bunch of BS  dont know.  However the mechanic that Installed the jakes on the motor gave me the micro and said have a ball..
    Another reason which I believe is correct is the same spot for the micro is occupied by the fast idle solenoid and that would require a different spot and type of soleniod for the fast idle soleniod. The parts may or may not be available anymore.   
   Is my memory correct   dont know   this discussion happened ten years ago..
     In any case I elected to install a foot switch and the electrical switches necessary to replace the other switch to do the job. THe pressure switch insures that a casual press on the foot switch wont activate the jakes because the throttle pressure switch would prevent that from occurring. THe reasoning is that I could activate the jake brake enable switch (I used the old reverse switch) and I would not have to reach over and turn the switch when I wanted the jakes on.
   In my case it was easier to install and calibrate  pressure switches then mess around in that governor box on my newly rebuilt engine.
     
     THe days of the savy detroit two stroke mechanic are drawing to a close.  most of the younger mechanics cut their teeth on 60 series type engines. The shop forman or senior mechanic may have plenty experience of he has not retired.
     FWIW.    This has been my experience as much as I can recall...
      REgards and happy bussin   mike
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« Reply #16 on: April 11, 2009, 02:48:25 PM »

       THe days of the savy detroit two stroke mechanic are drawing to a close.  most of the younger mechanics cut their teeth on 60 series type engines. The shop forman or senior mechanic may have plenty experience of he has not retired.
     FWIW.    This has been my experience as much as I can recall...
      REgards and happy bussin   mike

Mike

You are right about these young mechanics. They mostly just replace the parts that their computer diagnostic program tells them to replace. When you show up with something more than 20 years old, and no diagnostic port, they just scratch their heads. Huh  There are still some older "mechanical" guys around though, but you have to look for them. Even when these 2-stroke's were new, there weren't many guys who could set them properly. They could get them to sound all right but they wouldn't,t pull or get decent fuel mileage. I used to have a few of them in various trucks and have been very unhappy, at times, with the service on them. I finally found a mechanic who knew what he was doing and got him to show me some tricks to setting them up. It was mostly just paying really close attention to adjustments with a few little things thrown in. Injectors, and especially modified injectors, are extremely important to power and economy in these 2-stroke's.

On your Jake switch, if you have a high idle unit replacing the buffer screw, it should still have a place for a Jake switch on it (although I think that is a different switch if I remember right). However, if you are happy with it the way it is, then that is all that matters. Smiley

Later. . .
Jim
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« Reply #17 on: April 11, 2009, 04:39:56 PM »

Hello:    Yes I am very happy.     I dont remember about the buffer switch  sorry;   senior moment;  after all I will be 65 in may  so  I have a new excuse..   in retrospect however:
     My 72 MCI 7  came with a 4 speed spicer .  When my wife leaned over and said grind me a pound I decided a 740 auto was in order.
  So out came the engine and tranny.  I cleaned up the engine compartment including 40 hours of repairing the subframes and generally made everything whole that was holy.
    The 8v71 was modified from the stock 275 hp to a 318 with advanced timing set up with 65 injectors and jakes. Complete out of frame rebuild with a 740 bolted to it completely rebuilt also.  I put 45K miles on the bus with this powerplant. We moved to florida with this and a 24 foot carhauler. The engine has never let me down.
  But  I got bit with a bug to change things again so after much soul searching I decided to repower with another later engine and transmission.
  The new plant is an 89 Cummins L10 mechanical with an Allison B400R computer tranny. I bought a couple of transit buses and moved the powerplant to my bus.  There should be a couple of threads with pictures floating around in the archives.
     After much work the new plant is running and runs fine.  I changed the rear ratio to 4.625 to help out the OD gears and keep the rs down at cruise speed.  The engine is at 275 hp once more but If I need it I will bring it up to 300. SO far I dont seem to need the extra hp.  most of my driving is flatland.  It will climb in 4th or third if needed and the retarder works well  so life is good.
     The 8v71 has a new life and is presently being christined in another bus and ready to roll again.
  SO life is good and after painting the bus we will get it moving...
     Alaska in 2010...     and points west..
      Regards and happy bussin.   mike 
« Last Edit: April 11, 2009, 04:47:55 PM by mikelutestanski » Logged

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« Reply #18 on: April 11, 2009, 04:45:42 PM »

Hello:    Yes I am very happy.
       The 8v71 was modified from the stock 275 hp to a 318 with advanced timing set up with 65 injectors and jakes. Complete out of frame rebuild with a 740 bolted to it completely rebuilt also.  I put 45K miles on the bus with this powerplant. We moved to florida with this and a 24 foot carhauler. The engine has never let me down.
      The 8v71 has a new life and is presently being christined in another bus and ready to roll again.
        Regards and happy bussin.   mike 

For those that do not know, this is the new (to us) engine that is now in Orange Blossom Special II.  We have had our granddaughter the last few days, during her Spring Break, so I haven't quite got the bus ready for it's first test drive yet. I hope to finish the Jake Brake wiring tomorrow and re-calibrate our Tachometer, then take it for a test drive. Results will be posted
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« Reply #19 on: April 11, 2009, 04:56:07 PM »

    After installing the pressure switches on the air throttle and the transmission lock up test port, I installed an LED indicator in the dash that is connected to Jake Brake wire at the cylinder head. I did not have Jakes installed yet on our old engine but I had installed all the wiring (which is now being modified slighlty, changing from High only to High/Low). I took the bus for a drive and turned on the Jake Brake switch (wired for High only) to the left of the Driver's seat. Jake would only activate when throttle is a idle position (no air pressure on air throttle) and transmission is in lock up mode. When transmission shifts out of lock up (at about 12-15 MPH), Jakes shut down. A slight throttle application (3 PSI) also shuts down the Jakes. It takes 5 PSI on air throttle actuator to increase engine RPM from idle position.  Jack
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« Reply #20 on: April 12, 2009, 12:03:11 PM »

Excellent report!

Sounds good to me!

Oh to have the time to have fun....

slave to the man for another 7....

happy coaching!
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« Reply #21 on: April 12, 2009, 12:48:24 PM »

Jack, Why not use a single switch with a off and two on positions? A double pole, double throw will work.  Tom Y
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« Reply #22 on: April 12, 2009, 02:06:26 PM »

That's the way mine is setup & I have a toggle extension on it so I can reach down without looking at it and flip it off or on.
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« Reply #23 on: April 12, 2009, 02:17:18 PM »

I have added a "momentary on" foot switch to my system that works better than I would have thought. I can still use the panel switch if I want to but sometimes I only need a little bump and the foot switch saves me from having to slightly feather the throttle the whole time the panel switch is on. To much unintentional Jake activation causes lower fuel mileage.

About locking the Allsion Transmission; Several weeks ago I called Allsion to talk about oils and while I had the Tech on the phone I asked about the forced first gear lockup. The short story is: don't do it.
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« Reply #24 on: April 12, 2009, 02:45:30 PM »

I have a Series 60 with B500 tranny and I do have a Jake Brake.  I have low, medium, and high for settings.  I have rarely ever used anything but high when I do use the Jake.  Low and medium don't seem to do much.  I actually think I should be getting more from the Jake, but I have not driven anything else to know for sure.  The Jake was adjusted when I had my Series 60 tuned up a while back.

If your engine and tranny are computer controlled like mine you might run into an issue when you use cruise.  With the Jake and cruise both turned on, the tranny will start downshifting and upshifting every few seconds if the bus gets more than maybe 1 MPH above the set speed.  I don't think the Jake is coming on, but it will come if the speed gets more than about 5 MPH above the set speed.  I just turn off the Jake when using cruise.  If the terrain is hilly enough to need the Jake I probably wouldn't use the cruise anyhow.
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« Reply #25 on: April 12, 2009, 03:19:03 PM »

belfert, those thresholds are all programable. You can add a few mph to the gap between jake intervention and cruise set speed. You can program the jakes to intervene whether the jake switch is on or off, lots of combinations available, whether the transmission downshifts with the jakes or stays with the regular program, such that you can really screw your driver around.....

On a long downgrade, having the flexibility of multi stages of jakes, and the flexibility of gear choices, especially with a B500, the driver may shuffle the deck and find a combo or "hold the speed" that works under quite a range of road speed and degree of slope, without having to fool around turning things on and off with more limited options of too strong or too weak.

We don't always have the freedom to cruise down the hill at our preferred speed due to other traffic.

happy coaching!
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« Reply #26 on: April 12, 2009, 03:37:36 PM »

belfert, those thresholds are all programable. You can add a few mph to the gap between jake intervention and cruise set speed. You can program the jakes to intervene whether the jake switch is on or off, lots of combinations available, whether the transmission downshifts with the jakes or stays with the regular program, such that you can really screw your driver around.....

Interesting.  I have a DDEC III.  The local Detroit dealer says that is just the way it works.  They never mentioned changing any parameters.  I'm not sure I will change it now as myself and the other drivers just know to turn off the Jake when using cruise.  The Jake isn't really ever needed until we hit Western Nebraska or Wyoming anyhow. 

There probably aren't too many here that have electronic engines and trannies where this might affect them.
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« Reply #27 on: April 12, 2009, 05:16:33 PM »

Jack, Why not use a single switch with a off and two on positions? A double pole, double throw will work.  Tom Y

By having 2 separate switches at the Driver's panel, I can select which cylinder bank I want to use for the low setting. This may come in handy in the future for diagnostic purposes, should the need arise (and I had the space for 2 switches).  Jack
« Last Edit: April 13, 2009, 05:06:38 AM by JackConrad » Logged

Growing Older Is Mandatory, Growing Up Is Optional
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« Reply #28 on: April 12, 2009, 07:17:27 PM »

I had an oldtime detroit trained mechanic install my jake brake and he installed the buffer switch in the governor. He also found three bad rockers while doing the install and changed them. I am going to install the wiring to have high and low jakes which means three wire system. The book says that high idle was on front 46 but did not come out on rear 22 or I would have had the DPDT switch hooked up now.
anyway there are still some old and properly trained mechanics around to work on these detroits. Jerry
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1988 MCI 102A3 8V92TA 740
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« Reply #29 on: April 12, 2009, 09:43:21 PM »

Jerry

I'm glad to hear you found a good mechanic. They are too few and too far between these days.

I'm also glad to hear that you got your Jake set up properly. I'm sure you'll be happy with it, especially with your 8V92TA  Grin

Enjoy. . .
Jim
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Jim Luthje

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« Reply #30 on: April 13, 2009, 01:18:15 PM »

Belfert and BW,

Thanks for the tips on a S60 with a B500. We are going to get Jakes on ours this summer, so this info was helpful.

I tell you what. I love that S60 engine with the B500, that is one great setup!

God bless,

John
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MCI 1995 DL3. DD S60 with a Allison B500.
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« Reply #31 on: April 13, 2009, 07:42:53 PM »

Just a comment on the effectiveness of jakes ....
I don't know if anyone else has noticed this, but the jakes on my engine (Cummins ISM) are MUCH more effective at Minnesota altitudes than they are up at 10,000' plus out in CO.  I'm amazed at how much better they respond down at sea pressure than up at high altitudes.  They do make a difference at high altitudes, but you can definitely feel the effect of altitude!
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« Reply #32 on: April 13, 2009, 10:47:01 PM »

10-4.

We notice the same effect in our 8V71. At 7,500 feet, the Jakes are pretty weak.

Take care.

Tom Caffrey
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Tom Caffrey PD4106-2576
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1981 MC9 8V71, HT 740




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« Reply #33 on: April 14, 2009, 06:21:25 AM »


Jack,

I have 8v71 and 740 and only High switch Jake.

this bus is my only experience with all.

I use the Jakes to maintain "slow" down a hill and not necessarrally to stop.  I use brakes to stop.

I usually find that there is a speed that it will maintain and above that it will start speeding up.


I'm not sure how mine are wired up, however they cut out at a really low speed, and as far as the torque convereter.  Mine does not seem to unlock until a certain low speed in first.  I.e. locks after shifting into second on the way up and un-locks in first on the way down.

Just my 2 cents, skewed as it may be Wink
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It's all fun and games til someone gets hurt. Wink
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« Reply #34 on: April 14, 2009, 07:17:24 AM »

I too only use my Jakes to control speed, not to brake to a stop.  I'm not sure if the Jake is supposed to be able to hold the speed on a somewhat steep grade like I80 into Salt Lake City.  I have to brake every 60 seconds at least to control my speed.
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Brian Elfert - 1995 Dina Viaggio 1000 Series 60/B500 - 75% done but usable - Minneapolis, MN
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