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Author Topic: Need help wiring Jakes on 8V71 with auto  (Read 1444 times)
ChuckMC8
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« on: December 17, 2006, 08:48:59 AM »

  Somehow, I misplaced my notes on how the Jakes were wired on my donor truck.

I checked jakebrake.com, they have the info for the manual trans install, but notes check the "service letters" for apps with auto transmissions. Of course, I dont see that paticular document listed.

 I checked the BNO archives and the various MCI manuals on hand, and I can't seem to come to any conclusion (other than to ask for help)

  What I gather and looking at the engine, it seems that power would run thru the buffer switch to the front to the bus and and through the Jake selecter toggle and back to the two wires coming out of the head, With a slight varaition If one wants the 'high" and "low" (I guess thats powering only one side vs. posering both).

 It appears that the buffer switch allows currect travel only when the accellarator is at idle.

So, here's the question, why doesnt that kill the engine at idle if the jakes are "on"

And question #2, look at the buffer switch and notice there is a diode or resister on the terminal screw toward the left. Which of the terminal screws would be the "in" and which the "out"?

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Nick Badame Refrig/ACC
1989, MCI 102C3, 8V92T, HT740, 06' conversion FMCA# F-27317-S "Wife- 1969 Italian/German Style"
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« Reply #1 on: December 17, 2006, 08:52:39 AM »

Hi Chuck,

I don't know how to wire your jakes. But, man... I envy your very clean DD green engine!

Nick-
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DrivingMissLazy
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« Reply #2 on: December 17, 2006, 09:10:22 AM »

As I recall, a conductor that is hot when the ignition switch is on goes thru the buffer switch to the Jake switch in the front. The jake switch, I believe is a double pole, double throw, center off switch and is wired so that in the High position power is fed to both the leads going back to the Jakes themselves. In the Low position power is fed to only one of the leads going back to the jakes. That is why you have two leads going back instead of only one.

The adjustment of the buffer switch is critical so that the accellerator is not open when the Jakes are on. As I recall, it is supposed to close 25 rpm above idle speed.

The Jakes actually quit working at about 800-1000 rpm due to the engine oil pressure being too low to hold the solenoids open that actuate the exhaust valves.

The hot lead goes to the bar side of the diode, not the arrow side.
Richard
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ChuckMC8
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« Reply #3 on: December 17, 2006, 09:47:34 AM »

The hot lead goes to the bar side of the diode, not the arrow side.


Richard, can you clarify that for me? Would that be the screw on the left in the photo or the screw on the right?
Sorry for the incompetence- Chuck
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« Reply #4 on: December 17, 2006, 11:10:25 AM »

The hot lead goes to the bar side of the diode, not the arrow side.


Richard, can you clarify that for me? Would that be the screw on the left in the photo or the screw on the right?
Sorry for the incompetence- Chuck
Sorry, I mis-understood. I thought the diode was across the two terminals. I really do not recall from 20 years ago for sure but I strongly suspect the hot wire goes to the terminal on the right which does not have the diode attached to it.

I believe the diode is placed there to prevent arcing across the buffer switch terminals when a large transient, caused by the collapsing field of the Jake solenoids when they are turned off, is reflected back to the switch.

Do not take this for gospel. I am sure there are others that may have the Jake installation manual and can look it up.
Richard
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« Reply #5 on: December 17, 2006, 12:52:24 PM »

First, let me say that I have not installed my jakes yet (still need to get a set of longer fuel jumper lines), so this is theory only not BTDT. My plan is to install a pressure switch in the transmission torque converter lock-up pressure test fitting. This will be a NO switch which will be closed when the torque convert is in lock-up mode (pressure applied). With this switch wired in series with the buffer switch, both switches have to be closed (Torque converter in lock-up mode and racks at idle position). As soon as throttle is above idle or torque converter comes out of lock-up mode Jake is disabled.  YMMV,  Jack
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« Reply #6 on: December 17, 2006, 02:10:20 PM »

Jack, what speed does the torque converter come out of lockup mode?
Richard
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« Reply #7 on: December 17, 2006, 03:56:16 PM »

Allison 740 transmission.   Per Allison manual, lock up occurs in 1st gear at 12-15 MPH and remains in lock-up mode until speed decreases to 12-15 MPH.  Lock-up presure should be within 15 PSI of main pressure (175 PSI at full RPM).  Before installing this switch, I plan to temporarily connect a pressure gauge to lock-up test port to confirm pressure and release speed. Before connecting the Jakes, I plan to install a light in the dash connected to output to Jake brakes to confirm proper operation of lock-up and buffer switch.  Hopefully this will be a early 2007 project.  Jack
« Last Edit: December 17, 2006, 04:03:27 PM by JackConrad » Logged

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« Reply #8 on: December 17, 2006, 04:32:47 PM »

Jack, my Jakes always came off at around 15 mph, which I assume is when the torque converter dropped out of lockup. It was a pain in some very low speed mountain passes and this happened even if I had the tranny (740 Allison) pulled down into first gear.

I did not have my Jakes wired into the tranny and I really do not see any need to do so. You lose braking action when the tranny comes out of lockup and then the rpm drops to almost idle and the Jakes then are turned off by the buffer switch. I think wiring thru the tranny is just additional wiring that really does not accomplish anything. I was always interested in finding some way to keep the tranny from dropping out of lockup at low speeds so I could maintain Jakes down to a 5-10 mph speed. Just my opinion.
Richard
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« Reply #9 on: December 17, 2006, 04:56:26 PM »

I was always interested in finding some way to keep the tranny from dropping out of lockup at low speeds so I could maintain Jakes down to a 5-10 mph speed.

Someone  posted a while back how he modified his transmission.  He added a electrically controlled valve to maintain pressure in the lock-up circuit of the transmission. i don't remember the details, but he tapped into a fitting near the lock-up test port, to the valve, and then to the lock-up port.  Jack
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DrivingMissLazy
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« Reply #10 on: December 17, 2006, 06:34:23 PM »

That would be a great modification.
Another one would be to find out how to keep the 740 from shifting out of first at low speeds when you want to creep up a grade.
Richard
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« Reply #11 on: December 18, 2006, 01:09:14 AM »

[Someone  posted a while back how he modified his transmission.  He added a electrically controlled valve to maintain pressure in the lock-up circuit of the transmission.


That would be Brian Diehl. Pure genius, IMHO. Here's the link. I'll be attempting this on my V730 one of these days. It would make the Jakes more useful, but also make the tranny heat up less on steep climbs.

Brian B.
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« Reply #12 on: December 18, 2006, 06:40:38 AM »

[Someone  posted a while back how he modified his transmission.  He added a electrically controlled valve to maintain pressure in the lock-up circuit of the transmission.


That would be Brian Diehl. Pure genius, IMHO. Here's the link. I'll be attempting this on my V730 one of these days. It would make the Jakes more useful, but also make the tranny heat up less on steep climbs.

Brian B.

Jack an all, If it was me, I would follow Brians lead and do the lockup and not worry about the switching of the Jakes. They will take care of themselves. If you ever get out west and some of the real mountains, you will be grateful to Brian for what he has done.
Richard
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