| Author | Message | ||
| Jim Wilkerson (Wagwar)
Registered Member Username: Wagwar Post Number: 163 Registered: 12-2009 Posted From: 69.150.233.21 Rating: N/A |
I recently had jakes installed on my 1981 MC9 w/ 6V92T and Allison HT 740 D. I have wired it such that I can throw a toggle at the driver seat to turn the jakes on/off - one bank or two. I have thoroughly tested the wiring and the jakes and all is correct and working in the driveway by jumpering the transmission lockup port swithc. However, on the road the jakes do not work. I've tried different ports on the trans and still no joy. THe problem is either the switch (which I've tested and set to close at 35 psi) or the lockup port iteself. Does anyone know what the pressure should be on the lockup port for this trans? I'm hoping I just have the switch set too high? But I don't have a guage to test the port with. As best I can tell, there are only four ports on this trans: Main, Governor, Lube and Lockup with the lockup being the leftmost (driver side) port on the bottome of the trans. There is another switch on the side of the trans (driver side) with a two-prong socket that is currently disconnected. Does anyone know what that port/switch would be? Any suggestion? | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 1174 Registered: 8-2006 Posted From: 74.33.48.167 Rating: N/A |
What does the lockup have to do with the Jakes engaging should not be wired through the lockup that is only to hold the transmission engaged the buffer switch if you have one should control the Jakes | ||
| Brian Evans (Bevans6)
Registered Member Username: Bevans6 Post Number: 47 Registered: 5-2009 Posted From: 65.92.49.192 Rating: N/A |
I was thinking the idea was to only engage the jakes with the transmission in lock up, the same way my manual transmission is set up to only engage the jakes with the clutch engaged. But I don't think it's necessary. It should work without that, wired directly to the buffer switch. | ||
| Brian Evans (Bevans6)
Registered Member Username: Bevans6 Post Number: 48 Registered: 5-2009 Posted From: 65.92.49.192 Rating: N/A |
I just went and checked the jake wiring diagram for automatic trans in my MCI manual, and it doesn't use anything on the transmission at all. just the dash switch to arm it and the buffer switch to engage it, nothing else. | ||
| marvin pack (Gomer)
Registered Member Username: Gomer Post Number: 1462 Registered: 3-2007 Posted From: 76.4.118.153  Rating: N/A |
Jim I don't have a jake but I understand that whenever you have it on,and take your foot off the accelerator.a switch there will activate the jakes on the engine. Manual or auto doesn't have anything to do with it. Gomer | ||
| Tim Brandt (Timb)
Registered Member Username: Timb Post Number: 616 Registered: 10-2003 Posted From: 66.165.176.62  Rating: N/A |
there is a switch that replaces the buffer screw. when the govorner calls for no fuel it pushes on this switch and engages the jake. | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 1175 Registered: 8-2006 Posted From: 74.33.48.167 Rating: N/A |
They do run the Jakes through the transmissions on the electric control with retarders you see the late model stuff wired to the ABS brakes also good luck | ||
| Mike Eades (Mike4905)
Registered Member Username: Mike4905 Post Number: 211 Registered: 12-2000 Posted From: 70.126.183.226 Rating: N/A |
My 4905 with 8v71 was wired to a hot and ground and the buffer switch. Let off on the fuel peddle and it would turn on the jake brake. If I didn't let the fuel peddle all the way up the jake would not turn on. I could drive with the switch on and no brake driving slower. | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 1176 Registered: 8-2006 Posted From: 74.33.48.167 Rating: N/A |
What is the ground for ? I never wired one that way | ||
| Brian Evans (Bevans6)
Registered Member Username: Bevans6 Post Number: 49 Registered: 5-2009 Posted From: 65.92.49.192 Rating: N/A |
Mine ground through the solenoids. The switches are purely for the 24v hot signal. | ||
| Jim Wilkerson (Wagwar)
Registered Member Username: Wagwar Post Number: 164 Registered: 12-2009 Posted From: 69.150.233.21 Rating: N/A |
Thanks for the responses. The installation instructions from Jacobs and my mechanic both indicate the jakes should only come on with no fuel and trans in lockup. Not no fuel only. So, I thought I was wiring it correctly. I was told that if the trans is not in lockup, engaging the jakes won't slow down the bus because the trans would be freewheeling? I guess I could be wrong about that. | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 1177 Registered: 8-2006 Posted From: 74.33.48.167 Rating: N/A |
Free wheeling only happens when the 740 comes out of lockup in first gear, Jakes with the buffer switch will become disengaged at 900 rpm anyway the only way to stop that is wired direct which is not a good idea IMO Two strokes don't hold enough oil pressure below 900 rpms to make the Jakes work good anyway (Message edited by luvrbus on July 07, 2011) | ||
| R.C.Bishop (Chuckllb)
Registered Member Username: Chuckllb Post Number: 1549 Registered: 7-2006 Posted From: 70.219.147.203  Rating: N/A |
I 'spose it might depend on the engine setup...but...my Jakes (Cummins Turbo) work only when the coach is in motion; otherwise, the engine cuts out completely...and at lower RPM even in motion. I also have a dash switch--- ON...Off>>> So far, so good!!  AIR, lots in the Archives about the subject.?? RCB | ||
| Jim Wilkerson (Wagwar)
Registered Member Username: Wagwar Post Number: 165 Registered: 12-2009 Posted From: 69.150.233.21 Rating: N/A |
My 6v92 has a fast idle, so rather than lose that to the jake switch, I mounted a clutch type switch to be activated when the fuel lever hits the idle position. As long as that is "OK", then it sounds like I can bypass the lockup port switch and use the no fuel position only. Is that correct? Thanks for your help! | ||
| Jim Wilke (Jim Bob) (Pd41044039)
Registered Member Username: Pd41044039 Post Number: 649 Registered: 2-2001 Posted From: 184.0.13.120  Rating: |
Jim, I'm thinking that your clutch switch on the throttle arm will give you problems. The buffer switch senses when the governor is asking for idle fuel or any more than that. It also senses the NO fuel position (this happens when the engine is turning faster than the governor speed position. Like coming down a hill.) The throttle arm clutch type switch can not tell the difference between idle and no fuel. That happens inside the governor based on engine RPM. If you set the Jakes to come on at the idle position at the throttle, I think your engine will stall every time you come to a stop. But the correctly adjusted buffer switch allows the engine to run (idle) at idle position, but when the governor goes to no fuel, (coasting down that hill) THEN and only then is when it applies the Jakes. Does that make sense? | ||
| Brian Evans (Bevans6)
Registered Member Username: Bevans6 Post Number: 51 Registered: 5-2009 Posted From: 65.92.49.192 Rating: |
I think Jim Bob is right. the speed control lever can only tell if the engine is being asked for idle speed, it can't tell if the governor has gone past that and is at no fuel. If the jake was wired the way you say, it will try to stall the engine at idle except for the oil pressure issue - there isn't enough oil pressure at idle to operate the jakes. Based on the oil pressure thing, your set up might work, but it isn't right. I have no idea what the long term impact of having the jake brakes energized but not enough oil pressure to make them open the exhaust valve is. | ||
| Jim Wilkerson (Wagwar)
Registered Member Username: Wagwar Post Number: 166 Registered: 12-2009 Posted From: 69.150.233.21 Rating: N/A |
Thank you! What Bevans6 and Jim Bob are saying makes sense to me. I can understand how my current setup could cause problems. It seems to me the trans lockup port switch could solve this problem and I can keep my fast idle. So if the trans is not in lockup, the jakes will not be engaged and allow the engine to idle. Might that work? If so, I return to my original question - what pressure should I expect to find at the lockup port when the trans is in lockup? Thanks in advance. | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 1178 Registered: 8-2006 Posted From: 74.33.48.167 Rating: N/A |
If you are going to do it away lockup pressure is 140 to 175 lbs. Allison never intended for the converter to be locked up under way in 1st gear that was for lockup using the PTO(like on a fire truck)and off road that setup is going to cost you a flex plate if you are not careful (Message edited by luvrbus on July 09, 2011) | ||
| Len Silva (Lsilva)
Registered Member Username: Lsilva Post Number: 483 Registered: 12-2000 Posted From: 72.187.35.208  Rating: |
I think some responses may be confusing. I don't think Jim wants to lock up the converter, he just wants to know when it is locked up. That makes sense to me, that's how I wired up my exhaust brake. | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 1179 Registered: 8-2006 Posted From: 74.33.48.167 Rating: N/A |
The way I read it he wants to stop the free wheeling in 1st gear so the Jakes work all the time ? | ||
| Brian Evans (Bevans6)
Registered Member Username: Bevans6 Post Number: 52 Registered: 5-2009 Posted From: 65.92.49.192 Rating: |
No, he wants the lockup switch to control the jakes so they can only work when the transmission is in lockup, that way the jakes won't work when he is at idle, in neutral, or coasting to a stop in first gear. He doesn't have a buffer switch, just an on-off switch on the speed control lever on the governor and the lockup switch for the controls. It should work fine. Not the normal way, but it should work. His problem now is the transmission switch doesn't work, it doesn't close when it is in lockup. Brian | ||
| Bill Gerrie (Bill_gerrie)
Registered Member Username: Bill_gerrie Post Number: 513 Registered: 3-2006 Posted From: 216.198.139.38  Rating: N/A |
Len and Brian have it perfect. Jim just needs to know which port the N.O. switch goes into on the 740 to read the lock up pressure. My suggestion would be to try each port till he finds the right one. You can't hurt anything by putting the switch in the wrong port. Just extra work. Bill | ||
| Bill Gerrie (Bill_gerrie)
Registered Member Username: Bill_gerrie Post Number: 514 Registered: 3-2006 Posted From: 216.198.139.38 Rating: N/A |
Jim If you try each port and no luck check the possibility that your tranny isn't going into lock up when it should. That other switch you mention might be an unused reverse switch or in the lock up port for the PO's Jakes. Just some thoughts as I know you have worked on it for awhile. Bill | ||
| George M. Todd (George_todd)
Registered Member Username: George_todd Post Number: 1257 Registered: 8-2006 Posted From: 99.37.28.23 Rating: N/A |
Bill has it right in saying that Len and Brian have it right. Torque converters make a lot of heat while they are converting, and not locked up. This applies when the engine is either under power, or being retarded by Jake brake, which is why the lockup port is provided and wired into the Jake circuit. Throttle lever position, and fuel rack position are two entirely different things, as evidenced by Chuck saying his engine dies with his Jake switch on at idle. Obviously his Jake control is not wired thru his fuel rack. One last comment, there is a combination buffer switch/fast idle actuator made specially for buses, as trucks weren't usually ordered with fast idle. G | ||
| Jack Conrad (Jackconrad)
Registered Member Username: Jackconrad Post Number: 1408 Registered: 12-2000 Posted From: 75.246.207.69  Rating: N/A |
Here is what we did. I did not want to loose my fast idle or spend a bunch of money for a Jake buffer switch that had a fast idle feature. I temporarily installed a pressure gauge on my air throttle actuator on the engine and found that it takes 5 PSI to start opening the throttle. I then removed the gauge and installed a 3 PSI (normal closed) pressure switch at the air throttle actuator. I then confirmed Lock-up test port using a pressure gauge and then installed a (normal open) 100 PSI pressure switch. The 2 switches are wired in series so the Jakes will only operate when the there is less than 3 PSI (idle position) at governor and transmission is in lock-up. This has worked for a couple years with no problems so far. We also have an on-off switch on the dash WARNING: this is "my way" and not approved by anyone "official". YMMV. Jack | ||
| Luvrbus (Luvrbus)
Registered Member Username: Luvrbus Post Number: 1181 Registered: 8-2006 Posted From: 74.33.48.167 Rating: N/A |
If you worry about keeping a fast idle and need or don't have a cruise control you can buy the King Cruise with the fast idle feature for less than the price of a fast idle buffer switch or use a foot switch. A 2 step Jake on a 2 stroke is a waste of wire in IMO they shouldn't be left hot all the time anyway will cost you in fuel believe it or not,and being a go by the DD book guy a buffer switch it will be lol any of you can call Jake and get the service bulletin for hooking up the Jakes through the transmission but like Jack's hookup it takes 2 switches (Message edited by luvrbus on July 10, 2011) (Message edited by luvrbus on July 10, 2011) | ||
| Jim Wilkerson (Wagwar)
Registered Member Username: Wagwar Post Number: 167 Registered: 12-2009 Posted From: 69.150.233.21 Rating: N/A |
First, I want to Thank all of you for your help. Bill and Brian have it correct: I just want to know when the trans is in lockup via a N.O. switch in the lockup port. Here's what I've tried to no success. My HT 740D has four ports on the bottom, and so it matches one of the diagrams provided by Jacobs. The leftmost (driver side) port is supposed to be the lockup. The other ports are: Main, Governor and Lube. Main is obvious with a laarge square metal housing. So, I tried a 150 psi N.O. switch in the lockup port - no joy. I tried the same switch in the next port to the right - no joy. I then tried an adjustable pressure switch set to 35 psi in both ports - still no joy. So, not having the tools to actually test the pressure in each port while OTR - I was hoping that I just didn't have the pressure switch set properly. None of the diagrams show the lockuyp port in the 3rd position to the right - so I saw no reason to test that port - assuming it must be either governor or lube on all 740's. I hope that makes sense. |
