High & Low For Jakes or High Only?

JackConrad · 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

luvrbus · 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

bobofthenorth · 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.

junkman42 · 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

Utahclaimjumper · 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

rusty · 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

edroelle · 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

mikelutestanski · 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

Nick Badame Refrig/ACC · April 10, 2009, 04:41:51 PM

Quote from: edroelle 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

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-

JackConrad · 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

belfert · April 10, 2009, 07:21:57 PM

Quote from: Nick Badame Refrig. Co. on April 10, 2009, 04:41:51 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.

JohnEd · 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

luvrbus · 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

JohnEd · 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

Diesel_Gypsy · April 11, 2009, 12:54:58 PM

Quote from: mikelutestanski on April 10, 2009, 04:32:35 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