jake brakes on a 8v71 what 2 look for

[luvrbus]

Nick i have mine on a 2 postion switch where you can have a high and low

[Barn Owl]

Question, I never having Jakes before, what would be the best way to set them up with my 8V92T [silver] and HT740?  Switch, Throttle, or both?

I might not understand your question correctly but the switch with a high low selects the level of braking the jakes do. Low runs one bank (1/2 braking), high, two banks (Full braking). The position of the throttle turns it on/off. I find that having to remember not to completely let off the throttle is annoying at times, mostly on the interstate. I like the jakes the most around town (yes I know that is where you're not supposed to make all of that racket). In addition to the panel switch, I want to add a foot switch to my system that would allow me to only activate them when I briefly need them. It would be a momentary switch that would look like a high/low dimmer foot switch. This would allow me to activate them when going down a long steep hill if I needed them, and allow coasting down smaller ones when I didn't, all the while not having to feather the throttle. For most flatlanders they wouldn't have a problem with the traditional setup, but I spend most of my time driving up and down here in the mountains.

[lloyd]

Barn Owl, don't you have an on/off switch for the jakes? The reason they want the jakes to come on only when the throttle is released is because if you don't the fuel system will still deliver some fuel while jaking, which produces alot of smoke.
Lloyd

[Buffalo SpaceShip]

Nick, if the buffer switch is set up correctly, you should be able to leave the switch on and then the use of the throttle will turn them off. My Jakes do not have the two-position switch and I'll be adding this feature soon because mine provides a LOT of braking force with both banks going... great for going down steep grades, but too much for going down slighter ones and for slowing in traffic. A turbo motor like yours won't provide quite as much braking power due to lower compression, but I'd still opt for a hi-lo switch.

You'll also want to get a feel for when your tranny is in lockup, since any of the torque-converter ranges won't provide effective engine braking. Left on, the Jakes should slow the coach enough for it to downshift all the way down to your hydraulic 2nd or even 1st gear (depends on how your tranny downshifts), and then the service brake provides the rest when you need to come to a compete stop. Used properly, a Jake will add years to a set of brake linings (in RV service, anyways). I'm often able to come down winding roads and Interstate off-ramps with the Jakes alone, moderating speed with the on-off switch, all the way down to 15mph or so. My foot is always ready to apply the service brakes should the need arise, the linings and drums stay nice and cool.

Speaking of on-off switch, I like your idea of a momentary switch, Laryn! One foot on the service brake, one on the Jake... would save me a lot of fumbling for the switch. Love that busnut ingenuity!

Brian B.

[Nick Badame Refrig/ACC]

Thanks for the replies guy's.

Brian, I thought someone mentioned about a trans device...  what is this that I need for my 740?

Nick-

[DrivingMissLazy]

With the 740, all you need is a properly adjusted Buffer switch.
Although I've said it before, the most important part of the Jake installation is the location of the HI-LO-OFF switch. I had to move mine from the dash to the side switch panel because I had to lean forward to reach it. It should be within easy reach while you are in your normal driving position without having to fumble around or search for it in the dark. Properly used I think you will find it the control that you use the most while out on a trip.
Richard

Thanks for the replies guy's.

Brian, I thought someone mentioned about a trans device...  what is this that I need for my 740?

Nick-

[Barn Owl]

Barn Owl, don't you have an on/off switch for the jakes?

My switch is set up like Brian's, either off or on but no high/low. I would like to change it to select one or two banks for the same reason Brian has stated. My current setup, all or nothing, makes it uncomfortable for some driving situations. It's like I've dropped anchor or something.

[DrivingMissLazy]

I believe the tranny that Brian has (V730) acts significantly different than the 740 tranny that Nick has and that I had in DML.

There was really no way to detect when the tranny was in lock up or not. Significant braking is provided even with a turbo. If the Jake is left on in normal driving, this braking is very annoying and the ability to easily switch between HI and LO as well as OFF is, in my opinion, mandatory.

I stress that the proper adjustment of the Jake valve clearance and that of the buffer switch is of extreme importance.

Richard

Nick, if the buffer switch is set up correctly, you should be able to leave the switch on and then the use of the throttle will turn them off. My Jakes do not have the two-position switch and I'll be adding this feature soon because mine provides a LOT of braking force with both banks going... great for going down steep grades, but too much for going down slighter ones and for slowing in traffic. A turbo motor like yours won't provide quite as much braking power due to lower compression, but I'd still opt for a hi-lo switch.

You'll also want to get a feel for when your tranny is in lockup, since any of the torque-converter ranges won't provide effective engine braking. Left on, the Jakes should slow the coach enough for it to downshift all the way down to your hydraulic 2nd or even 1st gear (depends on how your tranny downshifts), and then the service brake provides the rest when you need to come to a compete stop. Used properly, a Jake will add years to a set of brake linings (in RV service, anyways). I'm often able to come down winding roads and Interstate off-ramps with the Jakes alone, moderating speed with the on-off switch, all the way down to 15mph or so. My foot is always ready to apply the service brakes should the need arise, the linings and drums stay nice and cool.

Speaking of on-off switch, I like your idea of a momentary switch, Laryn! One foot on the service brake, one on the Jake... would save me a lot of fumbling for the switch. Love that busnut ingenuity!

Brian B.

[Barn Owl]

Richard,

How does one adjust the speed at which the Jake disengages? Is it done by the buffer switch, or oil pressure, etc?

Laryn

[Barn Owl]

I should have mentioned that mine drops out around 35mph. I guess engine rpm might also have something to do with it. I would like mine to disengage at a lower speed, like Brian's 15mph.

Brian, are you letting your transmission shift on its own or are you using the TomC's method of shifting to get down to 15mph before your Jakes let go?

[Buffalo SpaceShip]

I believe the tranny that Brian has (V730) acts significantly different than the 740 tranny that Nick has and that I had in DML.

There was really no way to detect when the tranny was in lock up or not.

Richard, the torque-converter Allisons are all designed similarly enough to make some observations about lockup and how it affects braking and deceleration. Brian Diehl even went so far as to make an override solenoid on his old HT574: http://home.earthlink.net/~diehls0792/HT754TorqueConverterLockup.html , a brilliant device, IMHO.  If one has a tach and observes rpm drop or rise vs. the same in mph and compares throttle position to the same, it will soon become obvious if the tranny is locked-up or not. Noting the shifts of the tranny and when it goes in and out of lockup (and whether manual shifts make any impact on lockup... mine does) makes driving a coach, esp. in hilly conditions, much more safe and enjoyable.

Case in point, there's a long 10% downgrade into the Palo Duro Canyon (in TX) with sharp turns limiting speed to 15mph max. In hydraulic first (non-lockup mode) the Jakes were of no help, the tranny just "free wheeling" down, and I had to maintain heavy service brake use all the way down. Once I learned how to lockup my tranny in first, the Jakes could work along with the engine and I barely had to hit the service brakes at all. Huge difference.

For most flatland driving, lockup is not that big of a concern, but for coming down or even going up hills (for tans. cooling sake), it makes a huge difference being "locked-up" or not.

My $0.02,
Brian Brown

[DrivingMissLazy]

The Jakes disengage automatically as the engine oil pressure drops to the point that it is too low to hold the Jake' open. In my case it was in the 800-1,000 rpm range.

In reality, the Jakes generally disengaged when the tranny dropped out of lockup and quit spinning the engine. This generally only presented a problem on extremely steep grades in 1st gear when I had to go so slow (below 15 mph) that the tranny would not stay engaged. I believe there is some modification that can be made to the 740 to prevent this dropout, but I do not know what it is.
Richard

Richard,

How does one adjust the speed at which the Jake disengages? Is it done by the buffer switch, or oil pressure, etc?

Laryn

[Buffalo SpaceShip]

I should have mentioned that mine drops out around 35mph. I guess engine rpm might also have something to do with it. I would like mine to disengage at a lower speed, like Brian's 15mph.

Brian, are you letting your transmission shift on its own or are you using the TomC's method of shifting to get down to 15mph before your Jakes let go?

Laryn, the V730 in "D" mode is very "dumb" when it comes to shifting up and down. It was made for transit busses that seldom even hit lockup mode nor seldom climb hills. First off, if you don't have a tachometer, get one. Short of the temp. gauge, it's the most important gauge on an automatic-equipped coach IMHO. Ironically, I drove a stick-shift 4106 for years without a tach, and still wouldn't need one, since you shift 'em by the speedo and the 1:1 relationship it has with rpm.

The short answer is that you can control when it goes in and out of lockup with the shifter and the accelerator. The shifter determines the gear range and throttle position (on air modulators anyways) determines when and how the transmission will lockup. Usually just backing off the throttle a bit will allow it to lockup. If you have an hour and can find some empty roads, you'll get the feel of lockup and how it affects driving.

When going up hills, shift down at 1600rpm and up at no more than 2200rpm. Once you know when she's in lockup, try to climb hills that way to avoid heating up the tranny unnecessarily.

The absolute best thing to do would be to build Brian Diehl's solenoid lockup override mentioned above. Living here in the hills (and you have 'em, too), it's definitely on my short-list.

HTH,
Brian

[DrivingMissLazy]

Need someone that is very familiar with the various Allison transmissions. I feel certain the my 740 went into lockup while still in first gear, at about 15mph,  and remained in lockup thereafter as it it shifted to 2nd and then on up, while still locked up. But, I could be wrong. Would not be the first time. LOL
Richard

I should have mentioned that mine drops out around 35mph. I guess engine rpm might also have something to do with it. I would like mine to disengage at a lower speed, like Brian's 15mph.

Brian, are you letting your transmission shift on its own or are you using the TomC's method of shifting to get down to 15mph before your Jakes let go?

Laryn, the V730 in "D" mode is very "dumb" when it comes to shifting up and down. It was made for transit busses that seldom even hit lockup mode nor seldom climb hills. First off, if you don't have a tachometer, get one. Short of the temp. gauge, it's the most important gauge on an automatic-equipped coach IMHO. Ironically, I drove a stick-shift 4106 for years without a tach, and still wouldn't need one, since you shift 'em by the speedo and the 1:1 relationship it has with rpm.

The short answer is that you can control when it goes in and out of lockup with the shifter and the accelerator. The shifter determines the gear range and throttle position (on air modulators anyways) determines when and how the transmission will lockup. Usually just backing off the throttle a bit will allow it to lockup. If you have an hour and can find some empty roads, you'll get the feel of lockup and how it affects driving.

When going up hills, shift down at 1600rpm and up at no more than 2200rpm. Once you know when she's in lockup, try to climb hills that way to avoid heating up the tranny unnecessarily.

The absolute best thing to do would be to build Brian Diehl's solenoid lockup override mentioned above. Living here in the hills (and you have 'em, too), it's definitely on my short-list.

HTH,
Brian

[TomC]

The only time Allisons will lock up in first is if the shifter is in 1st.  If it is in 2-6th, it will start in 1st converter, go to 2nd converter, then 2nd lockup up to top gear.  This applies to HT740, HT754, HT755, HD4060, B500.  The MT640, MT643, locked up in 3rd. There were some derivations to this, but only on truck Allisons, like the HT750DR that had a real granny low and would normally start in 2nd.  Then it would lock up in 3rd. (they had a programming that would have each gear go from converter to lockup, so a four speed would be 1C-1L-2C-2L-3C-3L-4C-4L.  Kept the engines more wound up, but worse on mileage).  Good Luck, TomC