transmission retarder

[Bill1170]

This may have been discussed before but if so I missed it. While driving on interstate hwys or good 4 lanes ,without much stopping , do most drivers keep the retarder on or off. Does it seem to effect mpg?
It should not have been called a transmission retarder but I guess a Jake brake, I have had retarders on previous coaches.

Bill C

[Jon Wehrenberg]

The two (Jake and retarder) are different. I can generalize by saying when I had a Jake on my previous coach I turned it on as necessary.

I have a retarder now and I turn the "master" retarder switch on every time I am driving, and use the steering column mounted control when needed. By doing that I have retarder assistance standing by and ready for whenever I apply the brakes, and I can assist the cruise control by manually controlling retarder operation on the steering column mounted control.

Neither the Jake or retarder add "drag" or affect your mileage when driving. The Jake turns your engine into an air compressor and then dumps the compressed air at the end of every compression stroke when it is called upon to work.

The retarder acts like a torque converter when working by resisting the flow of transmission fluid with the amount of retardation varied by the control. While both are slowing you down, and can be seen as preventing the bus from taking full advantage of the energy stored by a bus starting to descend a hill, both are actually just using some of the energy from free wheeling down a hill to regulate the speed of a descent.

Whatever you have feel free to make use of it. There is no down side.

I would recommend you monitor the transmission temps when using a retarder, and although Allison says the transmission computer limits the temps, and that temps up to 300 degrees are OK, they also prove by their fluid change schedule that the resultant high temps from a retarder cut fluid life cycles in half.

There are no restrictions or limits relating to the use of a jake brake.

[dreamchasers]

Bill,

I can share the way I use the Jake Brake. On my Country Coach, a Jake Brake enable button is selectable, on or off. I normally like the Jake brake helping slowing the coach, so I keep it on or enabled most of the time. When the accelerator pedal is depressed, sending a fuel demand signal to the ECU, the Jake is enabled, but not actually engaged, slowing the vehicle down. When the fuel demand is off and cruise control off, the jake will engage.

Perhaps others can offer their feedback.

Hector

[dale farley]

Because I like the assistance of the Jake brake, I usually set it on "Low" while in urban/suburban areas and set it to "High" when in hills/mountains. I don't usually use it on the interstate if I have my cruise engaged, but I make sure I can quickly switch it on if needed.

[Bill1170]

Thanks for the replies,I ask for the info and then have been out of town.
I do like the way the jake brake works and so I leave it on most of the time and am glad to hear it does not effect mpg.

[Larry W]

I do not know if leaving my Jake on affects my mileage, I never turn it off. In fact I leave the jake on high most all the time. At cruise rpm (1500 to 1600) in 6th gear the jake does not do a lot to slow the bus down. Here in the west we have numerous roads that are up and down grade. I set the cruise to about 1600 rpm and when starting down a grade that is steep enough to make the bus speed up I will shift into 5th gear and most times the cruise will maintain it's set speed down hill. When slowing to exit the freeway for a rest stop I keep down shifting to the next lower gear when the engine speed drops to 1400 rpm. This allows very little use of the brakes. In urban areas I use a gear that will maintain a rpm range of about 1600 to 1700 rpm. When some pulls out if front of me the jake will start to slow the bus before I can put my foot on the brake pedal.
Just how I do it, do what fits you.

[Jon Wehrenberg]

The jake will work best at high RPM. It turns your engine into a very poor efficiency air compressor, so the more RPMs the greater the force of holding you back. A jake has a theoretical retarding force equal to about 1/2 your rated horsepower. The only downside to the use of any retarding device is it is dangerous on slippery surfaces.

If we all wanted to get ridiculously detailed we can say any type of retarding device does cost us mileage, but its cost in terms of fuel is insignificant compared to the safety benefits we derive. By using a braking device, either the transmission retarder or the jake, we are using some of the energy ot took to crest a hill and throwing it away in the form of asking it to slow the coach on the downhill side. We are covering the ground going down the hill at a slower speed rather than allowing the bus to coast down at whatever speed it can obtain, thus reducing the engine running time, and having a much higher speed at the bottom delaying the need to step back on to the gas pedal due to the momentum. This of course ignores speed limits and safety and just theoretical.

In a plane where there are no speed limits applicable this concept works.

But forget about that very small cost of using the jake or retarder. Their use helps us have much greater control of the momentum our very heavy buses have and provide a very valuable braking assist when needed.

[dale farley]

Jon, Among other things you mentioned, the slippery surfaces is a good point. I know the manual says don't use the Jake on slippery surfaces (rain, ice, etc.).

[Jon Wehrenberg]

I've got a lot of experience driving all sizes of vehicles on slippery surfaces. I can say with absolute certainty that if a jake or retarder is used on a slippery surface that drive axle could lose traction if the retarding force exceeds the traction available. That means out of the 8 wheels, you are now left with 4 to provide braking force and directional control.

Our braking systems are precisely balanced by Prevost engineering varying the brake surface area, the brake chamber sizes, and adjustments to the slack adjuster arm lengths to evenly apply braking forces. When you add a retarder to just one of the axles you lose that balance and that one axle is locking up with brake application. A locked wheel has virtually zero braking or steering force.

This is most evident in the snow belt, but I have learned here in the south that long periods between rain showers produce the same results when it rains. The oils that have dripped onto road surfaces for weeks between rainfalls create ice like conditions when it rains. So my advice would be to be very cautious with the use of the jake or retarder when the potential for slippery road conditions exists.

There are other snow belt drivers here and maybe they can add to these comments.

[jack14r]

If the coach has ABS and the ABS activates my Prevost manual states it will disconnect the retarder,I don't remember about the jake.

[Jon Wehrenberg]

Jack, I don't doubt what you posted, but a big concern is when a drive axle loses traction one of the problems besides the potential loss of braking force is the ability of the coach to get sideways. If no brakes are applied the ABS will not function to disconnect the retarder, and if the coach gets sideways the last thing a driver wants to do is apply brakes.

At some point it is possible for for the driver to become the passenger.

[JIM CHALOUPKA]

I can't add anything new, but I will certainly confirm what Jon has said.

ABS doesn't come on until you are usually into deep do do!
IMHO usually when the ABS comes on it is almost too late to do anything but go along for the ride. The retarder turning off at that point would probably be too late.
With the usual driver panic and or freeze (because he is surprised by the ABS) if for only a moment makes it easy to loose control. Even if you don't end up sideways and continue in a straight line, you could be in a bad situation.


JIM

[Jon Wehrenberg]

I have driven on icy or snow packed roads at normal posted highway speeds. I have done that a lot. Not real bright, but very satisfying when I get home without going off the road or hitting anything expensive. I have never been in the ditch, never had to get towed and never hit anything. But I have sure had instances where I pushed too hard and had to get it straightened out.

When the car or bus or truck is nearing the adhesion limits such as when driving on a slippery surface any change in forces must be done very carefully. For example you cannot make steering changes or brake applications like you do when on a dry road. If you do traction will be lost and at that point you are put into the position of trying to correct to restore control.

When the rear wheels are driving such as in our buses and traction is lost usually the rear end of the vehicle signals that loss of traction by starting to go sideways. The correct and necessary immediate response is to get your foot off the accelerator and steer in the direction the tail is skidding. With the proper control inputs the stability is restored and control is regained.

So when going down the highway, the exact same event can occur, but not due to driving forces, but worse....due to retarding forces. When going very fast at the absolute limits of traction a driver sloooowly lifts from the throttle to retain rear axle adhesion. If he lifts his foot fast he risks the same loss of traction as trying to apply too much driving force.

But add in a retarder or jake and when traction is lost how many drivers will have the presence of mind to kill the switch or step lightly on the gas to turn off the retarder? The answer is almost none. I use my retarder and did use my jake a whole lot. But when conditions get slippery I used them very carefully if at all. And I really back away from the cars ahead. I cannopt control them so I have no choice but to stay away from them. This has never been more true than here in the south where the ability of drivers to handle slippery conditions is virtually non-existant.

[Ray Davis]

This has nothing to do with jake, or retarders, but it made me chuckle this morning. It has to due with location perspective ....

Larry mentioned something like "out here in the West", and for those of us in CA, we don't think of CO as "in the west".

Likewise Jon mentioned something like "in the south", and I personally have more thought of him on the East Coast!

Of course, I've heard things about Ohio being in the "mid-west", and that has always puzzled me.


Oh well, it's all in fun ....

[Jon Wehrenberg]

It all depends on your perspective. To me Texas is considered the west, just like CO, UT, WY, CA NM, AZ, etc.

When someone mentions the east I never think of GA or FL, but instead think of NY, NJ, CT, DE, etc.

I don't know where OH being in the midwest comes from because I think of ND, SD, NE etc as being midwest.

I do know where the slippery roads are.

[Mark3101]

Jon, Among other things you mentioned, the slippery surfaces is a good point. I know the manual says don't use the Jake on slippery surfaces (rain, ice, etc.).

This is right on the money and why when my family had a fleet of trucks I never installed Jake brakes on ANY of them. Living in the upper Midwest (and operating there and in middle Canada) where we gets LOTS of snow and ice, we had accidents every winter where the cause was driving either too fast for conditions, or driving when you should be parked because the conditions were that bad.

Jackknife accidents were common and adding a Jake only increased the odds that it would happen. Too many drivers would not remember to turn them off and under the right situation, it could cause an almost instant jackknife. The newer abs systems and Jake will talk to one another, but to me it is already too late if the wheels are locking up..at least with a tractor/trailer.

[Larry W]

When traveling in our bus our rule is, icy or slick roads park this thing and wait until the roads clear. We all travel with the comforts of home so why would we want to drive on slick roads with our dream machine?

[sticks]

Still confused about retarder precautions with my 2005 Liberty. If I,m driving on potentially slick roads I can see where I wouldn't want the retarder, set on the steering column, to be past the first or second level so that going down hill with accelerator off wouldn't cause sudden " braking" which would unsettle the coach and possibly result in loss of control. However, with retarder switched on at the dash and the column lever all the way up would that cause a problem if you applied the foot brake ? On my previous Travel Supreme , I had what I thought was a jake break which I was instructed to leave on "high "at highway traveling to save the brakes. Please educate me , I,m all ears. Living in Iowa I unfortunately will be coming and going in marginal weather during winter months.

[jack14r]

The retarder on your coach is also connected with the ABS brakes and if the ABS is activated it will disable the retarder.I have never had this happen and I assume once the ABS is not active the retarder will become active again.If I was driving in slick conditions I would use the retarder in the lower positions,1-2-3 until I felt comfortable that I could use the higher positions.The Prevost manual has a good discussion about this subject,I would read it before driving in ice or snow for the first time.

[Jon Wehrenberg]

Our retarders are activated with braking, and supplement the braking at the drive axle. If you have the lever in the off position, but the dash switch for the retarder on, brake application and retarder application are proportional. The harder you step on the brakes, the more force the retarder will apply.

A good rule of thumb when driving on slippery surfaces is to modulate your braking (and speeds of course) to avoid ABS activation, but if it is activated and you realy need to stop keep your foot mashed on the brakes, The use of the retarder in slippery situations may induce the ABS because the braking force on the drive axle is going to be disproportionately higher than the tag or steer.

[jack14r]

Jon,I think that the switch must be on and the lever in at least the #1 position for the brakes to activate the retarder as you describe.

[Jon Wehrenberg]

Not on my bus, Jack.

I leave the switch on all the time, so if I have to make a quick stop I have all the help I can get.

My vintage bus has the transmission oil temp gauge and retarder light visible all the time and I know every brake application is accompanied by retarder activation. I manually use the lever only on long downhills, because if I left it on while on cruise control the retarder would be cycling on and off.

Don't you have a dash light to indicate retarder activation?

[JIM CHALOUPKA]

The way I perceive mine to work is;

the retard push button on dash is on (all the time for me)

when you are off the throttle the retarder is activated, but only to the degree of which the steering column LEVER is set

Zero thru Six. Six being the highest degree of retard and

ZERO being a degree that has no retard

ONE is the first lever position that will retard the bus (mine anyway)

TWO thru SIX have successively higher degrees of retard
_____________________________________________

I think Jon is saying he has a degree of retard at ZERO lever position.
I don't think that I do. (I can not feel it)
______________________________________________

I also don't think the ABS is directly affected by the retard any more than it is if say one is driving in 3rd or 4th gear and the engine is slowing you down as you reduce throttle.

I don't think the retarder will induce abs to activate any sooner than if you did not have retard button turned on.



JIM

[Jon Wehrenberg]

I did not say I have any retarding in the zero lever position. However, with the retarder switch "on" I have retarder application when the brakes are applied.

With the lever in any position but the zero position just lifting your foot from the accelerator applies the retarder. Two different things.

[sticks]

Well from reading your posts this isn't an open and shut case. But I think in normal driving conditions, I'll leave retarder in #2 position( with dash switched on at ALL times). If potentially slippery I'll go to #1 and if I'm stuck in SLIPPERY conditions and I'm just trying to nurse my way to a safe spot to pull over and wait it out, I'll put retarder lever in #0 position.

[JIM CHALOUPKA]

You've got it down Sticks, but don't be afraid to try the higher positions as conditions warrant.

You can work that lever a lot if you like to be involved :eek: in driving.


;):DJIM

[Jon Wehrenberg]

Sticks, I come from the western NY snow belt and when I saw your post all I could think about is the ass end of your coach trying to take the lead.

Under normal dry road conditions I don't think the use of the retarder is a concern. It will certainly help a lot when braking, and in the #2 position, with planning it is going to assist in going downhill without speeding up.

But having any assistance from the retarder, and that includes leaving the lever in the zero position, but the switch on, when in slippery road conditions needs to be considered.

Unless you are braking with the switch on, the retarder will be off in the zero lever position. Letting your foot off the throttle in the zero position will not engage the retarder. Braking with the switch on engages the retarder, but the ABS shuts it down if wheel slippage occurs.

With the lever in the #1 position however, the retarder cuts in with braking giving more power to the braking on the drive axle. Without braking it still could cause the drive axle to slip because it also drops the coach down a gear. That sudden gear reduction could break the rear end loose, and without using the brakes the ABS does not kick into play.

We drove a lot on snowy, slippery roads and the bus is very good and stable. But like anything else you want to be able to regulate how quickly you attempt to turn, stop or accelerate so I would suggest you practice on lightly traveled roads to see what retarder position if any is best. When the bus starts skidding you will not have the time or thought to turn the retarder on or off.

The sky is not falling. It does take a lot to break the back end of the coach loose or to get it to plow on the front end. When stuff like that happens you have been pushing the envelope. But a retarder doesn't have the feel you have as a driver who can modulate the use of accelerator or brakes. I wouldn't worry about the coach stability, but be aware the use of a Jake or retarder on slippery surfaces is probably not the thing to do.

[jack14r]

I only have a light which is a stop light on the dash and can be activated by the retarder or the brake pedal.I have my manual in front of me and here is what it states.
OPERATING THE RETARDER USING THE BRAKE PEDAL
With the retarder activated(retarder switch depressed),the accelerator pedal released and the output retarder lever in the initial position,apply the brake pedal as if using the service brakes.The further the brake pedal is depressed,the more the output retarder is applied.

The manual has a chart which shows the efficiency of the retarder
position efficiency
initial 0%
1 16%
2 33%
3 49%
4 71%
5 89%
6 100%

I thought that the word initial meant position 1 but it obviously means the position before position 1.

[sticks]

maybe it would be less complicated to move my whole horse operation to Florida than I don't have to worry about any retarder position

[Jon Wehrenberg]

Now you are catching on Sticks. There is a reason we moved out of NY, apart from dumb ass politicians. The snow was not fun to drive in and most of our use of the coach was when it snowed.

Move to Florida and use the retarder as you see fit.