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prarieschooner
02-12-2009, 02:07 PM
I took the '82 to get the tires put on yesterday. I could use a little help understanding the Jacobs Brake operation, when to use it and why.
Steve

chockwald
02-12-2009, 02:55 PM
Good morning Steve! I have a "Jake" brake on mine, also. I use it, obviously, on steep declines. I put the trasmission in a lower gear (3rd, 4th depending on the length and grade percentage) and then just flip the switch and coast. You'll feel and hear the "Jake" take effect. On really steep, long grades you may have to use the brakes to scrub some speed off periodically, but it works pretty well, and certainly reduces the need for braking 70-80%. To give an example, you may be familiar with Sherwin Grade (between Bishop and Mammoth Mountain) on HWY 395. It's about 6-7%, and about 7 miles long. At the beginning of the grade I put the coach in 3rd gear, and turn on the "Jake" brake. Typically this takes me down to around 30-35 mph. I can hold it under 45 for about 3 miles before having to scrub some speed off again. Usually have to use the brakes twice on that downhill. Best thing with these big coaches is to just take your time and preserve the brake lining. Without the "Jake" brake you would be on the brakes for the entire 7 miles, or in 1st gear the entire time, and still using the brakes a lot.

Another time when I have used it is when I have had to make what I would call a "panic" stop where just braking would not stop me in the required distance. I hit the brakes, and flip the "Jake" switch and it is amazing how fast you can stop the coach!

So, what kind of tires did you purchase?

fulltiming
02-12-2009, 04:47 PM
Clarke gave an excellent description of the use of the Jake Brake. Diesels not equipt with an exhaust brake or a Jake brake have significantly less inheritant compression braking than gasoline engines. Let off a gasoline engine and you can feel it slowing you down due to the butterfly or the throttle plate closing off the air intake into the cylinders. Let off a diesel engine, particularly a two-stroke diesel engine, and you don't feel as much slowing affect since there is no butterfly/throttle plate to close. As a matter of fact, the Detroit Diesel two strokes have a low pressure blower that is gear driven off the engine that continues to pump air into the cylinders even though the fuel is shut off to the cylinders. A true Jake Brake (engine compression brake) provides engine braking by turning the engine into a giant air compressor. A Jake Brake works by closing the exhaust valves on all or certain cylinders. It is important to note that the higher the engine rpm, as long as you are within the engines maximum speed range, the more braking power the Jake has. Therefore you want to gear down to keep the engine up close to redline to maximize the effectiveness of the Jake. It will help at lower rpms but typically, on an engine that redline's at say 2100 rpm, most of the effectiveness is above 1800 rpm.

EDIT:
The Jake brake on a four-stroke diesel engine has more braking capacity than a two-stroke diesel engine. Example: Series 60 (4 stroke) Jake has about 550 braking HP and an 8V92 (2 stroke) Jake has about 260 braking HP.

Using just the service brakes on a long grade is a recipe for disaster in a heavy vehicle as you will have to stay on the brakes to the point that they overheat and become ineffective. Use of gearing down the transmission alone may get you to the bottom safely but you might have to go down in 1st gear without the Jake to maintain a constant controlled speed as opposed to maintaining a constant controlled speed in 2nd or 3rd with the Jake Brake.

Some newer coaches have two speed Jake Brakes. With those you can switch between low and high to vary the number of cylinders that are aiding the braking effort.

ALWAYS be safe and obey the truck speed limit on long declines. It doesn't matter how fast you get to the bottom, it matters how safely you get to the bottom of the mountain. Avoid use of the Jake brake on wet roads.

wallyarntzen
02-13-2009, 12:32 PM
Hi Steve,

I was visiting a bus repair garage in mineapolis yesterday that I have work done on my coach and we were discussing the use of the jake brake. The manager is a very good friend of mine and he says to leave the jake on all of time. I never turn mine off except when I come to a comunity where they restrict the use of them. This garage is primarly a detroit place and they now them well.
I have an 88 coach and my last newell was a 78. Michael, I had a two stage jake on my 78 which had a cummins in it. It would run 4 cylinders on low and all 8 on high. It worked well but I rarley used low.

Michael and Clarke are right jakes save your brake and there is no question that they slow you down when in use and they are a nessity in the mountains or steep or long hills.

Besides all that I love the sound of them.

Happy travels, Wally

chockwald
02-13-2009, 02:15 PM
Wally, thanks for the information. I wasn't aware you could leave the Jake on all the time. Does it only activate on zero throttle?

Richard and Rhonda
02-13-2009, 02:47 PM
Yes, most are set up to act on zero throttle. There is supposed to be a "sweet" spot where you are just beyond zero, where you are off the throttle, but not engaging the jakes.

It is a very small spot in my Newell.

There are many different opinions about running with the Jakes on all the time. The one downside for running with the all the time is that you do tend to glaze your brake pads because you don't ever really get on them that hard. On the other hand, they really do help in a panic stop, and who will have time to activate them in a true panic stop.

I usually run without them on the interstate for two reasons. One, they crosstalk with my cruise control. Two, if I'm not on cruise, I don't like the brakes coming on just because I am out of the throttle. If I could adjust in a bigger sweet spot, maybe I would rethink that.

There is a way to wire them into the brake pedal, and not the throttle, so that they activate on brake pedal only.

I do run them around town and in any kind of heavy traffic.

And to prevent the glaze on the brake pads. I occasionally do a couple of intentional hard stops. It really makes a difference in the overall performance of my braking system. If the coach gets to a point where it seems hard to stop from 15 mph to zero, it is time to deglaze the pads with a couple of 60 to zero hard stops. Make sure everything is tied down :-)

One more thing, as others have said, you don't want them on in slick conditions, because they can break your rear tires loose.

Speaking of brakes, here is some trivia that I was surprised to learn. The major brakes on the rear. Just opposite from a car. The brake pedal activates a two stage air valve, and the rears come on first, and then the fronts. Made sense after I thought about it. In a car, application of the brakes shifts a lot of weight to the front, and takes it off the rear, so the heavy braking is done by the front. That is not nearly so pronounced in a bus, the weight is in the rear, on twice as much rubber, so the primary braking is on the drive tires.

chockwald
02-13-2009, 03:13 PM
Richard, thanks for the illumination. Makes sense to have it on around town, and in heavy traffic. As I have said, and others have said, this forum is invaluable. Each topic discussed is like attending a mini seminar.

prarieschooner
02-13-2009, 03:32 PM
That answers most of my questions about the Jake Brake. From what I read it would be alright to have it on all of the time and no problem with the Diesel Engine. It would be better to use it as needed when the Road Conditions allow and it will not effect Cruise Control, although my Cruise isn't working just yet (another search then questions later).
We now have 6 new GOODYEAR G395LHS tires on the Coach, I didn't have the $$$ for the Michelin and probably wouldn't have sprung for them right now anyway. The BRIDGESTONE tires that were on the coach were weathered badly, had flat spots and dated 1997 so I didn't want to travel very far to get the new tires making it necessary to get them here in Yuma. The only real Truck Tire Shop here in Yuma that can spin balance Tires this size (11R22.5) is Purcell Tires.
I will have to let you know what I think about them after we get a few thousand miles but I can tell you that they ride much better than the tires that haven't moved in a few years and it sure makes me feel better about new rubber! These are a combination Regional and Long Haul type tire that are good for all positions.
Steve

chockwald
02-13-2009, 03:58 PM
Congrats, Steve, on the new rubber! Do you know what make your cruise control is?

prarieschooner
02-13-2009, 04:04 PM
How does one know?

ABnormal
02-13-2009, 04:28 PM
Ok guys. I got lost at Richard's comment about slick conditions potentially "breaking the rear tires loose". I had never heard that before and am not certain what it means.

Richard, could you expand on that a little?

Larry P.

chockwald
02-13-2009, 05:29 PM
Good question, Steve.....might have to crawl in the engine compartment, clean off the unit and see if there is a brand name on it. A lot of them are Bendix, but mine wasn't. My mechanic had to remove the unit to get a look at it in order to determine who made it, and then found out they were no longer in business, hence my move to Cruise King.

Richard and Rhonda
02-13-2009, 05:44 PM
Sorry, it's that southern good ole boy talk. Breaking the tires loose means sliding them, a skid.

If you have the jakes on, the come on when you let off the throttle. They are not like regular brakes in that they are either on or off, the amount of braking is proportional to the engine rpm. So, if the road is slick, and you let off the throttle, it's like a very hard application of rear braking. The tires can start to slip on the pavement.

Unlike normal braking where you would simply let up on the brake pedal if this started happening, the only way to get the jakes to release is to feed it some throttle. It's not what one would do instinctively in a skid with a 20 ton vehicle. Plus if it's skidding I don't think I'll have the presence of mind to hunt for the jake brake toggle switch either.

I am not saying don't run with them, just be aware that descending a icy or snowy grade with jakes could have a behavior you need to be aware of.

One more thing, my jakes do interfere with my cruise. If the bus starts down a grade the cruise will back all the way out of the throttle and I feel the jakes come on. Somewhat aggravating to scrub off that speed that will help you up the other side. Not a big deal in flatlands, but definitely aggravating in rolling hills.

Hope this helps with the explanation.

2dogs
02-13-2009, 05:46 PM
on our coach the jake was wired in to low only. i located the purple wire coming out of the valve cover and with the help of my wife and a mirror on a stick found the other wire on the other valve cover put in a two position switch and some wire to the back and now high-low and the original switch is on-off Brian.

encantotom
02-13-2009, 11:00 PM
anyone know if the jake on the 1990 is a two stage wired to be a single stage as well?

i will have to look.

tom

fulltiming
02-13-2009, 11:21 PM
My 1992 has a single stage Jake but does operate all 8 cylinders.

2dogs
02-14-2009, 12:59 AM
from what i understand detroit diesel sent them out with jakes on both banks but for safety reasons (skidding) they hooked up low only. Brian

encantotom
02-14-2009, 01:02 AM
so low is one side hooked up and high is all 8 cylinders? where does the wire come out and i will go check mine.

thanks

tom

Marc & Lisa Hobbie
02-14-2009, 01:20 AM
My 93 is like Michael's. It is hooked to low only on all 8 cylanders. Thanks! Marc

2dogs
02-14-2009, 01:34 AM
Our jake was hooked up on the drivers side the wire is on the back side of the valve cover about midway the jake only runs one bank on low both on high if you have all 8 working on a 7-8 percent grade you have to use throttle on high! slows down to about 35 in drive. Brian

encantotom
02-14-2009, 01:40 AM
here is the installation manual for 8v92 jacobs brake.

http://www.jakebrake.com/service/pdf2/003879.pdf

it shows for ddec2, which i have has a connection that goes into the ddec...however i am sure that is not the way that i have it hooked up.

it also shows a high low switch.

so in the non ddec hookup, i dont quite get the connections.

is it one wire for each bank or two wires for each bank? one wire for low and one for high?

tom

2dogs
02-14-2009, 02:08 AM
Its one wire for each bank low is one side high is both......

wallyarntzen
02-14-2009, 04:27 AM
Hi guys,
Back to my discussion with my bus garage friend. He informed me that a jake brake and and exhaust brake are two different systems.
The jake is an internal system that does not cause any damage to the engine with it on all of the time.
The exhaust brake is a system in the exhaust system itself and can cause damage to the turbo and engine if on all of the time. He said that there are not many detroits that he is aware of that have an exhaust system but it something that you should be aware of if you do have one.

This topic sure has generated a lot of interest.

Happy travels, Wally Arntzen

fulltiming
02-14-2009, 05:29 AM
Although Jacobs now makes an exhaust brake, a true Jake Brake works by forcing the exhaust valves closed rather than by closing off the exhaust pipe to create back pressure. I have had a coach with an exhaust brake and it would not activate with the cruise control on or anytime the throttle was partially open. The exhaust brake has the advantage of being silent but doesn't have nearly the braking force of an engine brake.

I do find that my Jake Brake and my cruise control do not play well together with my 4 speed non-electronic controlled Allison transmission. I get some bucking when the jake tries to kick in as the cruise control closes the throttle. I may leave the jake on when driving without the cruise control but don't leave it on with the cruise control.

madson95
05-02-2009, 09:22 PM
anyone know if there is a fuse for the jacobs brake? mine just stoped working and I sure miss it.learning to down shift all over again.
the jack switch lights but no "bark" and no decell.
madson95
85 wb 40 8v92

Richard and Rhonda
05-03-2009, 01:59 AM
I believe mine is in the passenger kick panel.

fulltiming
05-03-2009, 02:24 AM
Yep on my 1992, the fuse is number 16 in the panel in front of the passenger's seat.

madson95
05-03-2009, 03:18 AM
thanks mine was #16 also and it checks good guess more troubleshooting tomarrow.
warren

fulltiming
05-03-2009, 05:05 AM
I suspected that when you indicated that the light was working. If I understand that your coach is a 1985, the Jake is manually controlled rather than being controlled through the DDEC (Detroit Diesel Electronic Control) that was introduced after your engine was built.

There are a couple of possibilities: 1) the wiring from the switch to the Jake has broken or 2) the wiring within the engine has disabled several of the cylinders when the Jake is on. Since you no longer hear the sound of the Jake, I suspect #1. I would first troubleshoot after the switch and light which are obvious getting current and the engine for a short.

Stick Miller
05-06-2009, 05:49 PM
What is the difference between a Jake Brake and a transmission retarder? I've seen a few of these listed, especially on the Barth site and wondered how, and if they work.

jdaniel
05-06-2009, 06:14 PM
My 91 has a "brake" pedal on the left side. I don't hear it when it's in use so I'm pretty sure its not a Jake. It feels more like it downshifts and pulls back.

fulltiming
05-06-2009, 07:29 PM
There are three types of retarding devices used on diesel power motorhomes; exhaust brakes, Jacobs (Jake) engine brakes, and transmission retarders (there are also electric drive line retarders but I don't know of any motorhome manufacturer installing them).

Exhaust brakes, typically used on coaches with diesel engines less than 10 liters, close off the exhaust pipe when activated to apply back pressure to the engine which helps slow the vehicle. These are typically the least effective of the three types but are the less expensive and can be installed on virtually any diesel engine.

Jacobs (Jake) brakes close down the exhaust valves in the engine and literally turn the engine into a giant air compressor. A lot of restraining horsepower is generated by a Jake brake, enough that in 4 stroke diesel engines, typically a switch is provided to reduce the engine braking from working on all 6 cylinders to working on only 3 cylinders to keep you from slowing down too quickly going downhill. Click Here (http://www.jakebrake.com/products/how-the-jake-brake-works.php) for drawings of how a Jake works.

A transmission retarder works not on the engine but on the transmission. It reroutes the flow of transmission fluid to a retarder vane provide braking within the transmission itself. These are extremely effective and can generate enormous amounts of retarding horsepower BUT they are VERY expensive and can overheat the transmission quickly under heavy usage so an inexperienced driver can cause damage not possible with either a Jake brake or an exhaust brake as well as potentially lose retarding just as it is needed the most. Transmission retarders are great as long as they are used with a careful eye on the transmission temperature gauge and retarding reduced before tranny temps get out of hand. Foretravel has used Allison transmission retarders for years. Only a few Newells have been built with them and Jimmy and Debbie own one (notice that it was a show coach which frequently incorporate new and interesting features to gauge customer demand).

To make things more confusing Jacobs now markets an exhaust brake but it is not an engine brake.

Richard and Rhonda
05-06-2009, 07:49 PM
The jake brake uses the high compression of a diesel engine to provide resistance. The way it does that is that the jake actually opens the exhaust valve as the piston reaches the top of the compression stroke and lets the compressed air escape through the exhaust manifold. That is the noise you hear when on the jakes.

A transmission retarder actually has a fluid circulation loop in the transmission that is restricted and acts as a brake. Most transmission retarders have multiple settings depending on how much braking help you want. Almost all of them have a cooling loop for the tranny fluid because it does get very hot. They work very well, and with more adjustability than jakes, but you do have to keep an eye on the transmission temperature.

jdaniel
05-11-2009, 04:32 PM
I have begun to use mine in the last 6 months since I now know what it is. We don't have a lot of hills in Alabama but when I pull my racecar trailer I can tell a big difference. I have never noticed my trans temp climbing but again, I'm not coming down steep grades like some of you guys out west.

zcasa
05-12-2009, 12:45 AM
We live in CO and climb and descend 6% grades regularly. The guy that I purchased our coach from said what you go up in, transmission gear, go down in. Seemed pretty simple advice and it has held true for us. We typically climb at 32 mile per hour on 6% grades and descend at the same speed, all in second gear on our Allison tranny. We run with an 8V92 500hp 42'9", towing 3,500 lbs. I keep the Jake Brake on except when on cruise control. It doesn't work when the cruise is on. I simply put my flashers on and don't look in the mirrors when going on these grades, that way I don't see anyone giving me a salute. lol. So far, so good on the hills.

David

fulltiming
06-08-2009, 10:59 PM
Page 9.2 of my Owners Manual in the section on the Jacobs Engine Brake is the following:

Your Newell is equipped with a Jacobs engine brake which uses engine compression to retard road speed. The Jake brake is activated with a switch labed "Jake" located on the shift console of the dash. When activated, the Jake will function any time the throttle is released while the vehicle is moving unless the cruise control is engaged. The Jake brake is an effective and important safety feature, especially while descending long grades. It reduces the use, and consequently the heat buildup and fading, of the vehicle service brakes.

So the manual for my coach SPECIFICALLY indicates that the Jake does NOT work when the cruise control is in operation.

Wally Arntzen
06-09-2009, 02:47 AM
Hi guys, I never turn my jake off and it does work with the cruise control on. When I'm driving on cruise with the jake on and touch the brake the jake activates and I tap the cruise when i'm ready and it reactivates in the cruise mode.
If i'm running in cruise mode and go down a hill the jake activates on its own and the curise reactivates on its own when the speed reaches the running speed that was set prior to entering the hill.
I do not know why mine is different from some of you guy's but maybee yours is electronic and works in a different fashion.
I rember the discussion at Austion where most of the coaches did not work while on cruise.

Thats my story and I am not hallucinating.

Wally

encantotom
06-09-2009, 02:56 AM
as for wally not hallucinating, i cannot confirm that and in fact i think have witnessed it a few times.....

, but the part about the jake brake differences is accurate. mine and michaels didnt work with the cruise on and wallys and clarkes did.

tom

fulltiming
06-09-2009, 04:06 AM
The difference is the mechanical engines versus the electronic controlled engines. With the electronic controlled engines, the Jake can be programmed either way but apparently all the DDEC II engines that Newell used were programmed with the cruise overriding the Jake. With DDEC III and above, at least some, if not most, were programmed to have the Jake work with the cruise control engaged.

With the mechanical engines, the cruise and the Jake didn't have a clue what the other system was doing so the Jake is still operational even with the cruise control actually engaged.

Pros and cons either way. Good to have the Jake help slow you down on a short downgrade with the cruise control on but they can fight each other under some conditions.

Wally Arntzen
06-09-2009, 05:19 AM
Tom, I spoke to my friend at the bus garage and he informed me that something can be done to make the jake work with the cruise on any of the 8v92's wether its electronic or not. If you check with Leo I bet he will have a way to get it done.
My friend said he thinks that its possible that Newell did that for several years for reasons unknown due to the fact that coaches for some years have it one way and other years a different way.
This has been an extended discussion and maybe we can get cleared up. Michael, maybe if you talk to someone at Newell they can help.
I'm not passing the buck, just that you are an engineer and I would not understand the solution if they gave it to me.
Many things on these coaches I can take on and fix or replace and others, like electronic stuff I leave to guys like you that get it. I am not an electronic guy and doubt that I ever will be, but I can assure you that there is nothing on my coach that does not work and I'm a fanatic about having stuff that does not work.
I hope I did not add any confusion to the discussion.

Wally

encantotom
06-09-2009, 05:35 AM
good idea wally,

next time i am talking to leo, i will ask him about it.

i would like the option of having it on like you do.

thanks

tom

zcasa
06-09-2009, 02:31 PM
I would love to have the jake work while on cruise. I am always having to watch for the hills and adjust the cruise off while getting ready to hit a major downgrade. It would be so much more comforting to know that I would have some assistance in backing the speed off while heading downhill, without always having to be ready for every hill, which out here in Colorado, are many. I'll be interested what the solution might be.

David

prarieschooner
06-09-2009, 02:45 PM
My Cruise Control is still the Williams Dana. I always turn the thing off when in Traffic or when there is a Grade.