Author Topic: Engine brake preselect  (Read 14348 times)

Dan n Lisa Lund

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Engine brake preselect
« on: April 27, 2015, 11:07:52 PM »
Hi guys and gals,
I have read the posts on changing the engine brake preselect from 4th to 6th gear which is something I want to do. The question now is where in the Phoenix area can I get it done. I called Massey's and got transferred 3 different times before being put on permanent hold, so I am not too impressed with that . Called Freightliner of AZ and talked to the service advisor and he told me that he didn't think what I wanted to do was a good idea. So they are off the list. Any more suggestions of an Allison shop would be appreciated.
Thanks, Dan Lund

David T. Richelderfer

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Re: Engine brake preselect
« Reply #1 on: April 28, 2015, 12:22:45 AM »
I had mine reprogrammed at Kenworth in Pasco, WA.  I see you are from Gilbert and there is a Kenworth in Phoenix.  You might give them a call....  1021 N 59th Ave, Phoenix, AZ 85043... (602) 258-7791.  Kenworth wanted to charge about $75 but since I'm a pretty nice guy, they did it for no charge.  lol  Actually, in the middle of the job the tech got a call from a truck that died on the freeway.  So he hurriedly finished the job and said he had to go, and have a nice day.  I thanked him and was gone in a few minutes.
« Last Edit: April 28, 2015, 12:30:24 AM by David T. Richelderfer »
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I had a dream... then I lived it!

Mike Groves

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Re: Engine brake preselect
« Reply #2 on: April 28, 2015, 12:36:27 AM »
I've read some of those posts, and I think it is important to understand that the jake brake effectiveness is directly proportional to the engine speed.  The reason it slips to 4th gear is to assure a reasonable effectiveness to the engine braking.  The danger is the engine speed may go over the recommended limit if you're already going too fast.  I've looked at this again and again, and everything I've read says leave it the way it is (4th gear), and change driving habits.

For example, those road signs give you notice of those steep declines and the literature I've read says crest the hill at the speed you want to descend it at.  I don't think many of us are cresting hills over 60mph which is probably what it would take to overspeed your engine if you then activated the jake brake.  Rather you're probably cresting the hill at a speed well within the engine's capability to slip into 4th, generate significant engine braking (due to the engine speed), and you safely go down the hill. 

When I first started driving my coach, I waited too long, didn't look ahead, then was going to fast, and pumped my brakes to cut down my speed to under 60, then used the jake.

That's not the way you should do it.  At least based on what I've read.  So, you could manually downshift first to 5th gear for example to slow down a bit, use your brakes, then set the jake.

The problem with leaving it in 6th gear is you won't have an effective jake due to the lower engine speed.  I think the engineers who designed this system have it right. 

For me, when I crest a hill I make my decision, and if I am wrong initially selecting the jake, I take it off temporarily, but before going too fast I set it.  If I need more, I select the 2nd level jake.  In other words, going downhill I rarely use brakes any more.  I control my speed using the jake.



David T. Richelderfer

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Re: Engine brake preselect
« Reply #3 on: April 28, 2015, 12:50:11 AM »
All I can say is you must not have engaged your Jake Brake when going about 65 mph.  The transmission's downshift from 6th to 4th takes the engine's RPMs from 1600/1700 up to 2300/2400 in about 1/2 second.  Many hills on freeways are designed to travel up and down at "freeway speeds," not at 45 to 50 mph.  Even on hills with a 6% grade my Jake will hold my speed down well enough to require only a "toe touch" on the brake pedal every 15 seconds or so... and I can still maintain a reasonable speed so as to not hinder other traffic too much.

If you like it the way it is, then don't change it.  I didn't like it, and neither did my brother who is a fuel truck driver packing about 7,500 gallons or more each trip.  It's simply a choice open to the chooser, and we don't weigh but half or slightly more compared to a heavy hauling truck.
2004 Beaver Marquis Sapphire

I had a dream... then I lived it!

Dan n Lisa Lund

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Re: Engine brake preselect
« Reply #4 on: April 28, 2015, 03:08:33 AM »
Coming from a trucking background of about 15 years I do understand how to use a jake effectively. There are many times I do wish to use the engine brake at 65 mph. If I need more rpm's to make the engine brake more effective I can and will manually select a lower gear. Thank you guys for the info  :)

Marty and Suzie Schenck

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Re: Engine brake preselect
« Reply #5 on: April 28, 2015, 03:53:56 AM »
Dan, I also came from a trucking back round. You will not regret having it reprogramed. What the motorhome public is missing in this debate is losing 30% of braking by disabling 6th and 5th gears. There are countless times I have been able to descend an incline or mountain pass in 6th or 5th gear and just hold THAT speed and not slow down because of TOO MUCH stopping power in which 4th gear WOULD have done. Sometimes we don't need to stop or slow down, we just want to maintain a given speed on a downhill and 6th and 5th gear choices allow this. On top of that, if you have the C-12, defaulting to 6th will prevent ever over revving the engine in a no load situation. Marty 

Andy Clark

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Re: Engine brake preselect
« Reply #6 on: April 28, 2015, 03:23:06 PM »
I don't undertand some of what I'm reading here. The Allison trans will not allow the engine to overspeed. If you have the engine brake on and a downshift will put the engine RPMs too high, that downshift will not occur. My exhaust brake is on all the time. When approaching a 5 or 6% downgrade, I approach at 1900RPM, between 60 and 63mph (ref back to the comment about freeway hills being designed to be travelled at freeway speeds). As soon as I lift my foot off the accelerator, the trans shifts to 5th and the RPMs go to about 2500-2600. This is usually enough to hold speed on the hill. I don't understand those comments about the trans "slamming" into 4th right away. As far as I know, that's not possible. If I decide to slow down on said hill, a firm application of the service brakes brings the RPMs down sufficiently that the trans then shifts into 4th, the RPMs go back to about 2500 and the speed is reduced from about 55-60 down to 40-45mph.
As I said, I run with my exhaust brake on all the time and it's programmed for a 2nd gear target, so I get the maximum amount of braking from it all the way down to about 15mph.
Maybe I'm missing something in this discussion, but what I just described works for me. Just returned from a 4000mile round trip and never had any instance whatsoever of the exhaust brake trying to overspeed the Cummins, either coming down Tehachapi pass or the Siskyous.
Andy
Andy Clark
1995 Patriot 37
300HP Cummings 6CTA8.3
Camano Island WA

David T. Richelderfer

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Re: Engine brake preselect
« Reply #7 on: April 28, 2015, 04:55:41 PM »
The first time my engine went from 1600/1700 RPMs to over 2200 RPMs in about 1/2 second I thought the engine was going to fly out the backend.  2200/2300 is getting close to an over speed condition, too close for my liking.  I sit some 40 feet ahead of the engine and generally cannot hear it.  What I can occasionally hear is the exhaust when accelerating and when the Jake is engaged because of the Aero muffler.  While it is true the Allison is supposed to not allow an engine over speed condition due to downshifting, it is also true that diesel engines run under higher internal pressures and longer stroke lengths - both of which cause additional strain on the bearings, pins and moving components.  I just do NOT want to submit my expensive engine to unnecessary strain by large and very rapid RPM changes, especially when under load.

Again, it's a choice.  I make my choices, you can make yours.  I much better like to switch on the Jake at the top of the hills and then manually downshift one gear at a time as needed.
2004 Beaver Marquis Sapphire

I had a dream... then I lived it!

Joel Ashley

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Re: Engine brake preselect
« Reply #8 on: April 28, 2015, 07:55:50 PM »
Ditto David.  Although our Monterey has essentially just a "Pac Brake", built by Jacob's, and not a Jake Brake type found on other models, nevertheless, I don't go down significant hills more than the posted Truckers speed, and kick on the exhaust brake at the top.  At those speeds downhill, commonly freeways at 55 mph and in 5th, the factory system works well for me, as does the 5th/6th shift points set, tested, retested, and prescribed for maximum efficiency by Allison at 57/63.

It's a learning curve.  It might go into 4th on a downgrade if I'm stuck behind a truck I can't pass or something.  Then its "jumpy" if I have to tweak the throttle to keep up and the pac brake kicks in again when I let off;  I've not learned to be particularly adept at balancing smoothly in that situation.  But on wide-open multi-lane freeway hills where it can stay in 5th at 55, the pac-brake works well, and depending on slope, it often will hold speed all the way down with little other input from me.

As David implies, we don't all drive the same, and make different choices accordingly.  If you can't adjust your habits to your existing configuration, than perhaps changing it is worth it to you.

Joel 
« Last Edit: April 28, 2015, 08:57:04 PM by Joel Ashley »
Joel and Lee Rae Ashley
Clackamas, Oregon
36.9 ft. 2006 Monterey Ventura IV, aka"Monty Rae"
C9 400HP Cat

Dan n Lisa Lund

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Re: Engine brake preselect
« Reply #9 on: April 28, 2015, 10:29:04 PM »
Marty and David ... you are exactly right! I don't always want to stop or want the "maximum" breaking from the engine brake. There is no way I want my C12 turning anywhere near 2200 RPM's with the engine brake unless I am in a true emergency trying to stop. I use the engine brake as a brake saver and not a means to stop the coach. As for the Allison not allowing the engine to overspeed........ I call BS on that! The first time I was at about 65 and turned on the engine brake I thought I was going to see parts scattered on the road behind me. Cats are not designed to turn high revs. The closer I can stay to 1500 rpm's the better I like it and so does the Cat. And as Joel said....  its all a matter of personal preference and driving style.  Just my 2 cents.
« Last Edit: April 28, 2015, 10:32:16 PM by Dan n Lisa Lund »

Edward Buker

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Re: Engine brake preselect
« Reply #10 on: April 28, 2015, 11:36:51 PM »
There is a lot of good info in this series of posts about the C12 in general.

http://beaveramb.org/forum/index.php/topic,1381.0.html

The max RPM and governor speed is 2100RPM with a turbo and a Jake break and although the C12 has tolerated a bit more, that is the safe RPM. In my opinion I would want my C12 to live somewhere near the 2000RPM range for braking effectiveness at higher driving speed levels on hills. If your maximum downhill speed was to be held at 60MPH then whatever gear has you at about 2000RPM would be a good match. If 55MPH was the max speed you would likely ever want then again you would want to match that speed to around 2000RPM. You could use 3 cylinder or 6 cylinder Jake brake as needed.

My unit used to slam into 4th as some have mentioned and over rev to 2400 to 2500RPM. There was some combination of C12s, 4000series transmissions, and rear end ratios that did not seem to have the right program implemented and they were not well protected with the Allison algorithms that were used. This is not true for all units it seems.

I had my unit reprogrammed to 6th and lived there for awhile and used manual down shifting. I then reprogrammed it to go to 5th with the Jake and I think I like that, as a best compromise, given that when I used the 6th gear Jake option I was downshifting to 5th most of the time. This is not to rehash too much of this info over again, just to get some of the new folks onboard.

Later Ed

Joel Weiss

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Re: Engine brake preselect
« Reply #11 on: April 29, 2015, 02:01:32 AM »
It's probably worth adding that, at least during the SMC Beaver era, the Marquis and Patriot Thunder C12's were geared differently.  I can let the Allison go into 4th with a speed as high as 65mph without the engine going beyond ~2100rpm.  Since my CR-V has a tow speed limit of 65 I'm unlikely to be going any faster than that especially entering a downhill run.

One nice thing about the gearing is that 4th is a great gear to be in when you're going through rolling hills.  I manually downshift it to 4th and leave the Jake on so when the Jake is engaged there is no downshift, just the stopping force.  Makes for a very easy ride and with a speed of ~55-60 the engine is nearly at max HP which provides lots of performance.

Lee Welbanks

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Re: Engine brake preselect
« Reply #12 on: April 29, 2015, 02:07:19 AM »
Marty and David ... you are exactly right! I don't always want to stop or want the "maximum" breaking from the engine brake. There is no way I want my C12 turning anywhere near 2200 RPM's with the engine brake unless I am in a true emergency trying to stop. I use the engine brake as a brake saver and not a means to stop the coach. As for the Allison not allowing the engine to overspeed........ I call BS on that! The first time I was at about 65 and turned on the engine brake I thought I was going to see parts scattered on the road behind me. Cats are not designed to turn high revs. The closer I can stay to 1500 rpm's the better I like it and so does the Cat. And as Joel said....  its all a matter of personal preference and driving style.  Just my 2 cents.

Give WW Williams in Phoenix a call as they are the Allison folks in Phoenix, I have got parts from them and found their service to be top notched
On another note Cat motors do not have Jake brakes, they are all Cat and no part is Jacobs. I had mine done up in Pasco Wa and like you coming from O/O trucking business I found it really stupid to shift into 4th gear. I could not get the PT to the shop fast enough to have that redone. Going down grades if 6th won't hold it PUSH the BOTTON to 5th and if that won't hold it, well you know the drill.
I also have had the motor over rev with the stupid trans setup, there is no way I want this C13 anywhere close to 2250.
We know why they put this into the trans because of the ones that have know idea what a engine brake is or how to use it.
Get the trans re-programmed and you will love it.
« Last Edit: April 29, 2015, 02:15:16 AM by Lee Welbanks »

Joel Ashley

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Re: Engine brake preselect
« Reply #13 on: April 29, 2015, 02:34:53 AM »
On another note Cat motors do not have Jake brakes, they are all Cat and no part is Jacobs.

As a clarification, if you have the lighter coach models, say with a C9 or smaller, your engine brake can be a "pac-brake" style in the exhaust system, which can indeed, like on our Monterey's, be made by Jacobs Vehicle Systems.  Others can have internal engine compression braking more commonly referred to as "Jake brakes", which like pac brakes may not be made by their inventors.

Joel
« Last Edit: April 29, 2015, 02:39:21 AM by Joel Ashley »
Joel and Lee Rae Ashley
Clackamas, Oregon
36.9 ft. 2006 Monterey Ventura IV, aka"Monty Rae"
C9 400HP Cat

Edward Buker

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Re: Engine brake preselect
« Reply #14 on: April 29, 2015, 04:18:22 AM »
Lee,

I'm not sure that is true about C12 not having Jake Brakes.

http://www.jacobsvehiclesystems.com/files/support/docs-pdfs/sle475.pdf

Later Ed