Jake Brake vs PAC Brake vs Retarder?

Topic: Jake Brake vs PAC Brake vs Retarder? (Read 2964 times) previous topic - next topic

Jake Brake vs PAC Brake vs Retarder?

September 04, 2012, 10:14:47 pm

I'm getting confused. Some people would say that that's my normal state, but we'll save that discussion for another time.

As I understand it, all three of these are meant to use the engine/transmission to help slow the coach, or help control speed on steep downhill slopes. One person told me that the PAC brake is akin to "the potato in the exhaust pipe" and the transmission retarder forces transmission fluid against the normal flow of the fluid. It sounds like the Jake brake is somewhat different in that it slightly opens the exhaust valves on varying number of cylinders.

Now the question. Which, if any, of these is more or less automatic? Can any of them be a "set and forget" operation, or are they all completely manual? Is there any great advantage of one over the other two?

We've pretty much narrowed our Foretravel research to 93-95 U300 models. If I read the information on Barry's site correctly, these all will have Jake brakes as standard equipment. Would one of the other two have been an option, or perhaps added in addition to or in place of the Jake brake?

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #1 – September 04, 2012, 10:23:18 pm

All work to slow the coach. When used in conjunction with the transmission, all three are effective in allowing you to descend a 6% grade with NO use of your regular service brakes.

Since you have no choice of which kind of brake a used coach will come with, it would not be something that would worry me.

Each works completely differently, but effectively.

While you can leave any of the three in "full time on", I would never do that, as it rules out my favorite gear-- COASTING!

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #2 – September 04, 2012, 10:32:06 pm

others will correct me but I think the trans retarder was not available on those yrs. I had the exhaust brake (Jake) on my 93 GV and would not change this Allison Trans retarder for it. Not even close in my H O . No big deal watching your temps on trans'. Others may disagree. I can bring my coach to a nice gentle stop (almost) with this one (and no muffler brake noise to boot), but do not think I could have done it with the other. The engine brake set up changes the engine from an energy producer to a compression engine.
I would think that it sounds like the amount of money you are willing to spend on a coach determines what you get, whether you want certain features or not. My 93 GV ORED was great but lacked all the things I wanted after having that one for 4 years. kept it in great shape and luckily only lost 6k in 4 yrs.
John H

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #3 – September 04, 2012, 10:58:01 pm

Trans retarder was first avail in '89, I seem to remember someone correcting me. Only on the U300 until 93/94. Most stuck with the standard jake as the trans retarder was a $10K option (until 97, I believe).

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #4 – September 04, 2012, 11:13:45 pm

We probably live with the highest percentage of hills around us as anyone on the forum. Our U300 has a Jake brake and it works great. Yes, you can just leave it switched on and we do leave the switch on all the time until we get down into the valley. It works well in all situations, with and without toad. Last week, going over Donner Summit on I-80 w/toad, I was able to stay in fourth gear (high gear) only lightly touching the service brakes twice all the way down to Truckee and never touched the brakes on the way home on I-80. It does not effect engine life, raise the temperature, lower fuel mileage or make a lot of noise unless you modify the muffler. Plus, it can't really be abused.

Retarders do work very well. The difference is the complexity and cost they add to the automatic transmission along with the opportunity to damage the transmission if not used correctly (by the same people that party too much and then can't back into a campsite). They do generate heat and have only a limited amount of duty cycle before bringing the transmission temperature up to operating limits. If or when the transmission needs to be overhauled, the cost will be more, a big factor in a 20 year old vehicle where the overhaul may be a significant percent of the total value of the motorhome.

I still remember the big yellow retarder light on the dash on one of our rigs. With 10,000 lbs of liquid on board, we only had so many minutes per hour before the yellow light came on and we lost use of the retarder.

But the best thing that appeals to a very juvenile mind is the cool noise Jakes make, especially in a tunnel.

Pierce

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #5 – September 04, 2012, 11:17:29 pm

My guess is that John had meant to say he had an exhaust brake (PAC Brake) on his ORED although I guess some of the OREDs might have had a Jake engine brake so maybe I'm wrong. That has been happening a little too often lately according to Peggy.

I have had both the PAC exhaust brake and the Jake engine brake. I have not had the Transmission Retarder. The Jake seems more effective than the PAC brake but that may be the way they were set up on each coach. We have been knocking around the NW most of the summer with the Jake so we have encountered some pretty big hills and steep down grades. As long as I didn't let the speed get too high on the grade the Jake has worked great. I have been able to keep the coach at 60 to 65 mph with only the occasional touch of the service brakes. With any of the three systems you have to watch your speed so that you don't go too fast to prevent a down shift if the grade gets steeper. All three system work better in a lower gear and higher rpm range. Sometimes downshifting could cause the engine to over rev if you have let the speed get too high and the coach may not let you down shift for that reason. Then you have to apply a lot of pressure on the service brakes to get back into the speed range required to shift into a lower gear.

My observation has been that the Transmission Retarder is overall the most effective but also can result in some expensive repair costs and may put an excessive load on the chassis. When you apply the service brakes both the front and rear of the chassis bears the inertia of slowing. The retarder is so effective it is like using only the rear brakes while the remainder of the chassis wants to keep going. I think some of the bulkhead issues have been caused by over aggressive use of the transmission retarder.

As far as performance, I would choose the transmission retarder but as far as reliability and maintenance costs I would choose the Jake brake. The performance of the Jake is plenty good enough. The PAC brakes are good if they were installed properly with beefier valve springs and lockup on the Allison Transmission but many were not. PAC brakes do require a lot more routine maintenance to keep up performance levels. They need to be lubricated monthly. They need frequent checks of the exhaust system to insure there are no leaks at the manifold or the exhaust pipes and they create a little more pressure on the turbo seals but their initial cost is a whole lot less than a Jake or a transmission retarder.

The bottom line is they all work good enough. Each has their pluses and minuses. Just make sure your new coach has one of them and that it is in good working order.

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #6 – September 05, 2012, 12:01:03 am

I have a retarder on my '91 U300 and have only used a Jake on a truck in my younger days and those were few. My own observation is I've seen mostly retarders on U300 in that vintage. What's important is to have either a Jake or retarder so there is no fear going down mountain grades. I haven't heard of any serviceability/reliability issue with either. The power trains are commercial heavy duty and don't see the mileage or nor carry the weight for their intended design. You will see from time to time roads signs that say something like "UNMUFFLED ENGINE BRAKE PROHIBITED" around some communities - referring to the Jake. Foretravels have mufflers so it wouldn't apply but sometime the signs don't specify muffled or unmuffled - more a nuisance than a problem. Since you've already narrowed your search to U300s you'll get one or the other so you can focus on other choices like length, floorplan and general condition. Or you can be like me and just find the nearest Foretravel and if the wife likes the interior you buy it

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #7 – September 05, 2012, 12:07:28 am

Quote from: Kent Speers – September 04, 2012, 11:17:29 pm

I think some of the bulkhead issues have been caused by over aggressive use of the transmission retarder.

Kent,

I don't think this is true. I vaguely recall one post hypothesizing such (not proven that I remember), but the posts which have shown bulkhead issues have all been corrosion-related, either from road salt, water leaks, spray, etc.

8 years with a transmission retarder now; I wish cars came with them.

Michelle

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #8 – September 05, 2012, 12:18:18 am

Maybe Pierce and us live in similar locations as we cannot really go anywere without going up or down anything less than 4000 ft(we are at 2000) and a few hours east it is 9000 ft + so my trans retarder does get used and as I am hopefully in the right gear it does not go into a dangerous temp. It did once north of PV mexico hit 300 high up in the jungle on a looonnng twisty road down to sea level but just that once. I then changed my fluid.
I have been using Amsoil trans fluid (as with all the fluids) and swear by it on keeping temps down and lubrication the best.For me forget Transynd, as I had it in and dumped it, as this fluid works way better temperature wise and shifts I think smoother. I also have 100% guarantee on it from Amsoil--no ifs or buts!!
Still think the trans retarder is the best.
John h

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #9 – September 05, 2012, 01:43:00 am

The exhaust brake is 20% effective. The jake is 40% and the retarder is 80% effective.

Roger from foretravel mentioned these numbers to me. Whatever effective means....

I have driven and used everything from being in the Rv business and going rving in my off times in used and new coaches.

The only two jakes that were impressive were the 2,4 or 6 cylinder mode on a 3176 cat in a marquis 20 years ago with the customer preference software installed so it worked on the cruise control and the pad next to the driver could be used to vary how many cylinders were being used as the jake was turned on. Lots of thank you's for that one.

The other was the m14 cummins in a signature. 855 cu in. 444 hp. 1850 pound feet.

Same selectable jake as the cat.

The retarder is stronger than both those. Yes it can heat up

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #10 – September 05, 2012, 08:46:16 am

Lots of different "effectiveness" posts about exhaust brakes. And there IS a range of proper answers.

Early engines (before 1993 on Caterpillar 3116 in the U240 for example) had valve springs that would only tolerate 35 PSI max exhaust brake back pressure. From then forward they tolerated 65 PSI exhaust brakes-- BIG difference!

And many years ago (but after the original exhaust brakes were fit) PacBrake came out with the PRXB exhaust brake which is quite a lot more effective at lower RPM than the original exhaust brakes. I was one of the original testers of the new generation PRXB brake.

Also, early 4 speed Allison transmissions did not have torque converter lock-up in all but the lowest gears. The Allison 6 speeds are locked in higher RPM's in 2nd and always in 3rd, 4th, 5th and 6th. Again much more effective.

Said another way, a PRXB exhaust brake in a 1993 or newer U240 which came with the Allison 6 speed transmission is quite effective.

Least effect exhaust brakes would be an original generation exhaust brake on a U225 with Allison 4 speed.

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #11 – September 05, 2012, 10:36:54 am

Quote from: wolfe10 – September 05, 2012, 08:46:16 am

Least effect exhaust brakes would be an original generation exhaust brake on a U225 with Allison 4 speed.

I would prefer to use the word "subtle" instead of "least effective", thank yew very much.

Even so, the older model Pacbrake is still better than just the service brakes alone. Coming down Snoqualmie Pass (3,000 feet to 700 feet in about 15 miles) a few months ago I was following a string of motor homes, 5th wheels and 18-wheelers. When I engaged the Pacbrake my use of the service brakes was almost zero while all around me red brake lights were flashing.

At lower speeds it's almost nothing, however. But at lower speeds using the service brake is probably better anyway.

I leave the Pacbrake off completely (I'm a big fan of "coasting", too) most of the time. I do like to use it on freeway exits because it lets me keep speed up on the freeway itself and still slow down quickly on the exit. I turn the Pacbrake off at speeds below about 20mph because it creates a lot of noise and vibration and isn't all that useful at those speeds.

It's easy to see the difference between the way my coach acts on a long downhill and the way other RVs act and I'm very glad to have mine. I should note that an examination of my service brakes showed 70% front and 90% rear remaining. And I know that the PO used the coach primarily to visit the mountains (they bought a mtn. cabin and sold the RV to me). Not bad for a 19-year-old motor home.

I'll probably upgrade to the later version... but it's not a cheap upgrade.

Craig

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #12 – September 05, 2012, 11:26:32 am

Quote from: wolfe10 – September 05, 2012, 08:46:16 am

Lots of different "effectiveness" posts about exhaust brakes. And there IS a range of proper answers.

Early engines (before 1993 on Caterpillar 3116 in the U240 for example) had valve springs that would only tolerate 35 PSI max exhaust brake back pressure. From then forward they tolerated 65 PSI exhaust brakes-- BIG difference!

And many years ago (but after the original exhaust brakes were fit) PacBrake came out with the PRXB exhaust brake which is quite a lot more effective at lower RPM than the original exhaust brakes. I was one of the original testers of the new generation PRXB brake.

Also, early 4 speed Allison transmissions did not have torque converter lock-up in all but the lowest gears. The Allison 6 speeds are locked in higher RPM's in 2nd and always in 3rd, 4th, 5th and 6th. Again much more effective.

Said another way, a PRXB exhaust brake in a 1993 or newer U240 which came with the Allison 6 speed transmission is quite effective.

Least effect exhaust brakes would be an original generation exhaust brake on a U225 with Allison 4 speed.

My Allison four speed locks up half way through second gear and is always locked up in third and fourth. Don't know what year they started doing that but if your four speed shifts four times and seems like a five speed, it has a locking torque converter.

Pierce

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #13 – September 05, 2012, 12:00:23 pm

These numbers...

The exhaust brake is 20% effective. The jake is 40% and the retarder is 80% effective.

... are one of the reasons why I chose Foretravel. I have seen these numbers before.

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #14 – September 05, 2012, 12:18:46 pm

As I posted above, there is no pat answer for effectiveness of an exhaust brake. Depends on what engine (and even what year engine), what transmission and what exhaust brake. A later model PRXB on Caterpillar 3116 and Allison MD3060 is quite effective.

So no single "effectiveness" number is accurate across the board.

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #15 – September 05, 2012, 12:21:58 pm

Boy, did I stir things up.

First, my dash switch for my two position (3 and 6 cylinder braking) Jake brake says RETARDER on the dash switch. It's just not a transmission retarder. So don't be confused like I was. Second is with my retarder/jake switch on in either position it only retards when the cruise is off so I do coast on the down hills until I touch the service brake pedal to turn off the cruise control. I echo Pierce's comment. My four speed Allison locks up in second gear and when the retarder/jake is activated stays locked up until I hit 10 mph during deceleration. However it is still not as effective at stopping the coach as the transmission retarder.

And regarding Michelle's comment, I don't have any data supporting my thought on the chassis issue. It just seems logical that if one has any issue with the rear bulkhead using the retarder in lieu of the service brakes puts more pressure on the rear bulkhead.The inertia of the 75% of the coach that is in front of the rear bulkhead will want to keep going while the back 25% wants to stop. I keep seeing comments that some Foretravelers with a transmission retarder saying they "hardly ever use the service brakes". IMHO its bound to accelerate bulkhead separation if there is an existing problem with the bolts or structural bulkhead rust.

The bottom line is they all work. It is my understanding that the only Foretravel coaches in the early 90's vintage that didn't come with an auxiliary braking system were the U225 and maybe the U240.

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #16 – September 05, 2012, 12:23:17 pm

Allison MT643 and 647 4 speeds stock only locked in 3rd and 4th. They could be modified to lock in 2nd.

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #17 – September 05, 2012, 01:22:23 pm

Quote from: Dave Head – September 05, 2012, 12:23:17 pm

Allison MT643 and 647 4 speeds stock only locked in 3rd and 4th. They could be modified to lock in 2nd.

Dave,

Every '90s vintage U300 I have ever seen locks half way through second gear and has a HT 746 transmission. Earlier U300s had a Allison MTB 648 transmission. Don't know about lock up on those. U280's did have a MT 643.

Regarding Kent's comment: Quite right, with the retarder switch (Jake switch) half way, the Jake only works on one side of the engine. And, yes, the Jake or any retarder could make a existing bulkhead problem worse. With good bolts and no rust, a retarder could be used a million times with no adverse bulkhead affect (in my opinion).

Pierce

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #18 – September 05, 2012, 07:54:12 pm

Craig,

Note that many of those other rigs may have a retarder linked to their brake lights too.

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #19 – September 05, 2012, 08:53:27 pm

My experience with the 8V-71, 92 DDA engines using the Jake Brake, while they do work, they are not nearly as effective as the retarder (Allison) and for best effect, you need it up at the max governor speed, why a 10 or 13 speed gearing is better than a 4 speed, you have gear choice for best effect. Never used the exhaust type brake PAC or C Brake or what ever, so no idea on those, but on a 4 cycle engine I am sure they are more effective than on a 2 stroke.
FAI
Dave M

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #20 – September 05, 2012, 09:09:10 pm

Dave,

If I don't have to use the service brakes very often, even on 10% plus grades on the approach to Jackson, WY (with toad), how much better do they have to be? As much as I use the brakes, the pads should last to the next millennium.

You just cast a lure for me, didn't you?

Pierce

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #21 – September 05, 2012, 09:20:31 pm

Quote

Earlier U300s had a Allison MTB 648 transmission. Don't know about lock up on those.

I have a MTB 648 on my '91 U300. Locks up in 3rd and 4th.

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #22 – September 05, 2012, 10:25:17 pm

Quote from: Dave Head – September 05, 2012, 12:23:17 pm

Allison MT643 and 647 4 speeds stock only locked in 3rd and 4th. They could be modified to lock in 2nd.

Wish I had known that long ago.

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #23 – September 08, 2012, 10:50:07 pm

I have a 1988 Grand Villa with 300 cat and 4 speed Allison,
Can any one tell me if it has a Jake brake, Pac or Retarder that came with it standard or was it an option for the buyer at the time,

Re: Jake Brake vs PAC Brake vs Retarder?

Reply #24 – September 09, 2012, 05:34:36 pm

Quote from: MR B2 – September 08, 2012, 10:50:07 pm

I have a 1988 Grand Villa with 300 cat and 4 speed Allison,
Can any one tell me if it has a Jake brake, Pac or Retarder that came with it standard or was it an option for the buyer at the time,

If it has a Pacbrake you can see it on the exhaust pipe leading from the manifold to the muffler. It will be a small cylinder with the piston operating a butterfly valve mounted smack dab in the middle of the exhaust pipe. It won't have a transmission retarder unless I completely misunderstand things. Might have a Jake but I don't have any familiarity with those.

Craig

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