do gassers offer anything like the DP engine brake

[kgard1225]

Hi, looking for a class A but will be in mountainous areas a lot and want to see if there is any type of extra braking available on the gassers. I searched the diesel vs gas posts but see no mention of this big plus on the diesels. Thanks, Ken

[rgatijnet1]

Canadian Rainbirds wrote:


A lot depends on wheel/brake size. I learned to drive in British Columbia and am quite comfortable with mountain driving.

Years ago we drove our 30' 1997 Triple E Commander, on a Ford 460 chassis down the Espinazo del Diablo (Devil's Backbone) in Mexico, from Durango to Mazatlan. From 6,000 feet up to 9,000 ft, down to 6000 then back to 9000 then to sea level.

At one of the very few places to pull off I stopped for a "rest" break. Bad mistake. With no air moving past the wheels the drums on the 16" rear wheels heated the brake fluid to the point that there was vapour instead of fluid in the brake system. I pulled out behind a bus and braked for the corner and the pedal went to the floor :E Fortunately I was still going slow enough that I could pull it into 1st gear. A lot of pumping on the brake pedal gave me a little (just enough) braking. After following the bus downhill and pumping like mad when needed I regained reasonable braking in about 20 minutes.

We now drive a small (32') diesel pusher with 22.5" wheels, airbrakes and a great Allison 6 speed an excellent cruise control and exhaust brake.

Since you didn't say when you had last had your brake fluid flushed, it seems like you rode the brake pedal too much. Just 5% moisture in your brake fluid system will lower the boiling point of your brake fluid to under 300 degrees.
If your brake fluid had been flushed every two years, as recommended but very seldom done by RV owners, then you never would have boiled the fluid as you rode the brakes down the hill.
The fact that you could pump the brake pedal to get a little brake pressure indicates that you had moisture/steam in the brake lines.
Proper brake maintenance and not riding the brakes on a descent is very important for any RV that travels in the mountains.
I am sure that the brakes and wheel size on each RV is designed by engineers to handle the gross vehicle weight of your coach, if maintained and used properly.

[MrWizard]

the new Allison trans with braking..for gassers is truly a wonderful piece of engineering

but..some facts about diesels and gassers are getting misconstrued
diesels have such good compression braking because.they are HIGH compression engines..like 20:1 much higher than gas engines
shut the fuel to a minimum and restrict the exhaust and it take a lot of energy to force that engine to rotate

diesel engines are "free breathers" ..the fuel is controlled NOT the air intake

gas engines both fuel and air are controlled..
BUT the air intake is restricted only when there is no throttle.. the gas engine does NOT have naturally occurring engine braking as some have suggested
restricting air intake..throttle body or carb flaps only reduces air into the take..(like suction).. it does not do anything to increase compression and reduce engine speed other than reducing combustion of fuel in the engine

diesel or gas ..tis all about low gears and good driving and Knowing how to use whats available

[Canadian_Rainbi]

rgatijnet1 wrote:
redguard just sent me this as a PM in reference to my post where I said that gasser RV's have no problems in the mountains with either the climb or the descent.

"you obviously have not driven a larger A gasser loaded in the rockies etc as this statement is pure bunk simply put UNTRUE "

I'll let those of you that have driven their gassers in the mountains respond. I have never had a problem with my Monaco gas coach in the Rockies, but I also never had a problem with the diesel coaches I've owned in the mountains.
Apparently he wanted to call me liar in private. Oh well! :B

As the above posts already seem to indicate, gas RV's do fine in the mountains.

A lot depends on wheel/brake size. I learned to drive in British Columbia and am quite comfortable with mountain driving.

Years ago we drove our 30' 1997 Triple E Commander, on a Ford 460 chassis down the Espinazo del Diablo (Devil's Backbone) in Mexico, from Durango to Mazatlan. From 6,000 feet up to 9,000 ft, down to 6000 then back to 9000 then to sea level.

At one of the very few places to pull off I stopped for a "rest" break. Bad mistake. With no air moving past the wheels the drums on the 16" rear wheels heated the brake fluid to the point that there was vapour instead of fluid in the brake system. I pulled out behind a bus and braked for the corner and the pedal went to the floor :E Fortunately I was still going slow enough that I could pull it into 1st gear. A lot of pumping on the brake pedal gave me a little (just enough) braking. After following the bus downhill and pumping like mad when needed I regained reasonable braking in about 20 minutes.

We now drive a small (32') diesel pusher with 22.5" wheels, airbrakes and a great Allison 6 speed an excellent cruise control and exhaust brake.

[Canadian_Rainbi]

OOPS!

[Terryallan]

Thing is. Diesel Exhaust brakes were developed to give diesels the braking, that gas engines already had. You want to slow down a gas powered vehicle. Drop a gear, want to slow down more. Drop another one.

[J-Rooster]

Gassers have a transmission brake as a lot posters mentioned! If your not aware DP's have a engine brake this is when a Jacob Head (hence the term Jake Brake) turns the engine into a compressor by closing all the valves in the engine, therefore creating back pressure! Good Question

[Golden_HVAC]

I have gone down some 10% grades in my older 97 Ford Bounder class A, 30' long and 16,500 pounds with a 17,000 GVWR! It has the same brakes as the then current F-450 and F-550 trucks. THey are HUGE disk brake rotors and pads about 6" tall and 2" wide! They are much larger than any car that I have ever changed.

Anyway going down the 10% grade, I would slow to less than 40 MPH and shift to second gear, and that brings up RPM to about 3,000. At 3,000 RPM, the engine braking is significant, and would help slow the motorhome a lot. Letting it rise to 3,600 would provide even more braking. That is about the limit that I would put to my transmission. The 2005 and later Ford transmissions can handle the engine turning 4,200 RPM downhill, and provide much more engine braking than my engine, plus most newer cars shut off fuel to the fuel injectors to provide more braking and help slow the vehicle, and save fuel too!

My motorhome will beat my buddy's Country Coach with a 10 liter diesel engine up a long grade, such as the climb to Mammoth Mountain! That is because it is lighter weight, and can run higher RPM than a diesel can. The V10 can run 4,400 RPM intermittently, and 4,200 RPM all day long. This is because of the tiny 0.68 liters per cylinder. Think of my 460 V8 (7.5L) as nearly 1 liter per cylinder (about the diameter of a 2 liter soda bottle, but 1/2 as tall). The 8.3L inline 6 Cummings DP would have about 6" diameter and 6" stroke, with 1.4 liters per cylinder. The Cummings 8.3L max RPM is only about 2,500 - 2,700 depending on the model and year. It is that huge stroke length that prevents them from going to such a high RPM, and prevents the DP from getting to much engine braking unless they also shut off the exhaust gas flow.

So don't be bothered by not having the engine brake. Gas engines can have just as much braking power as a DP, in perportion to their weight.

Also when going down a hill, DP or gas engine, make sure to get out of overdrive, and downshift one more gear if required. Turning on the engine brake on my buddy's Country Coach would shift it from 6 to 4th gear, and close off the exhaust airflow by about 85% to 90% covered.

In my gas motorhome, I would shift out of OD, then shift to 2nd gear if required (after slowing below 45 MPH in my case (with a 4 speed auto). This normally provides enough engine braking that I never need to touch the service brakes going down a hill on a interstate freeway (where downgrades are 6% or less steep). It is only a really steep 2 lane road, or perhaps coming up on a 35 MPH curve that I would use the service brakes in my motorhome.

Good luck!

Fred.

[RayChez]

You have to use a combination of engine braking and at times when it starts to rev up too much apply some brakes to bring the rpm's down.

[RedJeep]

kgard1225 wrote:
Thanks for all the replies. I wasn't sure if the engine rpms would get too high going down a steep descent keeping in a low gear. All of the late model gassers I have been looking at had Ford chassis with the V-10. What is redline on these motors ?

That is a good question. I don't know the answer but I've always wondered if the gas engine is effectively braking during a downhill run of say 10 percent what happens with the engine/rpms/transmission if the grade were to drop to say 20%…? Would the engine rpm continue to climb? Does the transmission further compensate in some manner? If you don't touch the brakes what blows up first; engine or transmission?

[mowermech]

RayChez wrote:
Yes gasoline motorhomes with big engines have lots of power, but man they eat gasoline like crazy. I had a 454 chevy pickup with a big overhead camper. I started climbing the Sierra's from Bishop to Mammoth. It went up easy, but I was almost out of fuel by the time I got to the top of the mountain. LOL! And the Ford 460 was even worse.

Many years ago, when I lived in the Flathead Valley of Northwestern Montana, not far from the West entrance to Glacier National Park, I had a 1969 Chevy C20 that was like that. I had a 9 foot camper on it, and it had the old 292 inline 6 with 4 speed tranny.
That thing had a terrible thirst for fuel!
I haven't done a fuel economy check on the Southwind (I don't really care), but from here to Great Falls it seems to take pretty much the same amount of fuel as the old Tioga 29 Foot Class C with the 460 Ford did.

[kgard1225]

Thanks for all the replies. I wasn't sure if the engine rpms would get too high going down a steep descent keeping in a low gear. All of the late model gassers I have been looking at had Ford chassis with the V-10. What is redline on these motors ?

[WyoTraveler]

Of course if we are going to try to confuse the issue with a money diet for fuel I would suggest a smart car and a tent. When I can't afford fuel I will sell my MH.

[RayChez]

If you know how to drive, either with or without an exhaust brake, using your gears it will slow you down to a crawl if you wanted to without using your brakes. Even with an exhaust brake on a diesel you have to tap the air brakes every once in a while if it starts picking up speed, and they will on long steep grades.

[wolfe10]

Paul,

I look at it a little differently.

The correct speed of descent in any heavy vehicle is the speed/gear/use of any non-service brake that keeps your speed in EQUILIBRIUM. That is you are neither speeding up nor slowing down and do not need to use your service brakes to do this.

We were descending a 17% grade in the Green Mountains of VT several years ago. 2nd gear with exhaust brake on-- doing about 22 MPH. We easily could have taken the curves at 35-40 MPH (so grade, not road shape dictated speed). Dianne was worried that someone would run up on us. Around the next bend was a loaded logging truck, doing his equilibrium speed-- about 8 MPH. We blasted right by him and continued on down the mountain. Both of us were descending correctly for our rigs.

[xctraveler]

I'll just pile on a bit here. We have driven over the Rockies, through the Canadian Rockies and down into Presidio TX in both a gasser (8.1L GM with Allison) and in our current DP with Engine Brake. No problem in either coach towing our car behind (RAV 4 behind the gasser and Jeep Wrangler behind the DP. The secret is to drive down the grade at the speed you came up, in the gear you came up. So if I crest at 30 mph in 2nd, that is how I start down and I use engine braking or EBrake to hold the speed. If the speed rises I apply the brakes firmly just long enough to get to 5 mph below my desired speed. Never let it get away from you, it will be a wild ride no matter what system you have, not that I have any experience of that.