Newbie question driving mountains on wet roads

[sunset4k]

Hi all!! I've read in other rv forums that you should not use your exhaust break on wet roads. I have a Winnebago journey, towing a jeep wrangler. I guess my question is how do you descend a mountain grade if you can't use it? Any experience with this would be helpful!!!!

[BFlinn181]

Go slow and use the engine brake. You don't want to try stopping all that momentum going down a slope with your friction brakes alone. They'll overheat and burn out very quickly without engine/exhaust brake to aid in keeping you going slow. The only issue would be if the exhaust brake engaged suddenly and wheels lost traction. That's why you go slow because of reduced traction on wet roads.

[sunset4k]

Thanks that makes sense and was what I was thinking. I'm thinking you could also gear down manually..

[jporietis]

If you have an exhaust brake, it will probably not provide enough braking force to lock up the drive wheels. If you have a true jake brake, in the highest setting it could lock your drive wheels. The roads would have to be quite slippery, ie more than just rain.

John

[sunset4k]

John we have an exhaust brake.. Don't believe it's a true Jake brake.

[BFlinn181]

Originally Posted by sunset4k

Thanks that makes sense and was what I was thinking. I'm thinking you could also gear down manually..

Because a diesel engine doesn't use air flow to limit power, it uses fuel injection, they have little to no engine braking on their own, that's why exhaust or Jake brakes are added. Downshifting isn't as effective as on a gasoline engine.

[Mr_D]

When we had the Dutch Star and ISC w exhaust brake I used the exhaust brake in everything but snow/ice conditions. With the Magna's three stage engine brake I might use the first position but not the higher two. Just too much force. Cummins says 600 hp of braking force on the high setting and I believe it.

The lack of engine braking is due to the high compression and lack of restriction in the intake tract. So they need to have some other way of retarding the vehicle.

[jporietis]

What I found was most likely to cause rear wheel lock up with my motorhome was not the exhaust brake but the fact that my transmission immediately pre selected 4th gear when the exhaust brake engaged.
Depending on my RPMs at times that downshift was quite "violent"
I have the Alison 3060 6speed.
My solution was to get the transmission to be re programmed so that my exhaust brake did not cause a pre selection of the transmission.
In other words I select what gear I decide, and I engage or disengage the exhaust brake at will.
I find this combination allows for a much smoother ride and much more dependable driving experience.

John

[Gary RVRoamer]

You don't want to try stopping all that momentum going down a slope with your friction brakes alone. They'll overheat and burn out very quickly without engine/exhaust brake to aid in keeping you going slow.

I don't think you have to worry much about that. The service brakes are designed to stop the coach GVWR, after all. We are talking about an occasional need, not frequent driving. The exhaust brakes helps a lot and reduces wear and tear, but stopping without it is still practical. You just want to be somewhat more cautious, which you should be doing on wet roads anyway.

That said, the main consideration is to leave the exhaust brake off until needed, i.e. avoid having it automatically engage whenever you remove your foot from the accelerator. Some coaches are set up to only use the e-brake when you touch the service brake pedal anyway, which pretty well avoids the concern. You just don't want unanticipated braking on a potentially slippery road.

[BFlinn181]

Gary, I should have said 'slowing' all that momentum going down a hill. Yes, brakes are for stopping, but I've lived most all my life in hilly areas, except the years I misspent in Indiana. Yesterday I was going down a 1/2 mile long hill near my house, I had downshifted my Subaru to restrain speed and I could smell the distinct smell of heated brakes. The car next to me was riding the brakes all the way down the hill and creating smoke. Certainly brakes are for stopping; downshifting or exhaust brake are for slowing. If you do use brakes on a hill to slow, step on them hard to drop speed by 10 mph then take foot off the pedal until you need them again. Walking up and down the hills of Cincinnati I smell brakes being abused all the time, just as I did growing up in suburban Philadelphia as a kid. Too many folks seem to think vehicles only have D N R and never think to use the numbers on the shifter to retard speed.

[Crasher]

FWIW, an exhaust brake "Can and Will" stop the rear wheels if conditions are right. Driving our 36' Discovery years ago. 1997. I had the exhaust brake on while leaving Corpus Christi on the level, I came upon very wet pavement from a down pour and touched the brakes to slow for a concrete bridge over a canal. When the transmission downshifted, the drive wheels broke loose and the rear end started drifting over into the oncoming lane. It wasn't until I applied power that they regained traction and the rear came back into my lane shortly before the oncoming car went by. I guess instinct took over from driving on WI winter roads. And that was just an exhaust brake and not an engine brake. I might be a little paranoid now, but I will not go down a long mountain grade with a wet road. I got lucky once, but never again.

[jporietis]

Originally Posted by Crasher

FWIW, an exhaust brake "Can and Will" stop the rear wheels if conditions are right. Driving our 36' Discovery years ago. 1997. I had the exhaust brake on while leaving Corpus Christi on the level, I came upon very wet pavement from a down pour and touched the brakes to slow for a concrete bridge over a canal. When the transmission downshifted, the drive wheels broke loose and the rear end started drifting over into the oncoming lane. It wasn't until I applied power that they regained traction and the rear came back into my lane shortly before the oncoming car went by. I guess instinct took over from driving on WI winter roads. And that was just an exhaust brake and not an engine brake. I might be a little paranoid now, but I will not go down a long mountain grade with a wet road. I got lucky once, but never again.

This goes back to my previous comments. It is not the exhaust brake as much as the aggressive downshift that I have found to create a problem. The exhaust brake on its own is not very aggressive,

John

[Mr_D]

Our previous rig, a 2002 Dutch Star with ISC would preselect 2nd, in fact even 4th gear braking was pretty mild. On the 2000 Dutch Star I had the preselect changed to 4th and hated it. Was going to have it changed back but we traded it off too soon.
The Magna preselects 3rd gear and I usually keep the switch on the lowest setting.

[Gary RVRoamer]

The point here is that the exhaust brake isn't doing anything more than what you do with the brake pedal, i.e. apply drag to the rear tires, but it may do it abruptly or when you aren't prepared for it. And if you feel a skid starting, you can quickly remove your foot from the brake pedal, but you probably can't quickly disengage the exhaust brake. Or at least that disengage action is not as instinctive as lifting your foot.

A skilled driver can use either service or exhaust brake, or both, in these conditions, but who knows what the individual driver's skills are? Thus the safety experts advise that you don't use the exhaust or engine brake, thus avoiding the issue altogether.

By the same token, a reasonably skilled driver can use the service brakes without overheating them. It's certainly not rocket science. Downshifting helps if a gas engine, and keeping the initial speed (top of hill) down is another basic technique. Otherwise, it's a matter of intermittent firm application of the brakes and then a cool-off period. It's called "snub braking" in trucking circles. This article may help:
Downhill Braking

If you are "burning up your brakes" going downhill, it's probably your braking technique that needs work.
There are also videos on YouTube.