# Can You Explain This ???



## Morgueman (Dec 3, 2006)

This past weekend, I took the family camping in Big Bear, CA (7100 ft elevation). On the way home, I pulled off the side of the downhill grade road (at 5000 ft elevation). I put the TV in Park and applied the emergency brake. Upon releasing the pedal brake, the TV-TT starting rolling forward down the hill







, and a grumbling noise/feel was quite evident







. I re-applied the pedal brake to stop us from moving, and I double checked...I was clearly in Park and the emergency brake was completely depressed. I tried taking my foot off the pedal brake again, and the TV-TT starting rolling downhill again. So I re-applied the pedal break again, and after a few minutes, I tried releasing the pedal brake VERY SLOWLY and the TV-TT didn't move. I let the car sit for another 25 minutes before I started driving down the road again, and no problem was encountered during the remaining 5000 ft descent and 100 mile trip home. So what explains the rolling down hill while in Park with the emergency brake on?

I will concede that the pedal-initiated brake system must have been really HOT as I forgot to turn on the Boost setting of the Prodigy brake controller, but I don't see how this would have caused the problem I had.









Any help would be greatly appreciated.









Sincerely,
Eric


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## egregg57 (Feb 13, 2006)

Wow Eric! I don't have the answer but it sounds to me like a Swiss Cheese effect. In the nuclear industry that's what we call it when a series of things that aren't supposed to happen line up just right and blamo. it sounds like slipping transmission coupled with worn or out of adjustment E-brake. but I am no auto mech. the good thing is that you were there and able to stop it. maybe some liberal use of chocks are called for until you've figured it out.Eric


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## W4DRR (May 17, 2005)

Setting the parking brake only engages the rear brakes, and it may not be able to hold both your TV and TT while parked on a hill. Putting the transmission in park only locks the driveshaft at the transmission end. In some situations it is possible for the vehicle to roll if at least one of the rear wheels is on snow/ice/gravel/etc. One wheel will roll, while the other spins backward due to the differential action.

Bob


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## battalionchief3 (Jun 27, 2006)

What they said, go buy a big wheel chock. Too much weight at the right spot on a the right hill and the planets all lined up right.


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## NJMikeC (Mar 29, 2006)

The answer why Park didn't work is it is only a tiny little "awl" that locks up. Park wasn't meant to hold the whole weight of a vehicle on a hill let alone 2 vehicles. It is really a tiny part.

Brakes, yup hotter then hell and just wouldn't hold since they were glazed.

Weird circumstances for sure but the correct way is to put vehicle in Neutral , set brake, let weight settle on brake then put in park. So using the correct method you might have noticed that the brakes weren't holding and would not have put it in park and let that awl get wacked up.

I suspect the weird growl you heard was the parking awl wacking around and I hope it doesn't show up in the future on you.

Use more trailer brake going down those hills, use a lower gear range and don't ride the brakes, pump them instead.


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## cookie9933 (Feb 26, 2005)

Here's some info: 
A parking pawl is a device fitted to a car's automatic transmission that locks up the transmission. It is engaged when the shift selector is placed in the Park position, which is always the first position (topmost on a column shift, frontmost on a floor shift) in all cars sold in the United States since 1965 (when the order was standardised by the SAE) and in most other vehicles worldwide.

The parking pawl locks the transmission's output shaft to the transmission casing by engaging a pawl (a pin) that engages in a notched wheel on the shaft, stopping it (and thus the driven wheels) from turning.

Most manufacturers and mechanics do not recommend using the transmission's parking pawl as the sole means of securing a parked car, instead recommending it should be used as a backup for the car's parking brake. Constant use of the parking pawl only, especially when parking on an incline, means that driveline components are kept constantly under stress, and can cause wear and eventual failure of the parking pawl. Replacement can be an expensive operation since it generally requires removing the transmission from the car.

It is also not recommended to use the parking pawl to stop a vehicle in motion. The pawl mechanism is not strong enough to stop a vehicle in motion or may not engage at all. Under that much stress, the pawl may break off in the transmission, leading to costly repairs.

Retrieved from "http://en.wikipedia.org/wiki/Parking_pawl"

But when the park pawl doesn't hold, it normally makes a continuous clicking sound as the pawl slips from one notch to the next.









Bill


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## Morgueman (Dec 3, 2006)

cookie9933 said:


> Here's some info:
> A parking pawl is a device fitted to a car's automatic transmission that locks up the transmission. It is engaged when the shift selector is placed in the Park position, which is always the first position (topmost on a column shift, frontmost on a floor shift) in all cars sold in the United States since 1965 (when the order was standardised by the SAE) and in most other vehicles worldwide.
> 
> The parking pawl locks the transmission's output shaft to the transmission casing by engaging a pawl (a pin) that engages in a notched wheel on the shaft, stopping it (and thus the driven wheels) from turning.
> ...


Thank you for all the replies. So if I made the brakes real hot (due to not putting the Boost on the Prodigy), does this make the Emergency brakes less effective. If so, it sounds like 13000 lbs (TV + TT weight) was pushing on the pawl and this is why it was rolling. Is this a likely explanation?


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## Carey (Mar 6, 2012)

I drive a semi here in Colorado. I go down big, long hills all the time, with loads of 80-85000 lbs.. If I screw up on a 6-8%, 10 mile grade with my weight I will die. So this is serious stuff for me. There are as many rv's who lose there brakes as semis here in Colorado. I see many rv's with smoking or overheated brakes every summer here.

I will include both, in your truck/ suv and what I do in my semi truck.

Here is for your truck/suv:

Decide how many miles down the hill first, if you cant see the bottom, or dont know the road, set yourself up for a long decent. If the hill is shorter than you thought, no biggie, at least you were preparred.

Dont worry about the traffic behind you. You do what is safe for your vehicle, if someone hits you, its there fault, always. I go down hills sometimes at 18mph, I never worry about traffic behind me. Yes its unfortunate if someone hits you, but your safety should become before anything else. Dont try to keep up with other rv traffic, or general traffic. Your rig is different than any other rig, do what is safe for you and your rig. Take your time.

Leave the tranny selector in tow/haul mode. This will keep the torque converter in lock up mode which makes the engine to the tranny/driveline more of a direct link.

Shift to D2 on the shift selector. Keep the rpms below 4000 on a gas engine. Optimum is 3000-4000 rpms. So use your tranny gears accordingly. this will put you in the 30-50 mph range, if you need to go slower, put it in D1 which will get you in the 20-30 mph range.

Set your brake controller a little higher than normal, but dont apply too much to the controller, or you will get your trailer brakes hot quicker than your truck. Dont rely on your trailer's brakes to slow you down in a panic on a hill, they are meant to be used in combo with the suv/truck. They cannot stop the whole rig, they are only rated for the amount of weight that the trailer weighs.

Apply light, constant, steady pressure to the brake pedal. Never pump the brakes as you are going down hill. Pumping the brakes will overheat the brakes very quick. The brakes will actually run cooler with a light steady pressure. Keeping the brake pads in contact with the drum/rotors allows them to transfer heat easier to the rotor/drum. If you pump them, you are getting the brakes very hot for a short time, then hoping they cool enough for the next round of brake application. If you make your brake applications too fast, you will lose your brakes or overheat much quicker, than a light steady pressure. You want to keep as little of oxygen as possible between the pad and rotor. Oxygen is the fuel for overheated brakes or brake fires. Without oxygen, the brake pads will run cooler.

A good guide to brake pressure for you is: If you ever have to apply more and more brake pedal as you go down the hill, you have picked the wrong gear, or are going to fast. If you are able to keep a steady pressure without appling more and more brake, you are in your rigs sweetspot on braking ability. After a few trys you will learn what amount of pressure works. If you are appling more and more brake as you go down, you are feeling brake fade, which happens just before overheat, or loss of brakes.

Here is how use truckers go down, which is very similar to what is explained above.

I decide how many miles the hill is. If I dont know, I prepare for the max.

I shift my tranny to the first gear in high range, which is 25mph at 2100 rpm.

I set my brake pressure to 10 psi of brake pressure at my foot.. ( we have a guage showing us how much pressure we are applying to our brakes) The max is the amount of air pressure in my air system, which is around 120-140 psi. If I go down the hill with 20 psi applied, my brakes will start smoking within 2 miles, and I will have total brake loss at 3 miles.

I keep my rpms close to max, which is 2100rpms. This gives me maximum jake brake horsepower. But by doing this I cannot downshift, as a truck tranny is not syncronized. Plus I will float the engine valves at 2300 rpm. I will break the camshaft at 2600 rpms. I will have to get the engine down to 1300 to be able to down shift If I have to, so pretty much its best for us to go down the hill in the gear we select at the top. Its better to shift up than down, so we select the gear for worst case scenerio.

I continue down the hill never applying more than 10 psi to the brakes. If more is needed, I will have to apply 30+ psi and slow the rig/engine to be able to down shift to the next lower gear. This is very dangerous for us, as many times we will smoke or lose our brakes before we can get the engine rpms down to 1300 to make the down shift. Many truckers have died only because they selected the wrong gear at the top, and are not able to downshift, then lose there brakes, going off a cliff.. sad stuff!

I will never let up, or pump the brakes, this gets the brakes very hot. many times the brakes will smoke if i let off of the brake pedal only, as they are not able to transfer heat to the drum anymore and will smoke as soon as they get oxygen between the pad/shoe and drum. I keep a light but steady pressure all the way down(10psi) If you do this, you could concievably go down a hill forever. The brakes will get warm, and stay that way, but never get hot or become dangerous.. If I only apply 10 psi of brake pressure I will always have enough brake left to stop the truck on any grade of hill if I need to. I try and not allow any oxygen between my shoes and drums always. Again, oxygen is the killer!

If you go down a hill with a steady but light pressure you will have very little brake wear, cool brakes, and be the safest possible. This goes for any vehicle. If you try this, you will be able to decsind any hill with confidence, and the big down hill worry will become a non-issue.

Carey


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## Carey (Mar 6, 2012)

I made duplicate posts for some reason, got rid of this one.

Carey


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## Morgueman (Dec 3, 2006)

Carey - Thank you for all of your valuable suggestions. Frankly, I thought pumping the brakes (...to supposedly allow them to cool) was the preferred method, but I will change my ways unless someone else provides a sound reason otherwise.

I'm still wondering if the heat created while braking affects the function of the emergency brakes...


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## Carey (Mar 6, 2012)

The emergency brakes use the same pad as the regular brakes, so yes, If your brakes are hot, the emergency brakes will not work.

Pumping the brakes is what the general public knows when going down a hill.. This was also the method for trucks till the early 80's.

It has been scientificly proven that a steady light pressure works best.. this change has been made, pumping to steady in the last 20 years in the trucking industry too.. Unfortunatly the general public still uses the pumping method which is not near as safe as the steady method..
So prolly the majority here will tell you to pump the brakes, cause thats all they know.. I have been to prolly 10 schools put on by the state patrol over the years.. This is what is taught and pushed by the feds for us truckers in this day and age.. it works excellent if used in the rv world too.

I have went down jillions of hills in my 2 million mile trucking experience.. I have saved countless flatland, eastern truckers here in Colorado telling them to use this method. Use western truckers use this method everyday.

Carey

ps just experiment with it.. do what works best, but try the steady method a few times.. You may find you like it..


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## tdvffjohn (Mar 10, 2005)

Nice explanation Carey









I believe your little stop for viewing purposes might have saved you an accident. From the sounds of it, you probably were very close to not having enough brakes to safely make it to the bottom. Lesson learned and not the hard way.

John


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## Sayonara (Jul 23, 2007)

Very Good Information!! Wow. Glad everything worked out for you.


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## Morgueman (Dec 3, 2006)

Lessons learned for going down long steep grades:

1. Don't pump the brakes. Instead, use constant firm pressure.
2. Don't forget to turn on the Boost feature, if using Prodigy brake controller.
3. Use lower gears than "Drive" (but be carefull to not shift during high RPMs).

If you don't exercise caution, you'll lose the pedal brakes AND the emergency brakes.
















Thank you Carey et al for the extremely valuable information!























Eric


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## Carey (Mar 6, 2012)

Eric, alot of the newer auto transmissions in cars/and pu's will not down shift if the engine is already high in rpms. If you are running in 2nd, and are at say 3500 rpm, and try to shift down to first, the electronics in the tranny wont allow the downshift, to keep from over-revving the engine.

I was just including the semi info for kind of a comparision. With semi's the max rpm is governed at 2100.. You can rev it all day and the engine will only rev to 2100 with no load, but in gear, with a load on it, it could rev way over 2100, but the engine will self destruct... For semis we have to use jake brakes(engine brakes) to help with down hill braking, and the jake brake works best the at the fastest rpm the engine is rated at.. So its sorta a whole different deal, comparred to auto engines..

If you are needing to shift up, from 2nd to 3-4th, and the engine is at 3500 in second, everything will be fine, but if you are at 3500 in second and try to go to 1st, that would not be good.

I thought I'd clarify that for ya..

Good Luck and I think tdfjohn is right, your prolly glad you stopped when you did.. Could have been bad..

Carey


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## kjdj (Sep 14, 2004)

W4DRR said:


> Setting the parking brake only engages the rear brakes, and it may not be able to hold both your TV and TT while parked on a hill. Putting the transmission in park only locks the driveshaft at the transmission end. In some situations it is possible for the vehicle to roll if at least one of the rear wheels is on snow/ice/gravel/etc. One wheel will roll, while the other spins backward due to the differential action.
> 
> Bob


To add. The GM parking brake is a completely different brake system.

At least with my 2003 van the Parking brake is a "little" drum shoe inside the disc brake rotor actuated via a steel cable.
The shoe surface is about 1" wide and 6" along the circumference. 
The service brakes are a separate system from the pedal to the disc rotor.

My parking brake will not hold the truck and an OB on a hill much over a 4% grade.

I use 2nd gear on any decent over 6% and let the trusty 5.3 scream and add a little brake action.


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## Sayonara (Jul 23, 2007)

Not that anyone here tows their OB with a Jeep Grand Cherokee but thought id add that those have seperate parking brakes too. I just did my brakes a couple weeks ago and learned that.


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## NJMikeC (Mar 29, 2006)

Good infor Carey!


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## W4DRR (May 17, 2005)

I would suspect that all vehicles with rear disc brakes have the same little extra parking brake drum that Kevin mentioned. It would probably be difficult mechanically to activate the calipers of a disc brake with a steel cable.

Bob


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## Carey (Mar 6, 2012)

Back in the 70's the cadilacs with disc rear had a cam that pushed the pads together.. I have seen some other models that way too, just cant remember what they were..

Yep, I think the new ones do have seperate pads for emergency brakes now that you guys mention it.. Thats kinda sad though. Kjdj said it wont hold his rig on a small hill.. The emergency brake is supposed to be just that.. Doesnt sound like that would be worth a @#%^.. I will have to try my dodge's emergency brake on a hill and see what it does.. Has my interest all perked now..

This site is great! lol

Carey


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