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RVing message boards => Motorhomes => Topic started by: ELeland on September 09, 2019, 09:34:51 AM

Title: Panic Stop
Post by: ELeland on September 09, 2019, 09:34:51 AM
I did a search and didn't see what I was looking for so thought I'd ask a question.  On my way home this weekend from Georgia on a 4 lane road I came up to a traffic light at about 55 MPH.  The light turned yellow and I figured it was a go / no go decision on whether to stop or not before it turned red.  I decided to stop, or so I thought.  The chassis is Freightliner and I was towing my 5,000 lb Explorer with an RVi2 auxiliary brake system set on "Large SUV".  I was about 10 to 15 feet over the stop bar before I came to a complete stop.  It was quite humbling as I thought it would stop me in a shorter distance than it did.  The exhaust brake was set to Off.  This is the first time in the 2 years I've owned this motorhome I've actually needed to use the brakes that hard.  No locking up at all even though once I saw I wasn't going to stop in time I pushed the pedal as hard as I could.

I'm not sure what is normal so I thought I would ask here.  I have a service appointment later this week for fluids and filters as well as servicing the air drier.  I can have them look at the brake system if this is not normal.  I use the exhaust brake mostly so never really used the chassis brakes this hard before.

Thanks for any help!

Title: Re: Panic Stop
Post by: Arch Hoagland on September 09, 2019, 10:03:18 AM
I've had three panic stops where the ABS system engaged causing the brake pedal to vibrate. Each time it was a car cutting in front of me to take an exit.

Did your ABS system engage?

It takes a lot more space to shut down a large RV and that's the reason I leave a lot of space in front of my coach.
Title: Re: Panic Stop
Post by: ELeland on September 09, 2019, 10:29:23 AM
Arch - I's a 2003 MH on a 2002 chassis.  I don't think it has the ABS.  I thought the same thing as my foot got to the stop bar before the MH did! I stepped on it pretty hard.  I will have them checked out as a precaution.
Title: Re: Panic Stop
Post by: garyb1st on September 09, 2019, 11:06:32 AM
Arch - I's a 2003 MH on a 2002 chassis.  I don't think it has the ABS.  I thought the same thing as my foot got to the stop bar before the MH did! I stepped on it pretty hard.  I will have them checked out as a precaution.

My old 1999 Aerbus on a Ford Chassis had an ABS.  I'd be surprised if your 2003 does not.
Title: Re: Panic Stop
Post by: Gary RV_Wizard on September 09, 2019, 11:21:22 AM
According to the Freightliner chassis specs for a 2002 Landyacht, it has full air brakes with ABS. (

The ABS only engages if a skid is imminent, so as long as the rear wheels were rolling rather than locked up, ABS would not alter the results.
There is no way to know if the brakes performed up to spec of not without measuring the stopping distance with the brakes just short of lock-up from a known speed. The RVI brake is another unknown - no way to tell whether it was braking heavily, modestly or not at all.

At a guess, the coach weighed in around 30,000 lbs plus another 5000 for the toad, so a stopping distance on the order of 400-600 ft is not unusual from 55 mph.   Reaction time alone can account for 60 feet. This brief article is perhaps a worse case scenario but gives you an idea of what to expect;  it concludes that 500 ft is within the norm at 55 mph. (
Title: Re: Panic Stop
Post by: Back2PA on September 09, 2019, 11:31:34 AM
After towing 2 different toads over 4 years with the same braking system, just before I sold the motorhome I had someone with me on of the last trips that brought along an IR temp gun. I found the toad brakes at ambient having just come down from Donner Summit - the toad brakes weren't applying enough to even warm up the brakes. The only way you'll really know is either if you can feel the toad pull away, or if you check toad brake temps after some moderate brake applications.
Title: Re: Panic Stop
Post by: Lou Schneider on September 09, 2019, 01:46:37 PM
It takes longer to stop a heavy vehicle, the greater mass in motion means there's more energy to dissipate to bring it to a stop.

That's another reason to leave yourself extra room when following a car ... they can stop faster than you and unless you allowed enough room you will hit them in a panic stop.

There are many YouTube videos showing what happens when someone cuts in front of a truck and then slams on their brakes.  Let's just say those large, flat bumpers on the front of trucks aren't just for show.
Title: Re: Panic Stop
Post by: youracman on September 09, 2019, 04:44:27 PM
Just a few notes on my 'sperience with the RVi2 brake, Ed:

I didn't believe that the brakes on my toad (2800 lb Kia Soul) were really doing their share, so I called the support folks there at RVi2 in Castle Rock, CO and asked them if they thought it would be OK to increase my "Vehicle Selection" from "Compact Car" to "Small SUV".  They said "no problem" so I did that and I could physically tell the difference in deceleration (from 15 MPH) when I pressed the "Test" button on the remote .....which I always do before heading out.  BTW- the RVi2 is a proportional device, but when you press the test button on the remote, it applies the max pressure for the vehicle setting you programmed in......that from the RVi2 tech folks.

In my case, that change doubled the actuation force (air pressure on the actuation cyl went from 5 psi to 10.) The only "test" (using the term loosely) I did was to have my wife verify that the toad wheels didn't skid on the surface there where I store the RV (that surface is made up if asphalt chips that were hauled in from road scarification in the surrounding area and then rolled out ..... so it is a bit more like tight gravel than real pavement.)

In your case, you would be increasing the actuation force by about 33 percent if you went from Lg SUV to Large Truck (from 15psi to 20.)

I should probably run a test using my IR Temp Gun, but I have towed my Kia just under 15K miles now with the higher braking force and all is well ...... no abnormal brake wear.  It's been a trouble-free toad brake; the main reason I bought it was for its fast response time (approx 1/2 second) and I wanted that for panic stops ..... like yours.

I was relieved (in a left-handed sort of way) to read about RV stopping distances in Gary's response.  I have always thought my Ford brakes were lousy (I recently replaced the front rotors, calipers, pads, and wheel bearings) but I actually believe I can easily stop my 17,000 lb gross comb wt well within those guidelines.)  But I'd still like bigger brakes.....and wheels/tires too. lol

Safe travels to ya..........

Title: Re: Panic Stop
Post by: billwild on September 09, 2019, 05:01:30 PM
Going through Salt Lake city on a trip south, and a family in an old van towing a trailer with everything they owned, decided he wanted my lane. He was just ahead of my front bumper when he pulled over. I absolutely floored the brake, 40' of motorhome towing a Honda CRV turned sideways almost to avoid an accident. His trailer came within inchs of hitting our coach. The brakes worked great, and for the next half mile, he heard the sound of my air horn. I do believe the antilock brakes did come on.

Title: Re: Panic Stop
Post by: John From Detroit on September 09, 2019, 05:47:34 PM
Road surfaces vary but there is a standard I will call a "Reference road" clear, Dry Concrete.

At 55 MPH with all wheels LOCKED and I mean all. MH and towed you will skid about 164 feet.. If the rig has ABS that may be different (I do not know how ABS affects it can go either way) and if the brakes do not QUITE lock it should be less. or more depending on how far from locked.    That's based on something let me do it by another method to confirm. Ok came up with 166 Feet

Note that dispite what they tell you about "It takes longer to stop a big rig"  This applies to everything from a Smart car to a fully loaded semi (It does take a fraction longer for the brakes to lock on a semi. A precise fraction in fact and I do not know what it is)

Now for those who do not tow with brakes on the towed.. The stopping distance goes way way up...

WHY:  Well when you do all the high level math The weight of the vehicle which is supported by the LOCKED wheels being the same as the weight of the entire consist.. Factors out so the size of the ride does not matter.

But when there is some weight back there pushing that's not braking.. Well... Lots more skid.

Oh  Long ago they taught me count seconds. from the time the vehicle in front of you passes under a bridge shadow for example till you reach the shadow. If less than 2 secons (one thousand one, one thousand two) you are two close.

I like to do FOUR seconds just to be safe.. had a few times where I was very very glad I did that.

Title: Re: Panic Stop
Post by: Molaker on September 09, 2019, 05:57:07 PM
Did you check your pants? Maybe your rear wheels and towed wheels were on slicker pavement than the front. ;D
Title: Re: Panic Stop
Post by: ELeland on September 10, 2019, 08:27:08 AM
Thanks for all of the input.  Yes I do have ABS.  I guess I knew that but it never registered at the time.  I'm going to go up a notch to "Large Truck" on the RVi2 and that may help as well.  I do carry an IR temp gun and usually walk around the rig during stops just to check all wheel and tire temps and will continue to do so especially with the change in setting of the RVi2.

Title: Re: Panic Stop
Post by: Kevin Means on September 10, 2019, 11:15:17 AM
Thanks for all of the input.  Yes I do have ABS.  I guess I knew that but it never registered at the time.  I'm going to go up a notch to "Large Truck" on the RVi2 and that may help as well.  I do carry an IR temp gun and usually walk around the rig during stops just to check all wheel and tire temps and will continue to do so especially with the change in setting of the RVi2.

That's one of the reasons I like our TPMS so much. It's constantly monitoring not only the tire pressures, but the tire temps as well. It's accurate enough to detect the higher temps on the sunny side of the coach and towed vehicle.

Title: Re: Panic Stop
Post by: SargeW on September 10, 2019, 01:11:31 PM
There are a few issues I see here as well. First, I would always leave the exhaust brake on. If you need it in a panic stop, you will never have the time or mind set to turn it on. An "Exhaust Brake" is not as efficient as an "Engine  Brake" but none the less will help contribute to slowing that huge mass of rolling steel.  I had to panic stop on the freeway when a truck pulled in front of me from a dead stop. Without the engine brake on I wouldn't be here to write about it.

Second, have you ever had your brake fluid changed?  Brake fluid can become diluted with condensation of a period of time. When it does is loses some of it's ability to apply max pressure to the brake pistons because high heat will cause the brake fluid to boil.  If your brake fluid is old and you can't get max pressure on the brake pads, you also won't activate the ABS function. 

It's a scary time to find out that your rig isn't braking at max performance, but better now than later.
Title: Re: Panic Stop
Post by: Larry N. on September 10, 2019, 01:47:26 PM
Marty -- just FYI, some rigs can't use cruise control with the engine/exhaust brake turned on, just one or the other -- my Beaver was that way, but my Newmar lets me do both.

Second, have you ever had your brake fluid changed?
I do believe the OP's air brakes change the "fluid" almost constantly.  8) ::) ;D
Title: Re: Panic Stop
Post by: ELeland on September 10, 2019, 02:27:11 PM
Thanks Kevin, Sarge & Larry -

I do have a TPMS and wouldn't leave home without it.  I had the temp sensitivity set too low as at one point I was getting a high temp alarm on the front left of the towed because it was right behind the exhaust discharge of the MH.  A couple of stops and a quick check with the IR gun later I figured out the cause and changed the settings.

I do try to leave the exhaust brake on for the reasons mentioned.  I don't like the idea of the brake lights coming on every time I lift the throttle though.  It bugs the crap out of me when I ride behind someone that is constantly hitting the brakes.  This was a wide, mostly level road so I flipped the EB to off for this portion of the trip.  The cruise control does work with the EB turned on.

 will make sure to ask for a brake fluid change when I have it serviced later this week.  I'll let you know what they say Sarge ;)
Title: Re: Panic Stop
Post by: Mile High on September 11, 2019, 09:22:09 AM
I have the RVi2 on a Wrangler, and living 12 miles from Castle Rock I've circled down there to get help setting it up correct (my issue was not setting for vacuum brakes properly).  I have had to panic stop and ABS kicked in on the Freightliner and the RVi2 did it's thing, however....I honestly don't expect the RVi2 to be as effective in a panic stop as some of the other powered brake systems that don't need to overcome the lack of brake boost such as the Air Force One. 

The RVi2 is an effective auxiliary brake and I love the fact it is portable, but in my opinion there is just no way it can effectively function in pressure or time in a panic stop as well as some of the others.  To me, it just keeps the toad from crushing the tow bar or riding the tow bar up into the MH radiator.  If I ever go to a heavier toad, I will probably change out to an auxiliary brake that continuously pulls vacuum on the power brakes of the toad. 
Title: Re: Panic Stop
Post by: Gottasmilealot on September 11, 2019, 01:01:51 PM
Which illustrates the point that it is very hard to maintain adequate stopping distance when every idiot on the road wants to pass you then cut right in front of you and eliminate your stopping space. My biggest annoyance when driving.
Title: Re: Panic Stop
Post by: ELeland on September 23, 2019, 07:55:33 PM
Follow up - Brakes were checked on Saturday during routine service and they said all is good.  I also had them change the air dryer filter with the Halidex kit I picked up from Freightliner.  I've owned this rig 2 years and never had the air dryer serviced.  I'm glad I did as it had a 2005 date written on the side of the filter.  I believe that is supposed to be an annual maintenance item.  No change in air or braking that I could tell.

Title: Re: Panic Stop
Post by: Gary RV_Wizard on September 24, 2019, 10:44:05 AM
In motorhome use the usual change interval for a Haldex air dryer cartridge is 24-36 months, depending on the model of the dryer, the engine run hours and the climate humidity.

Here is a link to the Freightliner document for the two types of air dryer they use. If yours is older than 2003 model year, it may not apply. Haldex has other models of dryer besides the PURest decribed in the document and they have 24 month intervals. (
Title: Re: Panic Stop
Post by: camperAL on September 24, 2019, 02:09:43 PM

SargeW, Gary B. or others in the know, my break fluid is three years old. Had it changed when I bought it, with other fluids. Truck place I take it for service doesn't seem to want to change it (use to working on semis) seem nervous about messing with it and bleeding off the breaks. Said it should be O.K. but I have heard about changing it once every two or three years. How critical is it in my moist, wet weather here? I'm just over the three year mark and want to change it soon.
Title: Re: Panic Stop
Post by: ChasA on September 24, 2019, 04:35:46 PM
Find a different shop. The owner's manual on my 2006 F53 said change every 3 years. It IS important.
Title: Re: Panic Stop
Post by: SargeW on September 24, 2019, 11:41:19 PM
I agree with Chas. If you can pop open the brake fluid reservoir and the fluid is a clear light amber color, you are probably OK. But most likely it will be a dark brown color meaning it's contaminated with debris and condensation (water).  That means reduced braking ability, especially if you need to step on them hard.  It's not expensive, but it is important.
Title: Re: Panic Stop
Post by: Gary RV_Wizard on September 25, 2019, 10:30:40 AM
Al:  As a practical matter, the chance that your brake fluid actually needs changing is very slim.  Typically a hydraulic brake system could go for a dozen or more years without the slightest degradation.  Tiny leaks, though, can allow in moisture, air or contaminants and thus a periodic change refreshes the system.

If your truck shop is accustomed to working on air brakes on a semi, go to another shop that handles hydraulic brakes. If you are nervous about 3 year old fluid, you should also be nervous about having work done by people who are unfamiliar with hydraulic brakes.
Title: Re: Panic Stop
Post by: camperAL on September 25, 2019, 03:30:15 PM
Hi Gary B, Sarge and all,

The truck shop said they didn't work on hydraulic breaks but didn't seem to know much about it. If a truck shop is going to offer advise, then they should be in the know enough to offer it. I have them lube, oil change and generator oil change and filters etc. on the rig. They did service my differential this year. They seem to do a good job and I am happy as they are close by. Found a place near where I store the RV that works on school buses for our area that can change the break fluid. They have to see it before they will give me a quote.

Before taking it there, I will check the fluid myself then make a judgement on if it needs changed or not. I have just seen lots of advise to change the hydraulic fluid in RV's. Apparently the fill cap can be an area where moisture gets in and can contaminate. Just want to be responsible to myself and more importantly others on the road.

Getting back to panic stops, the last thing you want is to hit the breaks and not have them work. We don't want to loose anyone here. Thanks for the good advise!!