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Topic: ABS Brakes (Read 1001 times) previous topic - next topic

ABS Brakes

In another thread on the Forum, where we are talking about the availability of parts for older RVs, I saw this statement:

Quote from: BillO –
With my 1997 (along with another owner I'm aware of) I've had to disable the ABS because Haldex obsoleted the front relay valve with no replacement.  After posting here, beating the bushes, and calling every source I could find I had to replace that valve with an old style non-ABS version and disable ABS completely.
I'm well aware of the "unobtainable ABS valve" problem from previous posts on the Forum.  I completely understand the frustration BillO must feel - being forced to disable a OEM safety feature on his coach because it can't be fixed.  But whenever I hear about "ABS" on a 15 ton motorhome, I always wonder how often such a feature is ever actually activated.

In the 5 years we have owned our coach, I have only felt the front wheels "skid" one time.  That was coming down a small hill, on rain-slick muddy pavement, in a camp ground, when we were going about 5 MPH.  Our non-ABS coach has (in my opinion) excellent brakes, but I very seldom ever need to utilize their full stopping power.  When I do, I get "The Look" from my DW.

Our car has ABS, and in the 8 years we have owned it, I have never felt the ABS activate because I have never braked hard enough to need it.  In fact, I took it out in a parking lot one time and purposely locked up the brakes, just to see what it felt like.  Slight shudder through the brake pedal and a surprisingly abrupt stop - but that's it.  Nice to know it does work.  8)

Perhaps we are just lucky drivers, or we don't ever drive in the kind of traffic that requires "panic" stops that would lock the front wheels.  It just seems to me, based solely on my almost 60 years of driving experience, that most emergency braking scenarios could be avoided by defensive driving techniques.  However, I also realize that many Forum members have a great deal more time than I behind the (coach) wheel.

How about it.  Have any members with ABS equipped coaches ever actually used the anti-lock feature?  Is there any indication to the driver that the anti-lock is activated?  What was the situation that required ABS?  Did it prevent a crash?  Could it have been avoided?

Not intending to insult or embarrass or second guess any of our members - I'm just curious about the real value of ABS on big motorhomes.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: ABS Brakes

Reply #1 –
The value of ABS comes into play in slick road conditions such as ice/snow or wet roads where hydroplaning can happen easily.  It is unlikely that it will ever be activated during hard braking on dry pavement with a large motor home.  I have had the ABS kick in a few times on our U320 under both of these conditions as well as when braking on a road with loose gravel.  If you drive in winter in Colorado with any vehicle you will get first-hand experience in ABS activation.  It does allow the driver to maintain a bit of directional control but does not necessarily keep you from sliding into a hard object or off the road.
Monti
2015 Born Free Triumph Royal 4x4
Previous:  2000 U320 3600

Re: ABS Brakes

Reply #2 –
When cleaning the brake relays to install the Air Force One under my coach, one of the ABS wire connectors disintegrated. OMG, I thought, what have I done. The sky is falling! Cause I had read that these parts were no longer available. I knew I "might" be able to get a new connector made, but after a while forgot about it. On our first ever trip, had to stop hard twice, and never worried that the coach wouldn't stop. It did. The ABS light is on in the dash, and one day I will either disconnect the entire system or try to fix it. But, yes, no worries about it here.
Truth is, these coaches are pretty amazing, yet very complicated, with  a gadzillion of parts. I think the bad thing is to not use them, to just let them sit idle and let them die a slow death.
'99 U320 40 WTFE
Build #5462,
1500 Watts Solar 600 amp Victron lithium
2012 Jeep Grand Cherokee Overland Hemi
Instagram bobfnbw
Retired

Re: ABS Brakes

Reply #3 –
To embellish on the statement that I made in the OP's reference I, frankly, wasn't (and still am not) particularly worried about the ABS.  For 5 years prior to buying this rig I drove an older Vogue which had neither ABS nor disk brakes and had no trouble stopping that heavier coach.  However, to be fair that coach also had a big CAT engine and Jake brake which would put the coach nose down if deployed on high.

The bigger issue was parts availability combined with the reluctance of mechanics to replace the bad ABS valve (the valve had an internal leak which took the air down from 120 to 30-40 overnight).  I pointed out the lack of replacement for the potential buyer to consider some form of stockpiling if he planned to keep a 2002 coach for some time because in 5 years he might be in the same boat.  Then, even if he can find a non-ABS replacement he may have to cope with the same issue I did of going to 5 different places before someone knew DOT regs well enough not to refuse replacement due to fear (i.e. thinking that dumbing out ABS was illegal).
Regards

1997 U295 40 with CAT 3126

Re: ABS Brakes

Reply #4 –
I have a leaking ABS valve on my 95, DO you have any info (part number, manufacturer) on the replacement non ABS part?
How involved was the substitution?
1995 U320C SE 40'
Jeep 4x4 Commander - Limited - Hemi
"The Pack"  Yogi and Diesel our Airedales -  Charlie our Boxer/Akita mix. Gone but NEVER forgotten Jake our yellow Lab.
NRA Law Enforcement Firearms instructor - Handgun/shotgun
Regional Firearms instructor for national Armored Transp. Co.

Re: ABS Brakes

Reply #5 –
Lon, Chuck and Others—We had a similar problem with our '95 and couldn't find the original replacement. I went to Foretravel and they used Part # P104036  - E6 BRAKE VALVE as a suitable workaround. They stock the part. I have had no (brake) problems since this fix. Hope this helps. Paul
Paul & Kathleen
1995 U320c SE 40'
Build 4681 --Cummins M11 /17511
"That Irish Girl"
Red MINI " 40"

Re: ABS Brakes

Reply #6 –
Long, long story short.  We cooked the "abs sensor"on the rear brakes when a brake pin wasn't releasing.  New rotor, pads and sensor.  That caused the Alison to NOT lock up in 4th, 5th and 6th gear and also NO retarder at all. ( disabled it ). It was a real pain ( 4 Phoenix shops ) to figure out.    Finally James (Bess his heart) at Foretravel said just unplug the dam thing if you suspect that's the issue.      Unplugging it fixed everything immediately ( Alison and retarder ).  The Fortravel shop replaced all the parts cause ALL of the other shops were clueless about Foretravels. 

 I guess moral of the story is. Malfunctioning ABS stuff can cause all kinds of issues !
Robert and Susan
 1995 36' 280 WTBI 8.3 3060r
 1200 watts on the roof, 720 Ah of lithium's
 Build # 4637. Motorcade # 17599
        FMCA  # 451505
        18  Wrangler JLUR

Re: ABS Brakes

Reply #7 –
Is that part number replacement for a midland-Grau abs box?  Is the valve something else other than the box mounted in my compartment?
"Riding and rejoicing"
Bob
1997 U320 40' Mid entry, build 5132,  wtbi ce27, 4th owner
2007 Solara convertible
2 prodeco tech outlaw ss electric bikes

1095 watts solar
08 Ls 460 and a sc430
2000 Ford F-250 superduty 4x4

Re: ABS Brakes

Reply #8 –
Quote from: Lon and Cheryl –
I have a leaking ABS valve on my 95, DO you have any info (part number, manufacturer) on the replacement non ABS part?
How involved was the substitution?

There is no single ABS valve, so no single answer.  The leaking valve in my case was the front one -- in this case a Haldex brand which incorporates all the ABS action within a single valve block.  Off the record one Haldex tech said I could replace it with any standard relay valve with a 4 psi break-open.

Foretravel appears to have used several different brands of ABS (with different configurations) during the 90's.  Some, like mine, are an integrated relay/ABS valve while others seem to have a relay valve with separate ABS valves between that and the wheel.  In any event I suspect that front and rear valves (ABS or replacement) would be different due to the tie-in of the emergency brake in the rear.

I think that the Haldex, integrated type valve might be easier to replace because it is physically about the same size as an old relay valve.  Consequently, there isn't any worry about air line length.

In my case replacing the valve and disabling the remaining system so it wouldn't interact unpredictably with the non-ABS part took about 3 hours, including leak testing.
Regards

1997 U295 40 with CAT 3126

Re: ABS Brakes

Reply #9 –
Quote from: Caflashbob –
Is that part number replacement for a midland-Grau abs box?  Is the valve something else other than the box mounted in my compartment?

Bob,
I believe that the part referenced is an actual air valve.  It goes between the tanks and feeds air to the brake canisters.  There is a control air flow through the brake pedal circuit that triggers this valve to open and apply main air to brakes.  In the original ABS configuration the air path to each brake has the ABS part that is controlled by wheel sensor and the control box in the bay to interrupt air pressure if a wheel locks up.  The replacement part is a simple mechanical valve that applies air to the brakes when triggered period.
Regards

1997 U295 40 with CAT 3126