Recent Experience with my DP Air Brakes

[BillO]

I recently had a scary experience with the air brakes on my older (1995) coach. On a fairly heavily traveled Texas secondary road (speed limit 55) I came to a traffic light turning yellow while I was about 300+ feet away. I hit the brakes hard and only decelerated very gradually, coming to a stop with my nose in the intersection just as the light turned red.

I cautiously, and very slowly, made my way to a shop that I knew to do HD truck brake work. The mechanic inspected the brakes, but found no obvious problem. He then liberally greased the two lube points (slack adjuster and S cam) with standard chassis grease and sent me on my way.

The brakes seemed to work better after that, but still not really well. I found that if I applied them really aggressively a couple of times it improved performance to an almost acceptable level but with some delay and grabbing.

I was not really satisfied, so managed to get the coach to Motorhomes of Texas and a mechanic I respected.

When I described the problems I was having with the brakes both the service writer and the mechanic had the same response -- "you've been getting lube at truck stops right". The mechanic went on to explain that most truck shops use the same grease (typically a lithium base) for all chassis points, including the air brakes and that's OK for trucks because they're used daily. However, with the more typical coach operating cycle -- run it up hot for a day, or a few, then sit for weeks, or more -- the typical lithium lube with an oil carrier starts to separate and congeal, especially in the fairly intense heat area of the brakes.

The mechanics solution was to displace all the lithium type grease with a clay based grease with which they have had good experience. This necessitated a minor adjustment of the brakes for the different lube characteristics.

After these steps I went for a test drive with the mechanic and there was a dramatic improvement in braking performance with him driving and I could feel it, as well when I finally drove away from the shop.

The mechanic's parting advice was two points: 1. If you get chassis lube with your regular oil changes don't let them touch the brakes, and 2. the brakes do not need a lot of grease so only relube with the clay based product every 2-3 years.

I am gradually getting an education in the maintenance and operation of these unique vehicles called motorhomes and pass this on for information and comment.

[wolfe10]

Bill,

I am curious-- is this their suggestion for all air brakes, just air disk brakes (which is mostly what MOT works on) or???

Would be interested in collaborating documentation from the brake manufacturers if this applies to other than the air disk brakes as used on Foretravels for example, which DO require clay-based grease.

[BillO]

Wolfe10,

This was for my older Vogue Prima Vista which has drum brakes, so it would appear to apply to all air brakes. The MHOT service people were the two Kieths (younger service writer and older mechanic) whom I suspect that you know. I don't know if they are simply extrapolating from Foretravel disk brake experience, but I think that the older Kieth has been around Foretravel and/or MHOT since before disk brakes were invented .

I have been tied up with some other work on my coach so haven't gotten to it, but I vaguely remember a mention of clay-based grease in the rockwell axle section of the owner's manuals that I received from the previous owner and plan to revisit that.

[wolfe10]

Yes, know the "older Keith" very well-- an excellent tech.

But, as you say, he grew up on the Foretravel air disk brakes. Again, the question is-- does/should this apply to all brakes or just the air disk brakes? So, still looking for supporting documentation from other than air disk brakes calling for clay-based grease.

BTW, I did a mechanical inspection for a buyer on a Foretravel yesterday and found regular grease (not clay-based grease) in the brakes. Called for a complete purge.

[BillO]

Brett,

I finally had the chance to dig out the manuals that I received from the previous owner to check the section on Rockwell axles and cam brakes. In all cases, save one, they list both clay-based and lithium complex greases as acceptable for cam brakes, including the automatic slack adjusters. I'm not sure why, other than historical sequence, but in each section they list the clay-based product first followed by lithium greases and then clay-based synthetics.

The one exception is a part, rather than a complete brake. They suggest lubricating the cam shaft spline with a calcium-based grease for it's anti-seize properties.

I would assume that the calcium product would be applied during a rebuild. My brakes only have two grease fittings and both areas are identified by Rockwell as the same grease. I can't see how to stage different greases in one of them to get at the spline and the manual has a footnote warning not to mix the calcium grease with other greases.

To complicate matters, I finally downloaded the Meritor manual that you had referenced in another thread and looked through that for lube recommendations. For one cam brake they start with "lubricate the automatic slack adjuster with a calcium-based grease".

So, while I now have functioning brakes again I'm back to another level of confusion.

As a curiosity, how were you able to identify the non-clay grease in that Foretravel? I bought a tube of the clay-based at MHOT and it is the same deep red color as the lithium grease I'm now using on the rest of the chassis fittings.

[wolfe10]

The grease in the Foretravel air disk brakes was gray chassis grease. I compared it with a tube of clay based grease I carry with me when I inspect Foretravels, as the clay based grease is required in all their air disk brake systems. Kind of a "show and tell".

[chuckprowse]

I have Meritor axles and air disc brakes, Clay based is recommended for the slack adjusters and calipers. My last lube job was at a truck stop in Phoenix and I expressly instructed them to use clay based grease for the brakes, they didn't and within 50 miles after a six month storage the rear brakes started dragging. $1500 repair for rotors, pads, and cleaning out the old grease on both axles.