maxi brakes

[christopher]

My friend is looking at an 04,
Any idea what it costs to put in maxi brakes(the brakes that activate when the air goes low)
Chris
mci 5c

[PCC]

Changing out the brake operators is a simple process, so the cost of the two double chambers, plus the air hose to the chambers is the out of pocket expense for parts.

They are each held in by a couple of studs and nuts (no innuendos intended) so the re and re is fairly straightforward.

[RJ]

PCC -

Yes and No.

You've got lots of room around the axles on your H5, so yes, it's a relatively easy install.

Not so on a 4104.  There's barely enough clearance for the single chamber brakes cans that are OEM, spring brakes won't fit without some modifications to provide clearance.

And that doesn't include the plumbing changes that have to be made, too. . .

Not that it hasn't been done, it has.

But it's not a simple bolt-on procedure on an '04.

Chris -

If the '04 still has the drum brake on the driveshaft, several busnuts have installed a spring brake chamber on it for parking brake operation.

FWIW & HTH. . .



FWIW & HTH. . .

[zubzub]

Hi, RJ it's the 06 (from what I've heard) that does not have room for spring brakes.  The 04 has just enough room

at least mine does.

[TedCalvert]

Mine too.


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[TomC]

If you have the room, it is a simple install. Just run the extra air line up to the dash and install the yellow air valve. The valve on the dash does all the sensing about low pressure and popping out when the air gets low. Just have to find an air supply for it. The amount of air going to the maxi brakes is not important. What is-is that they get full pressure.  They should be plumbed to the same air tank that feeds the normal service brakes. So if you have a failure on the service brakes and loose pressure, the maxi brakes will apply.

When driving truck, my exhaust pipe (horizontal exhaust to the back of the sleeper then up) came apart at the muffler. It sounded cool so I didn't get it fixed. Little did I know that the hot exhaust was melting the plastic air lines. When it did happen, my air pressure went down to zero in less then a minute and I came to a very quick stop from 70mph. It was nice to know that it worked so well. One other casualty of the hot exhaust was it melted my black tank (mounted on the fuel tank cross members below the drive shaft). That was a mess and was about like nuclear waste. But live and learn. Got the truck towed with an old KW with a 6x4 trans and a Cummins NH220. Was slow, but got us back to the shop. Got it fixed, ran the rest of the trip with a bucket under the black line at night, then installed a new tank when home. Good Luck, TomC

[Kenny]

TomC, isn't there more to just adding the spring brake canister and valve at the dash connected to the brake air tank?  If the spring brakes are applied and you depress the brake pedal, isn't the combination of both the spring brake pressure and the normal brake canister pressure going to over stress the S-cams and shoes? I thought there was always another valve in the circuit so normal brake pressure could not be applied unless the spring brakes were pressurized. Kenny

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[gus]

No, RJ is right, the stock can mount gets in the way of the maxi can so there some adjustments, metal cutting and welding to do.

Be sure to get the smallest maxi cans.

[buswarrior]

Go to Bendix and find a common schematic and lift the parking circuit plumbing and duplicate it.

Massive library of free information available on their site.

You will need an SR-1 spring brake relay valve and the aforementioned push-pull valve at the driver. It will take care of the compounding.

This would be an excellent time to add another tank and re-plumb to a dual circuit system, if you are so inspired.

A misconception that is far too commonly held is that the control valve at the driver is what determines the automatic application of the spring brakes under low air conditions.

The spring chambers themselves have already overcome the air pressure holding the big springs off and started to drag and squeeze progressively harder as the air pressure being applied to them dropped through 60 lbs. By the time the control valve pops, somewhere under 40 lbs, the coach will already be stopped.

happy coaching!
buswarrior