Vacuum Brake Controller


For you lovers of the Class 8's and bigger.

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Post Tue Jun 10, 2014 3:10 pm

Vacuum Brake Controller

I know this is not directly an IHC question, but is a ~1930-40 large truck question. I know the quality of the people here from the previous 2 versions OLDIHC forums, so I figured I would get good quality answers here (along with the normal assortment of `quality' comments).

I volunteer at a railroad museum here in Eastern Connecticut, and one of our pieces is a ~1934 7 person Railbus built by Fairmont Motor Car for the Maine Central RR. The brakes are Vacuum Suspended and controlled by a Bendix/Bragg-Kliesrath RH trailer controller (the unit normally was strapped to the side of the steering column like a Signal-Stat turn signal controller. The controller has been giving us problems and I am looking for someone with more experience in diagnosing and fine tuning them.

Using the Service manual, I found a few years ago, I have gotten it to the point where they work, but only as on or off, detent 1 is brakes released, detent 2 is release, detent 3-5 is sending air directly into the vacuum source line. Only took rebuilding, reexamining, rereading and readjusting about 8 times to get this far. :t0116: Service manual only lists pressures for released and applied. Is this how these controllers are normally set-up?

I have carefully checked the diaphragm and there are no cracks, the seats have been cleaned with medium scotchbrite are smooth and not scored, all the rubber seats don't feel any harder than I would assume they should be (about the same as an o-ring or faucet gasket), and all sliding parts have been lightly oiled with air tool oil (figured it was safest option short of Vacuum oil). When brakes are released both gauges read 16-18 inches Hg, when applied brake cylinder gauge drops to 3-5 in Hg, tank maintains 16-18 in Hg and within 6 seconds the brakes have gently applied before locking solid (last little bit is hard enough to jerk you in your seat).

Thanks for any help you can supply,

Rich C.
Willimantic, Ct
1949 KB-3

P.S. For those not familiar with Vacuum brake terminology, straight vacuum brakes run 2 ways, Vacuum Suspended and Atmospheric Suspended. With vacuum suspended systems, full vacuum is applied to both sides of the brake cylinder and the return spring retracts the piston to release the brakes. To apply the brakes, air is allowed into the backside of the cylinder and the pressure imbalance pushes the cylinder out thus applying the brakes. Atmospheric suspension is the direct opposite (zero vacuum on both sides for release, vacuum admitted to the front side to apply brakes). 19 inches of Mercury (in Hg) equals ~9 psi and 1 atmosphere (pressure applied by column of air measured at sea level) equals 30 in Hg (14.75 psi). The vacuum source is usually the intake manifold of the engine, but vacuum pumps have been also used. So when the brakes are applied you are applying about 45 in Hg (22 PSI) [30 in Hg (1 atmosphere) + 15 in Hg] to the backside of a 12"-16" piston (800-1100 Lbs at the rod end) which is connected to the brake shoes.

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Post Tue Jun 10, 2014 4:31 pm

Re: Vacuum Brake Controller

any stickiness in the brakes cylinders themselves? I know nothing about this type of system, but per your: "within 6 seconds the brakes have gently applied before locking solid (last little bit is hard enough to jerk you in your seat)" makes me think that something is sticking. Just a thought.

Golden Jubilee
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Post Tue Jun 10, 2014 6:00 pm

Re: Vacuum Brake Controller

I have one or two of those column-mounted units. Not sure if the same manufacturer...just in case.
1933 IHC Bus. Cpe
1933 IHC B-3 f
1935 C-1 IHC pickup
2 x 1936 IHC C-30 Fbs
3 x 1938 IHC D-2 Pickups
1938 IHC D-30 fb
1941 IHC K-1
2 x 1947 IHC KB-1 Pickups
2x 1953 IHC R pickups

Golden Jubilee
Golden Jubilee

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Location: Lyman, IA

Post Tue Jun 10, 2014 6:12 pm

Re: Vacuum Brake Controller

Also post on ATHS and Just old trucks websites. There are people who have Vacuum brake experance and connection to places that work on them.

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Post Wed Jun 11, 2014 6:00 pm

Re: Vacuum Brake Controller

To clarify, nothing is sticking, by locking solid enough to jerk you, I am referring to how hard the brake grips at the end as the cast iron tread brakes lock solid onto the steel wheels (feels like 0.5-1 MPH to 0 in half second).

Rich C.

Here is what the controller looks like:, Bendix/B-K Model Rh, circa 1935
Image Image

Golden Jubilee
Golden Jubilee

Posts: 1806

Joined: Tue Jun 25, 2013 5:26 pm

Location: Dinuba, central CA

Post Wed Jun 11, 2014 7:04 pm

Re: Vacuum Brake Controller

I'll check my stuff but it looks different. All the ones I've seen have a gauge installed.
1933 IHC Bus. Cpe
1933 IHC B-3 f
1935 C-1 IHC pickup
2 x 1936 IHC C-30 Fbs
3 x 1938 IHC D-2 Pickups
1938 IHC D-30 fb
1941 IHC K-1
2 x 1947 IHC KB-1 Pickups
2x 1953 IHC R pickups

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Posts: 7

Joined: Mon Jun 09, 2014 3:21 pm

Post Thu Jun 12, 2014 11:12 am

Re: Vacuum Brake Controller

When gauges are used with these, they go into the 1/8 NPT ports on the side (2 straight slot plugs in first photo)

Rich C.

Golden Jubilee
Golden Jubilee

Posts: 1806

Joined: Tue Jun 25, 2013 5:26 pm

Location: Dinuba, central CA

Post Thu Jun 12, 2014 11:35 am

Re: Vacuum Brake Controller

In all my years of looking at old farm trucks I don't recall your style controller.
Maybe they didn't sell in the western states?
1933 IHC Bus. Cpe
1933 IHC B-3 f
1935 C-1 IHC pickup
2 x 1936 IHC C-30 Fbs
3 x 1938 IHC D-2 Pickups
1938 IHC D-30 fb
1941 IHC K-1
2 x 1947 IHC KB-1 Pickups
2x 1953 IHC R pickups

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Posts: 7

Joined: Mon Jun 09, 2014 3:21 pm

Post Thu Jun 12, 2014 5:27 pm

Re: Vacuum Brake Controller

Not sure where they were sold, but Bendix was manufacturing them in South Bend, Indiana.

These controllers would have been found in trucks that handled trailers with vacuum brakes. The truck itself would have had a regular foot pedal valve for it's brakes.

Golden Jubilee
Golden Jubilee

Posts: 1806

Joined: Tue Jun 25, 2013 5:26 pm

Location: Dinuba, central CA

Post Thu Jun 12, 2014 6:26 pm

Re: Vacuum Brake Controller

Yes, I think we understand the concept of vacuum brakes...
My point is that I've never seen the style of controller you have EVER before.
1933 IHC Bus. Cpe
1933 IHC B-3 f
1935 C-1 IHC pickup
2 x 1936 IHC C-30 Fbs
3 x 1938 IHC D-2 Pickups
1938 IHC D-30 fb
1941 IHC K-1
2 x 1947 IHC KB-1 Pickups
2x 1953 IHC R pickups

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