Cam Rotation Meters

are

BRAKE WEAR INDICATORS.

Or Calibrated Spacer Washers

Mechanic establishes a Timing Mark on S-Cam

Proper sized S-Cam Rotation meter is chosen

Function highlights;

The meter is a circle = 360 degrees. The circle is divided into 3 sections 120 degrees each. The external arrowhead identifies ZERO degrees, each of the inverted arrowheads signals 120 degrees of accumulated travel. 120 degrees or more is an out-of-service condition. The outer ring of the BWI meter is a degree wheel

F = Full. S-Camshaft at zero degrees of rotation.

120 degree section, consists of Four sections, each with 10 marks indicating 3 degrees of rotation each.

3 = 3/4 full. As in a quick look at brake wear at this wheel end.

2 = 1/2 full. As in a quick look at brake wear.

1 = 1/4 full. As in a little longer look at brake wear at this wheel end.

E = Empty. This is 120 degrees of accumulated brake wear and the wheel must be pulled.

A trained mechanic registers a timing mark (with a cold chisel) on s-cam at ZERO degrees. Finish the brake work, adjust the brakes as always, and notice the timing mark has moved considerably. Anytime a brake wear reading is wanted, a mechanic will simply spin the meter to line up the external starter arrowhead with the current position of the timing mark to establish brake wear at any wheel end where the BWI meters are installed and read the accumulated brake wear.

Proper measurement of s-cam rotation is covered elsewhere in this material. Information is also in the AAMVA and CCMTA Inspection Manuals mentioned above.

Why should you consider installing Brake Wear Indicators attach S-Cam wheel-end now, or at the next brake reline?

1. Because they work.

2. Offers the best brake-wear information available to any

trained mechanic without wheel pulls.

3.  Inspecting the timing mark position of in-service meters

helps nip one-wheel brake wear issues.

Gold 1 ½" Universal Flatmeter

1.50 inch I.D.

This 1 ½" Universal BWI meter is becoming more common. Easy to install and very simple to read after installation.

Universal model floats like a washer until it's time to read brake wear, then the meter is rotated to line up with the TDC mark on the SCam to measure accumulated brake wear.

Gold 1 1/4" Universal Flat meter

1.25 inch I.D

The 1 ¼" Universal BWI meter is used on S-cams with a smaller O.D. beyond splines.

Green for Coach 1 5/8" Universal Flat meter

1.625 inch 1.D.

Designed for use on rear axle of Highway coach.

Chrome ½" Hole for Transit Coach Flat Meter Chrome plated copper.

Designed for use on the rear Rockwell axle of transit coach.

CA92DPCT
CA92GPCT
CA92B
CA92EC

Gold finish 1 ½" x 10 spline reversible Flat Meter

1.50 inch I.D. (Fruehauf /Propar).

In this position, the external arrow is in line with the right hand edge of one of the 20 teeth.

Circle is 360 degrees, divide by 20 = 18 degrees per tooth whether internal or external.

Therefore, this meter is 9 degrees right.

The reverse side would be 9 degrees left.

CHROME 1 ½" x 10 spline reversible Flat meter

1.50 inch I.D.

In this position, the external arrow is in line with the right hand edge of one of the 20 teeth.

Circle is 360 degrees, divide by 20 = 18 degrees per tooth whether internal or external.

Therefore, this meter is 9 degrees right.

The reverse side would be 9 degrees left.

Gold 1 ½" x 10 spline reversible Flat meter

1.25 inch I.D.

In this position, the external arrow is in line with the left hand edge of one of the 20 teeth.

Circle = 360 degrees, divide by 20 = 18 degrees per tooth, whether internal or external.

Therefor, this meter is 9 degrees left.

The reverse side would be 9 degrees right.
Gold 1 ½" x 10 spline Extruded meter

1.50 inch I.D.

This extruded meter has the arrow head lined up with the center of a tooth. This is called a TDC (Top Dead Center) or Zero application meter.

This may be necessary if the s-cam is undercut on the end of the spline

Blue 1 ½" x 10 spline Extruded meter

1.50 inch I.D.

This extruded meter has the arrow line up with the right side of a tooth, meaning this too is a meter with 9 degrees right.

CA92APCT
CA92APCT-C
CA92FPCT
CA92BPCT-G
CA92BPCT-B

Silver 1 ½" x 10 spline Cup meter

1.50 inch I.D.

This meter shows the arrow head lined up with the left side of a tooth, meaning this meter is considered 9 degrees left.


Gold 28 spline Cup meter

Fit ArvinMeritor/Rockwell style S-cams In a 28 tooth cam each tooth is roughly 6.4285 degrees. For fleet managers wanting positive lock indicators this extruded model does the job very nicely. All 28 spline meters are extruded due to undercut s-cams..


 

This is known as an undercut camshaft. The spline does NOT extend to the end of the camshaft.

Therefore, the customer has two choices. Can use the Extruded version if proper spline size is known and inventory is available. Alternately, you can use the UNIVERSAL blank model if the cam spline is not known.

1. Use a straight edge from center of clevis pin to center of S-Cam. Mark the upper half of the S-cam spline face with a pencil.

2, Make the pencil mark permanent, by using a cold chisel to mark the S-Cam at Zero degrees of rotation.

3. The Zero mark will always be the mark to rotate the external pointer to when you wish to identify total accumulated brake wear

 


To know what Universal meter you need for the axle you are working on, simply remove the lock-ring and measure the inside diameter of the outer spacer washer that it will replace.

It will be 1 1/4", 1 %" or 1 5/8".

CA92BPCT-S
CA92CPCT

Undercutt
Shaft

Installation
Key For
Universal
Meters

What
Meter ?

Park and service brake released.

Pointer lines up with the clevis pin with Brakes backed completely off. The other end of this s-cam is shown in the next photo.


 

 

Park and service brake released. This is where measured life begins with any scam brake .

This position is called Zero degrees of rotation.

 

 

This BWI brake meter is indicating 120 degrees of s-cam rotation, as viewed from outside the brake drum, again with the brake released.

The other end of this s-cam is shown in the next photo.


 
 

This photo shows 120 degrees of s-cam rotation when observed inside the brake drum, with the brakes released.

However the law requires s-cam rotation be measured from zero to shoe to drum contact.

So a trained mechanic would add about 5 degrees to this reading to allow for shoe to drum clearance. NO NEED to back-off auto slacks to identify scam brake condition.

Inspecting brakes on vehicles without BWI meters often means that wheel pulls are necessary.

With proper records and when there are no visible signs of a brake issue, or leaking oil seals, then checking s-cam rotation is a quick and accurate way of testing for how much brake life remains at each wheel end.

Trailer brake condition can be checked in minutes rather than hours.

Why are there so many different meters?

Answer: Many mechanics want the meters to be installed in a fixed, absolute (TDC) top dead center position for ease of monitoring brake wear.

Camshaft manufacturers DO NOT have a fixed reference point between the location of the S-Cam head and roller position, to the spline at the opposite end.

If the meter is to be fixed on the S-Cam, and the start position of the meter is offset from the clevis, the S-Cam rotation test readings will be inaccurate without a lot of extra calculations.

S-Cam rotation meter identifies brake wear inside the brake drum.

Brake life begins with the S-Cam rollers deep in the pockets of the S-Cam.

Make a timing mark in line with the clevis pin, on the S-Cam with a cold chisel.

Brake life ends when the external pointer lines up with that "timing mark" and the reverse notch shows 120 degrees of each rotation.

READING THE (BWI) BRAKE WEAR INDICATOR METER..

"F" = Full meaning rollers are at Zero degrees, meter pointer is aimed at clevis pin during a brake reline.

Mount the hub, brake drum and torque axle nuts, then adjust the brakes as normal.

"3" = 3/4 of the brake life remains. 30 degrees of rotation

"2" = 1/2 of the brake fife remains. 60 degrees of rotation

"1" = 1/4 of the brake life remains. 90 degrees of rotation

"E" = EMPTY. 120 degrees. The brakes within this wheel-end are Out- Of-Service.

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