M809-series (M818) Air Brake Retrofit

MyothersanM1

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All right my loyal followers, I am closing in a rear outboard brake drum solution with the help of Brother Glenngineer. It's not all locked down yet.
Be forewarned that the solution will require machining of the drive hub in order for the chosen drum to properly pilot to the hub. Next step is to obtain the drum, machine the hub, then dry assemble for fitment. The studs are also on order. I will divulge all part numbers once I verify that this will work.

Stay tuned...
 

MyothersanM1

19K M1 Armor Crewman
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So, with the help of Member Glenngineer, I have figured it all out. We now have rear outboard brake drums adding more ease of maintenance to an already more reliable brake system. This new mod, however, will require some modifications to existing equipment and purchase of new parts.

IMG_2158.JPGIMG_2159.JPGIMG_2160.JPG

You will be able to use the existing hubs, but they will require some machining in order for the chosen brake drum to fit properly. In addition, the axle flange outer diameter will need to be turned down slightly in order to accommodate the drum pilot. You will need four new brake drums, 20 right-hand and 20 left-hand studs. I ended up reusing the studs the original S-cam kit. I am posting part numbers below for the studs.

The following is the parts list to complete this mod:


  • Webb Wheel Brake Drum 56893F (AKA: 66893F), Qty. 4 (or equivalent: OTR 1603, Gunite 3166A, Dayton 122607)
  • IMG_2161.JPG
  • Wheel Studs, 12-1233L, Qty. 20 (or equivalent: BWP M-1291, Automann 201.6116L, WA07-6235, Meritor 20-X-853, Navistar 351138C1, Spicer 50-1183L, GMC 799619, Volvo 890040, Euclid E-5909L, BWP M-1291, Meritor R005909L, Leland W379, Meritor 20X853, NWRA X-1894, Dayton 13-1233L)
  • Wheel Studs, 12-1233R, Qty. 20 (or equivalent: BWP M-1290, Automann 201.6116R, WA07-6234, Meritor 20-X-852, Navistar 351139C1, Spicer 50-1183R, GMC 799618, Volvo 890041, Euclid E-5909R, BWP M-1290, Meritor R005909R, Leland W378, Meritor 20X852, NWRA X-1893, Dayton 13-1233R)
  • Rear Hubs, Drums and Axles (6).JPG
To be continued...
 
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All right my loyal followers, I am closing in a rear outboard brake drum solution with the help of Brother Glenngineer. It's not all locked down yet.
Be forewarned that the solution will require machining of the drive hub in order for the chosen drum to properly pilot to the hub. Next step is to obtain the drum, machine the hub, then dry assemble for fitment. The studs are also on order. I will divulge all part numbers once I verify that this will work.

Stay tuned...
I have installed my first outboard drum on the factory M931A1 brakes.Used the factory A1 studs and Webb 61577B Durabrake 14977 Automann 151.5703 or Gunite 3219ax drums ,hubs need to be machined to 5 thousands clearance in the area outside the bolt circle with the studs installed .the studs cause a 5 thousands deformation when installed .Webb 61567b or Durabrake 14967 may be a better fit ,the drum I used is a little deeper than the original and I may have to pry the dust shields back a little .
IMG_5563.JPGIMG_5568.jpg
 
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MyothersanM1

19K M1 Armor Crewman
Steel Soldiers Supporter
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Location
Culver City, CA
Rear outboard drums, continued...

Machining the hub:

In order for the hub stud flange to fit inside the outboard brake drum, the flange needs to be turned down. I had the flange turned down to 13.010” OD which affords plenty of clearance on the drum back plate inner diameter (I placed a hub backward in a drum to show clearance) . The hub has a ½” high shoulder at the base. This shoulder specs out to 8.66” OD. The brake drum has a pilot hole of 8.53”. Needless to say the drum will not fit over this shoulder. I had the shoulder turned down to 8.525”. The drum will now fit snuggly and pilot properly on the hub with .005” tolerance. Note, regardless of stud or hub-piloted system the brake drum always pilots to the hub.
IMG_6179.jpgIMG_6220.jpgIMG_6218.jpgIMG_6221.jpg

Machining the axle flange:

The axle flange is 8.620” in diameter and the drum pilot is 8.530”. In order for the drum to slide on the hub, I had the axle flanges turn down .120” to match the hub diameter of 8.5”.
IMG_6338.jpgIMG_6340.jpgIMG_6344.jpgIMG_6348.jpgIMG_6350.jpg

Brake drum modification:

The new studs will give you the proper standoff beyond the mounted drum of over the legal minimum of 1.31”. However, the stud shoulder will extend past the outer face of the stud flange. In order to fully seat the brake drum, all stud holes have to be reamed out to 1.00” on the brake drum. This particular size drum with the 8.53” pilot is not available in 1.00”ID stud hole variant hence the need for this modification.
IMG_2156.JPG

I would like to send a special shout out to Harry Vellio of Vellio's Machine Shop in Lawndale, CA. On Friday, I picked all the remaining parts and it was also the last day he would be open to the public. Harry is retiring after an over 45 year run. I couldn't of done this job with out their services. It's a shame all these great shops are disappearing. Enjoy, your retirement, Harry!!
 
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Rear outboard drums, continued...

Machining the hub:

In order for the hub stud flange to fit inside the outboard brake drum, the flange needs to be turned down. I had the flange turned down to 13.010” OD which affords plenty of clearance on the drum back plate inner diameter (I placed a hub backward in a drum to show clearance) . The hub has a ½” high shoulder at the base. This shoulder specs out to 8.66” OD. The brake drum has a pilot hole of 8.53”. Needless to say the drum will not fit over this shoulder. I had the shoulder turned down to 8.525”. The drum will now fit snuggly and pilot properly on the hub with .005” tolerance. Note, regardless of stud or hub-piloted system the brake drum always pilots to the hub.
View attachment 789467View attachment 789468View attachment 789469View attachment 789470

Machining the axle flange:

The axle flange is 8.620” in diameter and the drum pilot is 8.530”. In order for the drum to slide on the hub, I had the axle flanges turn down .120” to match the hub diameter of 8.5”.
View attachment 789471View attachment 789472View attachment 789473View attachment 789474View attachment 789475

Brake drum modification:

The new studs will give you the proper standoff beyond the mounted drum of over the legal minimum of 1.31”. However, the stud shoulder will extend past the outer face of the stud flange. In order to fully seat the brake drum, all stud holes have to be reamed out to 1.00” on the brake drum. This particular size drum with the 8.53” pilot is not available in 1.00”ID stud hole variant hence the need for this modification.
View attachment 789476
Congratulations on getting though all the variables that this project threw at you.
 

74M35A2

Well-known member
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Superb contribution.

So for an M939A2, are all parts required to switch to S cam readily available as off-the-shelf service parts, or must the "kit" still be purchased? This question is mostly pertaining to the rears, thanks.
 

MyothersanM1

19K M1 Armor Crewman
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Superb contribution.

So for an M939A2, are all parts required to switch to S cam readily available as off-the-shelf service parts, or must the "kit" still be purchased? This question is mostly pertaining to the rears, thanks.
You would have to go up to 16.5 x 7 s-cams. All the M939-series trucks are 15" diameter. Seeing how the the same spider for the wedge brakes is used across all incarnations of the M939-series and the M809 and the M939A1/A2 axles are the same, then the spiders, s-cam brackets, s-cams and chambers I used should work.

I am assuming the hub pilot is 8.78" on the A2 OEM hubs? And, my other question is what would be the proper depth of the 16.5 x 7 drum? My new drums are 10.62" deep. I am not sure of the exact depth of the A2 OEM drums.
Also, the smallest bolt hole size I have found is .94".
Webb 78502B at 10.54"D and 28503 at 10.12"D
 

DURIODESIGNS

New member
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Location
Lafayette, LA
I am still pretty green and learning about the Scam brakes. My M54A2 was converted by the oilfield company that owned it before me. From what I have read is you cannot flip the hub with Scam brakes correct?
 
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