M809-series (M818) Air Brake Retrofit

[MyothersanM1]

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]

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.



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)
• 
• 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)
• 

To be continued...

 

[Glenngineer]

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 .

 

[MyothersanM1]

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.


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”.


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.


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!!

 

[Glenngineer]

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.

 

[MyothersanM1]

Congratulations on getting though all the variables that this project threw at you.

And, that it did!!

 

[74M35A2]

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.

 

[Glenngineer]

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.

I think all the parts are available ,you would not need the whole kit because you already have air brakes.the parts list is on this thread.

 

[MyothersanM1]

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]

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?

 

[MyothersanM1]

From what I have read is you cannot flip the hub with Scam brakes correct?

Correct. Going to outboard drums was a project in and of itself.

 

[DURIODESIGNS]

I guess I will having the Scam brakes supercedes the looks of flipped hubs.

 

[MyothersanM1]

Here we go with an update! I finally tackled my front outboard brake drum job. Fair warning: I did not go cheap on this one though. I ended up using all M939A2 parts, including spindles, both spindle nuts and lock washer, inner and outer bearings, oil seal, hubs, wheel studs, brake spider slinger and drums, to upgrade. The brake spiders, air chambers, and shoes are all the same across all incarnations of the M939-series trucks. I have also replaced the 9/16" studs that hold on the spindle and brake spider with grade 8 bolts. The spindle will not be carrying any air pressure, so the air seal surfaces, and air passages need not be perfect. However, the air inlet on the spindle and outlet on the hub need to be deleted (plugged) to keep dust dirt and moisture out from inside the hub. I did this ahead of time so as I would not forget about it. I also installed all new left- and right-hand wheel studs in the workshop prior to the project.



I started by removing everything down to the knuckle and axle, including the studs. Now that the studs are gone, I had to create a 9/16" X 8" dowel pin in order to hang the spindle, brake spider and slinger until I could thread in a few of the new bolts and star washers. Removing the dowel pin, the rest of the bolts and washers were inserted hand tight. I then torqued all the bolts to 125 lb.-ft. in the proper sequence as set out in the TM.



The existing brake shoes and springs were reinstalled after I cleaned and regreased all plunger surfaces and retaining clips.
I inserted a freshly repacked inner bearing into the inner race followed by a new inner grease seal. These seals are actually an oil bath type seal. With a nice coat of grease on the spindle and on the inside seating surface of the inner seal, I installed the hub assembly onto the spindle firmly seating the seal on the base of the spindle. Then on went the outer bearing followed by the spindle nuts and lock washers. Preload was set per the TM and the outer spindle nut was torqued to 350 lb.-ft.
I had an extra set of front axle flanges that were freshly needle scaled and primed. They were installed with a fresh gasket and sealant. I used new lock washers on the flange bolts torquing them all to 80 lb.-ft.



Lastly, I slipped on the brake drum. There is a little coaxing involved particularly if the brake shoes are sagging a little. Just give them a little shove upward and everything should line right up. Ensure brake shoes are adjusted to spec.

Parts list:
Hub: A-333-X-3534
Hub inner seal: 4591SCR
Right hand studs: 20X-1816-Z
Left hand studs: 20X-1815-Z
Outer bearing: 598
Inner bearing: 594A
Bearing adjusting nut: 1227-D-1356
Adjusting nut lock washer: R002304
Clamping nut: 1227-E-1357
Spindle: A3213X1558
Brake spider slinger: 3286-N-1054
Brake drum: 3219S4829
CTIS hub delete 3/4"-16 thread plug: McMaster-Carr 50925K417
CTIS spindle delete plug: any 3/8" NPT pip plug (I used a brass Allen hex type)
Spindle/spider bolts and washers: 9/16"-12 x 2 1/2" Grade 8 bolts plus 9/16" star washers

 

[MyothersanM1]

And to top it off...
Fresh new General Grabber OA Wide Base 385/65R22.5 tires on steel 22.5 X 12.25 4.75" offset five hand-hole stud-piloted rims.
The rims had to be custom ordered. 5 hand-hole in this type are basically "unobtainium".

 

[MyothersanM1]

I decided to swap out the front General Grabbers with Bridgestone L315's; the tires I originally wanted but could not find early on. I could not find L315's in anything less than sets of four. I then found and ordered the L315's from a third party called OTR Tires and they actually shipped them from Simple Tire, the company I got the Generals from. Funny how that worked out. I was able to get a full refund on the Generals from Simple Tire.
The L315's match the T831's diameter and look much better. I have them at 95psi and they seem to have improved the ride a little better.


On another note, I found that the rear studs I used (13-1233L & R) were hanging up the rear brake drums too much making them difficult to remove even with the bolt holes reamed out to 1.00".
I changed all the studs to a slightly longer (3.37" vs. 3.34") overall length, but with a shorter shoulder (1.37" vs. 1.81"). The new shorter shoulder does not protrude past the outer surface of the stud flange. The brake drum now slips easily on and off the hub with the brakes released.

New studs:
Left: Dayton 13-1231L, EUCLID E-5896L, Dorman 610-0318.10
Right: Dayton 13-1231R, EUCLID E-5896R, Dorman 610-0317.10