Retrofit Meritor Q series brakes onto 5 ton toploaders

Hi Group,

I have been extraordinarily busy over the past few months, and one of the projects has been to retrofit S cam drum brakes to my front, 5 ton axle. These are Meritor 16.5x7" air brakes, which I feel are going to be much much better than the stock juice brakes. I had a set of these brakes already installed on the rear axle on my 5 ton bobber, as this is what Memphis trucks retrofits onto 5 ton REAR axles as their S-cam conversion, and I had horsetraded for a pair those rear axles with those brakes installed (along with a brake-less front, 5 ton axle).

But, I still had to take one set and (very nontrivially) retrofit them to the front. I'm posting here just to put the info out. In a forum that hosts such standout posters and such great documenters such as gringeltaube, I regret that I only have a few pictures.

Here's some items that I needed to do:

- Extensive modification of the backing plate, including precisely re-clocking the mounting holes and removing material from the "back" edges of the plate. This is one place where a custom fabricated piece would excel.

- Clearancing and clocking of the slack adjuster tube to slide down the groove in the knuckle just behind the kingpin, also cognizant of being able to swivel above the level of the leaf spring

- Light grinding of the knuckle (not enough to significantly compromise either steering or weight carrying, in my estimation)

- New placement of the return spring between the shoes, out of the radius of the hub


After all is said and done, I would have likely have been better served by swapping the axle in toto for a commercial, bottom loading, s-cam braked unit. However, I know the military axles very well, and I had all of these parts already (and the price was right).

I know that I have definitely de-rated the Q-series brakes to an extent, through removal of some material on the backing plate. I am not terribly concerned, however, and I intend to give this thing some panic stops (with subsequent inspection) as part of testing. My truck weighs somewhere around 14,000 lb and has 14" wide front rubber - I would imagine that brakes meant to service a 60k pound truck are probably going to be ok.

Total time to modify all parts was around 50-60 hours. The challenge itself spurred me on, and there were a few "showstoppers" where I found a creative solution to get around what would have otherwise been a no-go.

Overall, I'm relieved that it "went".

Anyway, I'm prevented from working on wiring the last of my truck by a rainstorm here tonight, so I figured I'd post up about this project.

Best,
Bob

If nothing else, this post should hopefully inspire someone to go look for, in my opinion, the next big thing for our trucks, which will be either disk brakes, or the location of stamped Meritor Q series backing plates, which can then be clocked accordingly and then welded to the knuckles, for an integral s cam air brake solution. I was using cast backing plates, which precluded welding to the knuckles (which would have gone along with proper prep and pre/post heat).

I realize that the M8xx 5 tons are old, but they're plentiful and strong. It could be that it's worth looking at the M916 fronts et al, but I couldn't easily find them, and they didn't quite fit for a variety of reasons. I also have to admit a bias towards S-cams v. wedge style brakes.

Final thought - please let me know if you have any questions or thoughts.

Best,
Bob

Where are the pictures ?

Oh yeah, smart eyed viewers will notice that the tie rod is in front. I simply flipped the axle around so that it would work with the M35 tcase. Maybe one day I'll hide the tie rod behind the axle.

I was doing a little light reading on these brakes recently, and I think I found a likely good candidate if someone was interested in doing a similar swap:

http://www.mpgseries.com/pdfs/Meritor_Q_Plus_Cam_Brake.pdf

The Q plus brakes use a stamped sheet steel "spider" (their term for the backing plate), and thus could be more readily modified than the old cast spider.

I realize that this might seem like a huge project, but by breathing new life into these axles via s-cam brakes, they become an actual drivetrain option to stick under a platform plumbed for air brakes.

Overall, is this easier than finding and buying a front drive axle with the correct ratio, and sticking that in your truck? Tough call. If you have all the parts (as I did), it was.

Interesting

Wow eh. I thought I had ambition, but this is awesome. Great job. Thanks for sharing.

Thanks for posting this great info. I was thinking of doing just this! I am building a Kenworth 6x6. I am taking a Kenworth with a Cummins 400 and Eaton 10 speed and a fresh depot rebuild 5 ton rolling chassis. I have brought Macks and freightliners back from the dead so, think should not be so bad. I am planning on pulling a lowboy double drop trailers and running 1600's so air brakes will be a plus! Are you using the stock drums?

Why not start with a chassis that already has air brakes such as a 900 series or a Seabees 6x6

Yeah. I am considering that too. I have the parts to do the swap. plus I like S cam brakes. They are cheap and easy to work on!

The 900 series use wedge brakes. But the seabees trucks use s cam brakes but I would stay away from the Marmon Herrington front axle, the spindle nut socket will set you back 8 bills

quickfarms said:

Why not start with a chassis that already has air brakes such as a 900 series or a Seabees 6x6

Click to expand...

Great question. I think a bobbed 900 series truck would be great. There are pros and cons for each option. In my case, a big pro was that all of the constituent parts to my build were fairly well available, and very economical.

We could also buy a new civilian truck too, but that would be NO FUN! If you have the parts and the time, then it is pure fun! That is what makes this hobby so addicting and what is more American then making a bad ass truck even better?