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A1R brake pedal valve up(down)grade.

GeneralDisorder

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Those of you who have not driven an A1R or A1P2 probably will not understand this post.

The C7 trucks (serial #100,001+) including both A1R and A1P2 have a different air brake pedal valve and if you have driven A0, A1, and A1R you may have noticed that the A1R trucks seem to have a brake pedal effort, feel, and modulation that is "stiff" and for lack of a better term.... "broken". Indeed when I first bought my truck I assumed that something needed to be adjusted or rebuilt, or wasn't working properly because the pedal effort was more than I could reasonably consider would be acceptable to the engineers that designed the truck......

I was wrong. The design just absolutely SUCKS, For reasons unknown to me they changed the WABCO brake pedal valve out for a Bendix E-7 rotated 90 degrees and a significantly shorter pedal and thus less mechanical advantage. Considering the entire rest of the braking system, ABS, axles, etc are 100% Meritor/WABCO this seems an odd choice. The WABCO valve is "unusual" in the US trucking market - the rebuild kit had to come from Europe. But that's also true of our wedge brakes, etc. The air brake shop local to me tells me all this stuff is "old" and they rarely see them anymore - despite my truck being a 2008.

The original pedal valve, bracket, and pedal lever was attached to the underside of the dash and had a pedal-to-pivot length of 10.5", The "new" Bendix valve was rotated 90 degrees and due to the new orientation and integrated cast aluminum pedal the length was shortened to 7.5". I find it interesting that when you search for "Bendix E-7" you get results such as this guy:


Which has an integrated 10.5" cast aluminum pedal. Which would be great except there's no room under the dash - the pedal would hit the floor. Even with the 7.5" pedal the location is lower compared to the WABCO and my size 12 EE is very close to the brake when operating the throttle. The WABCO, being the original design, affords more room for your foot on the accelerator.

In addition to the reduction in pedal mechanical advantage, the ports on the Bendix valve are all 1/4" NPT vs. the original WABCO valve being all 3/8" NPT. Both have 1/2" tube fittings. I don't know if this is significant but I changed out the tubing fittings to 3/8" NPT instead of using reducing bushings to ensure I removed this restriction in case it did effect operation.

Fortunately the cab and dash were largely unchanged and going back to the original design is not that hard - just have to get the entire assembly including the bracket for the A0/A1 and install it. The mounting points are still the same once you remove the Bendix adapter bracket and it only requires that you properly hookup the primary and secondary circuits and then sort out mounting the MMDC without the pedal bracket.

You can see here the stark difference in the pedal pivot and the mechanical advantage of the older assembly. The two pedal assemblies are lined up with respect to the pivot locations:

PXL_20240217_041625351.jpg

The adapter bracket created to hold the rotated Bendix valve and the MMDC:

PXL_20240217_014136592.jpg

For reference this is how my truck is configured with regards to the firewall hose routing. The two on the far right go to the Emergency/Hand Brake valve and aren't related to this install:

PXL_20240217_024213768.jpg

Overall this swap has DRAMATICALLY improved the braking on my truclk. Why S&S chose to replace the original valve with the Bendix is beyond me. I can't find any good reason. If you feel your A1R brakes don't work as well as you think they should - trust me this is the fix for it.
 
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GeneralDisorder

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Wow, thats a big difference. It also appears that the Bendix pivot to actuator distance is larger, further reducing the mechanical advantage of pedal to actuator … which is probably why it was designed for 3” more pedal lever length:)
I measured both of the assemblies pivot to actuator rod/roller and both were close to 1.5" but the Bendix is slightly larger I think.
 

GeneralDisorder

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Just an update on this. I've got about 400 miles on the new/old WABCO pedal valve (rebuilt it prior to install) and it works GREAT. Honestly it has totally changed the confidence level I have in the brakes. They went from kinda scary at high speed (can do 80+ MPH with the ECO Hubs), to VERY responsive.

In my opinion this change is absolutely in the top 5 best mods I have done to my truck. If you have an A1R you NEED this.
 

aw113sgte

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Hmm, not impressed with pedal feel but all the air brake trucks I've driven feel about the same. Wonder how much of a difference I could actually get...
It's a big difference from race quality hydraulics I'm used to and I know I'd never get close to that.
 

GeneralDisorder

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Hmm, not impressed with pedal feel but all the air brake trucks I've driven feel about the same. Wonder how much of a difference I could actually get...
It's a big difference from race quality hydraulics I'm used to and I know I'd never get close to that.
I can only subjectively tell you it's an absolute game changing difference.

I can add that I own a performance shop with a chassis dyno so I'm not unfamiliar with exceptionally good brakes. The Saturday dyno rental today was an Infinity Q50 that made 715 rear wheel HP.

Trust me you want this.
 

GeneralDisorder

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Have to use a lot less at the lights after switching to Eco hubs
I didn't really notice that.... not sure by what mechanism that would be the case. You sure you're not just getting used to how much effort it takes? I know that I certainly did over the last several years.

At any rate the A0/A1 pedal valve assembly takes a fraction of the pedal effort. You breathe on the pedal and it will almost throw you through the windshield. It takes a few drives to get used to how much more power it has.
 
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littlesfmtv

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Awesome info. Another thing on list! I have only driven my A1r truck which weighs 30k empty, and I thought some of my braking effort was just due to this load. I always thought my breaks were stiff, but the exhaust brake is unbelievably good, so I thought maybe they were trying to conserve pads.
 

GeneralDisorder

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Awesome info. Another thing on list! I have only driven my A1r truck which weighs 30k empty, and I thought some of my braking effort was just due to this load. I always thought my breaks were stiff, but the exhaust brake is unbelievably good, so I thought maybe they were trying to conserve pads.
The A1 trucks also have the exhaust brake. I don't think pad life was the concern. The military would rather have stopping power - they have enough problems with accidents to worry about brake pad life.
 

aw113sgte

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I didn't really notice that.... not sure by what mechanism that would be the case. You sure you're not just getting used to how much effort it takes? I know that I certainly did over the last several years.

At any rate the A0/A1 pedal valve assembly takes a fraction of the pedal effort. You breathe on the pedal and it will almost throw you through the windshield. It takes a few drives to get used to how much more power it has.
With the Eco hubs, 1/2 the normal torque is trying to turn the wheels while at idle but in drive. Not sure it makes a huge difference as brake pressure requirement to hold the vehicle is likely not a linear relation with drum brakes.
 

AKPacker

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Thanks for this writeup! I just bought a M1079A1R and am looking into doing this upgrade. How did you end up mounting the MMDC?
 

GeneralDisorder

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Thanks for this writeup! I just bought a M1079A1R and am looking into doing this upgrade. How did you end up mounting the MMDC?
For the moment it's just tucked into the pocket in the cab behind where the bracket was located. I'll probably just use adhesive cable tie mounts. It's a lightweight plastic module. Doesn't really need much.
 
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