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We were able to park on a 20% grade at GVW when new. And it was tough to fabricate a friction shoe lining that would do the job, and we were never able to out perform the OE product.. Not only was the lining important, but so was the contact profile and the adjustment, which Ford Engineering said was critical. They were right based on our work.
It's going to be tougher as components age, but I would ask about the parts you replaced and what brands, for my own curiosity.
We were able to park on a 20% grade at GVW when new. And it was tough to fabricate a friction shoe lining that would do the job, and we were never able to out perform the OE product.. Not only was the lining important, but so was the contact profile and the adjustment, which Ford Engineering said was critical. They were right based on our work.
It's going to be tougher as components age, but I would ask about the parts you replaced and what brands, for my own curiosity.
I did not use oem parts. I know I know. But what can they possibly do to it it’s just metal.
From my perspective, the low friction lining in the parking brake cables to minimize tensioning loses and the brake shoe lining.
It's just metal ...... Well, yes.
You're not going to find OE rear rotors out there, but I still have a stash of OE rotors made by TRW from the '99-04 years for my truck.
TRW was the manufacturer and the DIH area had a tight control on machining to maximize the grade holding capability. On all vehicles, SRW and DRW the surface was grit blasted to a unique and tight surface finish. While the service brake surfaces were held to a 30-60 Ra surface finish, the drum opposing surface was a higher range, measured on this one. The manufacturing range was tight, but that a detail I can't devulge. Static friction is a different animal then dynamic friction.
The other detail about the internal drum was the concentricity to the axle centerline. The DIH design is a floating design when engaged but it still benefits from good concentricity.
Paramount to the holding ability is the contact area of the lining. The standard aftermarket approach to brake shoes today is to grind the shoes to a universal size. Decades ago when shelf space was cheap sources such as NAPA (my company used to supply NAPA) you could offer over-the-counter shoes in different oversizes for turned drums, or shops had their own shoe radius grinding equipment such as the ones from Ammco. Asbestos took those away.
But the contact pattern is very important to the amount of self-energizing a primary shoe imparts on the secondary shoe of a duo-servo drum brake design like this one. And concentricity of the drum effects contact.
Another big impact on aftermarket manufactured shoes is the lack of concern in the shoe grind registration, another alteration in the contact pattern and brake effectiveness. Even within my old company which had significant OE sales, more then 50% of the total sales, getting the aftermarket side to understand this was a tough sell, especially when "all the other aftermarket companies are the same".
And then we have conformability, or compressibility, how ever you want to term it. There needs to be a certain amount of compressibility to the lining to have great contact, but no so much to cause excessive travel in the apply mechanism. The cable tension for a DIH brake assembly is about 2 times that of a drum service brake. Compressibility is a panel in my sales training PPT that I also can't show.
Aftermarket wise you can get away somewhat of all these hurdles by using a higher friction brake material. The OE material was already an FF rated lining, about mid-range of the F scale. Going higher then that gets pretty abrasive, but abrasive friction is static friction, not dynamic.
Anyway, all of the Superdutys from '99 MY passed the 20% hill hold requirement that FMVSS requires. NEW. The friction material manufacturers tested it, the foundation supplier (Dura) tested it, Ford tested it, and NHTSA tested it. It can be done. I'd rather have put a transmission mounted parking brake on it, but that's just me. Ford eventually did for the ambulance package.
After all that, I'm sure there are a few aftermarket shoes that work, I just can't tell you who they are.
What a DIH lining looks like after doing 20mph stops at GVW.
Wow jack thanks that’s great info! Well, I don’t know if I can specify the f rating on my pads, and I SHUDDER at the thought of getting the *******s off and on again (that was a challenge) but I was wondering if sand blasting the inside drums would help. And while I’m at it I can see if the shoes are making good contact and wide contact.
So so am I reading the chart correct that heel/toe biased contact is superior for holding?
This is truck is a manual so this brake situation is dire.
I can imagine the oem setup working 50% or even 100% better than a cheap autozone parts, but this setup I have is SO terrible that it needs about a 600% increase in holding to be even close to capable. It has almost no holding now.
We never got the business away from Nisshimbo, who was the OE supplier of these shoes, as well as most of the Ford vehicle lineup. We made a major push from everything from Explorer on up. What I was surprised at was the QC needed during manufacture. And due to that, manufacturing in the USA was cost prohibited.
Heel-Toe contact gets the brake torque higher, but with static friction surface area is also a big component. Therefore the Goldilocks notation. The ideal situation is having a slight undergrind with the right amount of compliance of the lining so it squeezes into full contact. And it’s one of the reasons that hill-hold capability degrades over time, from the shoes slightly contacting the drum running down the road wearing the radius, and the shoe lining baking in the DIH drum oven from rotor heat.
I'll throw in some more pictures and panels I used in my presentation.
A better image of the grit blasted surface.
A day of running a city traffic test route. This shows the temperatures of the individual brakes and the temperatures of the drum in hat shoe linings, thermocouples in all friction materials.
The way NAC got a compliment lining was in the state of cure, an early pull out of the ovens. Over time in the DiH easy bake oven can cause the material to shrink over time. This lining is an Explorer DiH after 75k of thermal exposure. These were never applied as a parking brake, but you can also see the environmental contamination of the rubbing surfaces, which can effect holding for better or worse depending on what it is composed of.
I believe this was data from the F-150, a higher volume truck so more of a prize.
And details of the forces going from an F-150 rear drum service brake to the F-150 DiH parking brake.
Showing a bunch of sales guys how in the field shoe profiles can be checked.
Plant production equipment is very different, but at the Vehicle Test Facility we had two of these, which were produced from probably the 40's. I bought one of the last sold in the early 80's to have a back-up. They went out of favor as over the decades they were an asbestos throwing machine, contaminating service garages with a huge amount of asbestos dust that continues to this day in the rafters and recesses of old garages. The later models came with a dust port. BTW, we were the first company to stop research utilizing asbestos products, lost a lot of business to Bendix by doing that.
Anyway, the point of the image was I was able to try all different shoe grind radius for the application. Not shown is a special patented bench setup that allow shoes to be precisely measured for the grind. Both those genders and test instrument showed Ford a major issue regarding brake shoes on the Explorer/Ranger/Aerostar due to change in grinding methods Bendix did on our produced linings with 6 Ford engineers and a supervisor watching over in a circle. Those were good tools in a little back woods skunk works.
Doing things in a controlled way DIY would be a tough situation. Ford has to pass 20% hill hold on a new vehicle or if there are enough complaints during the normal warranty period. This can get extended into a longer service life if there are enough vehicle run-a-ways, but even the folks at NHTSA accept some in-service degradation.
From my perspective its a brake that needs attention to detail. Dura is the company that supplied the parking system to Ford as well as many other companies. For this application if the brake cables need to be replaced, I use OE only. The cables have a low friction internal design and aftermarket is not going to do that. For my own purchase, I'd only use Motorcraft shoes. Some suppliers like Raybestos and Wagner may have good products and work, but I don't know what's being done today from them.
The drum surface is an important part, but it was grit blasted to generate the hold for the FMVSS 105 test performed by NHTSA. We did the test over a period of 4 days and 500 miles, not your typical service life. The ability of keeping the shoes off the drum degrades with any hysteresis in the cables and shoe actuation. And the shoe actuation is an important point. That little lever setup at the top of the shoes is very prone to rusting up which sucks up not only apply forces, but prevents full release.
And shoe clearance to the drum also is a factor. The old service drum brakes with their self adjusters would run a clearance of 0.020" to 0.025" total for most applications. With the DiH, Dura and Ford had us spec out a0.010" to 0.015" total clearance, which for use meant using a very large micrometer to set, not one of those cheap Ammco lining gauges. With the spring loaded take-up reel, that clearance got the full pedal force allowed at the center of the pedal throw, which was the most efficient place to get proper cable tension.
It's a complicated brake design. But in-service the truck should be able to hill-hold at GVW with 10-15% slope all day long if things are in good shape. I wouldn't bet the farm on 20% at 100k miles.
I’m getting the distinct feeling that you’re actually the right person to ask about this issue! Lol. Great stuff thanks. Okay I’ll do some examination. I know the adjustment is off, and the drum surface was not ideal. I do believe they were dura brand. But I can’t remember the pad brand or cables.
Thanks again for for all this effort you put into this, both then and now. I feel like I can get them to be the best they could be now.
10-03-2018, 12:42 AM
