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Old 07-22-2014, 10:23 PM   #15
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The reason for that is 2 fold. Backward compatibility being the first. No one is going to obsolete every trailer out there. Secondly, Air brakes means the brakes are operated mechanically, rather than hydraulically. Non-hydraulic actuated disk brake have never worked very well. Its very complicated, which is not what you want in your braking system. Drum brake actuation is not linear. Disk brakes are very linear. While there are many systems that combine the 2, none work very well, particularly on slippery surfaces.

Hmm, interesting criteria for "good" working brakes. I would think [b]all[b] the wheels should be able to lock up. Each tire should be approaching lock up at the same time.
Your 2 fold reasons are completely wrong and your understanding of air brake systems vs. hydraulic systems is too.

But whatever, I'm not going to argue with someone over the internet.

If you want to spend time and money on a conversion, then by all means, knock yourself out.

There, you win...
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Old 07-23-2014, 01:23 AM   #16
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Unfortunately making a statement without giving any technical supporting reasoning is an argument that helps no one.

In saying air brakes are mechanical, I was referring to the actuation of the shoes themselves. There is an S-cam inside the drum that pushes the shoe outward, much in the same way that the hydraulic cylinder pushes outward on the shoes. Regardless of if the system uses an S-cam or hydraulic, the outward force against the shoe is only part of the braking force. The actual rotation of the drum causes the shoe to rotate outward, harder against the drum. This causes an increase in braking force. It also means that the lever effort or position is not directly proportional to the amount of braking. It is non-linear, as there is extra braking force applied by the rotation of the drum. It also delays the application of the brakes. In contrast, discs are much simpler, as there is only the hydraulic cylinder pushing a pad against a moving surface. Braking is directly proportional to cylinder pressure, which is directly proportional to force against the disc. The result is that it is very linear.

Now the reason I know this is because when I did my conversion, I was converting a system with mixed brakes to all discs. The proportioning valve delays the front disc application until the pressure builds up in the rear drum brakes. This delay is intentional so all the braking is applied at the same time. (even though it is delayed) When I did the conversion, I initially left the valve in. There was some increase in braking performance, but there was still some delayed reaction. Once I removed the proportioning valve, the delay went away, and the brake response was immediate.

Don't know if you have ever seen non-hydraulic disc brakes, but every system I have seen left a lot to be desired in the effectiveness area. That is why most E-brakes are drums inside the discs - because the E-brake is mechanically actuated, which is difficult to do on a disk.

IF one were to design an air brake system for discs, it would have to be remotely actuated. Direct air pistons would be way to big to mount directly on the discs. That remote design would be very cumbersome.

I am a firm believer in technical reasoning. It is not for the purpose of argument, but for the purpose of understanding.
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Old 07-23-2014, 06:44 AM   #17
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Thank you for all the information. I really needed that . First I'm going to adjust them and see if they get any better , if they don't I'm going to do the swap. At least the front axle.
Thank you everyone that responded to question
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Old 07-24-2014, 08:09 AM   #18
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I'm going to change my opinion slightly as I did not realize you had drums all the way around. I would either recommend a complete conversion, or none at all. You will not realize the big improvement unless you convert completely. Just doing the front axle alone will only make a small improvement. That and mixing systems is messy. If you are only doing the front, i would not bother, as it is more trouble than it is worth. Either a full conversion or don't bother.
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Old 07-27-2014, 07:38 PM   #19
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You can convert only the fronts. Manufacturers did for years and some still do.

But, it is very important to switch to the proper master cylinder and install a proportional valve since each brake type needs different pressure.
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Old 07-27-2014, 09:47 PM   #20
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Bill, you don't think he could find a rear axle from a junkyard some place and change out the whole axle?
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Old 07-28-2014, 04:36 AM   #21
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Bill, you don't think he could find a rear axle from a junkyard some place and change out the whole axle?
Well sure. But it's a lot of work and expense. The front brakes take on the biggest load so one would get the most benefit from converting them. The rears have the parking brakes too which is more complication.

My 1991 Chevy G30 chassis has disc fronts and drum rears so it can be an effective combination.
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Old 07-29-2014, 09:38 AM   #22
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Its not so much the load, but the actuation. drum brakes just function differently. In a mixed system, the proportioning valve does not allow the front brakes to come on until the rears are fully pressurized. So you still have a delayed non-linear response.
Being that a motorhome has such a long wheel base, and so much high percentage of the weight on the rear axle, there is not much additional weight transfer to the front like there is in a car. The rears end up doing a larger percentage of the braking.
You really don't need to change out the master cylinder, as much as you need to find the residual pressure check valve in the system and remove it. Its still just a hydraulic piston pressurizing a line. No magic about it, except for the check valve. Sometimes the check valve is in the fitting on the master cylinder, and sometimes it is in the proportioning valve. You just have to find it and remove it.
If you can find a whole axle, the E-brake will be part of the assembly, so that should be easy to deal with. Yes, there are some larger trucks that use a drum on the back of the trans, but you should be able to find one without it. The other option would be to ignore the E-brake. If you consider the over all safety benifit as a whole, the improvement of discs over drums is a much greater jump up on the safety scale than the loss of an E-brake is a jump down. In other words, the good far out weighs the bad.
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Old 08-02-2015, 11:36 AM   #23
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I know its been awhile but you still have copies of those manuals? I just purchased or at the least put the down payment for one myself, plan on living full time in it, and needed some help with mine
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Old 08-03-2015, 08:04 AM   #24
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I know its been awhile but you still have copies of those manuals? I just purchased or at the least put the down payment for one myself, plan on living full time in it, and needed some help with mine
hey mullettman,
congrats on the new ride! send me a pm with your email
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Old 08-03-2015, 08:23 PM   #25
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Bill,
I had a '73 Concord with a 318 Dodge and had a lot of family fun in that unit. One thing to check on the drums, is to clean the rust from them, if they are all rusty, the brakes do not work efficiently unit rust is gone.
Dave,
They do make air driven disk brakes, they are not used much because the surface area is too small to generate enough braking power to stop an 80,000# truck. Although the last I heard they were getting better and starting to put them on the front axles of some trucks now.
Frank
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Old 08-04-2015, 12:25 PM   #26
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You might want to check out website: classic Winnebago's and vintage rvs.lots of dodge folks there.there is also Travco website
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