Disc brake discussion

[dznf0g]

Originally Posted by KJRitchie

Would it be possible to get a machine shop to tap a hole for a bleed screw in the inner calipers?

Why isn't Dexter addressing this issue or do their current line of calipers have bleed screws in the inner caliper now?

Kelvin

I have thought about that. But the thread and seat machining is very specific in order to set and seal properly. I wonder if machine shops would have the tooling to do this, as it would be a rare circumstance (volume) to tool for. I haven't checked into it. One would have to be able to determine the exact position for this port for it to be effective.

[GCinSC2]

I don't have time to research but I think this is worth looking into.

A Banjo Bolt with Bleed Screw fitting. Google it.

Pretty sure that our caliper can be connected to am M10 banjo bolt connection.

This offers a built in bleed screw and would need more research than I can look at right now.

[dznf0g]

Those would certainly work, and require little machining prowess, but one would have to make certain that the length of the threaded portion did not protrude at all below the inner caliper bore surface, as this would just let the air accumulate around the outside of the banjo threads and not be pushed out the bleeder. I have no idea what the dimension the wall thickness is. If it is not very thick, one could easily blow the whole fitting out due to not enough threaded material. That is why line fittings and bleeder fittings are usually located in a cast-in lug, or elevated portion of the caliper....more "meat" for the fitting to thread into.

[GCinSC2]

Rich,

I have a set of Dexter calipers at home. I'll take a closer look, measure and take a pic or two. Pretty sure the banjo bolt connection is common to many caliper connections. That is what I used to make my pressure gauge adaptor with.

Gary

[dznf0g]

Gary, are you talking about using the banjo on the line inlet port. If so, I think we'd have the same issue of "stratifying" or redistributing the air away from the bleeder as soon as the inrush of fluid from the line begins. I don't think that would gain anything except avoiding a 1/2 - 3/4 turn twist on the rubber line and bleeding through the input line threads. That's what I have done in the past....don't like it, but it works and so far, no sign of damaging the line.

[rmkrum]

Vacuum bleeding from the banjo bleed screw would be best. Avoids the air trapping turbulence.


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[dznf0g]

Yeah, Rmkrum, your right, this is our best solution. Gary, Wasn't it you who fitted your calipers with longer braided steel lines?

My AS is away in storage and can't examine, but I'd Like to develop a list here of:
Braided line
Banjo fitting
Banjo bolt
banjo washers
bleeder valve

with links for procurement. I'd like to have these in hand for spring maintenance at next tire rotation. I'm due for a brake fluid flush anyway.

We need threaded sizes and pitches for the line and banjo bolt as well as the bleeder. And a good length for the line. Anything else?

[SteveH]

I now have in hand the new Dexter actuator, the 2PSI residual pressure valve, and the necessary brake line, and although I've been recovering from diverticulitis and a perforated colon, I'll soon have some information if this is an improvement or not.

I was also thinking because I have a three axle trailer (six calipers), at a minimum, the time it takes for the actuator to get to effective braking pressure will be 50% more than with a tandem axle trailer, if my thinking is correct.

[dznf0g]

Ick, Steve, I'm sorry. My mother has dealt with that for years...not fun.
The 6 vs. 4 issue should not be, if all air is out. Since fluid does not compress, it matters not how many calipers there are....unless you also have excessive runout in the hub/rotor assemblies, pushing the pads back too much in their bores going down the road. Yes, theoretically, two more calipers pushing out the normal clearance would take a bit more fluid displacement, but it really should be non-discernible to the driver. Ramp up of pressure "should" be rapid enough to make it almost un-measurable from a time/lag standpoint.

[SteveH]

Thanks Rich. In my feeble mind, there must be some amount of fluid flow, albeit small, and each caliper must have the same amount of flow, so that's where I got the idea of additional time for additional calipers. I understand the fluid does not compress, but still, the caliper pistons have to move to clamp the pads onto the rotors. Anyway, just doing some thinking out loud.

Thinking now about how to avoid some of the worst of the bleeding, and think I'll raise the front of the trailer before disconnecting the bad actuator, then install the new one and fill with fluid. Then without energizing it, compress one of the calipers in an effort to push fluid back thru the residual valve and into the new actuator. At least it makes sense to me.

[dznf0g]

Originally Posted by SteveH

Thanks Rich. In my feeble mind, there must be some amount of fluid flow, albeit small, and each caliper must have the same amount of flow, so that's where I got the idea of additional time for additional calipers. I understand the fluid does not compress, but still, the caliper pistons have to move to clamp the pads onto the rotors. Anyway, just doing some thinking out loud.

Thinking now about how to avoid some of the worst of the bleeding, and think I'll raise the front of the trailer before disconnecting the bad actuator, then install the new one and fill with fluid. Then without energizing it, compress one of the calipers in an effort to push fluid back thru the residual valve and into the new actuator. At least it makes sense to me.

Yeah, you're right...I just don't think with a system purged of air and normal healthy bearings (adjusted correctly), true rotors and spindles, that it would be significantly more apply time than a healthy 4 wheel setup.

The only reason I say that, is in my discussion with the Tuson engineer, he was firm that their pressure ramp up was "instantaneous". I assume (perhaps incorrectly) the others do as well...although Gary's video, arguably, shows otherwise???? I forget what brand he was testing.

[SteveH]

Originally Posted by dznf0g

Yeah, you're right...I just don't think with a system purged of air and normal healthy bearings (adjusted correctly), true rotors and spindles, that it would be significantly more apply time than a healthy 4 wheel setup.

The only reason I say that, is in my discussion with the Tuson engineer, he was firm that their pressure ramp up was "instantaneous". I assume (perhaps incorrectly) the others do as well...although Gary's video, arguably, shows otherwise???? I forget what brand he was testing.

Yes, you can watch Gary's video, listen to the sound of when the motor starts, then loads up under pressure vs when the pressure comes up on the scale, and actually see the delay. By the way, that's exactly how my actuator sounds. Now, if that delay is a result of air in the system, or time the actuator requires to get to pressure is the real question.

My residual valve experiment might shed some light on the subject, hopefully.

[dznf0g]

I await with baited breath!

[ROBERTSUNRUS]

[QUOTE=SteveH;1550200]Yes, you can watch Gary's video, listen to the sound of when the motor starts, then loads up under pressure vs when the pressure comes up on the scale, and actually see the delay. By the way, that's exactly how my actuator sounds. Now, if that delay is a result of air in the system, or time the actuator requires to get to pressure is the real question.

My residual valve experiment might shed some light on the subject, hopefully.[/QUOTE]

Hi, I hope what you are doing makes this system work better; It's sad that individual owners have to figure out what the makers, sellers, and installers couldn't, wouldn't, and didn't do.

[barts]

Originally Posted by dznf0g

Bart, the Direclink does monitor, and act upon, the OBDII data stream. .... I can't say it for sure, but I do know the Direclink feels much better than any other controller I have used. I have not experienced the MaxBrake, but understand it performed very well.

I'd be happy to use the Direclink, but my 1996 diesel doesn't have this port.

- Bart

[barts]

Regarding delay in these systems, it will always take some time for the pump to move the pads out to the discs. This takes very little time ( a fraction of a second) so long as no additional air is in the system. Any air pockets will result in some delay; the more air, the more the delay.

The source of the delay with air is due to the limited amount of power from the electric motor available to actuate the brakes; it takes time for that power to compress the air in the lines to the 500->1500 psi needed to stop the trailer.

A vacuum or compressed air system would be less sensitive to such delays, since the amount of power instantly available would be significantly higher.

- Bart

[dznf0g]

Originally Posted by barts

I'd be happy to use the Direclink, but my 1996 diesel doesn't have this port.

- Bart

Oh, yeah, I forgot.

[dznf0g]

Originally Posted by barts

Regarding delay in these systems, it will always take some time for the pump to move the pads out to the discs. This takes very little time ( a fraction of a second) so long as no additional air is in the system. Any air pockets will result in some delay; the more air, the more the delay.

The source of the delay with air is due to the limited amount of power from the electric motor available to actuate the brakes; it takes time for that power to compress the air in the lines to the 500->1500 psi needed to stop the trailer.

A vacuum or compressed air system would be less sensitive to such delays, since the amount of power instantly available would be significantly higher.

- Bart

A high pressure hydraulic accumulator like autos have (hydraboost, etc.) is the ultimate answer here, but none of the actuators have them. Tuson engineer said it's not needed with theirs....I'm skeptical.

[SteveH]

Got some work done today. Not 100% yet, or I would have done it all. Installed the new actuator, and built a cable with a start button on one end so I can bleed the brakes by myself. Need a couple more fittings before I can install the residual valve.

While I was under there looking around, I did notice that on my trailer with the actuator where the factory installed it, the output of the actuator is lower than the input to the calipers when the trailer is level. Make of that what you will.

[GCinSC2]

Folks,

I thought maybe if I added a refresher about my testing and observations.

This is from my post Disc Brake Lag vs. Pressure 9/12.

"It is a simple 5 second shot of the PSI gage ramping up. Unfortunately we do have one variable in this, how much of a request for braking did my better half initiate from the MaxBrake slider control? Sorry. But using video editing software I was able to view a timeline from the audio track showing the audible start of the pump soundtrack vs. the response on the gage.
From the start of the audio it was only about 0.5 second to 200 PSI. and it peaked at about 700 PSI."

It is referencing a video of a pressure gauge and AFAIK the only documented test from an owner demonstrating just how quickly this system does ramp up .
I went through my files and found the original text to accompany my video test. I didn't post this as I was reserving it for some more actual driving feedback about the brakes.

" OK, what does 200-400 PSI braking feel like? The Carlisle is rated at 1,600 PSI and we’d be flat spotted and trailing smoke long before that. This summer (2012) we went to the upstate of SC actually just south of the Palmetto Cove campground on SC 11 going up and down its scenic foothills. I let the rig start rolling downhill letting a bit of gravity take over and then got into the brakes, you’d be surprised how much 300 – 400 PSI of braking really is, feels like we dropped anchor. You can get a rough PSI on the MaxBrake controller display."

So creating 200 PSI in about 0.5 sec as reported based on my actual use and driving is a lot of near instantaneous braking power.

Since my brake work of Sept 2012 I have done nothing else to my brakes other than enjoy them including running SB on I-77 down (Fancy Gap about a 7 mile 7% grade IIRC) from the Smokies coming back from a trip to Virginia Highland Haven.

Anyone considering modifications, sure would be interesting if you could quantify your pre mod baseline vs. modifications to see if you made any improvements. and please consider that just by bleeding your system completely post mods should make an improvement in your response that MAY NOT be due to your modifications. Tricky, ain't it.

Gary