How tight should the disc brakes be?

[FullStop]

I installed a new electric over hydraulic disc brake kit on a tandem axle '65 Overlander. The issue I'm concerned about is that the brakes are adjusted too tight. How much should the wheel spin by hand? I have to give them a decent push to get them to turn, and I don't want to burn out the brakes or drag the trailer along. Any advice is appreciated.

Thanks!

[dwightdi]

Disc brakes do not have an adjustment. They float free and ride just in contact with the disc. The slides or bolts on the caliper, that center them, should be lubricated. If the discs are warped you might have a bit of friction at various points.

[NWRVR]

Unlike drum brakes operated with a manual actuator, there is no check valve in a EOH disk brake system that could hold pressure in the brake line. The new pads/rotors should wear-in allowing a freer spin but the pads will always idle against the rotors to give you instant braking when pressure is applied.

[GCinSC2]

Get an IR temp gun and carry it with you. Check temps frequently as you learn this new setup and prove its OK or find issues.

[Excella CM]

Disk brake pads are retracted by the resiliency of the rubber seals around the pistons and that is usually sufficient to let the wheel turn freely. You can check for pressure in the system by opening one of the caliper bleeds. If it squirts out then you have residual pressure. Wheels should not have drag when the brakes are not applied.

[FullStop]

Thank you, all. I threw the wheels and tires on and they make it a good rotation and a half without too much of a push. I'll look into the IR temp guns, though. That's a good idea.

[JCWDCW]

I just check the nuts on the wheels each time I stop. If there is a big temperature difference between wheels then I have an idea there might be something wrong on that wheel. Testing Disc Temperature is kind of problematic. If you come off a hwy run and just stop in a rest area the discs will not be too hot. If you have just come off heavy stop and go traffic or down a long grade they will be hot. You need to be able to understand why.

Excella CM is correct; the square seals on the pistons flex when brakes are applied and pull the piston back when pressure is released. The flow of air on the rotating disc also holds the pads just slightly off the disc, but all disc brakes drag a bit. The heat also keeps the disc dry which is why disc brakes are usually more effective in wet weather
jcw

[TomKirk]

Like others have said, there's no adjustment on disc brakes.

Disc brakes are supposed to drag slightly and it shouldn't take much effort to manually roll the wheel over. But if they're too tight, something's wrong.

1) Caliper pistons are not retracting like they should.

For example, if pistons and caliper housings are not a "machined match," pistons could be getting "hung up" inside the housings. In my line of work, we see this from time-to-time in so-called "remanufactured" calipers.

2) Caliper "sliders" are not working properly.

Calipers need to slide from side-to-side on caliper bolts (that attach caliper to spindle/knuckle). As caliper piston pushes inner brake pad and then retract, caliper assembly is supposed to retract as well. If not, brake remains engaged. There's a special grease for caliper "sliders" (bolts).

BTW - Caliper bolts could be bent. Caliper housings and/or spindles could be improperly machined; caliper bolts are unable to align correctly.

3) Take AS for a test drive. Inspect brakes for heat. Use your IR gun. Compare heat with disc brakes on tow vehicle.

Tom

[perryg114]

This probably does not apply to this type of braking system but the only time I had disk brakes stay on was when I had the actuator pin adjusted too tight that pushes on the piston in the master cylinder. Since you have what amounts to a hydraulic pump I don't think this would apply. I assume there is a valve that releases pressure from the system when the brakes are not being applied? A little drag is normal and this will get less usually as the wheel turns and the pistons relax a bit. Also with new rotors the drag can be more.

Perry

[GCinSC2]

Originally Posted by JCWDCW

I just check the nuts on the wheels each time I stop. If there is a big temperature difference between wheels then I have an idea there might be something wrong on that wheel. Testing Disc Temperature is kind of problematic. If you come off a hwy run and just stop in a rest area the discs will not be too hot. If you have just come off heavy stop and go traffic or down a long grade they will be hot. You need to be able to understand why.
jcw

I think you've missed part of the point, checking at a rest area, should be operating temp range. What you're looking for is variations. Cold rotor, not contributing to braking. Excessively hot rotor, dragging brake.

Braking transforms the energy of the moving trailer into heat. Monitoring that heat while you get to know them.

Speaking from extensive hands on time with my Dexter 4 piston disc brake ownership and repairs.

And that IR gun has lots of troubleshooting talent and darn good at monitoring the temp of a cast iron griddle for pancakes!😋

[TomKirk]

Originally Posted by GCinSC2

And that IR gun has lots of troubleshooting talent and darn good at monitoring the temp of a cast iron griddle for pancakes!😋

YEP. And it'll also tell you how mad your wife is too.!! LOL

Tom

[perryg114]

A simple hand on the rim will tell you a lot and has never let me down. I have one of those IR things and don't really use it. I can tell which wheel is running hot or tire just by touching it. This is something I do on the way to the bathroom at a rest stop.

There are rare cases where a piston gets stuck or a line collapses letting fluid into a caliper and not back out. Also you need a good proportional controller that has a disk brake setting. If you have a typical on-off controller you might be using more brakes than you need overheating things.

Perry

[JCWDCW]

GCin SC2: Re my original post on wheel nut temps...I did say I'm looking for a difference!..That's the point. And an IR gun is great but you still need to be able to interpret the findings...Which is exactly what you said...get to know your rig.

Checking tire temps by feel is also a good idea. We came home from Texas with the TV rear tires running hot....The oil change experts in Harlingen thought they new better and let air out of my tires. Took nearly a day to find a working air pump.

jcw

[GCinSC2]

Jcw,

I don't have any guidelines but uniformity is a goal for me. Seeing similar readings on all 4 trailer brakes is the goal. So far doing really well.

Last year IIRC after coming down I77 VA into NC the Fancy Gap 7 mile 7% grade downhill I pulled into the rest area and shot the rotors. I didn't see anything alarming at all. Rotors were barely warm, not in trouble. Everything was very controlled. And part of the reason I've been kinda over checking my brakes is because one time on flat roads I had 800 deg F on one from a sticking piston. The brake was actually smoking. Written up previously.