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Comparing brake temps

Old 08-07-2022, 01:56 AM
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Default Comparing brake temps

Noticed surge brakes seem weaker than normal this year. Pulled off the wheels and calipers/pads look new. Brake fluid found full. Took apart the sliding portion of the Myco hitch to see if anything looked bad. Nothing bent, rusted or broken found but did discover 2 snubbers in there that I didn't know about. I assume they are there to dampen the shock when extending/retracting the sliding mechanism. Not sure if they need to be changed or not during drum/disc brake conv. If their length was wrong for the master cyl type, seems like they could prevent full actuation of brakes??

I swapped from factory drum (1989 vintage) to Kodiac Disc W/SS rotors 4 or 5 years ago and they seemed OK but never really had to push them. New/matching disc-rotor type master cyl was also installed with the discs. Brakes are only installed on front axle (tandem).

Today, I took it down a nearby secluded road for some brake testing. Brought a thermal camera with me to compare brake temps.

Made 7 or 8 consecutive "max braking" stops from 35-40 MPH and took temp readings.
Truck (2500HD) brake rotors were 260-265 degs F on all 4 corners.
Trailer brake rotors were 160 degs on both sides.
Truck and trailer brakes both started out "cold".

The 100 deg difference seems to confirm the trailer brakes aren't doing their share.
Anyone else tried this before and/or know about the snubbers??
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Old 08-07-2022, 03:54 AM
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If the trailer was empty during this testing I'd not expect the brakes to get as hot as the truck brakes. If loaded then I agree, you have either too little actuator travel (your snubber theory may be worth looking at some more) or a hydraulic problem, improper bleeding, etc.
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Old 08-07-2022, 12:32 PM
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Boat was on the trailer for the brake testing.
When I had the sliding mechanism apart, I looked at the breakaway brake lever mechanics and discovered it directly engages the master cyl, so the sliding part is removed from the equation. I removed the 2 pieces that would hold the lever up if actuated so I was feeling only the resistance of the hydraulics. It felt very firm so doubt there's much if any air in the system.

In regards to the snubber theory, maybe I can do some testing with the snubbers removed?? After doing some reading last night, found that removing the snubbers may cause violent oscillation or chatter of the brakes. I'll give Myco a call tomorrow and see what they have to say.

Only other theory I have is the brake pads may be contaminated, but since both sides were within 1 deg of each other, it seems unlikely.
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Old 08-07-2022, 12:56 PM
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I'm not sure you can compare rotor temperature between tow vehicle and trailer. It might not be an apples to apples comparison.
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Old 08-07-2022, 05:58 PM
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Originally Posted by underpsi68 View Post
I'm not sure you can compare rotor temperature between tow vehicle and trailer. It might not be an apples to apples comparison.
I agree it may not yield valid results. I know some members are pretty diligent in regards to checking stuff like this. Was hoping someone had tried this before.

One thing for sure, I'm not comfortable with how long it takes to stop. I know EOH is the way to go but the boat isn't getting used much (been out once this season for a maint run) and may not around a lot longer so hate to dump a bunch of money into it now.
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Old 08-07-2022, 06:02 PM
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I would put brakes on the other axle. Some states require brakes on both axles.

I had kodiac ss disc on my dual axle trailer with surge brakes and never had any issues. EOH is better in sure but I never had a need for it. Trailer was around 6500lbs loaded towing with a Tahoe.
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Old 08-08-2022, 10:26 AM
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The truck has to out-brake the trailer. That's what enables the surge brakes to work. You have probably 2-3X the pad size on the truck brake calipers than compared to the trailer. That additional friction alone will account for the difference in temps.
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Old 08-08-2022, 01:32 PM
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Originally Posted by Sydwayz View Post
The truck has to out-brake the trailer. That's what enables the surge brakes to work. You have probably 2-3X the pad size on the truck brake calipers than compared to the trailer. That additional friction alone will account for the difference in temps.
I agree the truck has to out-brake the trailer for the surge brakes to work but it seems like if everything was working correctly, the trailer master cyl would continue to compress and applying more and more press to the trailer brakes and should lock-up the trailer brakes at some point or at least get them really hot.

Also, since the boat/trailer weighs more than the truck and the trailer only has 2 smaller discs compared to the truck having 4 larger discs, it seems like the trailer brakes should be absorbing more energy and get hotter than the truck brakes.

In regards to the pad surface being larger on the truck causing more friction, you would have to assume the brake line press was the same. I'm thinking the trailer brake line press would be significantly higher since there's thousands of pounds pressing on the trailer master cyl during a panic stop.

Since disc brakes are not self-energizing like most drum brakes, you need more press to achieve the same amount of braking force. To get more brake line press, the master cyl piston would need to be smaller. A smaller dia master cyl piston would need more travel to provide the same amount of fluid displacement. If the travel was restricted, master cyl may not achieve sufficient press. Man, lots of variables involved with this. It's giving me a headache!
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Old 08-08-2022, 03:00 PM
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Originally Posted by zz28zz View Post
I agree the truck has to out-brake the trailer for the surge brakes to work but it seems like if everything was working correctly, the trailer master cyl would continue to compress and applying more and more press to the trailer brakes and should lock-up the trailer brakes at some point or at least get them really hot.
They're both decelerating at the same rate. So IMO for the trailer to progressively increase pressure the truck would have to slow at a faster rate.
How will it do that as they are connected?
Only within the travel of the brake coupler.

That's the whole nature of them, tow vehicle slows, trailer doesn't want to, it surges forward, applies the trailer brakes, it slows, which reduces the pressure applied to the trailer master cylinder, which in turn reduces the trailer braking.
So it's proportional to the rate the truck is slowing.
Anytime the trailer tries to out brake the tow vehicle (slow at a faster rate) it reduces the braking as the coupler then gets pulled out of actuation.

IMO you'll never get the trailer brakes to out brake the tow vehicle in a surge brake setup.
Think of this.
If the surge trailer brakes locked up and no tow vehicle brakes are even applied what happens? The trailer decelerates at a faster rate than the tow vehicle, inertia of the tow vehicle pulls the coupler out and no brakes are applied.


Originally Posted by zz28zz View Post
Noticed surge brakes seem weaker than normal this year.

Man, lots of variables involved with this. It's giving me a headache!
"Seems weaker" is so subjective especially if you had no baseline data from when you installed them.
I.e., brake line pressure, rotor temp, stopping distance.

If everything checks out and they've been installed 5 ish years.
I'd stop thinking about it and go boating.

.
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Old 08-08-2022, 05:02 PM
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In certain circumstances the surge brakes can out-brake the tow vehicle but just for a split second, then they release, trailer surges fwd and the cycle repeats causing a violent shudder. That's what the snubbers are designed to prevent.

Maybe think of it this way:
If braking system is working perfectly, the trailer should brake almost as well as the tow vehicle. The difference being what activates the brakes.
Since the tow vehicle has 4 large brakes and the trailer only has 2 smaller brakes (and the boat/trailer weighs a little more that the truck), the 2 trailer brakes would be forced to absorb more energy than any 2 of the 4 brakes on the truck and thus be hotter.

I realize my impressions are subjective however it's that 31 years of pulling boats and the seat-of-the -pants feel that tells me something isn't right. The truck is being pushed significantly more than it should.

For the last few years the trip to the ramp required very little braking along the way so the brakes never got a serious test. (when pulling the boat, I drive like a grandpa on qualudes)
Last winter they installed a traffic light at the bottom of a large hill that's also going around a curve. I've only been thru it once with the boat and it was green. It got me thinking what if it was red. I'm pretty sure I wouldn't have been able to stop in time with my current arraignment even approaching at 10 MPH below the speed limit. That's what got me testing my max braking capability. In other words, the brakes may have been like this the whole time.
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