Question on towing and rear brakes

[jms2112]

Hey gang - long time no post haha. This is going to be a long question so bear with me.

So I have a 2005 SR5 V6 and I am planning on towing a pop-up camper this weekend and I am getting ready to do that. It's a fairly large popup with like 2700 lb dry weight, so probably around 3000 lb all loaded up. Should be no big deal. The trailer has electric brakes and I bought a brake controller and hooked it up. So far so good.

I hooked up the trailer last night and took it for a test drive. When I got back the REAR brakes on my 4Runner were HOT. Why would this be? Fronts were OK.

Now, the electric brakes on the trailer are NOT working, and I can find and fix that issue, I'm not worried about that. It actually wasn't that hard to stop without them. But I'll fix those tonight. But I was wondering if WHEN TOWING, do the rear brakes on the tow vehicle DO MORE BRAKING?

If so, then maybe this explains it. If not then there is a problem somewhere and maybe fixing the trailer brakes will solve it.

The other thing to throw into the mix is that I just fixed/replaced a couple rusty brake lines in the rear. From the flex hose on the axle to the calipers. One was leaking and I replaced them both. That repair seems sound, no leaks. So I don't know if this has anything to do with (the issue of the hot brakes).

Note that the test drive was only about 15 minutes and only some small hills.

Tonight I will take the 4R out for a drive WITHOUT the trailer and see if the rears are hot....

Thanks for any help!

 

[ZebRuaj]

I just tow a utility trailer, with 2 ATV's at most so I haven't experienced any problems. But added tow weight should affect the braking system equally, not just the front or the rear in your case.

Also, I do not believe the truck can change its brake bias to the rear just because you are towing. It doesn't know the difference. If anything, the fronts may be hotter because they provide the majority of the braking force.

My money is on you having a brake problem, just enhanced now that you happened to be towing. Recheck your repairs. Or look for stuck calipers. Or maybe the rear pad materials are cheap?

 

[jms2112]

I just tow a utility trailer, with 2 ATV's at most so I haven't experienced any problems. But added tow weight should affect the braking system equally, not just the front or the rear in your case.

Also, I do not believe the truck can change its brake bias to the rear just because you are towing. It doesn't know the difference. If anything, the fronts may be hotter because they provide the majority of the braking force.

My money is on you having a brake problem, just enhanced now that you happened to be towing. Recheck your repairs. Or look for stuck calipers. Or maybe the rear pad materials are cheap?

That's what I was thinking - thanks.

 

[AuSeeker]

Since you're in the "rust belt" I'm guessing you have seized calipers, it could be the rears and why they're getting hot because the pistons aren't retracting thus causing the pads to be dragging/rubbing the rotor when the brakes aren't applied, OR it could be the fronts are seized to a point the pistons aren't moving towards the rotors and applying much if any pressure and thus the rears have to do most if not all of the braking.

 

[jms2112]

Well I drove the truck to work today and there are no hot brakes. So... I'm not sure why they're ok now. I'll keep an eye on them. :cheers:

 

[TheTurboMRT]

Braking trailer with no trailer brakes will require more energy be dissipated by the truck's brakes/rotors.
With the heavier (more mass) brakes in the front, they were probably heating up, but not as much as the lighter brakes in the rear.

Calculations show that, with a loaded 4runner at 7,000 lbs including truck and trailer, stopping from 70 MPH with all of the energy from velocity going into the brake rotors, the brakes heat up like this:
Front rotors (19.9 lbs): 174 degrees F increase
Rear rotors (14.4 lbs): 243 degrees F increase

And unloaded (4,400 lbs truck):
Front rotors (19.9 lbs): 110 degrees F increase
Rear rotors (14.4 lbs): 153 degrees F increase

Assuming front and rear put in the same amount of "work", which depends on piston area, pressure curves, power assist, etc.

So loaded the rears heat up an additional 90 degrees, but the fronts only heat up an additional 64 degrees (Fahrenheit) (theoretically)

In any case, it shows that the lighter rear rotor has the potential to get hotter than the heavier front rotor with the additional load to stop.

Using the trailer brakes helps move some of that energy off of the truck's brakes, and on to the trailer brakes.

 

[jms2112]

I checked the trailer brakes last night and they ARE working. I jacked up a side at a time and spun the wheel while my wife pushed the button on the controller and they activated. So I know they are good. They might just need to be increased.