The last time I drove on this particular steep and rough unpaved forest road, it was in my '85 Nissan pickup with 5 speed manual transmission. In those days, I made that trip several times over three summers. It was just less than 4 miles, and maybe 1800 feet of elevation.
The road might have been slightly better than back then, I did it mostly in second gear going up, and first coming back down. That was maybe 20 years ago.
Last week, I was in my Sienna minivan – with automatic transmission of course. This time, it was challenging. The few cars already in the “parking area” were more off-road compatible than mine – except for a Prius.
Descending was much more concerning. The road was steep enough that low was not sufficient for slowing the car enough for the rough surface, so I rarely lifted off the brake, and then, only for a few seconds at a time.
That made me concerned about boiling the brake fluid and losing braking entirely, so I stopped four times to let the brakes cool, once for at least 5 minutes. I had no sign of brake fade. But that took twice the time as the uphill trip.
So given that I was rolling between 5 and 10 mph, and sometimes less, was brake fade still a possibility? Or at that slow speed, was heat dissipating fast enough that there would not have been a problem?
Would this have been an unreasonable strain on the transmission, given the sustained downhill?
If you can’t smell the brake pads, a sharp acrid smell, you aren’t likely near to boiling the brake fluid. That said, brake fluid should be changed every 3 years no matter the mileage. And this is more critical in a fwd van because if the front brake fluid boils you will lose all your brakes, not just half, because the system is split diagonally.
This trip is harder on the transmission than running down the highway.
Tourists returning downhill to normal elevations after driving to the top of 14,000 foot Pikes Peak (Colorado) are usually stopped midway down by a safety officer, who feels the front wheels. If too hot, the driver is ordered to pull into the parking lot and let the car rest for 20 minutes. In your case, you’d have to be your own safety officer.
If you can’t smell the brake pads, a sharp acrid smell, you aren’t likely near to boiling the brake fluid
I didn’t detect any unusual smell – nothing at all – and I do recognize that smell from other vehicles coming down long paved roads at much higher speeds.
Having experienced brake fade long ago, I opted for caution last week. I did hop out to touch the wheels for a sense of how hot they were. That was at the extended stop I mentioned, near the half-way point. Reaching a finger through the wheel cover, the wheel felt warm but not so hot that I needed to pull my finger away. But that was just the outside of the wheel, not the disk or caliper which in retrospect, I wish I had checked.
Using an infrared thermometers, at what temperature should I start being concerned? I do have a view of the disk’s inside face when lying down under the bumper. Is there a better place to check in a case like this?
This trip is harder on the transmission than running down the highway.
I would guess that uphill is harder on the transmission, would that be correct?
There is fade from the brake linings and then there is boiled fluid. The first has a firm pedal with no slowing… The second makes the pedal hit the floor and no slowing. Either is an aww $h1t moment. The pads get hot enough to almost fade and that passes heat to the caliper pistons and the brake fluid behind them.
If the wheels were warm, not hot to the touch, and no smell, you were OK, not close to fade or boil.
Both up and downhill are a strain on the transmission but not enough to matter unless it is near failure.
Your brakes get hotter in city traffic than they will at 10 mph on a hill
I don’t do city traffic, can barely remember what that’s like any more, thankfully.
Your answer is kind of what I was wondering about. This rocky road surface was too rough to descend at 10mph, I was well below 10, mostly crawling…but for a long time, more than 30 minutes to cover 3 1/2 miles to the pavement. On the way up, a burly Jeep with big tires came bouncing down, going about as slow as I would go 8 hours later, but it was hard for the Jeep.
So in the moment, I wondered if the very slow speed over a sustained descent was less bad than coming down a long paved hill at much higher speed, where there’s much faster movement of the disk relative to the pads, but over a much shorter time than in the case I described.
One easy to do experiment that might provide a clue, rub your hands together slowly for an extended time vs rubbing them together very fast for a short time.
And if you did you probably would have pulled your finger back missing some skin…
At 118 degrees, human skin can sustain 1st degree burns, a 2nd degree burn injury can happen at a temperature of 131 degrees. Human skin is destroyed when temperatures reach 162 degrees, that being said a brake rotor can easily reach well over 200 degrees normally…
Trust any mechanic that has accidently touched a hot rotor, it hurts a little… lol
Yes going up a hill very slowly can make an automatic transmission over heat if you are pulling a trailer. Keep the engine above 3000 RPM in first gear to make sure it doesn’t over heat if it is a steep hill and you have a heavy load. Or take breaks and stop completely. Don’t creep up slowly.
That reminds me, we had a lot of RFT customers and they would come in and say they had a flat or needed a new tire and I would ask which tire, well due to not all tpms systems telling you which tire is low, most customers had no idea, I figured out fast that you can just walk around and feel each sidewall to tell which one was low on air, the low one was almost always vey hot…
Thanks @Mustangman, I appreciate the fleshed-out details. In the moment I was concerned about brakes, but now more attuned to considering the transmission too. I appreciate your responses.
I have been looking for a used 4wd rig like Xterra or 4runner with manual transmission, rather than abuse the old minivan. Now that I want to spend more time in the particular area that prompted this thread, I’m more motivated to get one. Don’t plan to go rock crawling, just want to something a bit more rugged.
Barely a bachelor’s senior project. The testing is easy to do.
Seems like the minivan did the trip successfully so why not just replace it when if no longer can? Off-roading is as much about ground clearance as anything. If you don’t drag, generally all is good.
I’ve done off-roading in part-time 4WD vehicles (RWD in 2-wheel mode) on rocky and sandy trails. Only very rarely did I need 4WD for traction. But far more often I needed the ground clearance.
At the time I visited Pike’s Peak, late 60’s , the safety officer appeared to be feeling on the inner side of the wheel. Not sure exactly where, possibly brake drum, but I expect he was wearing gloves.
I travel VERY steep hills in Idaho (and previously in Colorado including the one your are referring to) in a number of vehicles, mostly 4Runner, and never faced any that the 2nd gear wouldn’t be sufficient with maybe occasional brake applications.
never faced any that the 2nd gear wouldn’t be sufficient with maybe occasional brake
Not a chance. In second gear (automatic trans) I would have been destroying the suspension and tires. Had the road been smooth, first gear would have been fine with an occasional dab of second. But there was just no way with the extremely rough surface.
It was the COMBINATION of rough and steep that was the problem.
Remember I’m driving a minivan with 15" highway tires, I just didn’t want to beat up my car, but even so, second gear would only be an option with a nicely well graded road. Remember too that I saw a well outfitted Jeep bouncing down the road at a crawl.
