(Possibly) Stranded in Death Valley

[AC932]

Welp, road trip's been going pretty well so far.

Truck is a 74 Bronco with a bone stock 302, 3-on-the-tree, manual brakes and steering.

Coming down from the mountain pass, the road is about 10 miles of 6%ish grade. I had the truck in 3rd and foot off the throttle. About halfway down, the engine got disconnected from the driveline. No scary sound or anything. When we stopped, I put it in 4wd, no difference. Revving the engine in first then shifting to reverse results in grinding gears, but no power transfer to the wheels.

We ended up close to a hotel, so we got water, checked in, etc. Walked back to the truck for our stuff about 1 hour later, it gets going no problem, makes it back to the hotel just fine.

So, what do y'all think it might be? Clutch overheating? Nothing changed from when it was parked on the side of the road to when tried it later, except for the passage of time. Should I find a shop or just keep going and cross my fingers?

In case it helps, the truck did start running pretty hot coming up the mountain, we pulled over to let it cool off before it popped the cap. Had overheat issues in Colorado too, replaced the waterpump and put in a 160degree thermostat which helped immensely. Earlier today, doing about 70mph, the truck started bucking like crazy, died a few times, and blew the muffler up. We pulled over, replaced that, and ran at around 60mph the rest of the day without issue.

 

[onpier55]

How old is the clutch disc? Could be a slipping disc. Now that it cooled down. It works. If older with milage. Maybe time for a replacement. Good luck. Karl

 

[AC932]

Clutch & pressure plate are about 3 years old, have about 25000 miles on em. Got them from Napa. Is that about a normal lifetime or no?

 

[onpier55]

Depending on if you tend to ride the clutch (keep your foot constantly on the pedal) I would think you could 75k-100k from a clutch. Was the flywheel resurfaced? Slipping clutch will cause heat, then no clutch.

 

[onpier55]

My 71 Amc javelin has 25k on the motor and rebuild. Clutch is out now. So it’s not out of the question for the clutch to go out. But what caused premature failure.

 

[onpier55]

Death Valley? How hot was it today? Extreme heat could have caused the issue also.

 

[Bronco4x4]

Was it a rebuilt pressure plate? I'm sure they are not a popular item these days so most likely it was new. If not, I have had rebuilt pressure plates fail on a heep I had. They do not always change out the springs on those. Good luck and hope you get back rolling again.

 

[AC932]

Thanks for suggestions.

Pressure Plate was new when I got it.

We got in pretty late, was only around 106, was driving all day in Cali at about that temp, so I dunno if that was it. It felt a lot hotter than that though, so it's definitely possible.

I take my foot off the clutch completely when driving, but the flywheel could be an issue. I "resurfaced" it myself with an electric sander and some 100grit.

Regardless, we're gonna try and beat the heat outta here this morning, give the old girl a better chance. Fingers crossed it did in fact have something to do with the heat.

 

[knack]

When you said the drivetrain became disconnected going downhill, it sure sounds to me like the transfer case popped out of gear. The J-shift case in my '73 used to do that.
"put it in 4wd, no difference" makes me think you had the same idea. Maybe the gears weren't fully engaged when you were trying it?
Doesn't seem like how a clutch problem would act. If the clutch failed so completely that there was no power being transmitted at all - I don't see how it would later be OK.
I haven't dealt with those sorts of temps in an old Bronco before though.

 

[Broncobowsher]

Try shifting the transfer case with the engine off.

 

[Timmy390]

The J shift in my 74 has been a problem since day one of ownership. It's given me several WTH moments over the years.

Tim

 

[onpier55]

Good luck and happy trails.

 

[Justafordguy]

Sure sounds like the transfer case jumped out of gear to me. You need to twin stick it.

 

[Jfryjfry]

Man... your trip sounds like it has been far from problem-free so far!

So no power getting to the rear wheels.... if it was the clutch it was either stuck disengaged or it lost all ability to grab, which still likely would have shown some movement even if it couldn’t actually motivate it. But oil saturating the disc or it slipping really bad and overheating would be all that I can think of short of the throwout bearing sticking or the pressure plate breaking.

But it really doesn’t sound like the clutch. Maybe the throwout bearing sticking and keeping the clutch disengaged but you’d feel a difference in the clutch pedal.

Heat alone wouldn’t cause this - it would have to affect something that would effect the symptoms. I’m not even sure what the heat could do that would cause it.

Most things I can think of that would cause this also involve loud, bad noises and/or impacts in the drivetrain

Do a little diagnosing if it happens again. Try and see if anything is trying to move. See if the transfer case is in gear or if the gears are even turning at all. Same with transmission.

 

[Rustytruck]

Do you have factory limited slip? Maybe stripped the drive splines? Put the truck in 4wd high and lock the hubs and see if it drives. Did you go through Titus canyon?

 

[nvrstuk]

Like mentioned by a couple others already...you were going downhill and then "disconnected"...

Put the t-case into 4 hi or 4 low range and try moving it...I'll bet it popped out of gear. Very common for an older D20...many things can cause it...

Good luck...I think it's a simple fix for you...

 

[Bronco 4 life]

I would agree with the Tcase popping out of gear had it happen To me before...
Were there any smells like hot clutch you would think if it had slipped enough to not engage completely while on compression down hill you would have gotten a little whiff???

 

[AC932]

Thank you all for the suggestions. We were able to get outta Death Valley and haven't had any similar issues since.

I'm pretty sure it wasn't the transfer case slipping out of gear. When I went back to try moving it after it sat, I don't think I touched anything but the parking brake, pedals, and transmission shifter. When we were still coasting down the hill, I pushed it pretty hard into 2H thinking that was the issue.

Truck has a (I assume) factory open diff front and rear.

The only smell I was aware of was the brakes heating up since I wasn't able to engine brake alone any more. Didn't smell like clutch to me, but my sniffer ain't the greatest.

The clutch pedal did feel a bit lighter when it wouldn't move, would that be indicative of a sticking throwout bearing? I guess I'm not sure how it would have stuck to begin with though, seeing as it should have been fully disengaged when it happened.

 

[Bronco4x4]

Heat soak into pressure plate springs?

 

[onpier55]

Glad to hear you made it out safe.