Near accident: help understanding root cause

[ravenholm]

Hello All,

Was driving my '40 last night, and had a pants experience.
I'm trying to understand what went wrong so I can correct it and minimize the chances of it happening again.

Firstly, about me: I'm 28, been driving for over a decade. My Pa was an ER doc so I grew up with lots of horror stories of country road disasters, which scared me pretty effectively into becoming a careful driver. (Go Pops!). My in-laws joke about me driving like a grandma.
I don't in any way mean that operator errors of both technique and judgment might not be part of this - but it wasn't because I was getting overly friendly with the gas peddle.

Here's what happened: It's raining, dark, and I'm driving in the city. I come off a bridge that's also a rail-bridge, and head down the off-ramp at what seems like about a 5% grade. The offramp makes a gentle bend to the right, about 20 degrees, which the tracks follow. I'm traveling no more than 20mph. As I go around this turn, I feel all four tires wind up in the rail tracks. Almost instantly, the truck spins a little more than 180 degrees.

I've had back-ends break loose before, and have successfully countered it (like in an unloaded pickup going around a muddy turn).

This happened REALLY fast, like a big hand just swatted the butt of the cruiser and flipped it around.

I was lucky - no other cars around to run into, made a three-point turn and was back on my way, rather rattled but no harm done.

In other almost-accidents I've had, I've always been able to point to something and say, aha - that's what I did wrong.

I'm stumped here. Going slow, in a vehicle with good traction.

My guess is: The short wheel base makes it spin faster if it spins, so that's part of it. All four tires wound up on rail at the same time, and perhaps one of the big lugs on the 33x12.5 BFG MTs got stuck in the track. The horrible powertrax locker engaged as that wheel started to spin, breaking the uphill wheel loose and initiating the 180.

Is that a reasonable diagnosis?

I'm already working on doing the following to the rig before I drive it anymore in the rain: Removing the Locker of Death from the rear dif, and putting on BFG ATs instead. Roll cage to follow shortly thereafter.

Is this the right answer to what happened?

ANY ideas / thoughts from all you with way more experience on these rigs than I have would appreciated.

-Guy

 

[JohnnyC]

are they exposed tracks? or flush with the road?

 

[Pighead]

All 4 wheels suddenly on the slippery rails, as opposed to the less slippery asphalt, while in a downhill turn could certainly have thrown you into the spin...

 

[JohnnyC]

BFG MT's and rain never mixed well with me

 

[destin]

yeah be careful on the street car tracks in portland man!

They are slick business!

They can get pretty sketchy in a car sometimes too, wet plus polished metal.

 

[Eshu Elegua]

If you still need lockers at least go with ARB in the rear, put some fog lights-yellow bulbs help on fog and rain, full cage . check the same curve at day light to check the tracks if they are exposed or flush with the road

 

[fj404life]

Siped tires are a good idea in Portland! x2 if they are mt's!

 

[ravenholm]

Destin, yeah, I've has problems with the tracks before in my 4runner. Nothing like that... but they are sketchy.
Generally I try to not drive on them, but the curve in question is the one coming from eastside onto lovejoy across the broadway bridge, and 2 sets of tracks join in the middle, so it makes it kinda tricky to completely avoid them there.

OK, so sipe my tires, add a roll-cage, I have fog lights that work nicely. MTs and rain not a good combo.
Great suggestions.

Eshu and Johnny C have both asked if the tracks were raised or flush with the road...
Is that a city maintenance issue? They are streetcar tracks, not sure if that helps. I'll check next time I drive that curve, which is pretty often, actually.

I don't need the locker, so I'm just gonna pull the powertrax and put the money I'd have to spend (not that I have it anyways) on an ARB into a cage. This is a light trail truck at most, so locking diffs is pretty far down on my list of needs.

-Guy

Cheers,

 

[dgangle]

let me make sure I get this.....

wet, dark road driving over/parallel railroad tracks with arguably the worst tire for rain ever made on a short wheel-based vehicle with a relatively high center of gravity.

Duh!

 

[ravenholm]

dgangle:
I suppose it's a "duh." Didn't know MTs were considered possibly the worst rain tire in the world- now I know that little piece of trivia... Not my pick, came with the truck.
But there's a lot I don't know, which is why I asked for more experienced input, and am grateful you provided it. Assuming you know root cause when you don't have the experience to actually validate it is a great way to ensure the same thing happens again, so I try not to do that too often.
I guess the problem I have is that "well, don't drive in the rain anywhere near railroad tracks" is a bit tough in this town, so I'm trying to understand what other factors I can change to help the odds. Many other people in Portland have '40s and aren't dead, so they must know something I don't.

So, what might you have done differently? Left the cruiser at home? Obviously you'd have different tires. Anything is valuable to me!

Certainly the scenario I described would always require careful driving, but I had thought -at the time- that I was being relatively careful.

Best,
Guy

 

[msapers]

Well...

I think you were on the right track with your original thinking as to the locker contributing to the spin. BFG MT's are good tires, I've run them for many years on many vehicles without any problems. I also have similar lockers front and rear on my 40. Having it lock or unlock quickly on a slippery surface can bring about all sorts of fun consequences. You CAN learn to drive around this! The main thing to remember is to keep a "neutral" balance to the throttle (neither accelerating or decelerating) when going around corners. This will GREATLY smooth out the operation of the locker.

Here's my reccommendation: find an open slippery area away from traffic, set up a cone or marker and use it as a corner. Practice taking corners at a set speed under accelleration, deceleration and neutrally. See how your rig reacts to each (Did you spin? what were/weren't you doing, etc...)

The only way to be safe is to know exactly what your vehicle is going to do ahead of time.

 

[Pighead]

What kind of air pressure are you running in those tires? Perhaps airing down a few pounds might help in the rain...

 

[destin]

yeah i am running some bias ply tires now, probably switching em over to some sipped yokos for the winter.

tire looks like this

Yokohama Y742S 7R15 29.8” OD

 

[ZMANFJ40]

I would say siping the tires is a good start. You can make a great set of mud tires handle a lot better in the rain and snow here in Oregon with siping they will run cooler in the summer also and will wear longer, the only down side is if you run a lot of gravel roads, they will cut little chunks out. Also on the Mud tires just the center lugs need siping. I would also agree with the tire pressure comment, I usaully run 30-32 psi in the front and 28-30 in the rear unless fully loaded with gear.
Hope this helps!

 

[gisham]

improperly adjusted rear drums? were you on the brake at all?

 

[FJsnoozer]

You might look at Goodyear Wrangler duratracs. They have superior siping to most offroad tires and almost look like a snow/mud tire.


You have a simple case of wet rubber meeting polished Oily raise steel. Cars "track" with whatever groove the front tire is presented with. Even worse so if you have caster/camber issues that you dont know about and a worn out rag joint in your steering column.

Your rear has practically no weight and just followed, then inertia took over.

My uncle has these on his Jeep with his OME lift and it looks great. here is the 33x12.50

 

[nuclearlemon]

wet metal tracks are slippery and if you run a narrow tire, you're going to have less tire to grip the asphalt around the tracks. also a possiblity of hydroplaning depending on it water actually floods the grooves the tracks are in. i hydroplaned my old gmc shorty with 35x12.5os at about 35mph and almost did a 180...i understand the pants comment

 

[taro]

My 2 bits ... I'm a bit of a nerd about this topic ... not because I'm an expert, but because it interests me ... the locker, mts, tracks, and possible high air pressure were all probably contributing to your spin, but it's also good to know about weight transfer. This is particularly important on short wheelbase motorcycles, but also applies on short wheelbase 4 wheel vehicles as well. When you're slowing down, especially when your braking (but even lifting off the throttle abruptly can cause this), a good bit of weight gets transferred to the front tires, especially with the types of suspensions that we have. This has the effect of unweighting the rear tires, which makes them susceptible to losing traction, which when you're in the rain going downhill on a sharp turn on mts on railroad tracks is exactly what you don't need. Btw-this is why old Porsche 911s were also prone to snap oversteer-unknowing drivers would brake too hard or lift once into a turn and the momentum of the engine mounted over the rear axle would send them for a spin.

The fix for this is to slow down enough before the turn so that you can accelerate steadily through the turn (racers use this technique to go slow in, fast out). This keeps the weight transfer to the front from happening during the turn ... BUT!!! with the locker, this negates the accelerating through the turn strategy. The best thing to do is slow way down so you can slowly coast through the turn, probably much slower than you think is necessary-20 mph was too fast. Anyway, I've babbled enough. Hth.

 

[ravenholm]

(edited for typos)

Wow.
So much good information. You guys are awesome.

FJsnoozer- You're on to something here. I had originally thought the back broke loose, but as I think back over it, the tracks split at the point I lost control. My nose actually dove *left* first, following the tracks that split off in that direction (not the direction I was trying to turn). The tail broke free to the right, the dif locked, and away I went.

msapers - I hear you on the neutral throttle thing, and I'm starting to figure this out. I first, I had to drop the clutch to the floor going around turns, now I can keep it under power smoothly. Here's the rub, though: Even if I learn to master the autolocker, I really can't let anyone else who isn't comfortable with the lockers drive the truck in good conscience. For something that I'm going to need less than 0.5% of the time, I feel like right now, it's better to just yank it. If I really need a locker, I'll bite the bullet and stuff in a selectable locker of some kind at a later date.

Destin and others - thanks for the tire suggestions. Very handsome rig, to boot. I would kill for your tub.
I will definitely be siping my replacement tires.

ZManFJ40 /Pighead: Air pressure. several of you have asked, and based on your running specs I'm probably too high. I will bleed the tires down to "30-32 psi in the front and 28-30 in the rear" tonight.

GiSham: I'm running discs on all four corners, but good thought.

Taro, your 2 bits are fantastic. I'm kinda a nerd about any topic. I learned a lot from your explanation. I don't think I stepped on the brake, but I sure as heck let off the gas when the nose twitched left and I was probably in 2nd gear. Engine compression is enough that I might as well have stepped on the brake. What you describe is how I learned to drive (in slow, out fast) but with the locker in there those old habits become dangerous. I will take turns even slower than I think I should, and that locker is history.

And, be wery, wery careful with railroad tracks in the rain, period.

I really appreciate your help thinking this through and staying safe.

 

[akeyzoo]

Destin "quoted" my rig, wooohoo! I have made the big time!!

Ravenholm, thanks for your experience, reading replies has helped me.