Hungry Valley trip and the things I learned

[IdahoDoug]

This is strange. In all the years of driving offroad with production and prototype 80s I've never seen one stall. I've had 3 and the same holds. The engine was specifically designed to operate at extreme angles with several internal modifications to this effect.

DougM

 

[NLXTACY]

This is strange. In all the years of driving offroad with production and prototype 80s I've never seen one stall. I've had 3 and the same holds. The engine was specifically designed to operate at extreme angles with several internal modifications to this effect.

DougM

I'd say try what CHALDAEAN spec'd out and see if it actually does NOT happen to you. Try it on your 97. Then we can start listing what the differences are between our trucks and maybe then we can narrow something down.

I mean we have two 97 LXs that exhibit this, what if your 97 LC does not? I went through the toyotdiy site and went through the brake systems, just on a hunch, and it lists all the same part numbers for the brakes/ABS system for LX and LC.

 

[80t0ylc]

I got to disagree with Doug, on this one, about what is strange. I've been following this thread, staying out of it on purpose, because it looked to me like it was maybe a OB-II thing or maybe method of operator (the latter is where I think the stalling problem exists). Then it was shown that CDL & ABS didn't seem to matter.

On my '94, when I put it into 4lo, it'll damn near climb the hill with out even stepping on the skinny pedal. I mean idle forward powerfully on it's own, almost like a manual (hint, hint). It has to be big rock or steep hill to need input from me. So, when you reverse that force, and start tires, driveshafts, gears in transfer case and auto tranny turning in opposite direction, with throttle now at idle because right foot is now on brake pedal, and gear selector still in a forward gear, is it possible to stall the engine? Well, the evidence is in. If you look back through this thread, you'll see several, in almost the same circumstance, one even a different vehicle (4runner) stalling the engine. It doesn't happen every time, but enough to come to the conclusion that it could happen. Actually, I believe, the better shape the drive train is in, the better chance of stalling the engine, because there is less play or slip.

Which brings me back to method. Hill climbing, for me at least, has always increased the pucker factor. I've done it in both manual & auto trannys and for both, one of the things I was taught was, when or if your forward motion stops, get it in reverse ASAP to use engine braking for the trip back down. With a manual, it's a hell of a lot more important and I think that's where, it's possible, that some of us have gotten "spoiled" with the ease of the auto's operation.

The only mystery to me is why the brakes are sometimes inoperative. THAT is scary! Hopefully, this can be identified for the benefit of all. Thanks to all who are contributing their time, vehicles and efforts! Joey, and thanks to you for starting this thread! Who knows, you may have saved someone's life by bringing this to light.

 

[SeanAndHis80]

How effective are your back brakes. Back in the 80s I had a Chevy truck. I only learned that I had no back brakes when the front brakes went out. Talk about pucker factor try driving through a red light at a busy intersection at around 40MPH. Anyway do a skid test and see if you can lock the back brakes.

 

[SeanAndHis80]

Another test that might eliminate the LSPV would be trying to stall it out backing up the hill in reverse to see if the brakes act similarly when the truck stalls going forward. ...It will be another week before I could do such a test - no good hills here.

 

[chitown40]

Well, after reading everyone's theories, I can say this. The braking issue is most likely caused by the lack of power-assist. I just tried this out on a slightly sloped driveway last night, but rolling the truck forward with the engine "off" and then applying the brakes to stop the rolling vehicle. It was difficult to stop after the momentum got going. I don't think we realize exactly how heavy these trucks are even before any larger tires, armor, etc. The brake booster really is an integral part of our trucks being able to stop. So, think about this. You're on a steep inclined hill, you lose the engine, and therefore you lose vacuum to the booster. You maybe get one good pump of the brakes, but now it's your foot pressure on the pedal trying to stop 6000 lbs. It's just not going to happen.

Now, I'm not discounting the problem we're seeing with the engine stalling out, but I think the brake "issue" is not really an issue, but rather a symptom of the stalled engine. There's a reason for the power brake booster.

 

[Chaldaean]

... I think the brake "issue" is not really an issue, but rather a symptom of the stalled engine. There's a reason for the power brake booster.

My thoughts exactly, chitown. I'm going to test how effecting the brake is in two cases:

(1) Truck stalls and you give the brake pedal one single depression.
(2) Truck stalls and you pump the brake a few times.

I wonder what the difference, if any, will be.

 

[sleeoffroad]

In my case, the ABS was off because the CDL was engaged. I can't test it without the CDL at the moment as I took my front drive shaft off to replace the ujoints.

So your test was only with a rear driveshaft in?

 

[Chaldaean]

So your test was only with a rear driveshaft in?

That's correct, Christo; rear drive shaft only.

Do you think that variable skews the result?

 

[CreeperSleeper]

Just for referance, every time this has happened to me it has been on a failed attemp at a hill climb. I will notice that the engine has died while I'm stopped and going to shift into reverse to back down the hill. I have never had an issue where my truck did not stop and I have never rolled backwards. Also, this has never happend while crawling up a hill. It has always been WOT til I couldn't go any farther, stop, restart 80, back down. Think steep snowy hill. And it doesn't happen everytime. Usually the first attempt if it happens at all.

 

[Chaldaean]

At lunch, just now, I went out and tried a few things.


***TESTING THE LSPV*************************************

- I drove at 25mph on a dirt road and slammed on the brakes.
- The front brakes locked up each time.
- I only got the rears to lock up 1 out of 10 times.
- I tried going backward and got the same result (front locked every time; rears wouldn't).
- To see the results, I stuck my head out the window and watched the tires while braking. Also, I could see the skid marks in the dirt.


***TESTING THE GEAR CONDITIONS FOR A STALL***************

Conditions for a stall:
- CDL locked (didn't test unlocked)
- Transmission in D, 2 or L
- Transfer in L or H (it was "harder" to stall it in H; needed a bigger hill)

Conditions to avoid a stall:
- Transmission in R or N


***TESTING BRAKE PERFORMANCE AFTER A STALL***************

Just after stall, pump the brake:
- Slowed the truck down a bit, but not enough to stop the vehicle. I pretty much coasted to a stop
- Brake pedal got very hard to depress
- After a few pumps, brake pedal movement was little to nothing


Just after stall, pressing the brake once and holding it:
- This worked well. I was able to capture the residual brake boost and stop the truck on the hill.
- With one brake pedal depression, the pedal moves about a "normal" amount and doesn't get hard to depress


***CONCLUSIONS*******************************************

- If I ever stall on a trail, I think the best course of action is to:
(1) Immediately step on the brake once and hold it. (use the ebrake as well)
(2) Restart the truck
(3) Shift the tranny into R or N
(4) Back down and rerun the hill or try again from that point


***QUESTIONS*********************************************

(Q1) Should I be able to easily lock up my rear brakes while skidding to a stop on dirt? Should I look into an LSPV adjustment? (Jeez, 'MUD is great, but it sure makes you nit-pick your rig, eh?

(Q2) It took more than normal to restart the truck after stalling (a few seconds of the starter turning). Is this normal after a stall?

I hope this wasn't too much useless information; I'm sure a lot of you think this is common sense. However, I'm glad that I'm now ready to take proper action if I stall on a hill. The rigs behind me will be happy about that.

EDIT: Sorry, no videos; it was hard to find available helpers during the lunch hour.

 

[CreeperSleeper]

My answer for (Q2). It was always took a few cranks to restart mine, but I assumed it was because I was on a steep-ass hill!

 

[Beowulf]

(Q1) Should I be able to easily lock up my rear brakes while skidding to a stop on dirt? Should I look into an LSPV adjustment?

Yes, you should be able to easily lock up your rear brakes on dirt. To fix, you should adjust the LSPV for the amount of lift you have added to the truck.

-B-

 

[SeanAndHis80]

At lunch, just now, I went out and tried a few things.
Conditions to avoid a stall:
- Transmission in R or N

...


(Q1) Should I be able to easily lock up my rear brakes while skidding to a stop on dirt? Should I look into an LSPV adjustment? (Jeez, 'MUD is great, but it sure makes you nit-pick your rig, eh?

...

I hope this wasn't too much useless information; I'm sure a lot of you think this is common sense. However, I'm glad that I'm now ready to take proper action if I stall on a hill. The rigs behind me will be happy about that.

Thanks a ton for doing this. Weak rear brakes and LSPV might be the combo here. I assume from the comment that you could not get it to stall in reverse on the hill?
If you get a chance cay you kill your engine while heading forwards downhill (simulating a stall) and see if the brakes act similar to when in reverse? With the tail down the LSPV will be sending a lot of pressure to the rear - and if it is not effective what's to stop you - the weaker pressure delivered to the front brakes?

...and I don't think getting your rear brakes working properly is nit picking - especially if it will stop "toads wild ride" as George put it.

At my camp I have an off-camber 45 degree incline that has a ledge if you go straight back (and this is my driveway) - I would be in real bad shape if this happened to me there.

Joey - You have a real knack for posts that become extremely informative to me.

 

[Chaldaean]

Are you saying you could not stop the vehicle with the brake pedal?

-B-

Yeah, Beo, I pretty much coasted to a stop. The brakes may have scrubbed a marginal amount of speed, but I definitely could not stop the truck from rolling backwards by using the brake.

During the first day of testing, I must have been pumping the brakes a bit. On the second day of testing, I paid more attention to what my foot was doing.

Again:

Pressing the brake once = stopped the truck
Pumping the brake more than once = brakes weren't much help; didn't stop the truck

Sorry to relay murky info, Beo.

 

[NLXTACY]

Pressing the brake once = stopped the truck
Pumping the brake more than once = brakes weren't much help; didn't stop the truck

Unfortunately this was not my situation.

One one attempt I stood on the brakes, on the other I pumped them and both to same effect.

I really need to find time to test this out on my truck again.

 

[NLXTACY]

Joey - You have a real knack for posts that become extremely informative to me.

hahaha, I just push the envelope in stupidity. Anyone can do it

 

[Chaldaean]

If you get a chance cay you kill your engine while heading forwards downhill (simulating a stall) and see if the brakes act similar to when in reverse? With the tail down the LSPV will be sending a lot of pressure to the rear - and if it is not effective what's to stop you - the weaker pressure delivered to the front brakes?

After work, I went back to the hill. I started at the top this time and headed nose-down. I put the transmission in Reverse and let off the gas. The truck slowly crept down the hill and stalled.

So, it is possible to stall in reverse going forward downhill. No matter which direction you're headed, I suppose it's just a matter of back-driving the engine, eh?

Also, the brake pedal feel/performance was the same going forward as it was going backward. The hill I'm using isn't all that steep (pictures below), so I'm not sure if I would notice the change in the LSPV actuation nose-up vs. nose-down (especially due to the fact that mine needs an adjustment to compensate for the 2" lift). Note sure though, I don't know much about the LSPV .

Also, does it take longer to start the engine after a stall like this because burnt air is sucked out of the exhaust manifold, through the cylinder and into the intake and it's hard to ignite this pre-combusted mixture immediately?

For a real-world feel, referencing the pictures below, if I pushed the brake pedal once just after the stall, I could stop the truck on the incline. However, if I pumped the brakes, the truck would roll back and stop about where the second picture was taken from. Quite a difference.

I'm done experimenting with stalls for a bit; starting a 10 day vacation tomorrow.

 

[SeanAndHis80]

Thanks Chaldaean - I owe you

..I am guessing LSPV is not the culprit then.

 

[retrofive]

After work, I went back to the hill. I started at the top this time and headed nose-down. I put the transmission in Reverse and let off the gas. The truck slowly crept down the hill and stalled.

So, it is possible to stall in reverse going forward downhill. No matter which direction you're headed, I suppose it's just a matter of back-driving the engine, eh?

Also, the brake pedal feel/performance was the same going forward as it was going backward. The hill I'm using isn't all that steep (pictures below), so I'm not sure if I would notice the change in the LSPV actuation nose-up vs. nose-down (especially due to the fact that mine needs an adjustment to compensate for the 2" lift). Note sure though, I don't know much about the LSPV .

Also, does it take longer to start the engine after a stall like this because burnt air is sucked out of the exhaust manifold, through the cylinder and into the intake and it's hard to ignite this pre-combusted mixture immediately?

For a real-world feel, referencing the pictures below, if I pushed the brake pedal once just after the stall, I could stop the truck on the incline. However, if I pumped the brakes, the truck would roll back and stop about where the second picture was taken from. Quite a difference.

I'm done experimenting with stalls for a bit; starting a 10 day vacation tomorrow.

Thanks for your field testing nice job.