Very dangerous brake problem...

Hi DIESEL With respect why not avoid the problem altogether and start and finish the descent by driving thru the brakes - that way the brakes are applied 100% of the time. If you start the descent with out brakes applied, or if you are driving thru the brakes and you release the brake pressure then the beast will probably get get away from you:twisted: just like you experienced.

It's all about CONTROL.

Like you i'm no fan of HDC descents 'cos they're a bit quick for technical descents.

onebob

Quote:

---

Originally Posted by diesel

An array of comments, most of which totally miss the point.

I didn't really ask for common sense comments or quotes, nor advice on offroad driving. If you read my original post it was an experiment in a safe area that found the problem.
I can assure the few that posted in a derogatory manner that I'm more than aware of the basic physics of weight distribution, I'm also fully aware of how vehicles handle in different situations.

The point:

The front wheels locked, with no further braking force being allowed to the rear wheels. Yes, I know how to use HDC & the handbrake, that is not why I posted here. I also know why we use CDL.
I should have remained in full control with the brakes alone, it was a slow & controlled descent test.

Consider this:
The Prado, with no CDL or traction did what the disco could not, a little embarrassing to say the least.

This is a new problem, the Disco has performed this task without problem in the past. This thread is to discuss possible problems with electronics and the brakes without showing errors on the dash.
As the vehicle did slide it would have exceeded the 0.3g required for EBD, this was considered on site.
Also the HDC works fine.
I will be testing the shuttle valve switches and solenoid valves tomorrow as well as removing the SLABS ecu.

Thank you for all the replies, with the above taken into consideration I welcome further discussion.

---

I don't think anyone was having a shot at your competence level in their replies. they were simply pointing out possible solutions. The fact that you were apparently aware of 'driving through the brakes' etc vexes the question.... why didn't you do that rather than slide all the way down?

Anyway, I think you'll find that there are no faults in your system, it is just a fact of life that when you have virtually all the weight removed from the front wheels, the bigger brakes (yes, they're bigger than those on a Prado) will cause the lock up you experienced.

One final point, the Prado DOES have a CDL. It engages any time the vehicle is put into low range without input from the driver.

Quote:

---

Originally Posted by diesel

As the vehicle did slide it would have exceeded the 0.3g required for EBD, this was considered on site.

---

The rate of deceleration is calculated using the wheel sensors. If your wheels are locked and sliding there is no way the ABS can calculate deceleration.

Quote:

---

Originally Posted by diesel

I can assure the few that posted in a derogatory manner that I'm more than aware of the basic physics of weight distribution, I'm also fully aware of how vehicles handle in different situations.

---

Perhaps we are reading different threads? Every post I see in here is a pretty genuine attempt to address the issue. The issue with reverse descents in the D2 without cdl is well known and has been discussed many times in the past. What is being offered are possible ways to work around the problem.

The SLABS ECU is pretty thorough in logging faults so your best bet is to hook it up to diagnostic gear and check to see what faults are being logged. Any issues with the SVS or solenoids will give you the amigos, so if you have no dash lights it's unlikely you have problems in that regard.

cheers
Paul

Quote:

---

Hi DIESEL With respect why not avoid the problem altogether and start and finish the descent by driving thru the brakes - that way the brakes are applied 100% of the time. If you start the descent with out brakes applied, or if you are driving thru the brakes and you release the brake pressure then the beast will probably get get away from you:twisted: just like you experienced.

It's all about CONTROL.

Like you i'm no fan of HDC descents 'cos they're a bit quick for technical descents.

onebob

---

I understand what your saying onebob, I was doing this, hence the issue. As the vehicle left the level surface (with brakes controlling the vehicle) she slid.
Yes, if required in a situation I could use the handbrake or the HDC but I should have been able to descend slowly.

Quote:

---

I don't think anyone was having a shot at your competence level in their replies. they were simply pointing out possible solutions. The fact that you were apparently aware of 'driving through the brakes' etc vexes the question.... why didn't you do that rather than slide all the way down?

---

I did not take any responses as an attack, more of 'missing the point'. Maybe a little too direct, I was simply trying to keep it technical rather than "Remind me not to get in a 4x4 with you" & "The rules of offroading are"...
If I wanted these responses the thread would be titled "Advice please". I'm not attacking either, just really wanted tech more than advice.

Maybe everyone missed the first & following posts that say 'experiment in a safe area'... This is why I did not do any of the above in this instance, that would have been a pointless test, yes?
This is what triggered my response.

Quote:

---

Anyway, I think you'll find that there are no faults in your system, it is just a fact of life that when you have virtually all the weight removed from the front wheels, the bigger brakes (yes, they're bigger than those on a Prado) will cause the lock up you experienced.

---

The lock up should not have happened in the manner it did. Hence the thread. If more pressure was applied to the brakes,no more force was directed to the back wheels. In fact nothing above slight braking was found at the rear wheels.

Quote:

---

One final point, the Prado DOES have a CDL. It engages any time the vehicle is put into low range without input from the driver.

---

This would make sense after seeing it in action, the driver does insist that it does not. I know nothing about the Prado.

Now for an update:
It appears upon initial checks that there is an internal mechanical problem with a shuttle valve. This does require further investigating.

Hi mate, even if there is a small problem with a shuttle valve... and I'm wondering how you have established this to be honest since a shuttle valve problem will normally trigger the 3 amigo's, I really don't see that it is the cause of the problem with which you started this thread????
You have knowledge of the physics etc, those facts don't change, that's physics.
IF you had a CDL and it was engaged, your D2 would have behaved in a similar manner to the Prado.... better or worse.... who knows, but it would have been SIMILAR.
There is a group in Vic not associated with this forum who actually made it mandatory that a CDl be fitted to D2's if they were to take part in their trips since they tended to be on the more extreme side of things. The reason.... little or no control on steep descents in reverse.
I've owned 2 D2's, the first had no CDL when I got it, I had the entire thing fitted and transformed the off-road performance of the car. The second is a D2a which came with the CDL. I honestly wouldn't venture too far off road without a CDL (I also have air lockers front and rear these days).
Anyway... all the tests in the world won't change the facts. D2's with no CDL are **** on steep hills in reverse.

Spot on Wardy. If he got away with backing down a hill before without a problem then I would say that he was very lucky toget away with it. The simple fact is YOU NEED A CDL IF YOU ARE GOING TO DO ANY SERIOUS 4WDING.

I actually havnt heard of any issues lately except for yours but in the early days there were many "close calls" and serious accidents after people tried to back down a hill with no CDL.

Quote:

---

Originally Posted by walker

Spot on Wardy. If he got away with backing down a hill before without a problem then I would say that he was very lucky toget away with it. The simple fact is YOU NEED A CDL IF YOU ARE GOING TO DO ANY SERIOUS 4WDING.

I actually havnt heard of any issues lately except for yours but in the early days there were many "close calls" and serious accidents after people tried to back down a hill with no CDL.

---

Thanks for the info guys, I have a cdl, and use it, but didn't know about this issue, I might have been lazy one day and put myself in the same predicament not realizing the danger. Good heads up.

Cheers
Kev