Steepish inclines and 'faulty' brakes???

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Originally Posted by Samblers

If the centre diff is locked would this not tend to balance out the performance of the brakes anyway? Was the centre diff locked when you were doing all of this?

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I discussed this with my hubby.. as I was under the impression that it was but he insists that the front wheels were locked and sliding while the rear wheels were turning.. hence the jury is out on whether it was locked or not.

It was not locked yesterday, there was no need to lock it as the track was not difficult or rough etc. :)

A couple of things.
Was the center diff lock engaged?

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I discussed this with my hubby.. as I was under the impression that it was but he insists that the front wheels were locked and sliding while the rear wheels were turning.. hence the jury is out on whether it was locked or not.
It was not locked yesterday, there was no need to lock it as the track was not difficult or rough etc.

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If the track is steep enough to warrant the lower gears or low range being used, then do lock the center diff as well.

ABS has caused a bit of grief with a few vehicle's I have heard about that have been reversing down the steep stuff and the ABS does it's thing.

My purposed fix, but I haven't done this yet, so I invite comment about this.

Find the wire going to the center diff lock light and feed it to the coil of a normally closed relay with the contacts cut into the ABS wire coming from the fuse box.
So CDL light on, relay opens and there is no ABS as the power to ABS is cut by the opening of those normally closed relay contacts.
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Originally Posted by Sue

It was not locked yesterday, there was no need to lock it as the track was not difficult or rough etc. :)

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As per the above, this is not a good idea - if it's steep enough for low range the lock your centre diff. With the exception of steep driveway/trailer manoeuvring the best way to think of the centre diff lock is like a 2wd Jap truck's lever - I.e. If they'd be in 4wd, you should have your centre diff locked.

Beyond the drivability issues that not locking can create, it will also reduce your TC life dramatically....

Edit: not saying this is the main issue you're having - but it's relevant to your first 'incident'.

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Originally Posted by Sue

Thank you everyone!

I'll definitely go and get my mechanic to look at the transfer case selector shaft! I hope that is the problem and that I can get it sorted as I am now wary about any hill climbs which in time will ruin any sense of fun I get from a 4wd day out.. it's just not enjoyable wondering at which moment you're going to be careening downhill out of control.. :eek:

And just for the record, at no time was I trying to change the gears from low ot high and vice versa.. the lever has simply jumped out of place on it's own. I am wondering if that might have something to do with the angle the car is on as it's never happened on flat ground before.

And thank you Blacknight for the info.. it confirms that what I was trying to do what correct.. except it didn't really have an effect and I suspect that is because the front brakes I believe apply about 70% to the rear's 30% and with the cars nose in the air and all the pressure on the rear brakes they really didn't have a chance at halting the car quickly. Does that make sense or am I talking dribble?.. :)

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no you're about on the money.

you do need to be careful with the CDL selection, its also biased towards a centeral position (not designed that way but they do tend to do it because of the layout of the linkages and the boots on the lever) if its jumping out of range then its also just as likely to throw out of CDL when you're not expecting it.

The brake bias distribution problem VS weight distribution on hills is well known and most real 4x4's get around it by transferring brake torque through the driveline. (in part this is why when I teach beginner off road driving that for each obstacle you must pick the gear you need before you get there and just before you enter the obstacle you hook your clutch foot under the clutch)

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Originally Posted by wrinklearthur

A couple of things.
Was the center diff lock engaged?

If the track is steep enough to warrant the lower gears or low range being used, then do lock the center diff as well.

ABS has caused a bit of grief with a few vehicle's I have heard about that have been reversing down the steep stuff and the ABS does it's thing.

My purposed fix, but I haven't done this yet, so I invite comment about this.

Find the wire going to the center diff lock light and feed it to the coil of a normally closed relay with the contacts cut into the ABS wire coming from the fuse box.
So CDL light on, relay opens and there is no ABS as the power to ABS is cut by the opening of those normally closed relay contacts.
.

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My understanding is that you won't have TC if you disable ABS, which will probably mean you'll find yourself reversing back down more slopes.

Personally I've never really had an issue with reversing down and ABS. Reverse in low range being pretty slow, if you need to go slower just try not to lock up the brakes.

I have a TD5 so can choose to disengage TC if required, as BLK night said, although I very rarely do so.


Ian.

I think there's a risk that two seperate issues might be being conflated - might be better to try and isolate the issues in order to figure out what's going on. i suggest you get the 'jumping out if gear' issue sorted and then go and have another play with the brakes. This way you'll be able to determine if the brake issue was just related to the vehicle 'getting away from you' (due to the loss of an engaged gear) or whether something else is going on (and if something else is going on you'll have your gears to control it in any event).

Without trying to sound like a know it all, my Puma has done plenty of loose steep stuff with stops involved (for a number if reasons, including my bad driving practices!) and I've never had the kind of braking issue you've described - which makes me think you've either a) got a genuine issue with your brakes/ABS or b) it may be the initial loss of control leading to a speed condition that is uncontrollable while travelling in reverse with a (possibly (and not surprisingly) panicky) braking response.

Just some thoughts.

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Originally Posted by mools

My understanding is that you won't have TC if you disable ABS, which will probably mean you'll find yourself reversing back down more slopes. -------

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Thanks Ian

I must admit that the Traction Control ( TC ) function in the later Land Rovers was forgotten when I made the suggestion to disable the ABS, as I have only ABS on my model, a 1997 SE7 Discovery.

Does the TC function safely in reverse in a vehicle fitted with Traction Control?

If in TC equipped Land Rovers, that relay that I proposed, is switched not by the CDL light, but by the reverse light switch instead, would reversing then be safer with both TC and the ABS off?
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TC and ABS work both forwards and backwards.

ABS can cause an unwanted gain in speed on descents because of the following.

1 wheel locks, the brakes release on that wheel. In theory this means that it regains grip and the brakes reapply effectively. In some circumstances the loss of braking transfers the braking effort to other wheels which are right on the margin of traction, these now slip on the surface and lock up causing ABS to release the brakes on them. This cycle repeats and compounds as you gain speed on the loose surface. (its 1/2 of the same principle as why it takes an ABS vehicle longer distance to stop on a pea gravel road than a non ABS vehicle with the brakes locked)

TC shouldnt come into effect when executing a stall recovery as you are descending using the engine to retard wheel spin not applying power.

and yes, TC, ABS,HDC, Hill start Assist (some versions) and a lot of other brake related acronyms all rely on the same box of hudroelctramechanical mayhem to work, pulling the master fuse for it (or the fuses related to the controlling ecu/sensors power supply) fits into the catagory of "Bad Idea, if you wanted to drive like you didnt have it whyd you buy a vehicle with it?"

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Originally Posted by wrinklearthur

A couple of things.
Was the center diff lock engaged?

If the track is steep enough to warrant the lower gears or low range being used, then do lock the center diff as well.

ABS has caused a bit of grief with a few vehicle's I have heard about that have been reversing down the steep stuff and the ABS does it's thing.
.

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And that makes perfect sense, except this track was not steep enough to warrant using low range. I was in normal high and only changed to low to reverse down once I realised I had no gears. :)

The centre diff lock seems to often jump out of place, so when it is needed it is always applied - however the car seems to just pop it out quite often. I know I'm not the only person to have this problem as I've had a few people tell me that theirs does the same thing also. So as for the original question that was asked about the first incident.. yes the centre diff lock was applied.. but I'm suspecting it dropped out on the way up the hill. :)

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Originally Posted by Blknight.aus

you do need to be careful with the CDL selection, its also biased towards a centeral position (not designed that way but they do tend to do it because of the layout of the linkages and the boots on the lever) if its jumping out of range then its also just as likely to throw out of CDL when you're not expecting it.

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Yep that's exactly what it is doing.

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Originally Posted by Blknight.aus

TC and ABS work both forwards and backwards.

ABS can cause an unwanted gain in speed on descents because of the following.

1 wheel locks, the brakes release on that wheel. In theory this means that it regains grip and the brakes reapply effectively. In some circumstances the loss of braking transfers the braking effort to other wheels which are right on the margin of traction, these now slip on the surface and lock up causing ABS to release the brakes on them. This cycle repeats and compounds as you gain speed on the loose surface. (its 1/2 of the same principle as why it takes an ABS vehicle longer distance to stop on a pea gravel road than a non ABS vehicle with the brakes locked)

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That is actually a very scary thought! :eek::eek::eek: