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101RRS
4th November 2009, 05:26 PM
I was out doing some 4wding in the 101 yesterday and some of the descents were on fairly loose and powdery. As usual the rear end of the unloaded 101 was skittish wanting to over take the front and at times I am sure the rear unloaded wheels were turning in different directions due to diff effect - certainly sounded like it (rear Detroit going in this week will fix that).

I consider the main reason 101s have propensity for the rear to overtake the front is because of the load apportioning valve. When rebuilding my 101 I had the valve out and found that in the unloaded state there is virtually no brake fluid going to the rear brakes and I suspect that with the weight transfer to the front when going down steep hills and being unloaded the valve may actually be stopping the rear brakes from working.

So has anyone removed the valve and how has it impacted on braking - I guess the main issue will be rear brake lockup when unloaded - particularly in wet weather.

Garry

Blknight.aus
4th November 2009, 05:33 PM
dont remove the valve change the adjust ment of the rod on it.

its a fine art but doable.

fraser130
4th November 2009, 06:10 PM
Garry, I know it sounds wrong, but if the back wheels received no braking, it would skid forwards down a hill, if they were geting too much pressure and locking before the front, then it would try and turn around. Get a matchbox car and lock the back wheels with blue-tack and put it on a tray and tip it till it slides and it will do a 180!
Of course the main issue is probably just the fact that there is no weight in the rear to aid traction on a steep decent in a 101.

Fraser

Lotz-A-Landies
4th November 2009, 06:45 PM
One of the problems of the 101 has always been rear end wanting to overtake the front. Part of the reason for this is the short wheelbase in proportion to it's gentre of gravity and width. The problem would be nost noticable on steep decents and braking at speed when unloaded. You only have to look at pics of the rear wheels off the ground and the classic of the 101 ambo rolling in the UK - Salisbury plain I seem to remember.

Not a whole lot that can be done about the situation other than selecting the correct gear on downhill slopes and driving out of it when the rear starts to go.

otherwise you could add 20" to the wheelbase! :twisted:

Blknight.aus
4th November 2009, 07:08 PM
Garry, I know it sounds wrong, but if the back wheels received no braking, it would skid forwards down a hill, if they were geting too much pressure and locking before the front, then it would try and turn around. Get a matchbox car and lock the back wheels with blue-tack and put it on a tray and tip it till it slides and it will do a 180!
Of course the main issue is probably just the fact that there is no weight in the rear to aid traction on a steep decent in a 101.

Fraser

that correct but only for a wheels locked situation, When your trying to avoid "weight shift" braking problems it goes the other way round. if you're braking the front axle too hard on a down hill with a top heavy vehicle it can lift the back end to the point where theres not enough traction to hold the rear wheels even though they are still turning and then you slide sideways.

it depends on exactly why your loosing traction. trust me a 101 with a tall load up against the front of the load space is plenty easy to lift the back axle on a braked descent, try hard enough and you can do it on a mog too.

101RRS
4th November 2009, 07:08 PM
Thanks for the comments - nothing I have not already thought about - hence the question whether anyone has actually removed the valve and what were the ramifications.

Dave - there is only about 1mm adjustment so is a hit or miss affair. Full on or works a designed. Was thinking about an adjustable one with the adjuster in the cabin but I do not think they are legal.

Fraser - not so sure of your logic - the momentum of the light unbraked rear takes over and tries to overtake the braked front - like a semi jack knifing - all OK until trailer tyres loose traction and then the trailer momentum takes over and the trailer overtakes the braked prime mover.

Diana - you are spot on for the reasons - if you take a close look at the back tyres of that ambo at the start of the hill you will see the rear passenger wheel turning backwards due to diff effect on a very slippery surface - brakes would have been applied at this point but not operating the rear wheels. I am not saying having rear brakes will help the situation but it might help.

Cheers

Garry

fraser130
4th November 2009, 07:24 PM
I agree with both of you completely, however:), if you are on a steep decent, and you are getting to the point where the back wheels are light enough on the ground to lose sideways traction, I don't see how asking them to provide breaking traction would result in them not locking up, and you lose all traction anyway.

I think the problem is basically the weight distribution of the vehicle to start with, if the rear is in a situation where it is so light to lose directional stability, then I would be very surprised if it could provide any breaking effort. Ideally your front brakes should lock a fraction before the rear.

Hmmmm....this could be an ongoing debate....;)

101RRS
4th November 2009, 08:34 PM
I agree with both of you completely, however:), if you are on a steep decent, and you are getting to the point where the back wheels are light enough on the ground to lose sideways traction, I don't see how asking them to provide breaking traction would result in them not locking up, and you lose all traction anyway.

I think the problem is basically the weight distribution of the vehicle to start with, if the rear is in a situation where it is so light to lose directional stability, then I would be very surprised if it could provide any breaking effort. Ideally your front brakes should lock a fraction before the rear.

Hmmmm....this could be an ongoing debate....;)

While the rear is light it is not quite that light as evidenced in me wrecking a substantial ramp with the rear wheels (see my Oops Thread). If you drove a disco or a defender down a steep loose hill without any rear brakes a similar effect to the 101 would likely occur.

Back to the question though - any 101 owners got their valve removed?

Garry

Blknight.aus
5th November 2009, 12:05 AM
I agree with both of you completely, however:), if you are on a steep decent, and you are getting to the point where the back wheels are light enough on the ground to lose sideways traction, I don't see how asking them to provide breaking traction would result in them not locking up, and you lose all traction anyway.

I think the problem is basically the weight distribution of the vehicle to start with, if the rear is in a situation where it is so light to lose directional stability, then I would be very surprised if it could provide any breaking effort. Ideally your front brakes should lock a fraction before the rear.

Hmmmm....this could be an ongoing debate....;)


what hes after is lowering the torquing effect of the front axle lifting the back of the vehicle off of the ground and lowering the effectiveness of his rear brakes.

by putting more bias to the back axle it starts slowing things down before the reactive force of the front brakes can lift them off of the ground.

The proportioning valve is ment to stop it from happening but it doesnt once you reach a certain point because as the rear suspesnsion unloads the proportioning valve gives it "hang on theres not much weight here at the back I need to lower the brake pressure so that the back wheels dont lock up and we go ass about" what happens then is the driver mashes the brakes down harder to try and pull the vehicle up the front brakes bite on harder increasing the torque reaction and lifting more weight off of the back axle. As the rear suspension unloads...........

101RRS
5th November 2009, 07:42 AM
An extreme example :o
https://www.aulro.com/afvb/

Blknight.aus
5th November 2009, 03:01 PM
put the boosted LWB brakes on the front of an unladen series shorty and you can do the same thing if you drop the front tyre pressure.

Kermit used to be great at it :)

iain reed
5th November 2009, 06:36 PM
nice pic of my 101 ... yes i had some problems when i did the brake pads at lvs george and i were "drifting " in the old girl but a bit of adjustment pulled her up straight , less on the back from memory ?? work fine now

101 Ron
5th November 2009, 07:38 PM
I have a bypass pipe ready made to fit on my 101 proportioning valve .
My valve is locked solid and not working,
I have not fitted the by pass as everything is working well enough and any problems has been with the shoes or wheels cylinders ect.
The biggest problem going down hill in a 101 is the driver.
The forward control position of the driver tends to make the driver nervest at the best of times.
I find the stiff spring rates and tyres tend to make the rear jump around a bit at times..
I have found the 101 to have very good stability.
The trick is if you feel not happy going down a super steep hill and I usually use second low, plant the accelerator a bit if you think the rear is getting unsettled and then very slowly ease it off again.
With the 101s low gearing why would you want to use the brakes any way.

101RRS
6th November 2009, 12:08 AM
With the 101s low gearing why would you want to use the brakes any way.

Because some smart arse dirt bike rider coming up a hill in the opposite direction decides to cross from his side of the track to mine right in front of me ;) and the back end did not like it :( when I needed to stop in a hurry - was in first high.

Garry

101RRS
8th November 2009, 02:28 PM
The British Army reliability requirement for a 101 was a 95% chance of being able to complete a 75 mile radius mission (ie 5% of 101s breaking down is OK - ignores battle damage).

In 1978, 101s were only achieving 93% reliability in the British Army so a report was commissioned on these issues - data was obtained via a trial. The report makes interesting reading.

The brake section makes interesting reading.
http://i42.photobucket.com/albums/e334/gazzz21/101Test.jpg

Note that in 1978 the British Army considered the 101 to be dangerous to drive in the unladen state :o.

Unfortunately I do not have the report which says what was done about the apportioning valve - my assumption is nothing.

Garry