Excessive brake pedal travel

[frank rabbets]

Front rear bias is quite a serious thing to experiment with. I built a 500 bhp Ultima with 13 inch wide tyres. The only thing the factory locked together was the brake balance between the front/rear brake master cylinders. After I built the car it had to go to the factory for final checking and SVA approval. It was at this point that the bias bar was drilled and pinned. Even for track days you could not alter the bias without deliberately unlocking what the factory had done.

 

[frank rabbets]

Re RM184E Page BR 66.

Looks like the bias ratio should be 80 front/ 45 rear. That is with a rear axle load of 1150 kg/ 3535 lb . Not clear if that is the unloaded weight of the car ?? Anyone know??

 

[Bat21]

I don't know if that load sensing valve is a bit of over thinking or necessary. The theory is that it is a no no to have the rear brakes lock up because then you spin the car. The load sensing valve safely increases pressure to the rear wheels if you put more weight over the rear wheels. In by passing the valve it could be that all pressure goes to the back which would be dangerous.

Thanks Frank, I know the theory behind its function.... I just wondered if anyone here had done it and the results were acceptable.

I am going to call RoughTrax in a few minutes and order a new master cylinder £57 inc VAT, while on the phone I will ask if they will replace the faulty LSV as it is only a few months old.

... so just by pass it and go for a spin...

I take it you don't mean literally

 

[frank rabbets]

I've just done a google on other forums where people have bypassed the valve and have had rear wheels lock up when the car is lightly loaded on the back.

Chris's idea of an adjustable valve seams a good idea if the expense of a genuine is to be avoided. I'd rather have one of those than a cheap copy of the original. Also with the standard set up the valve needs adjusting and special tools are needed . Page BR 66.

Hope you sort your problem OK. Are you going to just change the valve and keep the original m/c in for a bit to see if it was the valve drawing air?

 

[Bat21]

Thanks once again Frank.

I have just had a look at RM184E and see that it looks very difficult to set this thing up without the correct gauges etc. So, I'm going to have a play with the original one and seal it up so that it functions open all the time. If it has serious effects on locking the rear wheels I will look at getting a 3 position valve that Chris mentions.

Out of interest does anyone know the fluid path through the LSV? Obviously there is the fluid in port, + the outlet to the rear brakes. Where does the 3rd line go to, it runs back to the front of the car but where to?

I have a feeling my master cyl hasn't been performing as it should for some time Frank, so I will be replacing that

 

[frank rabbets]

I don't know where the pipes of the valve go to without lying underneath and tracing them.

When you've set everything up you could try baking round a corner on wet grass with no weight in the back. If the rear wheels don't lock perhaps that would be good enough for the road. It's just occurred to me that there might be an upper limit on the rear brake efficiency for the MOT and again that might be somewhere to test it to see if it is safe. I would have thought the MOT tester would know a safe approach.

 

[frank rabbets]

I think that 4th pipe must go to the ABS actuator. If so replacing the valve or blocking it off might be a bit involved. Don't know for sure what to do.

 

[Chris]

The third pipe I do believe is a bypass. It goes back to the front of the car from memory. When the valve operates it doesn't just shut off fluid, it sort of siphons what it wants and returns the rest. OK OK it maybe something to do with ABS too, but in terms of the pipe I seem to recall that's where I traced it.

 

[Dave2000]

The loss of peddle pressure is almost certainly the LSV, for the money I would put in a MC just for the hell of it TBH. It does not take long for pressure to fall with even the smallest of leaks.

Shame about the Rough Trax failure, I doubt there will issues with them replacing it FOC but have never dealt with them.

By coincidence the other evening, I was in the middle of filling an order for the first time with RT for around 500 quid and noted some 'iffy' marketing which always rocks my boat and makes me shudder, I spent 400 with Milner's and the remaining 100 with EURO 4x4 instead!

Back to the LSV, it is supplementary to the ABS, removing it has been done but I am of the opinion it should stay as it is, even increasing ride height a couple of inches can ruin your brake balance. I have often wondered about the amount of people who have removed the ABS system on their cars, but not just 80's but many other older 4x4's as well, most if not all claim a great improvement but find it difficult to quantify WHAT they find improved. It does seem that every claimant has by coincidence lifted their vehicles which is easy with a couple of pairs of springs but, just how many take the vehicle to the dealer to have the LSV set correctly?

Noting the various comments about brake bleeders, vacuum or pressure, IMO much of a muchness TBH, I have used both in the trade but have always gone back to the pressurised system. Yes the vacuum system can pull air through the nipple threads but this does not affect brake performance as the fluid is still being pulled through the calliper. The issue is that as the air is being drawn through the threads of the loosened nipple it tends to reduce the 'pull' on the fluid so tends to take a bit longer, this along with the continued need to keep to keep checking the reservoir is my reason to stay with the pressurised system I use a pressurised vessel type, put 5 litres of fluid in, connect, a few pumps to about 10 psi, and simply walk around loosening the nipples, I can bleed a typical car in around 5/6 minutes. The pressurised system does have a couple of drawbacks though, you have to be careful of over pressuring ABS systems, modulator valve damage is a very real possibility, the other problem is the adaptor used for older cars, this tend to be difficult to seal up, I have modified mine so it now seals up first time every time, and if there is a leak of the seal, it makes a lot of mess very quickly, something the vacuum system does not suffer if you are careful with topping up.

Of course you could go and buy a Land Rover, I bleed them with my laptop

regards

Dave

 

[Chris]

The LSV really doesn't take any setting up at all in my experience. Having had one apart, there is no way that this thing is a highly complex bit of kit that on a 20 year old car need a scientist to set it up. I find that having a loosish surface is handy but not necessary. Drive forward, brake hard. Reverse up brake hard. Note the difference in braking effect. If it brakes harder in reverse than it does in forwards then you need to move the bias forward. Adjust until it brakes slightly harder going forwards than it does in reverse.

OK not scientific perhaps but I have lifted several 80s now and set them all up like this and not had any braking issues. In fact in Agadir this year I did have to do a full on emergency brake on Moroccan asphalt. All I can say was that I was mightily impressed and also more than a little relieved. Of course I wouldn't set up a Ferrari F40 like this, but frankly I think that if you went to a main dealer and said please set up my LSV for me, there'd be some pretty blank stares.

Even if you disagree with my farmer's method of doing this, just go and try your own vehicle on a quiet road and see how it feels forward and backwards. I cranked my LSV from one end to the other to see what difference it made to the bias and was frankly quite surprised. It really DID make a significant difference. My 80 GS has no ABS. Slotted discs all round, re-firbed calipers and braided hoses. Stops like a bitch even fully loaded. That's on 35's too.

As for the vac bleeder, best £30 I have spent. Oh well there was that time in Amsterdam I suppose ...

 

[Bat21]

The loss of peddle pressure is almost certainly the LSV....

Okay I will get this sorted before I look at replacing the master cylinder

.... for the money I would put in a MC just for the hell of it TBH....

I have two motorcycles but I'm guessing these aren't the 'MC' you mean..... probably a dumb question but, what is an MC?

There is no ABS on my 80, I like it that way as there is less to go wrong

The problem I have setting the LSV is knowing where to start. My 80 has a 3" maybe 4" lift and there is what appears to be a lengthened shackle on the axle.

Problem is the load sensing spring bar could be bent, is it supposed to be straight or is the bend intensional?

Given that there is only a 12mm adjusting range, I need to be starting off somewhere relatively in the middle. How much pressure should the valve end of the spring be putting on the piston pin to start off with?

 

[Dave2000]

All due respect Chris but that method IMO is not even close. The pressures are set 'static', reversing and braking will tell you nothing. Brake bias is always set for forward motion as the weight of the vehicle is thrown forwards, the front dives and the rear lifts taking the load sensing lever with it, the greater the distances between the body and the axle the less pressure is applied to the rear brakes. I know you understand how it works but I am pointing out why the reversing and braking method is flawed. As you said Chris not very scientific at all, you also said how much difference it made when trying the adjustment from one setting to the other, your 'farmer's' method may or may not be close but you simply cannot substitute a 'loose surface' for a decent set of gauges.

Not wanting to go too deep into this but, even the choice of spring rates can affect how the brake bias works, softer front springs equals less bias to the rear and vice verse. A manufacture sets the 'base' setting for the bias based on an asphalt surface with a typical coefficient of friction, I cannot remember the figures but when loading asphalt to pour into pavers we could not use too much 'release oil' or it affected the final friction factor, i.e. the typical traction environment the vehicle will be used in. We used bias valves in rally cars that would be on grippy or loose stages adjusting for each, and given that the typical road car will spend most of it's life on tarmac that is what the factory setting will be based on.

The more I think about this the more it worries me about the amount of cars lifted that have not had the brake bias recalculated. Don't get me wrong, this is an age self preservation thing and not a 'high an mighty' way of thinking, I am after all one of the guys years ago that used to fit Ford Classic front struts with disc brakes on our V8 Anglia's (stop nodding Frank ), and it did improve our braking power at the front but, the rear drums were useless and how much they contributed to braking is unknown but, they never locked so you never spun. Then we fitted the stronger 'Atlas' axles and got rear discs and they would lock the rear if you breathed on the pedal, we had dual master cylinders with adjustable push rods, at the end of the day there was never a perfect setting for all conditions.

Getting the brake bias right on a standard car let alone something raised, or with a drawer system or other unknown weight and so on is near on impossible. Suffice to say, if you get it working how you like it then that is good enough (for you) but, when in an emergency situation where you stand on the pedal and REALLY need to stop and god forbid you hit let us say a wall and suffered damage, would a little extra rear braking bias stopped you say a foot shorter and saved the prang? Given the various modifications people make to their vehicles that I would bet in reality there are very few cars set up correctly.

This is such a subjective issue that it generates all sorts of opinions but, IMO Mr 'T' got perhaps 98% of the LC 80 design right 1st time, the early braking systems being (shall we say) adequate were reworked, given the re-development they had to put in, I doubt they come up with the pressure figures for the LSV by chance.

regards

Dave

 

[Pumpy]

Of course you could go and buy a Land Rover, I bleed them with my laptop

Over here, they do it with a cash register Boom Boom! (I'll get me coat )

 

[Dave2000]

Over here, they do it with a cash register Boom Boom! (I'll get me coat )

Very good.....

regards

Dave

 

[Dave2000]

@BAT21 MC =Master Cylinder.

There is insufficient movement available in the stock mount, you will need the shackle or a mounting plate to match your lift and recover the adjustment. See comments above re setting LSV.

regards

Dave

 

[frank rabbets]

Twin cylinders on the Ultima and DB4gt's I had Dave. Twin braking systems but being separate cylinders allowed you to set the bias unlike a tandem. Some cars just have different hydraulic diameters to set the bias and others have a fixed valve, put in I reckon because the got the original calcs wrong or just used existing cylinders which were close and to hand.

BAT the bar is bent on the standard setup.

It could be that the design of the LSV is somewhat fail safe so may be safe if fully open or fully closed. i.e. there is no warning in the manual on incorrect adjustment.

 

[chapel gate]

There is plenty of info on mud about adjusting the lspv and removing it. Iirc for a 2" lift its moved a 1/4 inch, cant remember if thats up or down though...

Ruftrax do a mc made by aisin.

Iirc when i removed my abs pump the pipe going to thd front of the vehicle from the lspv went into the pump then to the mc. When the pump was removed i joined these together.

I have yet to adjust the lspv after putting a two inch lift on, i havnt noticed any difference though tbh.

 

[Chris]

Sorry Dave, respect back and all that, but I reckon you might be over thinking this one. This works extremely well. To say it's not even close is frankly a bit unfair. Of course, yes, I understand how it works and the effects of inertia but go and try your braking forward and in reverse, hard and you will be able to tell which way the bias is currently weighted. Sorry but it is in my view close enough. Brakes are the difference between living and dying and not something I'd take lightly so I don't need a lesson in persuasion trust me. I have stood on the brakes and it's very stable and extremely effective. I also tried it in snow to see if it was stable That was the point about a loose surface, it stops you creating flatspots and means you can get an easy indication if you are locking up. Remember that I said I don't have ABS.

I find it hard to imagine that I could stop my truck any better and as I said when I had to go to full condition 3 braking in Morocco it stopped very well. The absence of damage is testament to that. The LSV is not a sophisticated control device. In fact it's pretty rudimentary. The point about driving backwards and forwards with hard braking is that it very quickly DOES give you an indication of the balance and braking effort between the front and back. I think what is more dangerous than adjusting it is not knowing that it needs to be adjusted as you point out. I am very pleased with my braking (something that I am genuinely fastidious about) and this is the 4th 80 I have set up this way and two Colorados. Certainly none have ever failed their MOT on brakes nor crashed. But as I have said already, I wouldn't set up a performance car like this where I was doing 140 through the trees. In my view it IS better then 'close enough'

 

[Dave2000]

@Chris, I hear you Chris but this is where you invalidate your own claim.

Quote "But as I have said already, I wouldn't set up a performance car like this where I was doing 140 through the trees. In my view it IS better then 'close enough' " Unquote.

140 and hitting a tree is going to leave a bruise to say the least, hitting the same tree at 70 MPH in a car with a weight approaching three tons is not exactly going to be a shaving nick either. I think it is all about the 'what if' factor, i.e. what if the tree was a further foot away from you when you started your emergency braking, would you have hit it if your bias was perfect as opposed to IYO 'close enough'? I would concede though that when faced with the inevitable 'punching a hole in the scenery' and standing as hard as you can on the brakes then you have already pushed your luck too far and the accident will happen, the amount of brake bias is not going to make that much of a difference.

As I mentioned this is a subjective topic and as you pointed out the device is pretty basic, how much difference it would make in a real life emergency I do not know. As my tyres will be nearing the end of their life early next year I am inclined when I get xmas and other workload out of the way to try some braking tests using the ABS, disabling the ABS, and then moving the bias adjustment from one extreme to the other. I will then get a set of gauges on it and try after setting it to Mr 'T's' figures, an interesting test coming up.

My car having stock suspension/tyre sizes, and an all new brake system will make a good test bed IMO, plenty of quiet roads around here, I also note your comments about brake performance in snow, and would say without ABS your vehicle will stop quicker, we (off road club) always disable ABS when being 'unruly' in the campo, the build up of loose surface material acting as a wedge in front of the tyres will outperform the ABS as it continually tries to deal with poor surface conditions.

regards

Dave

 

[Chris]

Dave, be sure to let us all know how you get on with the factory gauge set up. Sure to be interesting and informative. Meantime I am not living in fear when driving mine I have to say.

It is interesting that in your words, this is subjective but somehow I am wrong even though you don't know how much difference it would make in real life.

Can't really say about the ABS and stopping in snow. Certainly you retain more control with the ABS but having two 80's the GS certainly has much better brake feel and much more pedal pressure. Given that mine weighs more than three tonnes and has a lot of rubber on the road, it's very hard indeed to get it too lock up. It tends to just stop. This is why the loose surface helps in actually allowing a lock up to see if the front out brakes the back. Otherwise it's very hard to tell; it doesn't shimmy about or anything. My other 80 is stock and hasn't had the LSV adjusted so I have a direct comparison. However, regardless of that the tyres are abysmal and bias isn't an issue when the car won't stop in the first place. The LSV is only one of many factors in getting the brakes right.