Brake bias valve?

18th November 2007, 14:01

With the ongoing saga I'm having with my brakes, some folk have suggested that the problem could be down to the braking bias. I.e., too much braking power going to the rear! Apparently, when you lower the rear of the car, there's a valve which detects the difference in height, and if it's lower at the back (as if more weight is in the back) this valve will apply more braking power to the rear. Does anyone agree / disagree with this?

Well, I've been under the car today, but I couldn't see jack shit! Here's some pics:

18th November 2007, 14:09

yup it's bang on, when you lower the rear the valve 'thinks' the rear is loaded so applies more pressure to the rear. it's piss easy to fix, jack the n/s/r of the car up and you'll see the valve - there are 2 springs, one small and one large - unscrew the longer of the two and test drive the car. then it's a case of testing until the car feels ok under heavy breaking.

18th November 2007, 14:39

yep agree, the valve needs to be adjusted and then test drove.

18th November 2007, 14:42

OK, thanks guys. But where is the valve? I've jacked up the rear near side, as to take those pics. But I didn't see anything anywhere!?

18th November 2007, 14:54

hi,

it will be attached to the chassis of the car, and the other end connected to the rear beam. i think its on the drivers side but iam not sure.

ill try and find a pic

18th November 2007, 15:03

definitely on the passenger side, look where the torx bolt for the torsion bar is (the left of the 2 torsions bars as you're looking at it) then look up and to the right and you should see it, it connects to the rear beam.
look here if you need more help

18th November 2007, 15:04

i carn't find any pics mate, but like above, its there.

18th November 2007, 15:31

It's not looking good. According to Williams, 3 plug ECU models (which I have) don't have this bias valve, they have something called a EBD... That's what I read in those previous posts.

18th November 2007, 15:33

Do you not have a spring that looks like this? This is the brake bias valve...

18th November 2007, 15:38

Nope, ain't got one. Mine's all electronic according to Williams... I guss that means 1 of 2 things: 1) My braking problem is not a result of too much force being applied to the rear, or 2) Something with the braking system is shafted. Either way, I'm not a happy bunny.

18th November 2007, 15:42

I take it with it being electronic, it can't be adjusted anyway then?........

18th November 2007, 15:45

I guess so... But that might not be the problem anyway. I spent so long trying to figure this braking problem out, and I still can't do it! I'm seriously fcuk'd off now. Nobody knows what to do.

18th November 2007, 15:58

cant you fit a bias valve in the car especially as yours is stripped out it will look at home

18th November 2007, 16:39

I would have no idea how to do that!

18th November 2007, 16:52

you will need to run the brake pipes through the car

does this help

http://www.saxperience.com/forum/sho...ake+bias+valve

18th November 2007, 17:24

No, doesn't help. I wouldn't have a clue what I was doing.

18th November 2007, 17:40

What a crap situation. I've got a serious braking issue, which is making me scared to drive the car, and I haven't got a clue what to do to cure the problem.

18th November 2007, 18:12

what's your braking problem exactly (can't find your other thread)? If it helps, I had a braking issue with the rears locking,even after adjusting the bias valve after lowering the rear bars. I fitted new rear calipers and the problem has gone. Get your car into an MOT station and ask them to put your car on the brake testing machine, they'll be able to tell you if both calipers are working at the same efficiency or if one is working harder than the other (ie one is sticking).

18th November 2007, 18:20

Quote:

Originally Posted by Toad

It's not looking good. According to Williams, 3 plug ECU models (which I have) don't have this bias valve, they have something called a EBD... That's what I read in those previous posts.

i too have heard of this pretty saw you are right

18th November 2007, 18:39

Here you go Sean. There's a fair bit of info in this thread: http://www.saxperience.com/forum/sho...d.php?t=110824

I've already had it on the rollers at an MOT testing station, it came out perfect... I've had the brakes stripped down, checked, replaced pads, flushed the system a couple of times, the list goes on and on... everything is spot on. I have no idea where to go next with this!

18th November 2007, 21:55

Having given that a quick read, I'm still thinking the brakes are at fault. Have you had the EBD (electronic brake distribution) checked by Peugeot? They could get it on diagnostics and check for a fault. Incidentally did you check the master cylinder?
The other two possibilities I can think of are worn suspension bushes, or your front springs are cambered for driving on the right ie continental roads (longshot I know) - was a fault on Mk1 renault lagunas, renault forgot to fit springs to compensate for the camber of driving on the left and all the early lagunas pulled to the left and had to recall all of them. Which springs are you running? If they're all made abroad then that could be an explination? Mine pulls to the left when I let go of the steering wheel even after new suspension bushes and full tracking, I suspect the springs but have no real way of testing it.

edit: I've just read you have polybushes so it isn't that....

I can only suggest the above plus having the suspension tested, looking for bent wishbones, strut being bent etc

19th November 2007, 08:55

Sean, if you have a mo, can you please have a read through this topic I raised too. It's about how my car pulls to the right, even after the tracking being spot on. http://www.saxperience.com/forum/sho...d.php?t=111212

I haven't seen Peugeot about this issue. I might have to I suppose... I try to avoid main dealerships like the plauge!

I haven't checked the MC. What would I check for? A Peugeot specialist told me it would be worth replacing it, but I don't want to go replacing bits in the hope that the problem might be resolved.

With regard to my suspension, it's by Koni, and consists of lowered, stiffened springs at the front ( - 35mm) with uprated dampers, and uprated dampers at the rear.

If you look closely at that diagram of my tracking, the caster angle is a fair bit different side to side, I wonder if that could suggest something is a little bent? Also, as Adsayer picked up on, the camber is different side to side as well.

19th November 2007, 11:27

I'm not really an expert at reading those results, but the results do differ at the front on each side. I'd look at top mounts and or/hubs, top mounts because they hold the strut in position and so if they become worn they could 'sag' a little if you get me; the hubs because that's what the wheel mounts to - basically you've checked the wheels so start looking inward from there.

19th November 2007, 12:41

Yes if the results are out something will be bent, out of line or worn parts mate.

As for the brakes. The load sensing valve is there to see when there is more weight in the back of the car then this will put more make the back brakes work harder. (Ie if no weight in the back they work less if you have a load of fat chicks in your back seat they will work more )

So this is the problem you have if you have your car lowered its thinking there are fat chicks in the back of your car and making the rear brakes work harder.

This will be the same if you have the EBD system. I think there is a sensor on the system which will have the same effect as above but electroinc rather than mechanicly.

So id say ring up your dealer and ask the question. I think there would be a good chance they can calibrate the system so it thinks your car is sitting at a normal ride height and will make them work correctly.

If you dont want to do this get a paving slab or 2 and stick it in your boot this will help stop the brakes locking up.

Dont put a break bias valve in the system you will end up giving yourself more problems than its worth mate

22nd November 2007, 12:50

Thanks for all the input chaps.

Latest update... I'm taking the car back to SHM on Saturday morning. I'm going to get a complete health check done on the suspension. So the tape measures will be coming out and all sorts! Hopefully something will show up in the wash. Hopefully will find answers as to why the car has less negative camber on the right, why the caster is different left and right, etc, etc. Fingers corssed that this may very well have something to do with the braking issue.

I've got a friend at work who races a lot. He races old Spitfires, being kindda old himself too actually. haha. Anyway... When I told him about my braking issue, he came up with an interesting point. When I told him that I upgraded the front brakes, his first question was "What did you do to the back?" My answer being "Nowt..." He suggested that my issue may be that I'm not getting enough braking at the back, so under heavy braking, the rear could almost be driving the car forward. Fair point I suppose, and another thing to consider.

Anyway, let's see what happens Saturday, and go from there. If I'm really going to get serious with the car and racing it, perhaps I should put this whole iTB business on hold, and start looking more at suspension and getting it setup correctly. It would be good to get a decent kit that would easily allow me to adjust certain aspects, such as camber for starters. If I've only got negative 0.5 degrees on the front, then that's a really bad thing. I would need at least negative 2 degrees I reckon... Also, if I'm going to get it corner weighted, I will need more adjustable factors than i currently have. Anyone got any opinions on suspension kits that fit the bill?

22nd November 2007, 22:24

still need to update your thread with poly window pics

23rd November 2007, 11:14

Thanks for the pointer Ben, lol.

I've kindda got more important things to deal with at the moment though I'm afraid. Need to get this car working properly and safely.

23rd November 2007, 16:25

Think your mate has a point there mate but that wouldn make them lock up.

As for suspension etc for setting up the car etc your best off askin on a racing forum if your going to get serous with it. Or ring Deamon Tweaks they will certainly point you in the right direction.

23rd November 2007, 22:52

good luck tommorow hope it gets sorted

24th November 2007, 10:32

Thanks chaps. Will find out shortly...

The rears haven't been locking up to the best of my knowledge.

24th November 2007, 16:05

how you get on

25th November 2007, 22:41

Chaps at Steve Hill spent a few hours searching and investigating. Nothing obvious came to light. Everything suspension wise is tip top, and the car is very healthy. However, they did notice that the ride height differed left to right. The front left sits 5mm higher than the front right...

They also think the problem is on the right side, and it might be the strut. If you pop the bonnet, and look at the top mounts, where the strut pokes through, you can see that the strut comes throught at a specific angle. If you look at both of them, you can see that one on the left (as you are facing the front of the car) faces more straight upward, as opposed to the one on the right, which faces at more of an angle. Coincidence? Hmmm...

Been testing things with the brakes more today, and I'm leaning more and more towards the fact that the issue migh be caused by the rear wheels not getting enough braking. So, I'm going to get some better discs, and some top notch pads, and see where I go...

28th November 2007, 22:08

New pads in the post. Got some Ferodo ones coming.

Possibly more importantly! I've noticed the pad wear on the rear left is MUCH more than the wear on the rear right pad. In fact, the right pad is about half way, and the left is almost finished completely! I did think that the car was pulling left from high speed braking... Coincidence? If the rear right caliper wasn't working properly, how can I test this? How can I see if it's sticking? Odd how the rolling road didn't show any issue up with the braking. I remember when those pads went on... Don't you think it's odd that one side would wear almost twice the speed as the other side???

29th November 2007, 08:46

I did yet MORE testing and I think I'm on to something. I think...

If I brake gently, but firm, I can get the car to pull up quite quickly, and it's smooth, with no side to side pulling. However, as soon as I press harder, and really try to get the car to pull up hard, I can hear a ticking from the front left (sounds like it's from the ABS sytem) and the car goes spastic! Swerving right and left, feeling like I'm aquaplaning!!! Even though I'm not actually locking the wheels (you can tell when that happens) the ABS system is up to something. Does anyone have any ideas?

29th November 2007, 09:43

Have you been letting your car drink bottles of vodka lol

The rollers will only show the brake effort until the wheel locks up if there locking up at pretty much the same pressure then it wont show a problem even tho there could be one.

If one side is worn more than the other then something is wrong. You dont need to check if its sticking just take the sliders out clean lube up and put back it wont take long to do mate.

I thought you said the rears were locking up ?? So getting good pads discs etc will make that worse.

The ride height difference at the front wont help the rear braking because there will be different weight distrabuition to each wheel.

Unless the wheels lock or start to lock the ABS wont work anyway and if it did you would feel the peddle go up and down

29th November 2007, 10:17

No man, never said the rear wheels were locking up.

Yeah, the uneven pad wear at the rear is odd.

Like I was just saying... Don't you think it's wierd how the braking is perfect when you don't brake too hard? You can pull up pretty quick if you do it right. But as soon as you brake that little bit too hard (and not kicking the ABS in) it's a different ball game! All over the shop!

1st December 2007, 17:20

Some updates...

Ben popped over today, and we did a little testing with the brakes. We disabled the ABS system for starters and went for some test driving. Braking from speeds of around 40 - 50 were pretty much normal. A little twitchy, but fair enough. But as soon as we went on the motorway and got up to a decent speed, a quick press on the brake pedal shot the car straight to the left. I tested this about 3 times, and everytime it would wickedly pull to the left. So I know the ABS system isn't causing the problem.

We changed the rear pads afterwards. The pads seemed to have a fairly even wear to them, so I was wrong when I mentioned that it wasn't even a little while ago. The rear calipers slided back and forth OK, and there didn't appear to be anything obviously wrong with them. I haven't tested the brakes since the new pads when on, as I want to give them a chance to bed in.

So I'm still no further forward with the braking issue. I really need to get this sorted ASAP, as the car is deadly at motorway speeds.

Thanks for all your help today Ben! Nice one.

16th November 2008, 22:49

I think I may have a solution for you - had the EXACT same thing on a POS 205 I bought for a 100 quid that the owner neglected to tell me was a death trap. Take a look at the rubber bush on the lower suspension joint at the front. Mine had disappeared consequently each time I so much as tapped the accelerator I near on went through a bush or into the central reservation!

17th November 2008, 09:21

I don't have any rubber bushes, they're all poly... and new...

7th April 2010, 11:55

Quote:

Originally Posted by Andy_S

Do you not have a spring that looks like this? This is the brake bias valve...

where does this spring connect to? my spring is just loose