Don't like the adverts?  Click here to remove them

Help! Bias Valve layout

majic79

Member
Joined
Nov 9, 2012
Messages
183
Ok, I've done everything and started re-assembling, but I forgot to take a pic and not which pipe goes where. There's two input pipes from the front of the vehicle, I know where one of them goes, the other is on the same side as the output (goes to the centre flexi hose and onto the axle) and I'm a bit worried about confusing the two! Don't suppose anyone knows which goes where? Or can take a pic that shows which way around the pipes go?!

Thanks in advance
 
Here's one I prepared earlier . . . .

Does this help ??


DSCN5634copy.jpg




A quick tip - Put PTFE tape around the threads on the bleed nipples and Pipe Nuts and you'll be able to free them off in the future.


Bob.
 
Awesome, thank you! Of course, that means I need to remake the lower pipe of the chassis rail as it's not quite long enough (was this pipe that burst originally and I didn't quite allow enough at the end to do it)
 
Of course, that means I need to remake the lower pipe of the chassis rail as it's not quite long enough (was this pipe that burst originally and I didn't quite allow enough at the end to do it)

As you can see, when I replaced my LSV I used Cupro-Nickel pipe and put some neoprene tubing over it where it passes over the rear suspension mountings.

I really don't like the standard Toyota varnished ferrous pipes - when I started working on my brakes the pipes on the rear axle just crumbled, they had rotted out from the inside :doh:.


Best of luck with it.

Bob.
 
I've never really paid much attention to the bias valve on Fiery! It's just there! how would I know if it was working or not? would it come up on the MOT? While trawling the net looking for people that had done the 80 series spring modification I stumbled over one chap talking about making a new bracket to alter the position of the bias valve as a result of the lift, is this critical? In reply to this chap someone else had said that there is already enough adjustment built into the OE bias valve bracket to compensate for any lift, again something else I wasn't aware of! Has everyone else adjusted their bias valve following a suspension lift and what difference did you notice if any.
 
Bob: Know what you mean about the ferrous pipes, I think every car I've had has had them as standard (ranging from euro boxes to japanese sports cars) and after 10 years or more they go and have to be replaced. Oh well, the whole rear axle's been done now, it's in tip-top condition and all bled, thanks for the help. Think I've just got plain Copper, not Cunifer (said copper on the reel!)

sae: When you put your foot on the brake, weight transfers forward and the back end lightens up, if the bias valve is working, it'll reduce the pressure to the back end (stop the wheels locking up), however if you've got load in the back (like tools or cargo) then it'll keep the back end down and so will require more pressure to lock up the wheels, the bias valve will allow more pressure through (all based on ride height). Easiest way to check if it's working is to get someone to put their foot on the brake and pump it while you look at the lever connected to the valve, it should flex up and down a little. Checking if it's in the right position can be a bit of trial and error - the aim is to have the back locking up at the same time or just after the front (however I use rear bias on my rally car to encourage the back end to be a bit loose)
 
Don't like the adverts?  Click here to remove them
And the $64,000 question . . . . Why do we need a Bias Valve AND ABS :icon-question: :wtf:.


Bob.
 
Good old Toyota - ABS only works on the front axle.

Also, it's a split hydraulic system, but the two sides come together at the Bias valve and are funneled into a single loop joining the rear axle before again splitting and going to either side
 
Good old Toyota - ABS only works on the front axle.

Also, it's a split hydraulic system, but the two sides come together at the Bias valve and are funneled into a single loop joining the rear axle before again splitting and going to either side

EH :think:.

There are ABS Sensors on the back axle (well, there are on mine).

One pipe goes to the LSV from the Brake Master Cylinder and the other goes from the ABS Modulator. I had thought that when the ABS Modulator detects the rear wheels locking it reduces the pressure in the M/C pipe by 'dumping' it back to the Modulator (then restoring it when the wheels turn again - hence the 'pumping' effect you feel from the brake pedal).

There is a single hydraulic feed to both rear calipers - so ABS can't selectively function on a single rear wheel.

The problem with my theory is "why do all that at the back via the LSV - it could be done at the front next to the ABS Modulator (and save 12ft of brake pipe :lol: )??".


Hang on . . What year is your truck (mine's a 1998) ???

Interesting . . . . .


Bob.
 
1997, but I think it's using the speed sensor from the back as a reference for slip - had a 1989 supra that had a similar system, ABS only actuated on the front wheels but there's sensors at the back end, best theory is that it's usef for ref as there's no output to the backend brakes

Also got a 1992 import supra that sold with "4xABS" rather than the stock system

Hmmmmm, gonna take a look at the abs unit and count the number of outputs!
 
Hmmmmm, gonna take a look at the abs unit and count the number of outputs!

This is a rubbish diagram - but it might help:


BrakePipesfittings-95withABS.jpg




I'll be interested to know what's really going on in there :wtf:

Bob.
 
found another link detailing the four main types of ABS unit, one of them utilises three solenoids, this has a strange split arrangment to the back end with a mechanical valve to provide the two wheel ABS. Wondering if the LC90 is using a variation of this?

The LC90's bias valve and pipe arrangement is also very strange, as one of the feeds goes back to the front end, the LSPV is providing a front end feedback if the ABS kicks in at the back by the looks of things, not acting like a pressure regulator as you may expect.
 
Last edited:
Back
Top