Omega Owners Forum

Please login or register.

Login with username, password and session length
Advanced search  

News:

Search the maintenance guides for answers to 99.999% of Omega questions

Pages: [1]   Go Down

Author Topic: Brake Bias Adjustment  (Read 1113 times)

0 Members and 1 Guest are viewing this topic.

05omegav6

  • Guest
Brake Bias Adjustment
« on: 19 September 2013, 17:33:57 »

Is there any?

Don't recall seeing a load sensing valve anywhere either :-\ could it hypothetically be tweaked in the ECU?

Basically, the standard car has a front piston area of 1x25.52cm2 working on a 296x28mm disc.

                                     rear piston area of 2x12.57cm2=25.14cm2 on a 286x20mm disc.

Proposing to fit the following...    front piston area of 50.1cm2 working on a 362x36mm disc.
                                 
                                                            rear piston area of 49.56cm2 working on a 330x32mm disc.
« Last Edit: 19 September 2013, 17:50:08 by ex taxi al »
Logged

05omegav6

  • Guest
Re: Brake Bias Adjustment
« Reply #1 on: 19 September 2013, 17:59:41 »

Is there any?

Don't recall seeing a load sensing valve anywhere either :-\ could it hypothetically be tweaked in the ECU?

Basically, the standard car has a front piston area of 1x25.52cm2 working on a 296x28mm disc.

                                     rear piston area of 2x12.57cm2=25.14cm2 on a 286x20mm disc.

Proposing to fit the following...   

front piston area of 50.1cm2 working a 78.3cm2 pad on a 362x36mm disc.
                                 
rear piston area of 49.56cm2 working a 57.4cm2 pad on a 330x32mm disc.

Edited to include proposed pad area, but not sure of current standard pad surface area :-\

Front discs have the potential to be 362x32mm if wheel clearance proves tight, car is an Omega 3.2 estate, with a 76ltr LPG tank and towbar, fitted with plod self levelling.

The concern is that the rear end might be over specced...
Logged

TheBoy

  • Administrator
  • *********
  • Offline Offline
  • Gender: Male
  • Brackley, Northants
  • Posts: 97496
  • Millennium Man
    • The missus mad
    • View Profile
Re: Brake Bias Adjustment
« Reply #2 on: 19 September 2013, 18:14:47 »

Generally done in the ABS block on ABS cars...  ...or is on Vx that I've seen...
Logged
I don't tolerate bickering, and I'm always grumpy.
And Lizzie Zoom says I'm a heartless bastid...and she's absolutely correct!

05omegav6

  • Guest
Re: Brake Bias Adjustment
« Reply #3 on: 19 September 2013, 18:25:31 »

Generally done in the ABS block on ABS cars...  ...or is on Vx that I've seen...
Is that something that is self adjusting then? presumably electonically...

This was the specific response from the brake supplier...

Quote
Having close to twice the piston area of the standard 2 pot caliper you quote, this would result in the rear being way over braked and could cause the car to swap ends under hard braking or in wet conditions. However if a limiting valve is employed in the rear brake lines or an anti-lock system is fitted to the car then either will reduce this effect. Being an estate car it may even have a limiting valve thatís automatically adjusted by adding weight to the load area, the heavier the load the more rear line pressure is allowed. But with big pistons it could still be prone to overworking especially an ABS system ceaselessly trying to stop the brakes locking up and that can prove annoying.

But, in percentage terms the standard rear pistons have 98.5% the area of the fronts, the proposed rear pistons are 98.9% of the proposed fronts. How critical is that 0.4%? and can the ABS manage it?
Logged

Kevin Wood

  • Global Moderator
  • *****
  • Offline Offline
  • Gender: Male
  • Alton, Hampshire
  • Posts: 34567
    • 3.2 MV6 (LPG), Westfield
    • View Profile
Re: Brake Bias Adjustment
« Reply #4 on: 19 September 2013, 21:33:57 »

Need to get 2woody on this case. On the face of it, you haven't changed the piston ratios much front to rear (but remember that opposing pistons do not add extra area). Not sure how that would affect the balance calculations - hopefully not much.

What he's saying about ABS systems isn't really valid. ABS or not, you want the brakes balanced, because if (say) the ABS cuts in early on one axle due to an imbalance it will affect the effectiveness and balance of the brakes dramatically. Also, in cornering, before lockup, a rear bias can still cause it to swap ends without warning. EBD in the ABS system can be used to proportion braking instead of a bias valve. The jury's out on whether the Omega has it or not. I think 2woody reckoned it might have, given the piston sizes at the rear of the later DBW cars. ABS ECU calibration could be completely wrecked by this change, too, since the sensitivity of the calipers to fluid pressure changes will be very different, and that's not something we can tweak.

The other thing to consider is that you haven't changed the master cylinder to match your increased piston area. You might well find the brakes to be over-assisted or, worse, that there is so much travel in them that you don't have enough reserve travel in the pedal.
Logged
Tech2 services currently available. See TheBoy's price list: http://theboy.omegaowners.com/

05omegav6

  • Guest
Re: Brake Bias Adjustment
« Reply #5 on: 19 September 2013, 21:42:58 »

You've just reminded me of summat, the 3.2 has 42mm pistons on the rear, that makes 13.56cm2 for each rear piston,

Which makes the rear pistons larger than the fronts, although the effort would presumably be halved by virtue of being opposing :-\

The calipers in mind are six pot fronts and four pot rears btw :y
Logged

Lazydocker

  • Omega Queen
  • ********
  • Offline Offline
  • Gender: Male
  • Woodbridge, Suffolk
  • Posts: 18785
  • Constantly Bullied by a certain Admin
    • View Profile
Re: Brake Bias Adjustment
« Reply #6 on: 19 September 2013, 23:25:51 »

I'm fairly sure the estate has a load adjusted compensating valve :-\
Logged
Whatever it is... I didn't do it

05omegav6

  • Guest
Re: Brake Bias Adjustment
« Reply #7 on: 19 September 2013, 23:33:13 »

You've just reminded me of summat, the 3.2 has 42mm pistons on the rear, that makes 13.56cm2 for each rear piston,

Which makes the rear pistons larger than the fronts, although the effort would presumably be halved by virtue of being opposing :-\

The calipers in mind are six pot fronts and four pot rears btw :y

Have an alternative rear set up...

Piston area of 32.15cm2 same pad area of 57.4cm2 with either 330x28 or 356x32mm discs.
Logged

05omegav6

  • Guest
Re: Brake Bias Adjustment
« Reply #8 on: 19 September 2013, 23:37:06 »

I'm fairly sure the estate has a load adjusted compensating valve :-\
You'd think it should have, but I'll be damned if I can recall seeing it under the car :-\ certainly, the only sensors attached to the rear axle are the headlight sensor and the suspension level sensor...

Does the level control talk to the ABS ecu :-\

To answer that, it does, BLRT speed signal connection...
« Last Edit: 19 September 2013, 23:43:47 by ex taxi al »
Logged

Kevin Wood

  • Global Moderator
  • *****
  • Offline Offline
  • Gender: Male
  • Alton, Hampshire
  • Posts: 34567
    • 3.2 MV6 (LPG), Westfield
    • View Profile
Re: Brake Bias Adjustment
« Reply #9 on: 20 September 2013, 09:43:59 »

Where you have double-acting calipers, it's the total piston area on one side of the caliper you need to compare with a sliding caliper, so 3 pistons for the 6 pot.

Or.. you can look at it as the OE floating front caliper having the fluid acting both directly on the piston, and indirectly on the back of the cylinder bore.

ABS has no input from the level control. Only way it could work out loading is by comparing fluid pressure to retardation and modulating the rear pressure according to some sort of map. Personally, I doubt it does it, because I've not seen a fluid pressure sensor on the ABS block or in the live data. I suspect this level orf sophistication is reserved for the mythical ABS/ESP system.
Logged
Tech2 services currently available. See TheBoy's price list: http://theboy.omegaowners.com/

05omegav6

  • Guest
Re: Brake Bias Adjustment
« Reply #10 on: 20 September 2013, 10:29:04 »

The level control uses the speed signal to control bump response. It won't pump up the rear shocks if you ground the rear end off a crest at 80mph, but if you drop 200kg of cement in the boot whilst stationary, it tends to react :y

Bearing in mind the point about only considering half the piston area at the front, the proposed piston area is a reduction of 0.15cm2 but with the increased disc diameter and far greater pad area, they would have significantly more leverage.

The rears are an increase of nearly 7cm2, (like for like as both are fixed calipers with opposing pistons),
so would the smaller disc option be a better bet :-\

Off to have another rummage...
Logged

Kevin Wood

  • Global Moderator
  • *****
  • Offline Offline
  • Gender: Male
  • Alton, Hampshire
  • Posts: 34567
    • 3.2 MV6 (LPG), Westfield
    • View Profile
Re: Brake Bias Adjustment
« Reply #11 on: 20 September 2013, 11:20:04 »

Pad area shouldn't matter, as more pad area means less force per unit area - same braking force in total.

Disk diameter will make a difference as the retarding force is generated further from the hub hence more torque at the wheel.
Logged
Tech2 services currently available. See TheBoy's price list: http://theboy.omegaowners.com/
Pages: [1]   Go Up
 

Page created in 0.165 seconds with 21 queries.