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Rear brake pressure reducing valve - recommendations pleases for IVA


Wavey
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1 hour ago, TomW said:

Yeah, I’ve been wondering about something like this,  the problem is if it fails iva for it, then fitting a valve means the entire braking section of the test needs to be redone which I’m keen to avoid, just wondering if I reduce the surface area of the pad would that decrease the braking force?

 

No the force is based on piston sizes in both MC and calliper.

 

 

1 hour ago, TomW said:

 

The pressure would still the the same just on a smaller point?

 

Yep. Pad size just impacts heat dissipation and wear rate. Hence I'm not sure how @jeff oakley's tip above works! It's clearly has for him!

 

I'd expect it to mean the rear pads would bed in even faster! Which would make the problem seen by others worse rather than better!

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Imo it has to be some sort of inconsistency either in the components, whether that being varying piston sizes, pad materials, master cylinder effectivity. Or an inconsistency in the installation, bleeding or pipe work kinks, bedding in etc. 

 

Because it does seem to be pot luck whether or not cars suffer with it or not? Some sail through and some don't. 

 

It'd be interesting to know that if any of you chaps that have the issue now get both the front and rears fully bedded in at proper speeds and still have the rears locking first.

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yep, I'm with Steve on this one; it does seem to be a minority of installations that have the problem, which suggests that it's not a major compatibility issue or basic design flaw.

 

Could it be a faulty batch, incorrectly identified batch, or a physical change in a component that's just starting to show up? (the latter seems unlikely, as it's randomly happened over a few years.)

 

it does make you wonder, beyond the basic parts fitted, what those with the issue have in common. 

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I’ve been wondering too,  especially since my brake lines etc were all done in the factory,  collected the chassis with the lines and the master cylinder attached.  Bled using a vacuum bleeder etc too.


The really weird bit is it passed all the other brake tests and just failed on dynamic braking. My kit was purchased about 2 years ago now.

 

The tester at my test centre said it’s the most common thing he’s seen on westfields lately and they of a know solution that’s being used but won’t say what it was... which was inferred to be wd40 on pads...

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Everything in the system needs to be balanced but the critical thing is that the area of the pads and the size of the disc acting upon them is not too large on the rear.

 

When braking hard in an emergency the rear of the car goes lighter and the contact patch of the tyre reduces as a result. This lessens the grip on the road which means the brake can then lock that wheel easier.

 

By reducing the swept area of the brake pad and disc slightly, that point at when they lock is altered.

 

Manufacturers go to great lengths to match all components so that at each application is correct and pad material can be a variable.

 

Under R90 regulations a brake pad from an aftermarket supplier can be 15% different in performance to the OE spec. So say you fit a White box pad on the front and an OE pad on the rear you have introduced up to 15% difference from what Westfield have designed and tested against, there are so many variables.

 

Tyre type is also a factor, a smaller width tyre or a ditch finder special will lock up easier than a super sticky tyre.

 

I do not have all the answers but my solution has worked well for me and passes every MOT easily on both foot and handbrake.

 

This would be an interesting project for a budding university engineer to ponder.

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Just a quick observation.  Westfield imply the brakes are 60 : 40 front bias and we know the piston surface area is greater at the front than the rear, and the pads are bigger at the front than the rear, then I would tend to agree that the rears may be bedding in faster than the fronts causing the fails even though there is more pressure on the front.  With respect to a pressure reducing valve on the rear, from my experience Westfield were anti this approach when I mentioned it, possibly because you would be heading to more like 70 : 30 bias or worse once the pads have bedded in.  

 

Wish me luck I am going for retest. Brand new pads on the rear, partially bedded in on the front.   Going on a trailer, so according to Westfield this should pass on the rollers no problem.   Unfortunately the rollers are not the problem, it is the dynamic test which seems to be quite popular with the testers at the moment.  

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I just passed with brand new pads on the rear, partially bedded in on the front.  Took it there on a trailer.

 

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31 minutes ago, Two7 said:

I just passed with brand new pads on the rear, partially bedded in on the front.  Took it there on a trailer.

 

 

Great news. Please do report back once youve got everything bedded in fully

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  • 5 months later...

Sorry for the thread resurrection on this one, but I've just found out that my car does the same. Rears lock before the fronts (and the handbrake is non existant, but I'll cover that in another thread...). Everything is standard fare in regards to the braking system. Discs front and rear, standard M16 front calipers and pads. XR4x4 rear calipers and pads. Standard master cylinder that came with the kit (cortina, I believe). No kind of proportion valve fitted. The pads, whilst not new, are not worn at all, so I didn't bother to replace them as it seemed unnecessary. 

The brakes do seem to be fairly good to be fair, but upon heavy braking the rears locked up before the fronts. I was thinking of fitting a brake proportioning valve towards the rear. I can get one for not a lot of money from a certain online auction site. 

Anyone fitted one of these, and did it work? 

Thanks, 

 

Gary. 

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Before messing with the plumbing, how much fuel is in the tank? My IVA tester told me that this was the most common fail for Westies, and he had always seen it fixed by simply filling the fuel tank. Assuming that the root cause is just the quicker bedding in of the rears as suggested above, I wouldn't want to fundamentally change the balance for a short term issue personally. Especially if a little more weight over/behind the rear axle can act as a containment while the pads even out. 

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I've currently got 3/4 full tank. I did wonder if that would make a difference as the back end of the car is naturally really light, and every little helps. 

I've often said that I thought my car was massively overbraked. I'm certain that a car that light doesn't really need discs on the back, but it's not really feasible to change to drums!

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Gary

just thinking outside the box.. can you buy a set of really cheap rear pads and then with the angry grinder reduce the surface area by putting slots across and therefore make them worse.. in order to balance up a bit.. or even do that with the existing ones...

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I will try this Martyn. If I can get the other set off you and then butcher my old ones to suit! 😂

I think the handbrake issue is to do with the old pads as looking at the mechanism on the calipers, it looks to be at full extent of the arms movement and the pads are not engaged enough. 🤔

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3 minutes ago, GaryD1971 said:

I will try this Martyn. If I can get the other set off you and then butcher my old ones to suit! 😂

I think the handbrake issue is to do with the old pads as looking at the mechanism on the calipers, it looks to be at full extent of the arms movement and the pads are not engaged enough. 🤔

Ok.. worth a go

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