I have wilwood pedals and front powerlite 4 pot calipers with bias set up. My master cylinders are 0.7 rear 0.625 front.
My rear calipers are rover 214 on discs.
The issue I am having is that on first press of the brake, there is a bit more travel as if the powerlite pistons have retracted since last use and then the pedal is firm on the second press.
The pedal has a bit more travel than I would like but I think this is because of the 0.625 master on the front circuit (bias is right over to fronts).
I think I have all of the air out but I haven't ruled it out as a cause.
The brakes aren't working well yet, but this is probably because of only taking it up the end of the cul-de-sac and back and they are not bedded in.
Just for added info, the masters are higher than the calipers and the resevoirs higher still.
Any tips/advice?

Cheers Martin

Just got an answer from wilwoods (after I posted!!!!) It might help someone else!
Martin,

Thank you for the inquiry and use of Wilwood Disc Brakes. Yes, for the 4-piston calipers, the 0625 master cylinder is much to small and is not providing enough volume to the caliper, making it necessary to pump the pedal twice.

With the Wilwood pedal assembly I recommend a 0.75" front master cylinder and a 1" rear master cylinder.

Regards,

MJ

Uh oh, same problem i had (only on the front) and I have 625's on front and rear... back's worked fine for me? I'll soon see when i've fitted the replacement MC's and drive to SVA again...


James

I'm going to keep the rears as 0.7 as they seem solid.
Looks like another order...

It's a bit annoying because I bought pedals and masters from rallydesign. Perhaps they should have questioned me?

[Edited on 13/3/2009 by nitram38]

Also to add, when its bled through and air isn't getting in my pedal is pretty rock solid with no discernable difference between first and second press

[Edited on 13/3/09 by cloudy]

Inded - Rally design are usually really on the ball when it comes to compatibility....

James

You've worried me now, I wonder if the front discs have slightly more runout causing a larger piston retraction in motion than the rear, meaning you need the double pump to get the pads back in contact. Would explain the issues and why it only appears when the car is in motion.... I could just get a .7 front, but the bias is already rear enough without making it worse.. Perhaps another two 7's ?

Thinking aloud here, it can't be that because once it goes its always like that untill you rebleed even whilst stationary...

You may find it just needs a more thorough bleeding....

James

Are you running 4 pot powerlites? Mine are vented discs, but I don't think that it will make a difference.
I would go 0.75 as per my email from wilwood and leave your rears alone.
It also depends what your pedal ratio is, unless you are using wilwood pedals too?

Spec is powerlites all round with .625 wilwood cylinders

Custom pedal box, so it may well be different (not that it changes the MC stroke, just the effort)

[Edited on 13/3/09 by cloudy]

I've bought my replacement of this ebay seller.
Seems a bit cheaper than rally design.
I'll let you know how I get on.

Question, are the pedals floor or top mount?
If floor mount you may need a residual valve to prevent fluid flowing back into the master cylinder.
Residual valve holds about 1-2 lb pressure on the caliper preventing drainback.

Top Mount.
I think the volume was the problem.

i have ordered .7 front and .625 rear for mine, running Midilites up front a sierra discs on back....Hope they are ok, dont fancy spending more on brakes.

quote:

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Originally posted by goaty
i have ordered .7 front and .625 rear for mine, running Midilites up front a sierra discs on back....Hope they are ok, dont fancy spending more on brakes.

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I have two 0.625 wilwoods for sale

Its a caliper problem to each caliper body clamp a dial gauge with the stylus touching the disc and measure the deflection when you pump the pedal it should be zero.

quote:

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Originally posted by nitram38
Are you running 4 pot powerlites? Mine are vented discs, but I don't think that it will make a difference.
I would go 0.75 as per my email from wilwood and leave your rears alone.
It also depends what your pedal ratio is, unless you are using wilwood pedals too?

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Sorry if you think I'm wrong, but I have taken the advice directly from wilwood technical, the people who make the pedals/brakes I am using.
I'd best give them a call to tell them they are wrong................
They have advised that a 0.625 master is definitely too small for powerlites and recommend a 0.75".
You are right about the ratio of the fronts being smaller as they recommend a 1" cylinder for the rears, if you are using wilwoods.
My rear brakes are rover so are different to wilwoods and so a 0.75 is fine.
My fronts need one press to bring the pads forward and a second press for them to work correctly, the volume of the master is too small.
I think Cloudy will need a 0.75 for his fronts to work correctly.
As to advice from someone who has got it "wrong", why is this a problem?
People who do nothing, never make any mistakes, but it is by making mistakes we find out about things.
Rally design supplied my pedals, calipers and master cylinders. I went by their recommendations.
I'd best give them a call too...........

[Edited on 17/3/2009 by nitram38]

The point daviep is making is if your bias bar is already adjusted fully to the front it suggests the rear master cylinder is already too small.

Fitting a larger diameter master cylinder to the front will exacerbate the situation, and you won't be able to achieve the correct balance unless you also increase the size of the rear master cylinder.

You are probably right but since changing the front mc is cheaper I want to take it step by step. I have never seen a 1? mc anywhere!

I've not seen the common Girling type in 1" either, though Rally Design do sell them with 0.813" bore.

Wilwood make 1" dia and bigger, I got mine from:

http://www.carshopinc.com

They were roughly US$55 each from memory.
You may get screwed at the current exchange rates though.

quote:

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Originally posted by nitram38
You are probably right but since changing the front mc is cheaper I want to take it step by step. I have never seen a 1? mc anywhere!

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quote:

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Originally posted by nitram38
Sorry if you think I'm wrong, but I have taken the advice directly from wilwood technical, the people who make the pedals/brakes I am using.
I'd best give them a call to tell them they are wrong................

No you're not they advised the use of a 1" rear m/c. Which you ignored

They have advised that a 0.625 master is definitely too small for powerlites and recommend a 0.75".
You are right about the ratio of the fronts being smaller as they recommend a 1" cylinder for the rears, if you are using wilwoods.
My rear brakes are rover so are different to wilwoods and so a 0.75 is fine.

Doesn't sound like it's fine to me if the bias is all the way towards the front.

My fronts need one press to bring the pads forward and a second press for them to work correctly, the volume of the master is too small.
I think Cloudy will need a 0.75 for his fronts to work correctly.
As to advice from someone who has got it "wrong", why is this a problem?

The fact that you designed your system incorrectly suggest to me you possibly shouldn't be advising others..

People who do nothing, never make any mistakes, but it is by making mistakes we find out about things.
Rally design supplied my pedals, calipers and master cylinders. I went by their recommendations.
I'd best give them a call too...........

If you gave them all the relevant data to be able to spec your system correctly then I would give them a call. However in your own words "It's a bit annoying because I bought pedals and masters from rallydesign. Perhaps they should have questioned me?" It sounds like you ordered specific components..

[Edited on 17/3/2009 by nitram38]

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What are you on about?
I have spent £19k on this project and i'd rather not spend money on extra parts just on your say so.
My brakes will be proven on the sva rollers, so what is your issue?
You don'know the capacity of rover rear callipers so what do you suggest? Maybe I should quit building until I get my slide rule out?

What you can be sure of is there will not be any problems left on my car. I'm just taking sensible steps.

I can add that 0.625/0.625 is now working fine for me, It was either faulty MC or vibration induced air ingress - The maximum braking effort is achieved well within the stroke...

Playing devils advocate - willwood's advice may well have been latching onto a potential problem you primed them with?

quote:

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Originally posted by nitram38
What are you on about?

I don't know why you are being so aggresive? All I'm on about is how I interpret the facts. It sounds as if you have too much braking on the rear as suggested by the balance being all the way to one end. A well designed system should have the correct balance with the bias bar roughly in the cntre of it's adjustment. I'm only making the suggestion that possibly the ratio between the front and rear calipers may be wrong.

I have spent £19k on this project and i'd rather not spend money on extra parts just on your say so.

I'm not asking you to, I'm suggesting that you look at what is causing the problem and not just at the symptom..

My brakes will be proven on the sva rollers, so what is your issue?

It's a bit like the self centering issue, you can make a car self center by toeing out and dropping the tyre pressures but that doesn't make it right.

You don'know the capacity of rover rear callipers so what do you suggest? Maybe I should quit building until I get my slide rule out?

It would have been the sensible thing to do before purchasing any components.

What you can be sure of is there will not be any problems left on my car. I'm just taking sensible steps.

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So what if you said I should buy a 1" MC and I don't need one, then I have wasted my money.
The wilwood email assumed I was running wilwood rears, so I don't want to base my buying on that.
All I wanted to do is change the fronts first and re-check my brakes and if neccesary change the rear MC.
I don't need comments about me having to design a system before I start as all I and most people have, is standard parts to work with.
I don't have the facility to create a 0.937 MC if it is needed so I have to buy what is available.
Cloudy has already proved that a 0.625 works with his set up, but he has probably got a different pedal ratio.
I feel like I have taken a caning for finding out and trying to pass the information on.


[Edited on 17/3/2009 by nitram38]

The pedal ratio won't affect the amount of fluid pumped per press unless you are artifically limiting the travel somehow...

I can only put your problems down to high runout on your front discs or the fronts needed more of a bleed (The powerlites are a bitch to bleed, they seem to retain air all over the place and the bleed nipples need more force than you'd think to seal off)

James

Wilwood say that with the wilwood pedals, 0.625 is too small.

If you push the pedal without fluid, what bottoms out first? the pedal or the MC? If it's the MC I can't see the pedal choice making a blind bit of difference....

James

[Edited on 17/3/09 by cloudy]

My cylinder doesn't bottom out.
First press and the brakes work, but they work better after that

The ammount of brake fluid the mastercylinder has to displace to make the calipers bite the disc should be really tiny --- properly setup the pad to disc clearance should be almost zero say 0.01 to 0.025mm.

Taking a 0.625" (16mm) master cylinder operating a pair of Cortina or Sierra calipers as an example then the piston in a 0.625" cylinder will require to move about 45 times the pad to disc clearance. Doing the sums that works out at very close to 1mm ! If the pedal leverage is say 6 to 1 then that is 6mm at the pedal pad --- not exactly a lot.

If the replacement calipers aren't massively bigger in terms of total piston area then these numbers don't alter much.

Even fitting massively bigger calipers with a 50% increase in caliper piston area won't result in more than 1.5 mm at the mastercylinder or 9mm at the pedal.



However if something else is wrong such as the caliper is not mounted squarely or i has trapped air or the caliper is flexing then it is a different ball game -- still using calipers with the same area as a cortina or Sierra if the pad to disc gap increases to 0.5mm (0.02" then the required movement of the master cylinder is now about 22mm or 132mm at the pedal pad ----- a little bit excessive.

If all the air is out the system and the wheel bearings are in correct adjustment large pedal movements on the first press sugest flexing in the system.

It would be productive to do a dial gauge delfection test on both the caliper mountings relative to the disc and the flexing of caliper body, --- . That Wilwood seem to automatically recommend very big bore mastercylinders makes me suspect the defelection results for the flexing of the caliper body would be of interest.

Britishtrident - excellent reply...

My problem turned out to me badly seated bearings in the alloy cortina hubs, giving a runout of around 0.5mm... (Same symptoms as you martin)

I seem to remember your uprights were homemade, did you make the caliper mounts yourself? Are those dead square?

James

The caliper mounts were welded on the uprights then milled so that they are true to the disc/hub.

As BT says, might be worth measuring the runout - If even you just do as I did and fire a laser from almost dead behind the disc just glancing it. It'll show up even the most minute variance

James

I will re-check the runout. My 0.75 arrived yesterday and I swapped it out. Tonight I will try and bleed the brakes.

Good luck

I bled the front brakes tonight and now they are spot on.
I even got to move the bias over a bit to the rears.

Result

quote:

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Originally posted by cloudy
Result

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Congratulations

Out of interest, what size pistons do you have in your powerlites?

Pass......

Just an update, the brakes started being soft on the first press in the morning after it had been standing.
I contacted wilwood who said that some calipers have round seals that will pull the pads back from the disc.
I've bled them to death so I tried the block of wood on the pedal overnight trick and for the last 2 mornings, the pedal is back to spot on.
Might help some of you with those last few small air bubbles...........

I don't normally respond to posts but there is so much confusion on this post that I felt compelled to respond.
I assume that enquiries to Wilwood you mean Wilwood Europe ie Rally Design not Wilwood USA?.
Before anyone at Rally Design can give a sensible answer on recommended master cylinder sizes on a balance bar system we need the following info-
1. The type of vehicle-FWD,RWD,4WD,Front Engine,Mid Engine etc etc?
2 Type of caliper-4 pot,2pot,single pot slider etc etc?
3. Caliper piston size?
4. Pedal ratio?
I am only posting because Nitram38 last post suggests in answer to Robv's question 'what size pistons in the Powerlites' he answers 'pass'-do I read into that don't know. If he doesn't know his piston sizes I just cannot see how we at RD could advise master cylinder sizes.
The sizes of 0.75 and 1.0 are very unusual for these type of vehicles,I would like to know what info you supplied to my guys to respond with these sizes.
Anyway while I am posting the following may be helpful.
The largest pistons available on the Powerlite caliper are 1.38" with a 4:1 pedal ratio the ideal master cylinder size is 0.56" which unfortunately is not cheaply available(but RD is considering manufacture),0.625 is good on a 5:1 pedal ratio and 0.7 is good on a 6:1 pedal ratio.
I don't know the size of the pistons in the rear Rover calipers....were these calipers off the front or rear of the donor Rover?-we are often horrified at work when we are asked to quote m/cyl sizes when front calipers are used on the rear of these lightweight cars...a popular mod is front XR3i calipers/discs bolted onto an English rear axle,they bolt on easily but the effective swept piston area is very high(calculate 3.142xpiston radiusxpiston radius x 2)we sometimes have to recommend 0.813 or even 1.0 master cylinders on the rear circuit but this is to overcome a bad caliper selection better to use smaller piston sizes in the first place.
All this misinformation is one of the problems of these forums....if you supply insufficient or wrong information you cannot expect to get a helpful answer and then everybody puts in their input and the error gets confused and compounded....if Nitram38 gives me the info as above I can give a sensible answer.
The Wilwood balance bar set up in the Rally Design catalogue is very helpful in setting up the balance bar-it is rarely at right angles at rest,the longer pushrod is normally on the front circuit.
Hope this helps .
Senior brakes designer,Rally Design

Thanks for the clarification.
The trouble with brake systems is there are so many permutations for the amateur and even when everything is accounted for it is not working.
By talking on here, hopefully we learn and others can benefit from our mistakes.
TBH I wouldn't buy wilwoods again because of all the issues I've had with threads (had a leak on the tapered inlets of both caliper) and the dual chamber bleeding which is a PITA.
I am using the rover rear calipers on mine and not the wilwoods. This also was why wilwood (usa) suggested a 1" cylinder?
Anyhow, mine seem to feel right on 0.75 and 0.75.
The fronts lock before the rears.

The sva rollers will be the final judge!

[Edited on 4/4/2009 by nitram38]

Be interesting to compare, I'll scan the 2 page brake report the SVA man kindly gave me (you have to request it)

James

Explains all-I did not appreciate that your enquiry was to Wilwood USA...out of interest what piston sizes(front and rear) and pedal ratio did you advise to them?

I gave them the part numbers from the wilwood box but not the rears as that circuit was fine.

But you cannot consider the rear line in isolation,the master cylinders for front and rear have to be considered together.
For Wilwood USA to be able to specify any recommendation they need to know the same info we need.What pedal ratio are you using?
I noticed you had both inlet ports leak,that is very concerning...what type of union and thread of union were you trying to screw into the port?

I have the standard wilwood pedalset supplied by rally design so you should know the ratio!
They obviously made assumptions about my rear caliper size.
Like I said, I am an amateur who has to take advice and try and make the best of what is available. I've learned the hard way........... by trying.
I've sold the MC's on for not much of a loss. It's just the constant going over things. My standard rover rear calipers worked straight away and no leaks or issues. It has just been the front circuit.
The leaks were caused by tapered aluminium adapters ( supplied with a braided hose set from Russ Bost) that I thought were seated. I didn't want to over tighten them in case I split the thread in the caliper.
So maybe it was me being too careful. A bit of ptfe tape has stopped the leak.
I thought getting rid of the standard rover calipers was going to improve things (like weight) but the hassle of bleeding/leaks and cylinder sizes has made me want to buy another brand of caliper in future.

Here is a pic of the pedals:


Description

[Edited on 4/4/2009 by nitram38]

You will keep going over things unless you advise the correct info,it's an expensive way to end up with the right result...I have driven many vehicles built by amateurs who thought their brakes were performing well and surprised at the improvement when the hydraulics are set up correctly...it is such a simple matter to measure with a vernier the od of all the pistons and with a ruler the pedal ratio of the pedal box...your photo appears to show the Wilwood reverse mount box,which is available in 6.25:1 and 5.1:1,assuming 1.38 piston Powerlites you would normally use a 0.70 with the 6.25 and 0.625 with the 5.1.If you use a 0.75 that will give less power/less stroke and a firmer pedal.
The inlet ports use a 1/8 NPT thread,taper thread form.
I'm guessing on the rears but normally a 0.75 m/cyl is the norm if you have used rear calipers from a front engined donor.
On these very light vehicles unless in race conditions it is often difficult to get enough heat into the front pads...my current favourites are Mintex M1144,which have plenty of low heat bite.
The pedal box would normally be adjusted with a long pushrod on the front,especially if using the lower pedal ratio/0.625 master cylinder combination,to allow the maximum travel on the front m/cyl avoiding lock up in the balance bar.
Within the limits of the info you have provided thats as close as I can recommend.
By the way the Powerlite and Midilite calipers were designed in the UK so we tend to have more experience with them than the Yanks.
Hope that helps you and others with a similar set-up.

The MC's are 0.75 Front, 0.75 rear.
0.625 was too small on the fronts.
The front cylinder pushrod is set as the longest and the rear shortest and the front pushrod pushes in until the bias bar is about straight before the brakes become firm.
I now have a firm pedal, which I like. It just remains to be seen what the sva brake rollers make of it.
The mintex pads seem like a good option, so I might change them from the wilwood ones I was supplied with, if they don't perform.
Cheers Martin