Wilwood 16" kit caliper issues

[ailwyn]

Maybe you could find us a 1 inch bore (or even a 1 1/8 inch bore) BMC to push all that extra fluid into the pots as well. Seem to be having problems sourcing one that doesn't require new brake pipe couplings to be made.

TBH if you are going to change the BMC you may as well fit new pipes while your at it... most of the work is already done and you can make up the pipes yourself quite easily (and fairly cheap) - although I am getting a flashback now to some comment previously about not being able to use copper piping in the US, so steel pipes might not be possible diy.

[Elanlover]

Most brake piping is a nickel copper alloy i think. Easy to bend even by hand. The problem is in flaring the ending properly and you really need the right tool to ensure connecitons that won't leak. But, trying to get at and remove the pipes so you can create new ones with re-sized conneciton fittings will be a royal PITA. Would prefer to avoid that if at all possible. Probably not though

[ailwyn]

Blair,

I'm not familiar with the LHD setup, but the biggest bit of work when I changed my BMC was getting the BMC off and back on. You need to remove all the connectors to the bmc anyway, so it's then just a case of disconnecting them in the front wheel arches and the rears have a union behind the plenum.

The flaring tools are fairly inexpensive, and I just bought the pipe and connectors and did it myself. I used copper pipe though, which was easy, not sure how your alloy pipe would be to work with. Took me about 6" of pipe and 6 attempts to get the flaring down.

Anyway let's bring this back on topic

Ailwyn

[Elanlover]

The LHD setup is very different. The BMC almost looks easy to remove (although I haven't tried it yet). Easier than in the RHD version from the reports I've read.

We're "semi" on topic I think. It really seems like anytime a bigger brake setup is being considered then a larger bore BMC has to be part of the equaiton to get decent pedal feel. With only the fronts done, the pedal travel is longer. Can you imagine what new front and rear calipers will make the pedal feel like? After a fair amount of research I do think that new piping will be required to do a BMC as well - not enough coupling reducer options out there.

[bobbrown]

Wrong!!!!!!!!!!!!!!!!!!!!!!
Larger calipers do not necessarily mean you have to fit a larger diameter brake master cylinder
It would depend on how large in terms of overall brake caliper piston area you went
For example a total area of
4.8 sq. in would require a 3/4” bore master cylinder
9.6 sq. in would require a 7/8"” bore master cylinder
14.4 sq. in would require a 1” bore master cylinder
The Elan has a tandem 7/8” master cylinder and is split diagonally so effectively you have two cylinders so this should be more than enough for say a pair of 38mm 4 pot calipers.
Some people seem to think that massive caliper pistons will give you great brakes this is not the case, it is a balance, too big and you will lock the brakes far too easy, too small and you will not be able to achieve locking the brakes (unless you have realy strong legs)

I have good pedal “feel” with 7.37 sq in on each front caliper which comes in close to most of the conversions it is only if you go for say 44mm + caliper pistons does this become an issue and I feel that 44mm is far to large
Aston Martin do not fit that sort of size to the DB9, OK it is running a 350mm diameter disc, but it’s a car twice the weight of the Elan.

"A common problem in many applications is a spongy pedal. Brake systems inherently have slack in the system that must be taken up before work can be done by the pads. Slack comes from two factors: retracted pistons must be moved back out, and misalignment caused by deflection in the axle and housing mis-alignment. One of the most common misconceptions is that a larger master cylinder will create more pressure. While a larger master cylinder creates a larger displacement, it takes more force to create the same pressure as a smaller bore. While a larger master cylinder will take up system slack with less pedal stroke, it will take more force to create the same system pressure. The result after adding the larger master cylinder is a harder pedal which needs much more pedal pressure to create the same amount of braking force. For instance, moving from a 3/4" master cylinder to a 1" requires 77.7% more force on the push rod."

[ailwyn]

Bob,

That's where Blair is coming from, when we've swapped to the wilwoods what used to be a solid pedal with little travel became a softer peddal (not spongey) with a lot of travel.

What Blair is trying to do is restore the feel in the pedal to something that does take some effort to apply. I saw the stark contrast in the systems when I bought my SE and drove it home with the stock setup, I had to press the pedal a lot harder, but with less travel to get them to apply.

I think this is down to the increased capacity of the caliper, so there is more brake fluid to pressurise and therefore the pedal travels a lot further before it becomes solid - hence the want to send more fluid down the pipes.

Happy to stand corrected, but this makes sense to me.

Ailwyn

[Elanlover]

Bob, appreciate the feedback but I have to tell you that everyone who's upgraded their fornt brakes, seemingly regardless of the caliper type, has reported a much lower brake feel than before. And, its not a bleeding issue. So, for whatever reason, it seems that on the Elan, larger pots on the calipers requiring more fluid to be pushed is resulting in an undesirably lower pedal. The pots on the OEM calipers are so small its not surprising really.

We're not talking about needing more brake pressure. Just a higher brake pedal. There's an interesting site (which I can't recall right now) that provides a crap load of math if someone wanted to figure out all the calculations for fluid flow, pressure, caliper sizes, blah, blah, blah. All too technical for me (which is probably why I didn't bookmark it ). But, experience for almost everyone with larger brakes says that the pedals too low and a bigger bore BMC will help that.

[bobbrown]

It is true that a larger master cylinder will increase the amount of fluid moved but will require greater pedal pressure to give the same fluid pressure.

I have looked at just about all the upgrades out there.
as far as caliper areas are concerned they look like this in square mm

Standard 46mm dia 3324
4 pot 34.6mm dia 3761 +13% (Hi -spec)
4 pot 38.6mm dia 4681 +40% (Hi -spec)
4 pot 41.2mm dia 5333 +60% (Hi -spec)

I used the Hi-spec conversion in these figures but the Wilwood and other all sit in there some where and although I can see someone doing it anything over 42mm is pointless.
I went from stock to 4752mm calipers and although there is a a little more pedal travel it is not unreasonable.
I have engineered braking systems in the past from scratch and have never had to resort to anything over a 7/8 master cyl, ok they were competion systems with dual master cylinders and adjustable brake bias but the principal is still the same.

If the system is correctly bleed then there are a number of other factors to take in to account like disc run out and caliper alignment.
The best way to check(with the engine off) is to pump the pedal to get all the vaccum out of the servo and to see how the pedal feels stationary.
If the pedal feels quite good in this situation but when on the move it is not very good then there is something that is causing this and disc run out is the first thing to check.

[Elanlover]

Bob, all good points for sure. It can't be thin discs. Obviously, the fronts were new and on my car, the rears were almost new with only 3,000 km on them. The discs and pads were bedded properly using the correct technique. With the car off, the pedal is very low. I can get pretty close to the floor. Again, there is consistent feedback form virtually everyone that's done a brake upgrade that the pedal is too low. The brakes work great. Its just a long push down. I'm personally not to worried about needing to apply more force with a larger bore BMC. I have big feet

[ailwyn]

Bob,

Can't argue with the science, but for whatever reason it seems the brake setup we have does not supply enough fluid if you go for wilwoods - don't know if this si the same for hi-spec, I can only go on experience.

I too can easily get the brake pedal almost to the floor with the engine off, but if I push the pedal I can easily lock the wheels, what seems to be required (to a layman) is more fluid to be pushed through the system, and (to a layman) the BMC seems to be the weak link.

If you have any other ideas on how this can be improved then I'd be glad to hear them.

Ailwyn

[RayD]

For comparison... with standard callipers the pedal moves approx 1.5 inches.

What piston retraction method is being used on the various callipers I wonder? Are any of them relying on disc run out?

Ray

[bobbrown]

I would have to ask what that fluid is doing if the pads are in the correct position then there should be very little movement required before they bite on the disc
If on the other hand the caliper is allowing the pads to return too far then this could explain alot.
The Wilwood calipers are not much different in terms of area than what I have and I do not have excessive pedal travel!

If you are running the Wilwood calipers 120-6816 (16" rims)then these are 44.1mm pistons and may account for the pedal travel!!
These give an area in excess of 6000sq mm which is almost twice the stock.

I am looking at a race setup with two master cylinders and an adjustable bias which may solve some of these issues but it will not include the servo
and will be a front to rear split

[bobbrown]

For comparison... with standard callipers the pedal moves approx 1.5 inches.

What piston retraction method is being used on the various callipers I wonder? Are any of them relying on disc run out?

Ray

the stock calipers use the seals and the little rubber ring in the slides to retract the calipers.
Usually if the seal is of a square section then this distorts slightly when the pressure is applied and moves the piston back slightly when the pressure is released.

In some cases there are springs behind the pistons to stop the pistons from moving back and apply a very slight pressure to the pad.
The same can be acheive using residual pressure valves in the brake line these keep a few psi (2 psi) in the line after the pedal is released.

[ailwyn]

If you are running the Wilwood calipers 120-6816 (16" rims)

Yes.

[Elanlover]

Yes as well.

[bobbrown]

That tends to explain a lot

44.5mm pistons is a little bit of overkill and it will mean that the master cylinder is not big enough for that size of piston!
At 6222 sq mm they are a lot bigger than the stock at 3324, 87% bigger add in the 310mm diameter discs and talk of over kill.

I would have be more inclined to fit the 35.1mm pistoned calipers as these would have been a closer match to the stock item.

Which was why I was looking at the Midlite caliper with 38.1 pistons as this gives 4561 sq mm (37% increase) couple that with a 295mm diameter disc and you have a more than enough.

As for getting the issue of too much brake pedal travel fixed, to me there are two options, change the calipers or the master cylinder.
The first is easy as it should just be a case of changing the calipers to the 120-6806 and changing the master cylinder has all sorts of problems and by the time you have fitted one it will probably have cost as much as changing the calipers.

I really wonder just what the brake balance is like it should be almost none existent, if it was 20% rear I would say you are going to be lucky to get 8% rear
I would not mind having a bet to see who can stop the quickest, stock brakes against the 44mm Wilwooods I would tend to favour a good stock system as all 4 wheels will be braking not just 2.

Bob

[Elanlover]

That tends to explain a lot

44.5mm pistons is a little bit of overkill and it will mean that the master cylinder is not big enough for that size of piston!

Well, I think that's what we've been saying the whole time.

I would not mind having a bet to see who can stop the quickest, stock brakes against the 44mm Wilwooods I would tend to favour a good stock system as all 4 wheels will be braking not just 2.

I can state for a fact that the cars stops significantly faster than with the stock setup. And I went from a virtually brand new set of calipers, rotors and pads to the Wilwoods. There's no comparison at all. I'm not sure that there will be any impact on rear braking after installing ther Wilwoods (or any larger front caliper). The same amount of fluid is still being pushed to the rears regardless of what's on the fronts. You just have to push the pedal further - as we all seem to experience Now, the "feel" may be of more braking a the front but that should be just it. More braking at the front not less at the rears. That might make the car feel like its more front end braking biased - which it actually is. The braking with the Wilwoods now makes the car stop "like it should". It now brakes like a Lotus should. I don't think I'd like the idea of going to a new caliper that basically provides the same braking ability of the stock caliper due to smaller pots than the Wilwoods (if that's what the impact of a smaller pot caliper would be).

I doubt changing out the BMC would come close to the cost of replacing the Wilwood calipers although I might consider that if I didn't also have to change the rotors and hats as well (only adding to the cost). Easily $1K for the calipers PLUS whatever else you need to mount them, etc. I can get a 1 inch bore BMC for $200 and build the pipes and connecitons for maybe $100 more if I buy all the tools. But, its WAY easier to replace the calipers. That's for sure.

[Doug]

I really not trying to stir the pot (and I'm no brake engineer), but since you all are getting technical on the pistons, remember that the OE single is a floating/sliding design and thus the piston has to travel more, as it is moving for both sides--while the pistons on each side of a fixed will move less distance than would that OE one.

[Elanlover]

Do you mean on the rears Doug? Were the front's floating too?

[Doug]

Were the front's floating too?

you betcha