Master Cylinder Upgrade?

[Clois Harlan]

I am considering changing my master cylinders to one of the Wilwoods available. My choices are:

http://store.summitracing.com/defaul...h.asp&x=26&y=8

PN # 260-4894
PN # 260-8556
PN # 260-7563


My questions would be:

1. Does anyone have any first hand experience with any of these options.
2. Pros and Cons if any.

I am running the Wilwood dual piston 11.18" fronts and the Fox Body SVO rears.

Thanks,


Clois

[byron w]

Clois,
Why don't you call Wilwood and get thier advice. They should
know. Please post what they recommend. Goog Luck!!
Byron W.

[Clois Harlan]

I am still waiting on them to reply on my email. I may try and call if I don't get a reply by the end of the day.

Clois

[flipper35]

I called them and got prompt help. The ones I have work great, though I was borderline on the sizes. If I were to do it over I would have gone one size smaller. The pedal is firm but not as firm as with the original MII/Girling setup.

[Richard Hudgins]

Clois.

1. Why do you wish to change? Pedal effort? Clamping force? etc?

2. You really need to understand sizing between the MC and the caliper. Then you need to understand the pressures required and the bias amounts.

3. You need to understand the dynamics of the braking system and the chassis.

The bottom line is this: if you are not a engineer that understands braking systems, you can screw things up in a big hurry.

I recommend getting with rdorman as he understands braking systems and has posted many technical bits that apply to your post.

[Clois Harlan]

Richard,

I have read Ricks posts and am wanting to replace an existing (factory 75 Mustang II) MC that is in need of a rebuild or replacement. I am choosing a replacement with one of the Wilwoods mentioned . My intent is to use a replacement MC that will accomodate the upgrades to my braking system. Although I am not a mechanical engineer I have set through more than my share of engineering classes while in college.

The intent of this post was to determine the physical differences between the three models other than price. Price does not drive all my decisions but it is by all means is a consideration. As you said it is very easy to get everything all screwed up and that is what I am trying to avoid. In my past I have created my own nightmares a time or two. Thanks for your advise.

Clois

[Clois Harlan]

I just received a reply from Wilwood and their recommendation was to go with the 260-8555 (1" Master Cylinder). Reasons were that the improvements in design and fit charachteristics benifitted non power brakes and similar applications. Wilwood Tech also recomended using an adjustable proportioning valve on the rear brake lines.

Clois

[petek]

Clois,

Why go with Wilwood rather than a stock master cylinder?

[rdorman]

Originally posted by Richard Hudgins


I recommend getting with rdorman as he understands braking systems and has posted many technical bits that apply to your post.

I take that as quite a compliment coming from you Richard. Must be something with guys named Richard Did you see my post about the Dax Camber Compensating suspension system? Thoughts?
Rick

Oh! Just to post something on topic, Clois, sounds like you have it handled up!

[Clois Harlan]

If you ask my wife it is just so I can get another UPS delivery but the truth is they are lighter and New. Also, because there was no Perfectly Matched manual factory M/C to go with my setup.

Rick,

Getting the exact pedal ratio is a real pain in the ARSE and best suited for a contortionist. I got a little help from the Wilwood guys in fact he knew what I had and what I needed.

Thanks everyone.

Clois

[ItBites]

Clois,

Make sure wilwood is aware of your pedal ratio limitations (if any) when they are recommending a 1" bore master cylinder. Many of these cars do not allow a long enough pedal to achieve the 6-7:1 ratio mostly used with these types of master cylinders. In my Cobra, I have just under a 4:1 pedal ratio, which, even when combined with the smallest 5/8 bore master cylinders, results in very high pedal forces to stop the car, given the caliper piston areas I have (C4 Vette calipers).

Just make sure they really understand all the aspects of your application or you can get the "standard" recommendation for what may not be a standard application. They need at least: Pedal ratio, caliper piston areas (front and rear), rotor size. You should also give them: pad type. As I recall you should be able to develop 1200 psi or so at 76 lb of pedal force (thanks for the correction by Richard Hudgins) or something like that. You should do a little sanity check on the wilwood recommendation before you plunk down your cash...

[Richard Hudgins]

Hi Guys,

Clois,

First, is your pedal effort good now? Can you lock the brakes without a herculian effort?

If so. stay with the same bore size. If not, speak with rdorman.

ItBites

As to system pressures. 1200 psi is more in the correct range at 76 lbs pedal force for non boosted systems.

rdorman

I have not seen the system that you are speaking of. But I have seen many schemes to allow for perfect camber and I think that they are all way too complex.

As every tire manufacturer has different constructions, the camber curve requirements are all over the place.

I just design in curves that make sense and then try to control the masses with dampers and roll bars.

That is the most my small brain can deal with.

[ItBites]

Hudgins,

Thanks for the correction (I fixed my above post, so I don't look like I have CRS diseaase ). I knew I was low, but with the low pressures I develop, I didn't want to try to recall how low I really am.

Also, everyone should remember, if you use two master cylinders (one front, one rear), the pedal force seen at each mc piston is divided by the balance bar ratio split between them.

[Clois Harlan]

Thanks for everyones help on this. It is amazing how many varialbles must be factored into what seems like a very simple decision.

Clois

[ItBites]

Clois,

Gotta say, I'm no expert like RH, but when I heard Wilwood was recommending 1" cylinders, I became concerned you'd end up with excessive pedal force and thought I should chime in. Vendors seldom take the time to really understand your application and frankly don't have the vested interest you have.

Good luck.

[flipper35]

I had to measure everything and ended up with 1" for the front and 1 1/8th" for the rear, but they are drums in the rear. Pedal is firm, but not as bad as the little MII rotors and 7/8ths" bore Girling.

If I had not asked knowledgeable people I would be using the same 7/8ths bore front and rear. Since I was borderline though, I may move the 1" to the rear and go 7/8ths" on the front. Might have a little too much travel though.

[Clois Harlan]

I am using Wilwoods frt and SVO rear combination disc brakes. When I bought my Wilwood Fronts I questioned Wilwood about my setup and they recommended that I change my rear brake lines from 1/8" to 3/32" (which at the time seemed rediculous) when I installed their bigger brake kit. They told me the 1/8" rear lines were better suited for rear drum brakes. Brakes worked great once I got all the air out. Changing the rubber lines to braided made a big difference too.

Clois

[DonB]

I haven't read the whole article yet but I thought if you need more info the is a pretty good article in the Aug. 2005 Street Rodder magazine. It shows comparisons of differnt piston sizes and what the pressures do with differnt MC piston sizes and varying caliper piston sizes. Hope this helps. Don

[Michael C Henry]

I have mid sized GM disk and rotors front brakes and OEM Jag inboard rear brakes.Two 3/4" Tilton master cylinders and a balance bar. Clutch used to have a 7/8" master cylinder but I couldn't have enough travel to have full release and free travel. Jumped up to 15/16"Tilton 15/16" master cylinder for clutch.Now works great.I gave up some eas of operatio for more travel.Other than the box, someone would have to show me the difference between brands. I use the full pedal travel with some to spare on the brakes ,everything is as it should be and no power assist. I don't want the brake pedal against the fire wall on heavy application.