Help !!!!Brakes & Master Cylinder

[priobe]

Hello All,

I have been dealing with some braking issues for some time now. When I originally ordered my replica I chose to not get the Ford Granada brake caliper package.
I did however receive the 3/4 Tilton Master Cylinders.

I have been researching Master Cylinders and it seems that the Wilwood and Tilton Cylinder are identically the same. Of course neither one of the manufactors will admit to that.

I am running a Wilwood Superlite 4 piston Caliper with a piston size of 1.75 each. In the rear I am using the Dynalite Wilwood 4 piston calipers which have a 1.38 piston size.


I contacted Wilwood for a sugestion on what M/C to use. They responded back by saying to use a 3/4 for front and 7/8 for rear. In order for Wilwood to reach this decision they only asked for piston caliper sizes.


I also contacted Tilton which requested pedal ratio, tire size, weight distribution, caliper piston size and quanity. After providing them with this infomation they suggested to use a 7/8 front and 1 1/8 rear.

Who do I go with ?


The problem I am experiencing with my 3/4 M/C, is when I bleed the brakes the pedals are rock solid. Pedal travel is about 1 inch. If I hit the brake pedal and hold it down the pedal does not sink. I have checked for leaks and the system is completely dry. When I pull the car out of the garage and it begins to roll back and I hit the brakes, the pedal has more travel maybe 5-6 inch. As I approach a stop sign if I pump the pedal 1 time the pedal becomes hard again but the car does not stop well.

I am very confident that the system does not have air. Here are some of the methods of bleeding that I have tried. I have bench bleed all M/C before installation. With the pedal pumping method I understand this could damage the seals in the M/C but it is the only way to get a hard pedal and it is not leaking.


1. Phonenix Hand pump which pushes fluid backward throught the system. = soft pedal

2. Pressurized system = soft pedal

3. Pedal Pump Wilwood / Tilton recommendation: lift driver side pedal pump bleed aand have 2 people release pressure from caliper first outboard , then in board. After complete repeat steps on passenger side. = This I receive a hard pedal , rock solid but vehicle does not stop.

If you are running the Wilwood caliper setup please post what M/C you are using. I really dont want to buy a Wilwood caliper setup then a Tilton caliper setup.

Sorry for the long post

[Wayne Maybury]

Sounds like you have been at this for a while and have tried most methods that should have worked.

When I built mine, I used Tilton M/C and remote resevoirs. I was told that it was extremely important to make absolutely sure that there was no air trapped in the hoses between the resevoirs and the M/C's. Is there any possibilty that you may have over looked this? It sounds like you get the system properly bled, then you get air back in it somehow.

Sorry I can't add more but maybe someone else will have answers.

Wayne

[rdorman]

Give me this information:

"I also contacted Tilton which requested pedal ratio, tire size, weight distribution, caliper piston size and quanity."

Plus, pad compound, tire type, wheelbase (90?), rotor diameter. I can help. How do you like your pedal, high and as hard as a brick wall or approaching the feel of power brakes?

After that, head on out to the garage and make sure the calipers are normal to the rotors, that the pads are on the OD of the rotor and measure your rotors for axial and radial runout. Let me know what kind of rotors you are running. If they are wilwood (or any kind of non one piece hub rotor setup), did you index them?

You did not mention where you MC are located. Are they above or below the level of the calipers?

[priobe]

Wayne,

I really dont think it is an air issue. I have disconnected entry points and exsit points and fluid flows with gravity. When I used the phoenix pump and pressurized the systme backwards this would have eliminated any traped air.

I have a strong feeling that the problem lies with the sizing of the M/C.

What M/C are you using and do you have simular caliper setup?

[priobe]

Rdorman,

Here is the infomation

Front Brake Information

Number of pistons within each front caliper: 4 Are pistons on one side or
both sides of caliper: both

Diameter of pistons on one side of caliper (list all):

Piston 1: 1.75 in
Piston 2: 1.75 in
Piston 3: 1.75 in
Piston 4: 1.75 in
Front rotor diameter: 12 in

Rear Brake Information

Number of pistons within each rear caliper: 4 Are pistons on one side or
both sides of caliper: both

Diameter of pistons on one side of caliper (list all):

Piston 1: 1.38 in
Piston 2: 1.38 in
Piston 3: 1.38 in
Piston 4: 1.38 in
Rear rotor diameter: 12 in

General Information

What is the motion ratio of your brake pedal (5.5:1, 6.2:1, etc)? 6.5:1
If using a Tilton pedal assembly, please provide part number: - Vehicle
weight (with driver and fuel): 2350 pounds Vehicle Weight Distribution (with
driver and fuel): 50 / 50 Vehicle wheelbase: 90 in.
Front tire diameter (outer): 25 in
Rear tire diameter (outer): 25 in
What is the vehicle being used for (street, road racing, circle track, drag,
etc)?: street

Yes, the rotor has been indexed.
Pads are Wilwood not sure of the compund I would assume soft


As for the pedal feel I would say hard as a brick - but honestly I just want to stop

Rotors Rear are 12" cross drilled / slotted Wilwood
Rotors Front are 12" cross drilled only Wilwood

M/C are located upper foot box

[rdorman]

Working....... are you sure the rotors are not 12.19?

What kind of tires are they and what is the size (ie 275/60-15)?

Send me an email so I can send you the results. I will put a shortened version here but all the information is to much to post.

[priobe]

Rdorman,

email sent

[rdorman]

Got it, do you know the part numbers? Look on the sheet you got from Wilwood. Seems that most of your type ship with the bp-10 pad but it is important that I know.

[rdorman]

I this your pedal assembly? http://www.tiltonracing.com/content....list2&id=4&m=b

[priobe]

BP-10 rear - #6208
Front 7320- rapco

[priobe]

Very simular to the tilton.

This was made by EM
Pedal ratio 6.5:1

[rdorman]

I am trying to get a CG height for your car, at least one like it, to help out.

[priobe]

ok standing by

[rdorman]

You still have the 3/4 mc's on the car correct? Have you noticed the rear bias? Locking up in the rear first... that is assuming you can even get them to lock.

[priobe]

Yes, I have the 3/4 still installed onthe car. I am not able to notice the rear locking upi because neither front nor back can lock up

[rdorman]

What ever happened with the chrome plated master cylinder rebuild? From what I have been able to tell from looking at your prior posts, the system has never worked right? Can you summerize what was done and what where the results after?

It looks like you have done some solid work and also, your home work. I am assuming that the pads of been bedded: http://brakepads.wilwood.com/03-tech/index.html

That you have your balance bar set up correctly: http://www.tiltonracing.com/ins/98-1250.pdf

The MC pistons are allowed to fully return, the balance par is perpendicular to the MC pushrods when the pedal is fully depressed and the bar does not bind at any point during travel correct?

I sounds like you bled them correctly (you where careful not to open the bleeders to much right?).

One of the big variables I don't have for your car is the CG height. If you care to measure it, I would really like that! http://www.longacreracing.com/articles/art.asp?ARTID=22

If you master cylinder reserviors are remote, they are mounted above the master cylinders with no point of the line connecting the two below the MC correct?

Did you put in residual pressure valve and if so, what psi rating?

This may sound like a strange one but it helps know what kind of pedal pressure is acceptable for you. How is the leg? Seats overstuffed? Try placing a small bath scale on your pedal and press as hard as you think is reasonable, what does the scale say?

The brake pedal does not overcenter does it? That is it does not travel past perpendicular to the line of force (hip to pedal) does it?

Have you properly adjusted your bias? Probably impossible at this point I understand.

Do you have access to a set of brake pressure guages. Hard data is a wonderful thing.

Back to your problem. Considering what I have read, I would say that the problem is related to one of the set up items above (such as balance bar and pushrod adjustment, reservoirs, bedding, the plated MC's, etc.). I would go through the process of elimination on these first.

As far as master cylinder size....... EM seems to think the CG is below ground, Tilton about the height of an SUV and Wilwood some where in between. The varied pedal issue of course has nothing to do with the MC size, although after all those cylinders have been through, it still could be them!

Try the CG height on the spreadsheet I sent you and watch what it does to the graph, makes a big difference doesn't it? Basically what you are trying to do with that spreadsheet is to line up front and rear brake pressures with the front and rear pressures for the master cylinder given for the desired rate of deceleration and pedal effort. Study that chart and vary the master cylinder sizes and you will see what I mean.

If you look at the spreadsheet I sent you, notice how the front and rear master cylinders are the same and that they line up fairly well for a .5g stop with just under 50 pounds of pedal pressure. Count over to .9 g's (fifth red and blue line from the left) and notice how much more front pressure you need. At this rate of braking, you have entirely to much rear bias. Now, play with the balance bar. Change cell I18 to 1.1 and notice how nicely that between 40 and 50 pounds lines up with the .9g stop.

This can not replace real world testing, but it does let you play with the vairables before you spend the time and money chasing parts. Let me know if you have any questions.

[rdorman]

OH, and you don't have a proportioning valve in the system do you? And don't forget the importance of a good alignment on brake performance.

[Robert Beede]

I do not know all the specifics of your system. Obviously, you have considerable time invested in research and problem solving. I had a similar problem on an original car, and read in Carroll Smith's "Prepare to Win" book that when the master cylinder is below the calipers, solving the soft pedal problem after thorough bleeding can often be as simple as installing a 2psi check valve between the MC and whereever the feed line breaks into serving the calipers.

I did this, and have solved my problem. I hope this simple answer might be the trick for you. Good Luck! Bob

[priobe]

Robert,

Thanks for your reply.

My MC are mounted above the calipers.

I was able to solve the problem with the following combination

1) replaced calipers with 3/4 front 7/8 rear
2) sand brake pads possibly glazed
3)sand rotor

I took the car for a drive and hit the pedal agressively and the car locked all four tire.


Thanks for your post.

[COBRAGAR]

Great ! How Go Cook Your Turkey .Happy Thanksgivng