Brake Question

[Jim Yergin]

I have installed four wheel disc brakes on my '41 Plymouth. AAJ's kit in the front and Ford Explorer rear axle with discs in the back. I have an underfloor dual reservoir Corvette master cylinder from ECI with their brackets to use the original brake pedal. I have 2lb residual valves in the lines and an adjustable proportioning valve on the rear brake line. I have pressure bled the system and have a good hard pedal. The brake pads are new. My problem is that the brakes just do not perform very well. I cannot get the car to stop short or even lock up the brakes. I would welcome any suggestions or thoughts as to what I am missing.

Thanks.

Jim Yergin

[Robert Horne]

I believe the proportion valve should be near the MC to control how much pressure goes to

the front, and how much pressure goes to the rear. The residual valve is to keep some

pressure on the brakes when not in use....

[mhawkins]

Power booster?? and how many miles on the new set up? the pads may need to wear in to the rotors.

[Don Coatney]

What is the bore size of the master cylinder? If the cylinder bore is too large it will take a lot of foot pressure to activate the brakes. Smaller the bore, less foot pressure required.

 

What is the pedal ratio? In other words how much mechanical advantage do you have with the stock pedal to activate the master cylinder. Does the ECI setup offer compound linkage same as the one I have pictured below?

 

 

[Jim Yergin]

Robert,

The valve is completely open.

 

mhawkins,

Manual brakes, no power booster. A few hundred miles on the rear brakes. A couple of thousand on the front.

 

Don,

The bore is 1". The m/c was supplied by ECI for use with four wheel disc brakes. The linkage is similar to yours. I do not know the pedal ratio.

 

Jim Yergin

[Don Coatney]

What is your brake line size?

[Jim Yergin]

I spoke to ECI. They said the problem is that there is no way to provide enough pressure with my set-up to make the Explorer rear brakes work properly. They said to remove the Explorer rear end and install a Ford axle with drum brakes.

Jim Yergin

[martybose]

I spoke to ECI. They said the problem is that there is no way to provide enough pressure with my set-up to make the Explorer rear brakes work properly. They said to remove the Explorer rear end and install a Ford axle with drum brakes.

Jim Yergin

Not a very useful answer.  My question would be about the proportioning valve.  It's purpose is to limit the pressure to the rear brakes to prevent lockup.  Since ECI says there isn't enough pressure to the rear, I'd try backing the proportioning valve down and see if you can lock up the rears in a panic stop.  If you can, start adding in some proportioning valve adjustment until you can't.

 

Marty

[Don Coatney]

I have also had some less than desirable conversations with ECI. It appears that if they do not have a product to fit your application they frequently suggest that you start all over and get the parts that work with what they sell.

 

I agree with Marty that a proportioning valve adjustment may be in order. I would certainly try that before doing another rear end swap.

[Jim Yergin]

Marty,

When you say "backing the proportioning valve down" do you mean decreasing the flow?

Thanks.

Jim Yergin

[Dave72dt]

Backing it down means reducing the restriction so it would increase the flow to the rear brakes.  A 1" m/c isn't that unusual.  I think it's more of a leverage issue than anything else.  Manual brakes need a different leverage ratio than power assisted do. 

[Jim Yergin]

The valve is fully open.

What I think I may do is try a master cylinder with a smaller bore, maybe 7/8". My understanding is that a smaller bore increases pressure.

Jim Yergin

[martybose]

The valve is fully open.

What I think I may do is try a master cylinder with a smaller bore, maybe 7/8". My understanding is that a smaller bore increases pressure.

Jim Yergin

That would have been my next suggestion if the proportioning valve wasn't the issue.  Just be aware that a 7/8" MC piston has about 3/4 of the surface area of a 1" MC, so if the brake pedal goes down (for example) 2" with the 1" MC, it will probably go down almost 3" with the smaller MC.

 

Marty

Edited May 5, 2014 by martybose

[Dave72dt]

http://www.markwilliams.com/braketech.aspx

There's a calculator at the bottom of the page that may help you out with understanding ratios, m/c size, etc.

[Young Ed]

I spoke to ECI. They said the problem is that there is no way to provide enough pressure with my set-up to make the Explorer rear brakes work properly. They said to remove the Explorer rear end and install a Ford axle with drum brakes.

Jim Yergin

 

So the same company that sold you a mc for 4wheel disk tells you to remove the disks and go back to drum. That doesn't seem right. Jim I can't offer anything to help you out but keep at it and you'll get it.

[DJ194950]

JIM,

if you can install a "t" type of fitting and attach a pressure gauge that will show well in the 500-2000 lb. range, I think I would start there before changing MC's, brake pedal leverage ratios, rear ends etc.

Like the previous post shows that arround 1000 lb. pressure is required with disc brakes-slightly less will work for drums.

 

Best

 

Doug

[suntennis]

As far as I know all present cars with 4 wheel disk brakes have some form of power assist. My first thought for the fix is to install some form of power assist. Years back centered metalic brake shoe lining was a way to get long lasting brakes that would hold up under heat. When used,the stopping was not as good as a softer lining without power assist.

[BigDaddyO]

I spoke to ECI. They said the problem is that there is no way to provide enough pressure with my set-up to make the Explorer rear brakes work properly. They said to remove the Explorer rear end and install a Ford axle with drum brakes.

Jim Yergin

That's a pretty dumb thing to recommend.

 

 The m/c was supplied by ECI for use with four wheel disc brakes.

Jim Yergin

Especially if it was supplied by them for this application.

[Jim Yergin]

In fairness to ECI, back when I ordered it they made it clear that they could not guarantee it would work with any set-up except one of theirs.I was reminded of that in my latest call.

Jim Yergin 

[Dave72dt]

Just in case you're curious, my 05 Explorer runs a 1.06 dia master, factory, albeit power and ABS so the difference is in the leverage you can apply.

[BigDaddyO]

 

From;

MBMBrakeBoosters.com under the Tech heading, topic; Which master cylinder is for me;

 

DISC / DISC

A four wheel disc brake master cylinder is designed to supply more fluid pressure and volume to the rear disc brakes than the disc / drum master does. This is achieved through an internal piston re design. The piston that feeds the rear brakes on a disc / drum master will run out of stroke, limiting the amount of fluid pressure and volume that may be supplied to the rear disc brakes.

The four wheel disc master re design delivers the extra needed volume and pressure to the rear allowing your rear disc brakes to function properly. If you attempt to use a disc/drum master on a four wheel disc system you will get poor rear brake function and experience a spongy brake pedal with a long pedal travel.

 

 

This is from SpeedwayMotors.com;

Universal Power/Manual Master Cylinder, 1 Inch Bore, Corvette-Style

SAME DAY SHIPPING! Most orders ship within 24 hours.

Item # 91031445

$59.99

Quantity:

In Stock

Add To Cart

Add To Wishlist

Not what you're looking for?

 

View Other:

Brake Master Cylinders

Specs

Centerline of Holes:

3.38

Material Type:

Steel

Overall Height:

4.75

Overall Width:

4.50

Sold in Quantity:

Each

Finish:

Natural

Mounted Length:

8.00

Bore Size:

1.00

Feed:

Dual

Outlet Fitting:

3/8"-24

Garage Sale:

No

Notes

Pushrod to mounting flange is 5-1/2". Two 3/8"-24 IFF outlet ports on both sides of the cylinder. Plugs are included for the unused ports. Works with both manual or power brake setups.

 

 

 

Details

Reviews

Q & A

These high-tech corvette-style master cylinders were designed using OE specifications and 100% tested.  They have a 1" bore and are suited for disc/drum combinations. Each master cylinder is ported on both the left and right sides, allowing for installation in many different applications. This exclusive design features a mating flange that works with applications requiring 3-1/8” through 3-3/8” bolt patterns.  These master cylinders will work with manual or power brake systems and can be quickly changed with the included adapter pin to plug the deep well.  The wide body and low profile gives this master cylinder the clearance you need when installing in tight areas and yet it maintains a large volume of fluid necessary for 2 and 4 wheel disc brake applications.

• 1" bore
• 3/8"-24 IFF outlet ports on both sides
• Plugs are included for the unused ports
• Mount spacing is 3-3/8" on center
• Works with power or manual brake systems
• Compact, for installation under floor or on firewall
• Suited for either disc/disc or disc/drum combinations 
• Stroke of this master cylinder is approximatlely 1-1/16"

This is from PirateJack.net

 

Can I use a disc/drum master for four wheel disc brakes?

Usually not. For 4 wheel disc brakes to function properly you will need a master that has a longer stroke.

Edited May 6, 2014 by BigDaddyO

[BigDaddyO]

This is an excellent article on the subject;

www.motor.com/article.asp?article_ID=1969

 

I couldn't copy and paste or download and share or whatever the heck go be able to post it here, so I copied it and typed it in.

I hope this allows you to find it and read it.

[Jim Yergin]

Here is an update. I installed a 7/8" bore master cylinder. It is for a 1980 Buick Skyhawk. I altered the cover to use with my remote reservoir.

 

Because the piston did not have a deep pocket for the push rod, I had to fabricate a new shorter push rod and a retainer to keep the push rod from falling out of the master cylinder.

 

The braking is much improved and I am pleased with the results. However, I determined that my pedal ratio is 4.5-1. I believe that is too low and should be 6-1 or better. My next project is to try and see if I can increase the ratio and make the brakes perform even better.

Jim Yergin

[Robert Horne]

Jim, have you thought of using an Explorer master cylinder,

since you are using an Explorer rear setup?

[Don Coatney]

Sounds like you have made some improvements. I will be interested in seeing how you can improve the ratio.