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-   -   Very Hard Braking! (http://www.hotrodders.com/forum/very-hard-braking-201335.html)

27Tall T 07-02-2011 11:10 PM

Very Hard Braking!
 
:sweat: I have a '39 Chev Fatman frame with power disc/drum brakes. I took it for its maiden voyage today and found that I had to stand on the brakes just to get it to stop. According to Fatman they use metering valves for their disc/drum applications......a 2psi residual pressure valve between the master cylinder and discs and 10psi residual pressure valve for the drums. I've pumped the brakes while the engine was off and started the car. The pedal went down ever so slightly (obviously the booster is working). The engine is a stock 350 and the 7" dual power booster gets its vacuum from the intake manifold behind the carb. What am I missing that's causing this condition? :confused:

aosborn 07-02-2011 11:31 PM

If the booster is working properly and your pedal ratio isn't way out of whack, the problem is most likely too large of a bore on the master cylinder.

Just curious, do you have a combination valve or seperate residual pressure valves and a metering valve? If the valves are seperate, do you have a proportioning valve?

Andy

pepi 07-03-2011 07:05 PM

I am thinking booster also, to check the booster, with the engine off, depress the bake pedal and hold, start the motor it should, the pedal move down some.


a good place to start looking.

http://www.mpbrakes.com/technical-su...ng-disc-02.cfm

27Tall T 07-04-2011 09:37 PM

Still hard brakes!
 
:welcome: The residual valves are inline, a 2psi going to the front and a 10psi going to the rear. There is no proportioning valve any where in the system. I've adjusted the rear brakes, checked the fluid level and did the test for the booster. It does go down slightly when I start the engine so I assume that it is working. The motor is stock and as yet I haven't checked the amount of vacuum that I have. This I will do tomorrow. Other than that I'm open for any more ideas. Keep them coming, there's got to be a solution. :)

unix 07-05-2011 07:56 AM

I agree with pepi master power's web page is a good source for troubleshooting a brake system. Other then a mismatch in parts they pretty well cover all the aspects of brake problems over there. The proportioning valve allows the system to brake in proportion too the front and rear, front first. That is just a snapshot of how it works and what it is for.

27Tall T 07-05-2011 10:52 PM

Call in to Fatman
 
:( After monkeying around with the brakes and checking this 'n that and getting nowhere, I finally made a call into Fatman to see if they can figure out the problem. After all they're the ones that built the frame and installed all the goodies. They should at least have some idea as to what is wrong. This one has me stumped.

aosborn 07-06-2011 06:45 AM

What is the bore of the master cylinder? As I stated before, if the booster is working and the pedal ratio is reasonable, what will cause symptoms like you are having is too large a bore on the master cylinder.

Smaller bore=higher pressure

Andy

27Tall T 07-06-2011 09:28 AM

It is a 1 1/8" bore with a 7" dual diaphragm booster.

Irelands child 07-06-2011 10:04 AM

Brakes!!! I have Wilwood 4 wheel discs. They were terrible to the point of being frightening until I had gone through 4-5 complete break in cycles as described by Wilwood's instructions. Since that break in, they are probably about as good as any car I've ever owned. I'm not a fan of that so called metering valve(hold off valve), preferring a straight proportioning valve on the rear brakes plus the two residual valves(assuming the MC is below the floorboards).

Dave W

aosborn 07-06-2011 07:08 PM

If everything else checks out as you say, install a 1" bore master cylinder. Hopefully you can get the same style as what you have currently installed, just with the smaller bore diameter. That will make the swap easy.

Andy

pepi 07-06-2011 07:32 PM

Quote:

Originally Posted by Irelands child
Brakes!!! I have Wilwood 4 wheel discs. They were terrible to the point of being frightening until I had gone through 4-5 complete break in cycles as described by Wilwood's instructions. Since that break in, they are probably about as good as any car I've ever owned. I'm not a fan of that so called metering valve(hold off valve), preferring a straight proportioning valve on the rear brakes plus the two residual valves(assuming the MC is below the floorboards).

Dave W


Did you bed the pads or just drive them out of the box?

pepi 07-06-2011 08:16 PM

Just a thought, doing a little reading of your post 6, you say new. it may very well be that the pads need to be bed. It is a common practice. Said the booster was checked out and working, that is pretty much all there is to hard brakes. They built it, and most likely has parts that match, not familiar with the company so I give them the benefit of the doubt.

http://www.wilwood.com/TechTip/TechPadBedTip.aspx

27Tall T 07-06-2011 09:27 PM

Bedding the Pads?
 
:confused: I've never heard of this procedure. Is it something that is applicable to Wilwood pads only or is this a recommended procedure for all disc brake pads? Also is it possible that my disc pads are too hard for this application? In the past they used to sell different grades of pads (soft and hard - economy and heavy duty) and I wonder if this still is a practise today.

aosborn 07-06-2011 10:48 PM

Quote:

Originally Posted by 27Tall T
:confused: I've never heard of this procedure. Is it something that is applicable to Wilwood pads only or is this a recommended procedure for all disc brake pads? Also is it possible that my disc pads are too hard for this application? In the past they used to sell different grades of pads (soft and hard - economy and heavy duty) and I wonder if this still is a practise today.

Bedding pads used to be common on racing brake pads and less so for street cars. No street car pads that I am aware of anymore require being bedded in. Wilwood's may need to be because that is a racing brakes company, but I doubt that is the problem. "Green" pads (before being bedded in) do have poorer stopping performance, but not to the point that it takes both feet to stop the car from highway speeds. There are many different techniques to bed in pads, but most call for several medium fast stops followed by several high speed stops just to the point of lock up and then let them cool completely. It doesn' cost anything but fuel and pad material to do it, so give it a shot and then let us know how it came out. Just give yourself plenty of run-off room in the process.

Yes, there are different pad materials and compounds. Organics tend to be soft, semi-metallic are more aggressive, and carbon tend to be harder yet, but some of them work very well cold (amazing stuff!). Many race pads don't start to work well until they get up to temperature so consequently are not typically the best for street driving.

Andy

Irelands child 07-07-2011 04:53 AM

You sure as heck didn't read my post #9 !!!!!!!!!


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