Brakes (again)

[timkins]

I just put the Master Power brakes master cylinder w/1" bore and a combination valve on my car. The master cylinder is under the floor. I also installed a 2# residual on the front with a 10# residual on the rear. The front brakes are GM Metric Calipers with Grenada 11" discs. The rear are Ford 8" drums  out of a 76 Mustang and are 1.75 wide. The rears are all brand new and the fronts are less than 12 months old. I bench bled the master cylinder and used a Mity Mac bleeder to bleed the system after installation. I have a very nice firm pedal BUT (you knew there had to be a but) the car still does not stop right. I don't know what to do next. Any suggestions would be greatly appreciated.

[Dave]

I just put the Master Power brakes master cylinder w/1" bore and a combination valve on my car. The master cylinder is under the floor. I also installed a 2# residual on the front with a 10# residual on the rear. The front brakes are GM Metric Calipers with Grenada 11" discs. The rear are Ford 8" drums  out of a 76 Mustang and are 1.75 wide. The rears are all brand new and the fronts are less than 12 months old. I bench bled the master cylinder and used a Mity Mac bleeder to bleed the system after installation. I have a very nice firm pedal BUT (you knew there had to be a but) the car still does not stop right. I don't know what to do next. Any suggestions would be greatly appreciated.

And? whats not stop right? I may be the wrong one to answer but untill I started using residual valves my stuff worked great. Under the floor M/C and plumb it and bleed it. In fack ive never bench blead a M/C

   Maybe its just me but on my 32 i never got the brakes i wanted till i scrapped the 9 inch drums and went to discs on the rear. Yep rock hard pedal but it didnt stop right and its still not what i want but it will do. The last car I did was a 30 model a disk frond 8 inch drum rear. Bought one of them new m/c's with the ports on both sides . plumbed it  no residual junk no prop valves bled it and it stops better than my 32...
Dave

[Bob Paulin]

I just put the Master Power brakes master cylinder w/1" bore and a combination valve on my car. The master cylinder is under the floor. I also installed a 2# residual on the front with a 10# residual on the rear. The front brakes are GM Metric Calipers with Grenada 11" discs. The rear are Ford 8" drums  out of a 76 Mustang and are 1.75 wide. The rears are all brand new and the fronts are less than 12 months old. I bench bled the master cylinder and used a Mity Mac bleeder to bleed the system after installation. I have a very nice firm pedal BUT (you knew there had to be a but) the car still does not stop right. I don't know what to do next. Any suggestions would be greatly appreciated.

I spent a few minutes doing a bit of research.......

Here are the results......

The 1976 Mustang rear wheel cylinders are 7/8-inch bore

The 1978-1985 GM 108" Metric cars use 3/4-inch-bore rear wheel cylinders in conjunction with the 2.5-inch Metric calipers......

.....so, right away, you have increased the rear brake percentage in the front/rear ratio using these calipers.....

They also use a 7/8" M.C. on the GM 108" Metric cars.........

With the one-inch M.C., you are creating LESS pressure than normal for these calipers......

Just guessing, I'd say that the car feels as though the rear brakes are doing most of the work.....with what seems like excessive pedal effort required.......

Okay....here's one possible solution.......

First, I would change the M.C. to 7/8-inch.......

Next.....

The NAPA/United part number for the Mustang replacement wheel cylinder is 37029.....7/8-inch-bore.

According to my NAPA reference Illustration Guide, that crosses over to illustration #114.

Now, under the illustration #114 listing, the following NAPA/United part numbers are 3/4" bore wheel cylinders based on the same casting....

37276; 1971-'74 Toyota Celica

37400; 1983-'87 Cougar T-Bird

37404; 1980s Toyotas

37574; a number of Ford trucks - Aerostars, Rangers, etc.

All the above have an inverted flare tube connection.

If it were me.....I would take my 7/8-inch wheel cylinder from my eight-inch Ford down to my Friendly, local NAPA store, ask for either of the Ford replacements, carefully match the mounting bolt holes, pin setups, etc. and change my rear axle over to 3/4-inch rear wheel cylinders.

(THAT's how I used to do in when I ran the NAPA store.....)


AND......

I have bored out the 2.5-inch Metric calipers to 2.75-inch and installed a Ford/Mopar piston for the race car. (NAPA #85003 - add suffix "S" for steel, "A" for aluminum, "P" for phenolic)

A good counterman - now, there's an oxymoron -  can look these up in the parts *books* - but, usually not in the computer.

This mod gives you about 20 percent more braking force output.

There is a company serving oval-trackers, that does this and sells the calipers for around $75 per. They also sleeve the calipers down to smaller pistons for use on the rear.

Oh yeah....on the race car, we also install some Chevy S-10 rear wheel cylinders which bolt on, but are a larger bore - 7/8-inch - than the stock 3/4".

We also use a 3/4-inch M.C.


Hope this helps.......

B.P.

[phat rat]

Have to ask are these manual or power brakes? If power and using Master Power Brakes booster also  "SCRAP IT" it's a piece of "JUNK" I went round and round with them 4 years ago with the brakes on my cpe. I finally replaced their booster with one I bought in the junkyard and my brakes have been fine since. Bob K had the same experience with their stuff that I did, took my advice and now his brakes are also fine.

[timkins]

The system in NOT a power brake system. I logged on to MP Brakes website and they say that the combination valve can be tripped when bleeding thus only using one half of the braking capabilities. I have to determine which half has the pressure and then open a bleeder screw on that half and depress the brake pedal and this will reposition the valve in the combination valve to center.  When I tried the brakes last night it seemed like it was trying to stop using the rear brakes only. When I applied the brakes it was like the car was on gravel, it slowed the car down BUT it would not stop without excessive pressure on the pedal and even then it did not stop the way it should.

[PeterR]

I have bored out the 2.5-inch Metric calipers to 2.75-inch .......on the race car, we also install some Chevy S-10 rear wheel cylinders which bolt on, but are a larger bore - 7/8-inch -.......We also use a 3/4-inch M.C.

Bob,
When you use the 2-3/4" caliper and 7/8" wheel cylinder with 3/4" MC, is there much pedal stroke in reserve.

Peter

[Bob Paulin]

I have bored out the 2.5-inch Metric calipers to 2.75-inch .......on the race car, we also install some Chevy S-10 rear wheel cylinders which bolt on, but are a larger bore - 7/8-inch -.......We also use a 3/4-inch M.C.

Bob,

When you use the 2-3/4" caliper and 7/8" wheel cylinder with 3/4" MC, is there much pedal stroke in reserve.

Peter

It appears to me that there is somewhat more travel, but it doesn't seem to be near the end of travel to me.

The driver has never complained about it......so, it is a non-issue to me.

Keep in mind that the rears are adjusted weekly, and the fluid is topped off weekly while bleeding - so it's unlike a street operation where pedal travel might become an issue over time due to shoe/pad wear.

I wasn't suggesting that setup to Tim......just giving it as an example of how brake systems can be modified.

For example:

A lot of our competitors - using the 108" Metric chassis with required "stock" brakes - complain about brake fade in longer races.

We went with the phenolic piston and have experienced no brake fad since.

On the other hand, I don't believe I would use the phenolic in a street application.

B.P.

[timkins]

I think this last post should end it. I put the old Mustang II calipers and rotors back on the car this afternoon. I guess the information that ECI Hot Rod Brakes puts out is true, that 11" rotors and 78 up GM midsize calipers only give an 11% increase is true.  That is what happens when you try to by something from a NO NAME distributor to try and save some money.The car stops much better now that I have gone back to the 9" rotors and Mustang II calipers. Thanks to all for their suggestions.

[rooster]

The system in NOT a power brake system. I logged on to MP Brakes website and they say that the combination valve can be tripped when bleeding thus only using one half of the braking capabilities. I have to determine which half has the pressure and then open a bleeder screw on that half and depress the brake pedal and this will reposition the valve in the combination valve to center.  When I tried the brakes last night it seemed like it was trying to stop using the rear brakes only. When I applied the brakes it was like the car was on gravel, it slowed the car down BUT it would not stop without excessive pressure on the pedal and even then it did not stop the way it should.

This happend on my sons s10 a few months ago after a line broke in the rear. To reposition the internal valve we spiked the pedal once with the bleeder open on the front. then we could bleed the system. When the valve was not in the right position the "BRAKES" light on the dash would light. It was alot of help!

[PeterR]

Keep in mind that the rears are adjusted weekly, and the fluid is topped off weekly while bleeding - so it's unlike a street operation where pedal travel might become an issue over time due to shoe/pad wear.


....We went with the phenolic piston and have experienced no brake fad since. ....On the other hand, I don't believe I would use the phenolic in a street application.
B.P.

Bob, glad to hear a person with experience in both areas make a clear distinction between the different rigours of racing and street use.  There is a notion held here particularly by young constructors "if it is good for the track it must be better for the street" and they get real * if anyone tries to convince them otherwise.

And another question for you, has anyone made ceramic caliper pistons to cut heat flow?  I remember reading they have been trialed for diesel pistons so they should be durable enough.

Peter

[Bob Paulin]

Bob, glad to hear a person with experience in both areas make a clear distinction between the different rigours of racing and street use.  There is a notion held here particularly by young constructors "if it is good for the track it must be better for the street" and they get real crappy if anyone tries to convince them otherwise.

Peter.....

I cannot count the number of street guys who have stopped by the shop complaining about their cars not having the power they expected from their self-built engines, only to tell them to take their vehicle out on the nearby highway, leave it in third gear (as opposed to fourth), and accelerate up past 3000-3500 RPM just to see how the engine felt there.

Every single one of them comes back more educated than when they left.

(I used to take them out myself, but I was getting a stiff neck from all these cars coming up on the cam when we hit the right RPM range.)

Then I tell them that the old saying "Some is good, more is better, and too much is just right" does NOT, obviously, apply to camshafts.

And another question for you, has anyone made ceramic caliper pistons to cut heat flow?  I remember reading they have been trialed for diesel pistons so they should be durable enough.

Peter

I've not seen such a component - but I would be interested in trying some in the race car.....providing, of course, that they don't double the overall cost of the race car....

We run on a fairly skinny budget.......LOL!!!!

That's why we're using phenolic. They cut down on heat transfer to the brake fluid - and it seem to be working quite well.


B.P.