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Weird brake issues #3096723
11/24/22 01:37 AM
11/24/22 01:37 AM
Joined: Feb 2010
Posts: 18,205
Granite Bay CA
Kern Dog Offline OP
I Live Here
Kern Dog  Offline OP
I Live Here

Joined: Feb 2010
Posts: 18,205
Granite Bay CA
I have a thread on the Handling forum that originally pertained to my Borgeson steering box installation but since that veered away from that and onto my brake system, I'm starting this thread.
In summary.....
In May of this year, I installed the Borgeson steering box. Within 10 days, the cam went flat in the 440-493 and I pulled the engine to go through it.
While the engine was out, I decided to upgrade the brakes.
THAT turned out to be the biggest hurdle of the whole project.
The car is a 1970 Charger. It weighed 3940 lbs and has a Tremec 5 speed transmission.
Before the engine removal, I had 11.75" Cordoba front disc brakes with 2.75" single piston calipers, the Dr Diff 11.7" rear disc brake kit with 1.5" single piston calipers and a 1975 Dart power booster and 15/16" master cylinder. Braking was decent but not excellent.
I wanted to improve the braking to a level on par with newer cars so I ordered a 13" front brake kit with drilled and slotted rotors from Dr Diff and while I was at it, matching rear rotors. He also sent me an experimental hydroboost unit to install, test and report about.
I formed the hydraulic lines for the hydroboost, sourced a Saginaw P/S reservoir with 2 return line nipples, the suggested 79-93 Dodge D-150 2 bolt 1 1/8" master cylinder and screwed it all together.
Right away, the HB provided no boost while the steering worked normally. I bled the brakes and still, the HB was inop but soon, the steering assist began to fail. I put in another pump and the same thing happened again. A 3rd pump started going bad so I removed the HB and boxed it up to return it. I tried a number of bleeding attempts with the HB system with no success so I felt that I gave it a fair shot.
I installed a 15/16" master cylinder in an attempt to make a manual brake system work. I've driven and owned several manual disc-drum A bodies and the braking is excellent with them. I expected similar results from this car but was disappointed in the feel and performance. Pedal effort was very high and brake force was very low. I don't have gauges to test the pressures.
to
Yesterday I noticed that when I bench bled a master cylinder, that the front port (which is supposed to serve the rear brakes) got fluid and bubbles first. This surprised me because with the front brakes assuming the majority of the braking force on street cars, I'd have expected the rear port (which is supposed to serve the front brakes) to get the fluid first.

Today I lined up all the master cylinders that I have gathered....

Three are cast iron 4 bolt units. One at 1" and two of them 15/16".....They all had 9/16" front ports, 1/2" rear ports and when bench bled, pushed fluid equally in time front and rear.

Two of the aluminum units were 1.03" and had 9/16" front, 1/2" rear ports and pushed fluid equally.
One aluminum one was 15/16" and had weird 3/8" ports. The front reservoir was longer but the whole reservoir was sloped.

It pushed fluid to the front first.

The final two MCs are the ones I've been working with lately. Both 15/16" and 1 1/8" units have identical ports and push fluid to the front reservoir first.

Re: Weird brake issues [Re: Kern Dog] #3096760
11/24/22 09:42 AM
11/24/22 09:42 AM
Joined: Dec 2014
Posts: 4,362
ohio
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ruderunner Offline
master
ruderunner  Offline
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Joined: Dec 2014
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ohio
The oddball master with the small fittings is likely for FWD.

For reference, I have a 69 Roadrunner with the Cordoba ft brakes, 10 inch drums no assist, 1.125 aluminum 2 bolt master. Wheel cylinder are too small but car stops quite well.

Regarding fluid flow when bench bleeding, it doesn't matter. Once both sides are bled out they function in tandem with a possible miniscule difference where the port closest to the pedal will flow first. This is basically from the slack as the seals expand etc.

Caliper bores are going to be needed, see Feets thread on brake math.

What are you using for a proportion valve? A properly balanced all disc system shouldn't need one.

On the hydroboost I wonder if you had the lines reversed.


Angry white guy
Re: Weird brake issues [Re: ruderunner] #3096850
11/24/22 02:39 PM
11/24/22 02:39 PM
Joined: Feb 2010
Posts: 18,205
Granite Bay CA
Kern Dog Offline OP
I Live Here
Kern Dog  Offline OP
I Live Here

Joined: Feb 2010
Posts: 18,205
Granite Bay CA
Originally Posted by ruderunner
The oddball master with the small fittings is likely for FWD.

For reference, I have a 69 Roadrunner with the Cordoba ft brakes, 10 inch drums no assist, 1.125 aluminum 2 bolt master. Wheel cylinder are too small but car stops quite well.

Regarding fluid flow when bench bleeding, it doesn't matter. Once both sides are bled out they function in tandem with a possible miniscule difference where the port closest to the pedal will flow first. This is basically from the slack as the seals expand etc.

Caliper bores are going to be needed, see Feets thread on brake math.

What are you using for a proportion valve? A properly balanced all disc system shouldn't need one.

On the hydroboost I wonder if you had the lines reversed.


Your car stops well because the drums at the rear require little pressure to operate and they are "self energizing". When I had a disc-drum arrangement, my car stopped about the same as when I changed to the 11.7" rear discs. I didn't expect much of an improvement anyway, I wanted the improved appearance of the disc rotor.
The caliper bores are Front : 2 pistons @ 1.59" Rear: 1 piston @ 1.50".
The front to rear bias matches a 1994-2001 Mustang Cobra as stated by Dr Diff. The bias matches the 2 to 1 goal which is what Andy Finkbeiner says is the desirable target.
There is no proportioning valve. The lines all merge into a drum-drum distribution block which has no proportioning factor to it.
The hydroboost was plumbed correctly. There were no mistakes there. Apparently, the bleed process can take quite a while or it can bleed fast. It can vary. Some HB units require more pressure and volume than a standard pump can produce. I used Saginaw pumps because that is what was on the car, the brackets I have fit the Saginaw units and they are OEM in Chevy trucks with hydroboost.

Re: Weird brake issues [Re: Kern Dog] #3096950
11/25/22 02:32 AM
11/25/22 02:32 AM
Joined: Feb 2010
Posts: 18,205
Granite Bay CA
Kern Dog Offline OP
I Live Here
Kern Dog  Offline OP
I Live Here

Joined: Feb 2010
Posts: 18,205
Granite Bay CA
Dr Diff sent me a link to an article on how to "Bed in" the pads and rotors.
I've never had to do this before. It was a surprise to me.
***************************************************************************************************************************************************************************************************************************************************

Caution: Immediately after installing new pads, rotors or a big brake kit, the first few applications of the brakes will result in very little braking power. Gently use the brakes a few times at low speed to build up some grip before blasting down the road at high speed. Otherwise, you may be in for a nasty surprise the first time you hit the brakes at 60 mph.

If you just installed rotors with zinc plating or if the rotors have an anti-corrosion phosphate coating, you should postpone bedding until normal driving has allowed your pads to polish the rotors clean and removed all traces of the plating or coating. If your new brake rotors have an oily anti-corrosion coating, clean this off thoroughly with brake cleaning spray and/or hot soapy water before installation.

Read and understand these instructions completely before starting. If you have questions, give us a call or email. Do not substitute higher speeds for the 60mph called for. The heat in brakes goes up exponentially as you increase the speed from which you brake. Repeated stops from 80 or 90mph with street pads will overheat the brakes and you may end up having to replace pads and rotors.

When following these instructions, avoid other vehicles. Bedding is best done when traffic is light, as other drivers will have no idea what you are up to and may respond in a variety of ways ranging from fear to curiosity to aggression. A police officer will probably not sympathize when you try to explain why you were driving erratically! Zeckhausen Racing does not endorse speeding on public roads and takes no responsibility for injuries or tickets you may receive while following these instructions. Use common sense!

From 60mph, gently apply the brakes a couple times to bring them up to operating temperature. This prevents you from thermally shocking the rotors and pads in the next steps.

Make eight to ten near-stops from 60mph to about 20 mph. Do it HARD by pressing the brakes firmly, but do not lock the wheels or engage ABS. At the end of each slowdown, immediately accelerate back to 60mph, then apply the brakes again. DO NOT COME TO A COMPLETE STOP! If you stop completely, with your foot on the brake pedal, pad material will be imprinted onto the hot rotors, which could lead to vibration and uneven braking.

The brakes may begin to fade after the 7th or 8th near-stop. This fade will stabilize, but not completely go away until the brakes have fully cooled. A strong smell from the brakes, and even some smoke, is normal.

After the last near-stop, accelerate back up to speed and cruise for a few minutes, using the brakes as little as possible to allow them to cool down. Try not to become trapped in traffic or come to a complete stop while the brakes are still hot.

If full race pads, such as Hawk DTC-70 or Performance Friction PFC11 are being used, add four near-stops from 80 to 20 mph.

After the break-in cycle, there should be a slight blue tint and a light gray film on each rotor face. The blue tint tells you the rotor has reached break-in temperature and the gray film is pad material starting to transfer onto the rotor face. This is what you are looking for. The best braking occurs when there is an even layer of pad material deposited across the rotors. This minimizes squealing, increases braking torque, and maximizes pad and rotor life.

After the first break in cycle shown above, the brakes may still not be fully broken in. A second bed-in cycle, AFTER the brakes have cooled down fully from the first cycle, may be necessary before the brakes really start to perform well. This is especially true if you have installed new pads on old rotors, since the pads need some usage to conform to the rotor wear pattern. If you've just installed a big brake kit, pedal travel may not feel as firm as you expected. After the second bedding cycle, the pedal will become noticeably firmer. If necessary, bleed the brakes to improve pedal firmness.

Re: Weird brake issues [Re: Kern Dog] #3097036
11/25/22 12:47 PM
11/25/22 12:47 PM
Joined: Sep 2003
Posts: 16,852
north of coder
moparx Offline
"Butt Crack Bob"
moparx  Offline
"Butt Crack Bob"

Joined: Sep 2003
Posts: 16,852
north of coder
i put ceramic pads on my "bus" [1999 caravan] and was disappointed on the stopping power i expected from them, during casual driving.
i then did a bed in process on the road that goes past my house, after it gets out of the "city". when that happens, it becomes a road with little traffic, and has many places this can be done safely.
after the bed in process, the pads improved tremendously !
it's a process well worth doing ! up
beer

Re: Weird brake issues [Re: Kern Dog] #3097037
11/25/22 12:52 PM
11/25/22 12:52 PM
Joined: Dec 2014
Posts: 4,362
ohio
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ruderunner Offline
master
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Joined: Dec 2014
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ohio
I'm aware of the self energizing effect on the drum brakes. I did also mention the too small wheel cylinders.

I think you're in the ballpark on balance front and rear.

Bedding in pads or shoes isn't a new thing by any means. Though many brands today are pre baked for customer convenience, it seems that the brand you have isn't.

There's also the difference in materials. Higher temp formulas tend to not grip well at lower temperature and vice versa.

At this point, I'd look at getting the brakes bedded in without the hydroboost and see if the basic system can perform.


Angry white guy






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