Brake thought for the month.

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brian
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Joined: June 26th, 2006, 12:31 pm

Brake thought for the month.

Post by brian »

Bleeding brakes is probably the most critical and most misunderstood process in the brake world. Drum brakes are more demanding than discs about being bled. Because drum brakes use a bit more pedal travel and utilize return springs, eliminating all air from the system is absolutely required.

Air, like all the elements of nature takes the least path of resistance. If the bleeding screw is not at the top of the system, meaning the backing plate locates the wheel cylinder at 12 o clock, you have a possibility of trapped air that will never get removed. Take a water bottle and imagine the bleeder in the middle and rotate the bottle. Watch as the bubble or air space moves around, it always stays at the top. There is only one position where the air will leave the bottle and that's when the bleed screw at it's the highest point relative to the fluid.

Anyone who runs the rear backing plate rotated for "aero" reasons and everyone who has the stock front wheel cylinder at 9 or 3 o clock can run into this issue. In both cases, I rotate the rear axle or front backing plate to move the wheel cylinder to 12 o clock when bleeding after assembling a dry system. We used a high pressure bleeding system in our brake shop and the force and turbulence of the system would usually get the air out. Doing it manually won't work. We once had to jack the rear of old Ferrari several feet into the air to get the wheel cylinders high enough to get that last bubble out.

Assuming the shoes have been properly adjusted, the master cylinder operating shaft should not travel more than 1/2". If your pedal assy includes a balance bar, disconnect one side at a time and make sure both side provide a hard pedal in a very short distance. If your system is fully bled, and there isn't more than 3mm difference between master and wheel cylinder, there is no reason why the stroke of the pedal to be further than 1" max. I use 5/8 masters and have typical 19mm/22mm wheel cylinders. If you are taking a second stroke to get a hard pedal, you need to bleed again.

Another issue particular to drums systems is bleed back caused by return springs or by the fact that the master cylinder is lower than the wheel cylinder. Ever notice modern cars have the master cylinder mounted high on the firewall? In addition to ease of access, it is to prevent bleed back into the master caused by gravity. Wilwood makes a check valve for drum systems that is set at 10 psi to prevent bleed back and sells for about $25 and is a worthwhile investment.

Our systems, while not as severe as bigger cars, suffer significant heat cycles within the brake fluid. I have never suffered fluid boiling typical of heavier cars but have seen corrosion in the cylinders caused by moisture generated by heat and time. I prefer to bleed out the old brake fluid about every 3 or 4 weekends. If you use a clear hose, which you should, you will see when fresh fluid comes out and all the old stuff is in the bucket. You do not need uber expensive synthetic fluid. DOT 4 is fine, and if you bleed out the fluid like I do, and do it once more just before storage, you'll never have to buy another wheel or master cylinder due to corrosion.

One final thought. Brake line size does not effect pedal travel. Once the system is free from air, a one cubic inch displacement at the master will, in all cases, result in a one cubic inch displacement at the wheel cylinder. Brake line flex or bulging is a function of psi acting on the internal surface area of the brake line so folks like to run as small a line as possible claiming that a -2 line will give a firmer pedal than a -3. I'm not sure with our drum system we are even approaching the kind of psi that would create that difference but have no data to dispute it. Frankly it may be a case of placebo effect on the part of the driver but if you want to spend more money, the smaller lines certainly won't hurt your performance.

Hope this helps, be safe out there.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
SR Racing
Posts: 1209
Joined: June 24th, 2006, 1:58 pm

Re: Brake thought for the month.

Post by SR Racing »

Good post Brian.
Wilwood makes a check valve for drum systems that is set at 10 psi to prevent bleed back and sells for about $25 and is a worthwhile investment
.

They also make a 2 psi residual valve which is probably a bit better for our use (if needed). (BTW, OUR price is under $20 :lol: )
BUT.. I would not recommend a residual valve for any drum brakes unless you KNOW you need it.
claiming that a -2 line will give a firmer pedal than a -3. I'm not sure with our drum system we are even approaching the kind of psi that would create that difference but have no data to dispute it. Frankly it may be a case of placebo effect on the part of the driver but if you want to spend more money, the smaller lines certainly won't hurt your performance.
Another big agreement.
FV80
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Re: Brake thought for the month.

Post by FV80 »

Another thing that hasn't been mentioned is the DRAG created by poorly maintained wheel and master cylinders .. MOSTLY *WHEEL* cylinders. Occasionally (few weekends - once a year?) you should take each drum off and visually watch the wheel cylinder travel (make sure you don't blow the puck out with overtravel!) when the pedal is depressed.. mostly you should be watching the wheel cylinder (brake shoe) return movement when the pedal is RELEASED. If you do not change your fluid often enough .. or maybe NEVER do any work on your wheel cylinders, they tend to 'crud up' and DRAG. When you press the brake pedal, the wheel pucks *WILL* go outward - you can apply too much force to keep them from being able to resist. HOWEVER, when you take your foot off the pedal, the only thing that takes those shoes away from the drum is the SPRINGS. You can easily have more DRAG in the wheel cylinders than the springs can override.

Of course, if you properly maintain your system, you'll likely not have ANY problems. As a minimum, I always take my WC's apart and clean them .. maybe light HONE if needed over the winter and refill with fresh fluid. I also use semi clear fluid reservoirs so that I can observe the COLOR of the fluid every time I take the nose off my car. If I notice any darkening, *THEN* it's time for a fluid change.

A rough alternative to all of the above is to rebuild your master cylinders every year and REPLACE your wheel cylinders every season. New wheel cylinders are only about twice the cost of a rebuild kit and will save you a reasonable amount of effort :mrgreen: .

Steve, FV80
The Racer's Wedge and now a Vortech, FV80
To sign up in the FV Registry for updates about SCCA Formula Vee, please send me an email or PM with your name, location (city/state), make/model of car, phone # and any other appropriate info.
brian
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: Brake thought for the month.

Post by brian »

Great input guys. It's what makes this forum a great resource. I forgot to mention:

Brake fluid is isotropic, that means it absorbs moisture like a sponge. Don't buy large containers of BF. Buy two small bottles and save the sealed one to fill new systems. Buy as you need.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
jferreira
Posts: 19
Joined: November 2nd, 2011, 1:12 pm

Re: Brake thought for the month.

Post by jferreira »

I have ONE wheel, Right Rear, that I have a problem with. After about 2 sessions (20 minutes each) I get brake drag. I back off the adjuster, make sure I have no drag, but after 40 minutes, it's dragging again.
Cleaned it, checked out movement, all seems fine. Any thoughts?
(No, I am NOT going to put disk brakes on ...) :roll:

John
FVartist42
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Joined: May 17th, 2013, 11:54 am

Re: Brake thought for the month.

Post by FVartist42 »

Could you possibly be missing the adjuster tabs?
brian
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Joined: June 26th, 2006, 12:31 pm

Re: Brake thought for the month.

Post by brian »

Frankly I have the same problem from time to time and it could be several things. Make sure the contact areas on the backing plate are free of grooves and are smooth. If not, grind smooth. Make sure the hold down pins are the right length and check and see if the shoes move back and forth. Check carefully to see if the backing plate is straight and true. Make sure the wheel cylinders are returning all the way by carefully operating the brakes with the drum removed and make sure the cylinder returns all the way. Convert to a taped adjuster if straights are used. You can grind the shoe to work with the tapered adjuster. If the drum has been turned make sure there isn't a lip left of the inside to make the shoes stick. As mentioned before, if nothing is noticed after all these checks, change the wheel cylinder, they're cheap.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
brian
Posts: 1348
Joined: June 26th, 2006, 12:31 pm

Re: Brake thought for the month.

Post by brian »

I have just completed a race weekend and tested the semi-metallic Chinese shoes. They are quite cost effective, about $20 for a pair of fronts, did not require any bedding and seemed to be very kind to the drums. They do not work quite as well as the CT's and require more pedal pressure but for the budget minded, vintage or racers that run on tracks that don't require super heavy braking, I think they're fine. I would have raced the Majors with them but wanted to do a back to back with Kevlar and didn't have time to do both. Once again, a fellow competitor mentioned that he was having great success with the Porterfields.

I'm pretty sure the semi metallics are available from CIP. (Cal Import Parts) and maybe SR. CIP advertises in Hot VW and are on the internet. If enough folks ask, I can make a purchase and redistribute but it's probably easier on line with one of the vendors mentioned.

I'm working with another supplier on a kevlar shoe that I am now testing. So far the tests look favorable and in the near future I will do a back to back test session against the CT's. If the R&D shoes are comparable, I will pursue further on price and production.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
sharplikestump
Posts: 183
Joined: January 12th, 2009, 2:28 pm

Re: Brake thought for the month.

Post by sharplikestump »

Great posts, guys!
Question on the adjustors: I have gone back and forth on the straight vs. angled adjustors. Is it the general consensus that the angled (tapered) are better? (I just set a friend up with the straights...gulp). Which were the successors from VW?
Also, after 40 years of dealing with these systems, I have started applying a VERY light coat of syn. grease to the contact points of the shoes/backing plates, as well as the shoes/slots. That came from another good post on this forum.
Maybe an old dog can learn a new trick! :oops:
The only possible constructive point I might add is that I think it is wise to periodically test all of your spring tensions, as they do tend to weaken with age, corrosion, and heat cycles, along with using springs from the same manufacturer on both sides.
Mike P.
brian
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Joined: June 26th, 2006, 12:31 pm

Re: Brake thought for the month.

Post by brian »

Here are the Bendix US made hardware kits: H7179 & H7162. Good stuff, certainly better than off shore and readily avialable.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
hardingfv32-1
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Joined: December 1st, 2006, 8:01 pm

Re: Brake thought for the month.

Post by hardingfv32-1 »

sharplikestump wrote:Is it the general consensus that the angled (tapered) are better?
What is the reason for the angled adjusters? Does it cause the shoe to move toward slave cylinder reducing the retracted shoe gap on the slave cylinder end of the brake shoe? Could this effect induce shoe drag?

Brian
brian
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Joined: June 26th, 2006, 12:31 pm

Re: Brake thought for the month.

Post by brian »

The angle adjuster assists in centering the shoe making the contact area more consistent.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
fvracer27
Posts: 247
Joined: October 25th, 2009, 8:40 pm

Re: Brake thought for the month.

Post by fvracer27 »

brian wrote:I have just completed a race weekend and tested the semi-metallic Chinese shoes. They are quite cost effective, about $20 for a pair of fronts, did not require any bedding and seemed to be very kind to the drums. They do not work quite as well as the CT's and require more pedal pressure but for the budget minded, vintage or racers that run on tracks that don't require super heavy braking, I think they're fine. I would have raced the Majors with them but wanted to do a back to back with Kevlar and didn't have time to do both. Once again, a fellow competitor mentioned that he was having great success with the Porterfields.

I'm pretty sure the semi metallics are available from CIP. (Cal Import Parts) and maybe SR. CIP advertises in Hot VW and are on the internet. If enough folks ask, I can make a purchase and redistribute but it's probably easier on line with one of the vendors mentioned.

I'm working with another supplier on a kevlar shoe that I am now testing. So far the tests look favorable and in the near future I will do a back to back test session against the CT's. If the R&D shoes are comparable, I will pursue further on price and production.

Great info from everyone on this thread I like seeing stuff like this being discusses like this.

Brian I have been using the Porterfields and I did not do a back to back test but I did compare my Data laps running CT and the RD4 Porterfields and my stopping distance is almost exact if not better with the RD4s. I'm very happy with them and at a track like NHMS which is pretty demanding on brakes they never fad and are very very consistent, I adjusted the brakes and again after the fist session once they cooled and I may have moved them 1 click after 3 weekends. This past weekend I did not even check the adjustment they just felt awesome.
Mark Filip
NER #27
Womer EV-3
brian
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Joined: June 26th, 2006, 12:31 pm

Re: Brake thought for the month.

Post by brian »

Some reports of swelling and dragging have been made regarding the more agressive Portherfields but the issue can be dealt with by backing off a couple of clicks on adjustment or adjusting while hot.
The above post is for reference only and your results may vary. This post is not intended to reflect the views or opinions of SCCA and should not be considered an analysis or opinion of the rules written in the GCR.
sharplikestump
Posts: 183
Joined: January 12th, 2009, 2:28 pm

Re: Brake thought for the month.

Post by sharplikestump »

Nothing new to add here....I was scanning through, and think this is such an excellent post by Brian, I feel it may be worth reviewing by others. It was for me.
fv22
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Joined: June 24th, 2006, 8:38 pm

Re: Brake thought for the month.

Post by fv22 »

Is there a reason wheel cylinders are placed vertically at the 9 or 3 o'clock position? Obviously makes it hard if not impossible to bleed properly when mounted like that. Seems to me they should always be at the top with bleeder up at highest point but I have seen them in different positions on different cars.
BLS
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Re: Brake thought for the month.

Post by BLS »

I'm assuming you are asking about the rear regarding location, since they can be relocated while the fronts cannot.

I'll guess that many locate the rear from the original upper position thinking it is more aerodynamic. I don't think it matters.

The top position is the better one to properly bleed the brakes.

On the fronts, I will initially bleed them without the shoes and by turning the cylinder to place the bleeder at the top. Clamp the pistons. This gets all the air out. I don't think many people do this, believing all the air will get out anyway. I've bled the brakes the normal way, then done this and found a tiny bit of air. YMMV.

If the rears are not mounted at the top I would do the same thing.
Barry
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FV80
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Re: Brake thought for the month.

Post by FV80 »

The rears are 'normally' mounted at the top. The fronts are not. I have not had any problems bleeding the fronts at the 3 and 9 positions. If done right, it is not an issue. Bleed the brakes by installing a bleed tube that is immersed in brake fluid (standard 'bleeding' container - if you make your own, make certain that the tube extends deep into the bottom of the bleed container enough to be below the level of fluid in the container). Open the bleeder screw enough to allow fluid to escape, but not enough to allow AIR to get back in (takes some 'touch' - using CLEAR tubing allows you to SEE any bubbles and tell if they are being drawn back towards the wheel cylinder). Then slowly depress and release the brake pedal several times until no more air can be seen coming from the end of the tube in the container. Close the bleeder and 'bang' the pedal several times, then press and hold the pedal while releasing the bleeder screw until fluid comes out. Watch for bubbles. If you don't see any, you are done. Also, if you have clear bleeder tubes (and you SHOULD), make sure they exit the bleeder UPWARD, so that any air will be visible immediately. If the wheel cylinders are in good condition and this process is done correctly, the internal WC seals will almost touch each other in the center at full release of the brake pedal. There really should be no place for air to be trapped. Banging the pedal a couple of times should ensure that there is no trapped air. Visually confirming that there is no air remaining in the tube should be adequate. If in doubt, repeat the process.

For both front and rear, it's best to JACK the car so that the wheels being bled are above the master cylinders. That should endure that any air that is in the system will gravitate to the bleed screw. Make sure you always bleed enough fluid to purge the entire line from the master to the wheel cylinder each time. That will ensure that only CLEAN fluid remains in the system. To minimize fluid waste, I generally dump almost all of the fluid in the master cylinders before starting the bleed process. Dump as much as possible without getting it below the input valve at the bottom. (If there is any residue in the master cylinder reservoir be sure to CLEAN It thoroughly before proceeding, even if it means exposing the port in the bottom. CLEAN fresh fluid in the system should be your primary goal.) . Then add enough fluid for a couple of pumps.. allow the fluid to get down to the bottom but NOT expose the input port. Add enough more fluid and repeat the process at least twice. Just be sure to flush enough fluid to make SURE that any air trapped at the MC has had enough time to make it to the wheel cylinder and get out.

OH.. one more thing.. as a start, I generally open BOTH rear bleed screws that the same time to ensure that there is no air trapped at the splitter between the rears. Then close both and proceed with bleeding of one, then the other. Not much of a problem in the front since the line is split right at the master cylinder instead of several feet away.

Steve, FV80
The Racer's Wedge and now a Vortech, FV80
To sign up in the FV Registry for updates about SCCA Formula Vee, please send me an email or PM with your name, location (city/state), make/model of car, phone # and any other appropriate info.
BLS
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Re: Brake thought for the month.

Post by BLS »

Almost forgot about this.
You should read and listen to Steve of course.
One thing I remember I discovered later - I was using one of those bleeder devices with the check valve. Works pretty good. However, my report of a bit of air left in the front wheel cylinder was actually a problem with this. I found that while the check valve worked just fine, when you released the pedal a very small amount of air would get sucked back around the threads of the wheel cylinder bleeder screw. That doesn't happen when you open and close the bleeder screw with the stroke of the pedal. I actually didn't have any problem once I realized that.

They make bleeder screws with the check valve in them. Those have a bit of sealant on the threads to prevent the air from going by the threads. I have not tried them but they are cheap enough that they might be worthwhile.
Barry
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Re: Brake thought for the month.

Post by FV80 »

BLS wrote:...I was using one of those bleeder devices with the check valve....
I have tried those 'auto-bleeders' as well and also found that they leaked air back into the system.
Follow the process and DOUBLE CHECK using CLEAR bleed tubing. You won't regret it.
Also, make sure to apply a small amount of hi-temp lube to the shoe contact areas on the backing plates... and make sure to CLEAN and reapply every time you inspect the shoes.
The Racer's Wedge and now a Vortech, FV80
To sign up in the FV Registry for updates about SCCA Formula Vee, please send me an email or PM with your name, location (city/state), make/model of car, phone # and any other appropriate info.
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