Brake Problems

[Bruce Baier]

As received from MRP Customer, Mr. Hastings.

From: Paul Hastings
To: garry@mrpmotorsport.com
Sent: Tuesday, March 16, 2004 11:39 AM
Subject: New front brakes


Garry,

I have purchased several parts from you in the past. I have a 125shifter, I believe the chassis is CR32. I do not use the kart too much so it sits in my garage a lot. This is the second time I am having front brake problems. I can hear air in the front calipers so I did a rebuild and found pitting in the calipers. This happened once before and I am not sure what is going on. The rear has never been replaced and seems to be fine. There is also a slight bit of fluid rising from the front master cylinder. Last time out I had dangerously little braking power.

What are you recommendations? New front calipers? New front calipers, master cylinder and lines? Are there different brake options for this chassis?

I would greatly appreciate your help. By the way, as you may know the pricing is not accessible on your website so please include pricing.

Respectfully,

Paul Hastings

[Bruce Baier]

Good Morning Mr. Hastings.

Mr. Lobaugh has referred your question on brakes to me.

Brake problems are common on all karts whether you use the kart a lot or just occasionally. Obviously wear / heat is the factor if used frequently. Occasional use subjects the system to other factors. The largest factor is moisture. We are not able to use synthetic brake fluid in these systems, and so DOT 3 or DOT 4 is the choice. Both of these fluids are hyroscopic in nature, which means they attract water. Even though the brake systems are semi-sealed, water still finds its way into the fluid. The water is then the source of corrosion that you find on the aluminum bore of the calipers. If the kart is not going to be used for a long period of time (over 90 days) then the system should be dis-assembled and washed carefully in warm soapy water. Re-assemble prior to next use and bleed the system with fresh fluid (from a closed container). This will prevent corrosion of the aluminum components. (Remember to store extra fluid in a tightly closed container. If left open to the atmosphere, the fluid will attract moisture from the air and become contaminated.)

Some pitting of the caliper is generally not a problem, so long as it is not too deep and is away from the area that the caliper seal travels on. Most often, the pitting can be removed by using either very fine sandpaper or fine grade scotch brite. It is also possible to "hone" the bore of the caliper with a brake cylinder hone, but that is usually a last resort. Stick to the fine sanding if possible. If the pitting is deep and lower in the bore where the seal travels, then it may be necessary to replace the caliper. I will assume that your caliper housings can be reused. Sounds like you have already re-built these, but still have some problems.

Front Brake Caliper rebuild kit: 10.1735.00
Front Brake Pad : 10.0892.00
Front Pad Spacer 0.5mm : 20.2624.10
Front Pad Spacer 1.0mm : 20.0957.10
Front Brake Caliper Assy : 10.0947.00 (right)
Front Brake Caliper Assy: 10.0948.00 (left)

Three areas are left that can cause "dangersously little braking power". The first thing to look for is clearance between the brake pads and the brake disc (rotor). If the pads are worn, the air gap between the friction material and the rotor gets larger, requiring the caliper piston to move further to make the pad contact the rotor. The bore of the caliper is 1 1/4" and so a lot of fluid is needed to push the piston the distance needed to make pad contact with the rotor. The bore of the Master Cylinder is 7/8" and of course the one master is moving two 1 1/4" pistons (one in each of the front calipers). As a result, pad clearance to the rotor is critical for proper brake operation.

It is possible to place FreeLine brake spacers between the caliper housing and the brake pads to reduce travel. These spacers are available in 0.5mm and 1.0mm thickness. You may use up to 1.5mm of spacers on each of the inner and outer front brake pads. New brake pads may be needed to return the system to proper pad to rotor clearance. Make certain that you have no more than a total of 1.5mm air gap pad to rotor on each front caliper. Shim or replace pads as necessary.

The second area of concern is the Master Cylinder. Because of the small amount of fluid that the master is capable of moving (7/8" bore), it is critical that the cylinder be FULL of fluid, and have absolutely NO LEAKAGE. Rebuilding this component is a bit tricky because of the double seal piston. It is common for the bore of the master to be damaged usually due to intrusion of dirt past the cover and piston. Once damaged, the housing is no longer useable. Dis-assemble the master, clean and inspect the bore. If damaged, replace the cylinder. If it is O.K., then rebuild with overhaul kit. (NOTE: it is possible to replace the housing only. If you need a rebuild kit too, the best way to go is with a Master Cylinder Assembly, it comes fully assembled.)

Master cylinder Assy 22S : 10.1720.00
Master Cylinder Kit 22S : 10.1736.00
Master Cylinder Housing 22S : 20.1557.10

The third and last area to concentrate on is the bleeding procedure. It is critical that absolutely NO AIR be left in the system. I strongly recommend using a brake bleeder specifically designed for use on a Kart brake system. The brake bleeder is designed for gravity bleeding of the system. Follow the instructions found on the MRP web site at:

www.mrpmotorsport.com

In addition to the above, I strongly recommend that you rebuild the rear brake system too. It is subject to the same corrosion that happens to the front. I am certain that when you take apart the rear caliper, you will find lots of good reason to have gone through the process. Same process is needed for air gap between the pads and the rotor surface. Shim or replace pads as necessary, make sure there are no leaks and the system is properly bled. Inspect the rear system Master Cylinder as well, and follow the above suggestions.

Rear Brake Pad: 10.0890.00
Rear Brake Pad Spacer 0.5mm : 20.2625.10
Rear Brake Pad Spacer 1.0mm : 20.0781.10
Rear Caliper Overhaul Kit : 10.1734.00

It is unlikely that you will need to replace any of the brake lines, unless they are damaged or leaking. The lines on the kart are high pressure stainless weave with a vinyl covering. Be careful not to over-tighten line connections, as it is possible to damage the fittings.

In answer to your other questions, there is no different brake option for the front of your kart. Depending on the year of the chassis, it may be possible to upgrade the rear system. In terms of what you need to restore the system to proper operation, this can only be answered once you have dis-assembled the system(s) and determined what is needed. Once that is done, let us know what you need, and we will be happy to provide you with prices for the pieces you need.

I hope that you find this information helpful. Thank you for your continued interest in Birel / MRP products and services.

Kind regards
Bruce Baier

MRP Motorsport.

[Scott Donovan]

Bruce;

I'm having issues similar to those referemced in the original post. My brakes have been rebuilt, and the piston cylinders on the calipers have been polished, though some leaking continues in the front right caliper. There was some slight pitting which I will attempt to remove in the hope that the leaking will stop.

After reading the response to the original post, two questions come to mind:

What is meant by semi-sealed in reference to these brake systems?

Why is synthetic, DOT 5 brake fluid not suitable for these systems?

Thanks,
Scott Donovan

[Bruce Baier]

Hello Scott

Thank you for your brake related questions.

First of all, sounds like you may need to hone the caliper bore to get rid of the last bit of leakage. If this is the case, your local auto parts store should be able to provide you with a fairly inexpensive brake cylinder hone. Don't go overboard with this tool, as removing too much of the bore sizing will render the part useless. Good luck with the procss.

By semi-sealed, I simply refer to the fact that from time to time the system is opened to the atmosphere - to add fluid etc. This allows for the intrusion of moisture. Once you replace the screw in the cylinder, it is for all intents and purposes, "Sealed".

The problem with synthetic brake fluid is that it attacks and breaks down the seals used in this simple brake hydraulic system. Using synthetic fluid causes the seals to swell and failure of the system is just a matter of time.

By the way, it does no harm to polish the caliper pistons, but this will not provide any change to the operation of the caliper. Originally, the pistons were anodized to help protect them. Removing any rough areas on the surface of the piston (that may happen through normal use) is a good idea and helps reduce wear on the caliper bore. Polishing is optional (for the information of readers on this forum).

I hope this helps with your questions, and thanks again for visiting the MRP / Birel Forum.

Regards
Bruce Baier

[Scott Donovan]

Bruce;

Thank you for the considered response and thanks to MRP for the new forum. Every bit of information helps.

MRP's new discussion board should turn out to be a great resource for the karting community and may reduce your need to repeatedly answer common questions.

Congratulations for implementing a great idea.

Scott Donovan

[RobbieNelson]

The second area of concern is the Master Cylinder. Because of the small amount of fluid that the master is capable of moving (7/8" bore), it is critical that the cylinder be FULL of fluid, and have absolutely NO LEAKAGE. Rebuilding this component is a bit tricky because of the double seal piston. It is common for the bore of the master to be damaged usually due to intrusion of dirt past the cover and piston. Once damaged, the housing is no longer useable. Dis-assemble the master, clean and inspect the bore. If damaged, replace the cylinder. If it is O.K., then rebuild with overhaul kit. (NOTE: it is possible to replace the housing only. If you need a rebuild kit too, the best way to go is with a Master Cylinder Assembly, it comes fully assembled.)

I've taken one of my master cylinders apart to inspect and clean. Everything look "OK", but I can't get the piston back in. The housing looks the same as what I've seen online (http://www.mrpmotorsport.com/community/showthread.php?t=1267), but the piston looks different. The piston does not have o-ring type seals. It's using some sort of cupped seals. I can get the first seal in, but the second seal won't go into the cylinder. I've lubed it with brake fluid, wiggled it back and forth and applied lots of pressure. It won't go in. Is there a trick to this or could the seal be swollen?

Also... I have 6 master cylinders; all of them the same. None of them have the clip or the boot on the end of the cylinder. They also use the cupped seals (if that's the right term). Are these cylinders a different model than what I've seen online (http://www.mrpmotorsport.com/community/showthread.php?t=1267)?