Troubleshooting brakes
From Crankshaft Coalition Wiki
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| − | + | ==Brake pedal goes to the floor== | |
| + | You will need a helper for this. | ||
| − | + | #On a level floor or better still on a car lift, raise car, and if necessary, use axle stands that will safely support the weight of your car; obviously you dont need axle stands for car ramp/lift. | |
| + | #First make sure the brake master cylinder is filled with good quality fluid, preferably new and from a sealed container | ||
| − | + | If it is empty check for leaks, if found repair leaks and continue, if not continue to next steps | |
| − | + | #Surround the master cylinder with some clean rags just in case of any accidental spillage of brake fluid. | |
| + | #On most cars, trucks, etc. | ||
| + | #Now your helper, who is in the driver's seat, presses the brake pedal. If the pedal still goes to the floor, it is time to attempt to bleed the master cylinder. You can use a master cylinder bench bleed kit which will install into the line ports and have an attached hose that goes back into the reservoir. Push and release the pedal until there are no air bubbles. Reconnect lines, check pedal. | ||
| − | + | If you still have no firmness on the brake pedal then it is time to bleed the rest of the system. Have your helper push the pedal 3/4 of the way to the floor and open the bleeder on the wheel furthest from the master, close bleeder, release pedal and repeat until there is just fluid coming out, no air. Go to the next furthest wheel and repeat until all wheels are done. It is important that the pedal not be released while the bleeder is open or you will suck air back into the system. Once you have completed this procedure you should have a good pedal. | |
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| + | When trouble shooting brakes do the easy things first. In order to develop good customer satisfaction for your shop and not waste your time, focus on getting to the true root cause first and fast. | ||
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| + | Check the fluid level of the master cylinder and look for obvious leaks around master first. Fill the master and replace the top, then pump up the pedal with the engine off. If the pedal becomes firm and then slowly leaks down; the leak is internal in the master itself, or it is external and small. If the pedal leaks down fast, you have an open line. This is a burst flex hose, missing bleeder, broken line, failed (open) wheel cylinder, leaking caliper or other mechanical damage. If the pedal will not pump up at all, there is a large leak or the master internal piston seals have split or failed. You will need to rule out a large external leak. If the pedal pumps up, gets spongy and then stays firm and doesn’t leak down you have air in the line and not a leak. You will have to bleed the brakes and then diagnose how the air got in. | ||
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| + | Start at the furthest rear tire and check the back of rear drum for signs of leaks, fluid slinging on the tire or discolored patches where the leaked fluid has collected dirt. Trace brake line to other tire until you find indications of a leak. Follow the path of brake line to the flex hose and then along frame until you see signs of a leak. Check the proportioning valve near front of the frame, check left front tire, caliper and flex hose for signs of leak. | ||
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| + | Follow brake line back to firewall and master, then follow line across to passenger side (right front) tire and look for leaks. After all this and no signs of leaks are found look at this caliper. Is everything within normal limits or is the caliper all the way out, rotor excessively worn or cut? Check the other rotor, is the condition and wear patters similar to the other side? | ||
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| + | Assuming the fluid level in the master is still good, take a pair of pinch–off pliers and pinch off the Flex hose that joins the rear breaks to the frame. Pump up the brakes. Is the pedal now firm and not leaking down? If yes, then the problem is in the rear. Remove the wheels and inspect the rear drums, shoes and wheel cylinders, or inspect the Rear Rotors, pads and calipers. Repair, remove and replace the items needed to restore the system to OEM specs and serviceability. If pinching off this hose made no change, then leave the hose pinched off and then continue to diagnose the system. Follow the lines along the frame back up to the master and try to notice any signs of obvious leakage. | ||
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| + | Find the flex hose on the left side caliper and use another set of pinch off pliers to pinch off the flex hose between the line and the caliper. Check the level of the fluid and pump up the brakes. Is the pedal now firm and not leaking down? If yes, then the problem is in this caliper. If the wheel is still on, remove the wheel and inspect this caliper and surrounding structure. Repair, remove and replace the items needed to restore the system to OEM specs and serviceability. If one caliper is bad expect to do both as the brakes should always be done as a set. | ||
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| + | Find the flex hose on the right side caliper and use another set of pinch off pliers to pinch off the flex hose between the line and the caliper. Pump up the brakes. Is the pedal now firm and not leaking down? If yes, then the problem is in this caliper. If the wheel is still on, remove the wheel and inspect this caliper and surrounding structure. Repair, remove and replace the items needed to restore the system to OEM specs and serviceability. As noted before; if one caliper is bad expect to do both as the brakes should always be done as a set. Likewise always fail safe (go/no-go) check your rotors with a micrometer and re-true them. Rotors also should always be replaced in pairs. | ||
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| + | If after all this and the pedal still will not pump up or hold a pedal, re-inspect all the lines from the master to the flex hoses, use a flash light if needed to inspect the lines running along the frame and again look for leaks and signs of leakage. | ||
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| + | To Positively rule out a bad master cylinder, unhook both brake lines and cap them off with brass caps of the proper thread. Plug the outlets of the master cylinder with the correct threaded brass or steel plugs and top off the cylinder to the proper level. If the pedal pumps up and holds a pedal the master is ok. If the pedal pumps up, is spongy but then holds a pedal and doesn’t leak down, then it has air in the outlets and needs bled. Bleed the master cylinder and reconnect the lines. If the pedal will not pump up or will not hold a pedal at all, the entire master is not good and needs replaced. | ||
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| + | You should now know where the leak is and how to correctly price out the repair for your customer. | ||
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| + | Destructive testing method is even faster, but by its nature if there is a problem…, you will be fixing something!!! | ||
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| + | Set the car on the lift and get it ready but don’t lift it. Open the hood check the fluid level in the master, top it off and securely replace the cover. | ||
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| + | Check the obvious first and verify that the brake pedal is connected properly to the actuator rod and not broken or bent. | ||
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| + | Get in the car, engine off, radio off and simulate a panic stop. | ||
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| + | Pump the brakes full travel 3 – 5 times hard. If there is a weakness in the system, it WILL break!!! | ||
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| + | Listen for pop and hiss from the brake lines and wheels. Get out of the car, check the fluid level and replace the top, and lift the car. | ||
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| + | With a flashlight, trace and inspect all your lines, the backs of all of the tires and look for signs of leaks. If there is no leaking, and you had no pedal at all, then the master is trash. You will need to R & R the master. | ||
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| + | Inspect the front and rear brakes and price out what you have to do to bring car back to OEM specs. If all the pads and shoes are good, then at a minimum figure on inspection (Micrometer) and re-truing (turning) the drums and rotors and button up. | ||
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| + | Remember…, air is compressible and liquid is not. | ||
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| + | If the pedal is spongy it has air in the system. | ||
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| + | If there is no pedal or will not firm up or hold a pedal, you are lacking fluid. | ||
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| + | Loss of fluid usually means a leak. | ||
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| + | [[Category:Brakes]] | ||
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| + | [[Category:Troubleshooting]] | ||
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