Noob question about bleeding brakes
Discussion
I'm just about to do my first ever set of discs and pads.
The car is an MG ZT. I've watched two how-to guides on this and neither of them mention anything about bleeding the brakes.
e.g.
https://www.youtube.com/watch?v=TwLbJZmG6gU
I had it in mind that bleeding the brakes is an important part of this process, and something you need to do, and do properly.
Am I wrong? When do you bleed brakes, if not during the process of changing pads and discs? Is it only on older cars or something...?
Thanks!
The car is an MG ZT. I've watched two how-to guides on this and neither of them mention anything about bleeding the brakes.
e.g.
https://www.youtube.com/watch?v=TwLbJZmG6gU
I had it in mind that bleeding the brakes is an important part of this process, and something you need to do, and do properly.
Am I wrong? When do you bleed brakes, if not during the process of changing pads and discs? Is it only on older cars or something...?
Thanks!
Bleeding brakes is done when you've either split a hose or when you want to change the fluid as a matter of course.
You don't 'need' to do it after changing pads, if anything the act of pushing the pistons back to fit the new pads will push any bubbles back, and you may have to extract excess fluid from the reservoir.
You don't 'need' to do it after changing pads, if anything the act of pushing the pistons back to fit the new pads will push any bubbles back, and you may have to extract excess fluid from the reservoir.
Most people would bleed brakes every 3 or 4 years, you can buy a tester to check for moisture content in the fluid reservoir but i've never bothered.
Bleeding the brakes when you change pads and discs makes sense, usually it will be about time they were done.
The problem with leaving things too long between bleeds is that the bleed valve corrodes in place and you won't be the first person to snap a bleed valve off, so i'd give the bleed valves a squirt of plus gas or other penetrating oil a few days before doing the job (not WD40), you could give the top of the bleed valves a little tap with a toffee hammer before attempting to undo them, also make sense to do this job when the motor factors are open in case you do end up needing a new caliper or fitting kit.
Note, even if not bleeding the brakes at the time i've been know to just crack the bleed valves to make sure they'll still undo when needed.
Two main methods of bleeding, one is with an assistant operating the brake pedal whilst you get a good shot of brake fluid straight in the eye down at the business end, or you use a pressure bleed bit, the good old Gunsons easibleed makes the job simple enough so long as one of the various tops fits your master cyl, there's probably better kit available now but the two person method and the Gunsons kit has done everything for me for decades.
Whichever method, have a decent length of clear pipe which fits tight over the bleed valve and hangs down in the recepticle you are catching the old fluid in.
Do not let the master cylinder run low of fluid whilst doing this job, if you get air in the ABS system it can be a bugger to get it out, sometimes needing to be connected to the specific diagnostics to sort it out again.
Don't forget to exercise the pistons in their bores, ie pump them out and push them back in several times to make sure they're moving freely...worth leaving one pad in next to the piston if on your own, that way the piston won't get pushed fully out and you'll be able to lever it back again easily, if the piston is pushed tight up to the disc it can be difficult to lever it back.
If you're definately bleeding the brakes, instead of pushing the pistons in and pushing the old fluid up into the system (not recommended but we all do it) you can loosen the bleed valve and expel the dirty fluid out as you push the piston(s) in, some people say they do this every time they fit new pads but its easy to allow air to enter the valve doing it this way so best if you're bleeding them out at the same time.
Enjoy.
Bleeding the brakes when you change pads and discs makes sense, usually it will be about time they were done.
The problem with leaving things too long between bleeds is that the bleed valve corrodes in place and you won't be the first person to snap a bleed valve off, so i'd give the bleed valves a squirt of plus gas or other penetrating oil a few days before doing the job (not WD40), you could give the top of the bleed valves a little tap with a toffee hammer before attempting to undo them, also make sense to do this job when the motor factors are open in case you do end up needing a new caliper or fitting kit.
Note, even if not bleeding the brakes at the time i've been know to just crack the bleed valves to make sure they'll still undo when needed.
Two main methods of bleeding, one is with an assistant operating the brake pedal whilst you get a good shot of brake fluid straight in the eye down at the business end, or you use a pressure bleed bit, the good old Gunsons easibleed makes the job simple enough so long as one of the various tops fits your master cyl, there's probably better kit available now but the two person method and the Gunsons kit has done everything for me for decades.
Whichever method, have a decent length of clear pipe which fits tight over the bleed valve and hangs down in the recepticle you are catching the old fluid in.
Do not let the master cylinder run low of fluid whilst doing this job, if you get air in the ABS system it can be a bugger to get it out, sometimes needing to be connected to the specific diagnostics to sort it out again.
Don't forget to exercise the pistons in their bores, ie pump them out and push them back in several times to make sure they're moving freely...worth leaving one pad in next to the piston if on your own, that way the piston won't get pushed fully out and you'll be able to lever it back again easily, if the piston is pushed tight up to the disc it can be difficult to lever it back.
If you're definately bleeding the brakes, instead of pushing the pistons in and pushing the old fluid up into the system (not recommended but we all do it) you can loosen the bleed valve and expel the dirty fluid out as you push the piston(s) in, some people say they do this every time they fit new pads but its easy to allow air to enter the valve doing it this way so best if you're bleeding them out at the same time.
Enjoy.
Air in a hydraulic line is bad, air can be compressed - brake fluid cannot.
You only need to bleed your brakes if you've introduced air into the braking system, either by cracking open a bleed nipple, split a hose or let the fluid drop, or if you're changing the brake fluid at service time.
One tip for changing pads though - when you push the pistons back into the calipers, make sure the cap is off the brake fluid reservoir and put lots of rags around and underneath the reservoir to catch any fluid that might leak out. Someone may have topped up the brake fluid while the pads were low.
You only need to bleed your brakes if you've introduced air into the braking system, either by cracking open a bleed nipple, split a hose or let the fluid drop, or if you're changing the brake fluid at service time.
One tip for changing pads though - when you push the pistons back into the calipers, make sure the cap is off the brake fluid reservoir and put lots of rags around and underneath the reservoir to catch any fluid that might leak out. Someone may have topped up the brake fluid while the pads were low.
Brake fluid is hygroscopic - it attracts water from the atmosphere. When in use this water can evaporate and the system will become ‘spongy’ with a long pedal. The recommended life for brake fluid is two years in a vehicle.
When changing pads, there is no need to change fluid. You should, however, extract some fluid from the master cylinder to give the fluid some room when the caliper pistons move. A cheap turkey-baster from a kitchen shop will do the job.
When changing pads, there is no need to change fluid. You should, however, extract some fluid from the master cylinder to give the fluid some room when the caliper pistons move. A cheap turkey-baster from a kitchen shop will do the job.
To avoid all this unnecessary mess at the reservoir, take this God-given opportunity to at least change some of your old fluid... I cannot see why people still insist in this out-dated habit of pushing tired/ old/ contaminated fluid backwards uphill through the delicate ABS system... 
...braking systems have moved on from Morris Minors/ Ford Cortinas when this practice was acceptable.
This method is so simple and mess free:
Clamp the relevant flexi hose.
(Optional, but now's a really good time to remove, clean, grease, & refit the nipple...
)
Attach a bleed hose to the nipple and put other end in a jar or whatever.
Open the nipple, retract the piston(s), expelling the excess fluid.
Close nipple.
Remove clamp.
If you want to change more fluid (without even having to bleed the brakes, if that scares you), suck out what you can from the reservoir (turkey baster/syringe/vacuum extractor) and refill with new fluid.
After refitting new pads and the calipers, pump the pedal until firm, and top up the fluid again.
Be aware that there are all sorts of different brake fluids on newer cars now (eg synthetic/ low viscosity/ specific ones for ESP systems), make sure you use the correct one! Manufacturers vary in their recommendations between 2 and 3 years to change brake fluid (but rarely practice what they preach anyway!), and most in the trade agree that triennially is sufficient.
Before going on your road test, ensure that you have removed any hose clamps, that the pedal is firm, and that the reservoir is at 'max'.
...braking systems have moved on from Morris Minors/ Ford Cortinas when this practice was acceptable.This method is so simple and mess free:
Clamp the relevant flexi hose.
(Optional, but now's a really good time to remove, clean, grease, & refit the nipple...
)Attach a bleed hose to the nipple and put other end in a jar or whatever.
Open the nipple, retract the piston(s), expelling the excess fluid.
Close nipple.
Remove clamp.
If you want to change more fluid (without even having to bleed the brakes, if that scares you), suck out what you can from the reservoir (turkey baster/syringe/vacuum extractor) and refill with new fluid.
After refitting new pads and the calipers, pump the pedal until firm, and top up the fluid again.
Be aware that there are all sorts of different brake fluids on newer cars now (eg synthetic/ low viscosity/ specific ones for ESP systems), make sure you use the correct one! Manufacturers vary in their recommendations between 2 and 3 years to change brake fluid (but rarely practice what they preach anyway!), and most in the trade agree that triennially is sufficient.
Before going on your road test, ensure that you have removed any hose clamps, that the pedal is firm, and that the reservoir is at 'max'.
You only need to bleed the brakes when you've disconnected one of the brake pipes somewhere in the system, the fluid has run low, or as part of a periodic renewal of brake fluid.
Changing discs and pads doesn't normally require you to remove any brake pipes, therefore it's not necessary to bleed the brakes.
Changing discs and pads doesn't normally require you to remove any brake pipes, therefore it's not necessary to bleed the brakes.
witko999 said:
You only need to bleed the brakes when you've disconnected one of the brake pipes somewhere in the system, the fluid has run low, or as part of a periodic renewal of brake fluid.
Changing discs and pads doesn't normally require you to remove any brake pipes, therefore it's not necessary to bleed the brakes.
And bizarrely non of the other replies appeared for me before I wrote this. I'll get me coat. Changing discs and pads doesn't normally require you to remove any brake pipes, therefore it's not necessary to bleed the brakes.
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