Bled the brakes before a pad slap?

[SC Maintenance]

Was doing a pad slap on the front brakes. So decided I would bleed the front brakes first - so when I compressed the calipers I didn't push all that old gunky fluid into the ABS control valves. Only added like a minute to each side with the wheel already off.

Bled them after as well.

Anyone else do this?

 

[The Critic]

I always bleed after for optimal pedal feel, never know who was in there before you. I don't personally see a point of opening the bleeder valve, there isn't enough fluid movement to cause trouble anyway IMO.

 

[Urshurak776]

I open the valve and put a tube on, then press caliper piston back. @The Critic is right, it isn't much fluid, but I would still rather not push it back into system.

 

[BHopkins]

I've never done a brake fluid bleed at the same time as a brake pad change. But I follow your reasoning, and it makes sense. The brake fluid right behind the brake piston is always the nastiest, since it gets more contamination.

 

[TnT_M]

never done it before the pad and rotor change, I do it after. I drain the reservoir first then pump new fluid through the system from a re-filled reservoir. I start at the RR and then LR, RF, LF. Furthest from master cylinder first. Flush until fluid runs the same color as the new stuff.

I use an old peanut jar and a clear plastic hose to avoid getting air into the system from the bleeder screw. Works like a charm.

 

[spasm3]

I always open the bleeders, to compress the caliper. Then i let them drip onto a pizza box , or cardboard box. Slow way of flushing the older fluid out. When done, i burn the boxes.

 

[PandaBear]

Sometimes I do, sometimes I don't. I change brake fluid whenever I feel it being mushy and brake pads when it runs thin. If you do them frequently enough it doesn't make a difference to me.

 

[JohnnyG]

Sounds like a great idea to me!
I always open the bleeder before retracting the pistons too, no need to force that crud back toward the reservoir.
Then, bleed after and you're good.

 

[slacktide_bitog]

I do it after the pads, not before.

 

[iCurious]

I open the valve and put a tube on, then press caliper piston back. @The Critic is right, it isn't much fluid, but I would still rather not push it back into system.

Same. This way, I dont need to worry about the reservoir overflowing also its much easier to compress the piston in.

 

[The Critic]

Same. This way, I dont need to worry about the reservoir overflowing also its much easier to compress the piston in.

Your brake fluid reservoir should never overflow…unless you overfilled during a brake fluid service.

 

[Donald]

Was doing a pad slap on the front brakes. So decided I would bleed the front brakes first - so when I compressed the calipers I didn't push all that old gunky fluid into the ABS control valves. Only added like a minute to each side with the wheel already off.

Bled them after as well.

Anyone else do this?

Some do a modified version. Open the bleeder before compressing the piston(s).

 

[mk378]

Your brake fluid reservoir should never overflow…unless you overfilled during a brake fluid service.

This is people who can't help but "top off" the fluid even though it is above the MIN line. The fluid should be at MAX with new pads and then normally it goes down toward MIN as the pads wear causing more fluid to stay in the calipers.

 

[Mechanician]

The fluid doesn't circulate, but it sure gets a lot of "back and forth".
Think of the number of times the pedal is pushed on every drive, and the action within the system that takes place with each push.
With that in mind think of what can happen when the pedal is pushed beyond it's usual travel, during a manual bleed.
Pushing the pedal to the floor moves the master's internal seals into sections of the cylinder they haven't been to for a very long time, that may damage them. The master can go belly up.
Using a pressure bleeder is the only way to go, especially if the fluid has been nasty for a long time.

 

[artbuc]

I have heard this claim many times over the decades but never heard anyone say they had to replace a MC because of excess pedal travel.

…Pushing the pedal to the floor moves the master's internal seals into sections of the cylinder they haven't been to for a very long time, that may damage them. The master can go belly up.
Using a pressure bleeder is the only way to go, especially if the fluid has been nasty for a long time.

 

[Bailes1992]

I usually clamp the hose, open the nipple and then push the piston back.

 

[Mechanician]

I have heard this claim many times over the decades but never heard anyone say they had to replace a MC because of excess pedal travel.

I've seen it happen - it's a tough call to a customer explaining the newly acquired need for master cylinder replacement.