What part is responsible for providing brake caliper piston retraction? Ft.Tool Girl Lilli

Ever wondered how a brake caliper really works? What actually 'pulls'the piston back into the caliper body after you release the brake pedal?
Knowing what 'part'is responsible for this action is important when trying to diagnose brake faults. Understanding what factors can affect the distance the piston actually moves when retracted can assist in diagnosing issues like excessive pedal travel or binding brakes.
So, with Tool Girl Lilli's assistance we fit an old front brake caliper from a Toyota Rav4 to the test rig, bleed up the hydraulic system & then test to see if this caliper shows any piston retraction and if so, how much.
From then we remove the piston & take a look at the hydraulic seal. A full explanation of the theory behind the operation follows & finally a summary.
This is Tool Girl Lilli's first on the tools' video & I'm sure you will agree, she does a great job.
Check out the other videos on the channel covering various brake caliper rebuilds & piston retraction testing.
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Andy Mechanic

[@daveco1270]

I knew the piston sealed pulled the piston it back in, but I didn't really know exactly how it worked. Lilli is great, she seems to have a genuine interest in learning this stuff.

[@chr11sf]

Lilli seems awesome!...you can clearly see that she's really keen and attentive...nice work guys

[@andrewthompsonuk1]

Excellent video. I never knew about too much retraction. I was given a car a few years ago to fix up. It had a single worn out brake pad at the rear on the piston side of the caliper. So I replaced them paying attention to removing the rust from and contact points etc. Because the piston pressed in ok and it required a hammer to remove the pads I thought I had found the problem. However after a few minutes of fast driving the brakes would start to shudder as if the discs were warped along the hot brake smell. So I decided the caliper was not retracing properly and I removed the piston and replaced the seal doing nothing else. Problem completely solved.

[@wagonbldr]

Very well done. Never really thought about the operation, but your real world issue makes sense. Well done indeed. Thank You Andy and TG Lilli

[@michaelverrillo9269]

I’m envious wish I had all the help you get

[@whitedoggarage]

Great video, thanks Andy and Lilli, good to hear your real life examples too Andy, looking forward to the next one.

[@justinsherwood1911]

You learn something new every day! Solved some previous mysteries.

[@deanchenry]

Awesome Andy!

[@bobdelaplage690]

Really interesting Andy ijust subscribed, Bob Belgium🇧🇪

[@AndyMechanic]

Thanks Bob, welcome aboard! Cheers Andy

[@stevewright2271]

Hi Andy, just watched #1337 video and interested in the "piston retraction" and specifically about the bit towards the end when you said about the "grease" that some people use when installing pistons back into the calliper, I have just had mine cleaned and this guy made a point of using this Red grease, but I cannot get a good leaver(on a motorbike) it comes back to the handle bar, I have bleed it numerous times, but with no luck, but I did put a cable tie on the leaver over night, but noticed that fluid had leaked out of the bottom of the calliper, so I stripped it down and wiped the remaining grease out and just used Brake fluid and some what better (not perfect) but do you think that the grease is my problem? Brilliant Video by the way and like your helper (lol), thanks Steve

[@AndyMechanic]

Hi Steve, Thanks for all the info. The calipers will need to be stripped, all of the red (rubber grease) removed, components cleaned (brake cleaner only) & reassembled using only brake fluid on the seals to aid assembly. The rubber grease is causing too much piston retraction - it's not air in the system causing the excessive lever travel. sorry, you have work to do! Have had this issue many times on calipers others have rebuilt hope this helps. Cheers Andy

[@simonrawle7885]

go Lilli not scared to get stuck in , ive got a pile of bike caliper to get ready for the spring wen ppl get there bikes out and the brakes stick on after the winter

[@glowmar]

Great Video and Lilli is really cool she rocks.

[@AndyMechanic]

TG Lilli really does rock. ...she's very cool. Cheers Andy

[@Polecat54941]

very interesting and informative Andy well done! and not seen Tool girl LIlli before but would say Lilli is a Tool girl you would actually employ in your garage to help fix cars?

[@AndyMechanic]

Yes, she's awesome. Most attentive; -)

[@stanimirpavlov]

Thank you for this great video lesson. My car got low and spongy break pedal that sinks to the floor after the rear brake pads change and brake fluid change in a service shop. And after eight months and several brake bleeding procedures I'm still unable to get back my old firm brake pedal. Tried another master cylinder too - same sinking pedal. Now when I saw this video I started to think that this might be the actual reason for the low pedal. Maybe during the change the mechanic pushed the rear brake caliper piston too far to be able to put the caliper over the new pads and that somehow changed the contact between the seal and the piston possibly leading to the bigger piston retraction. But I don't know how much the usual retraction should be. A tenth or two of a millimeter? Maybe more or less? Can you tell me? The obscure thing here is why I have the same low and spongy brake pedal when the parking brake is engaged and the brake pistons are in contact with the pads but depressing the brake pedal gives the same spongy feeling and sinking to the floor. Stupid and unexplainable to me. I've published a video here kzbin.info/www/bejne/m4C7po2XqKlqj7s

[@zuranku]

Okay have you discovered the problem? I'm going thru the same issue.

[@stanimirpavlov]

@@zuranku Still no. How did your brake pedal become soft? What is your case?

[@zuranku]

@@stanimirpavlov I think there is still just a little bit of air stuck. After bleeding the first few pumps will be soft and then it hardens

[@CalvinsCorner72]

Convoluted! Lol hey most mechanics just plug and play. Replace parts till they get it. Cost more money but it’s ours not theirs. Sadly. Thanks Y’all

[@Bighead-he8zb]

Hey Andy, I thought the two springs in the master cylinder and the spring in brake booster pull the caliper piston in when the springs uncompress. Also, I have a 2005 Nissan Armada. I recently replaced the booster(OEM) and master cylinder (after market). My brakes are now dragging. I want to adjust the push rod from the booster inward but it doesn't appear to be adjustable to me. Are some boosters nonadjustable?

[@AndyMechanic]

Hi, nop, nothing to do with Springs in the master cylinder, they are there to return the primary and secondary pistons to their rest positions after brake applied. Cheers Andy

[@AndyMechanic]

If you can't adjust the push rod length then just add thin washers between the master cylinder and booster ;-)

[@Bighead-he8zb]

@@AndyMechanic Thanks for the advice. I will try it.

[@simonrawle7885]

Andy you missed a bit wen you did your diagram . the grove in the caliper is machined at slight downward angle angle so the base of the seal has a slight lip. some seal are also angled

[@andrewthompsonuk1]

It was interesting you measured about 0.2 mm which is just over the typical max run out of a brake disc.

[@AndyMechanic]

Yes....there must be a link there! :-)

[@johnthake7401]

Andy if you had a vacuum bleeder that you connect to a air compressor it would such the brake fluid out

[@iyubmohamed9894]

Great information thanks

[@wjcarlile1]

Keep have her on your show

[@AndyMechanic]

Definitely :-)

[@harrisvalues8172]

What happens if there's air in your system will it cause the caliber to bind......please answer this question because I've replaced my entire caliber system and break line and it works fine and then my passengers break locks up again until I loosen the bleeder valve then I can drive a day or more and it will do it again just the same one caliber........im so frustrated HELP ME PLEASE SIR I also put new fluid as well and I have new pads

[@AndyMechanic]

Hi Cory, simple answer is definate NO. Air in the system or the brake fluid has nothing to do with piston retraction. Cheers Andy

[@harrisvalues8172]

@@AndyMechanic well why do they work properly and then lock up after all I have done please help

[@AndyMechanic]

Ah...that's easy....you either have no brake pedal free play or the push rod between the brake booster & Master Cylinder is a little too long & not allowing the piston in the master cylinder to reach its rest position - this blocks the compensating port & prevents the increasing volume of fluid in the system (thermal expansion) as the coolant warms, to leach back into the reservoir. This causes the pistons in the circuit to be pushed out resulting in the brakes binding. There is a video on my channel covering this. Cheers Andy

[@harrisvalues8172]

@@AndyMechanic thank you so so very much ......have a great rest of the week mate

[@vedantjoshi6191]

Is piston retraction failure by piston seals the only reason for binding brakes(wheel locking without pressing the brake pedal)?? Can any other factors or components such as the master cylinder be responsible for binding brakes?? I am from a car team and we experienced binding brakes in the front even though our calipers were brand new.

[@AndyMechanic]

Hi, thanks for the comment. There are a number of issues that can cause brakes to bind on. Piston retraction is just one. I'd check the following: Push rod clearance between master cylinder and brake booster (servo) - this is critical as if no clearance (push rod too long) then the compensating port in the master cylinder is blocked by the main seal on the primary piston. As the brake fluid heats up it expands & cannot leach back into the reservoir, instead, pressure builds & pushes the pistons out binding the brakes. If there is no freeplay between the brake pedal and brake booster it can also cause the same symptoms. If you have floating calipers then check the sliders are free and lubricated Okay, hope this helps. Let me know how you get on. Cheers Andy

[@Force1Com]

I have massive piston retraction. I can't even ride it because it's so bad. I have to keep pumping constantly. Please help!!

[@kaleshh6988]

Awesome..!!! Thanks a lot for sharing your knowledge.. Love You..

[@kwunmeichan8013]

35:39 disc brake self-adjusting

[@fiaziqbal3279]

Who else just kept staring somewhere else?

[@tineshreddy623]

great video, Andy how to service honda carburetor

[@Force1Com]

Microphone quality so good I can hear her doing kegels

[@michaelsawyers1002]

piston seal in the caliper

[@MrFishface5]

where is Hanna?

[@embreesmith7613]

where's Jade ..??

[@AndyMechanic]

Under the house with the other Tool Girls. She'll be let out to help me on Saturday so you'll see her next week :-)

[@CalvinsCorner72]

So I’m guessing that Hanna won’t be returning? Lol

[@AndyMechanic]

Hi Calvin's Corner. Unfortunately not for the foreseeable future.

[@CalvinsCorner72]

Andy Mechanic ok 👌 I understand. Cheers