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Senior Member
Changing Front Wilwood Cylinder
All
Looks like my front brake master cylinder is leaking through the piston. I'm going to remove the cylinder and probably replace it.
Question: Any good tips on draining the brake fluid and replacing the cylinder without getting brake fluid all over the place ? ( body on and painted )
thanks!
mark
Build 1: Mk4 Complete Kit #9312 Ordered 1/27/18, Delivered 3/24/18, CA SB100 Registered 9/11/19 - Gen 2 Coyote TKO600, IRS, Power Steering, Wilwood Brakes, 17" Halibrand.
Build 2: Gen3 Coupe Complete Kit #309 Ordered 1/25/21, Delivered 6/9/21 - BluePrint GM 427 LS T56, IRS, AC, Power Steering.
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Senior Member
Open both front caliper bleeders and let them gravity drip into two pans.
FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.
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Senior Member
I had to service the front MC on my Coupe build. After it was all together with fluid, bled, etc. I too was concerned about fluid going everywhere (hate that stuff...) but it wasn't that bad. Took the reservoir hose off first and quickly capped it. Then removed the brake line off the front. It dripped slightly at first, but not bad at all and easily caught with a rag underneath.
Build 1: Mk3 Roadster #5125. Sold 11/08/2014.
Build 2: Mk4 Roadster #7750. Sold 04/10/2017.
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Build 3: Mk4 Roadster 20th Anniversary #8674. Sold 09/07/2020.
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Build 4: Gen 3 Type 65 Coupe #59. Gen 3 Coyote. Legal 03/04/2020.
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Build 5: 35 Hot Rod Truck #138. LS3 and 4L65E auto. Rcvd 01/05/2021. Legal 04/20/2023.
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Senior Member
1. Clean the area where you will work. Remove any dirt/crap/etc. from around all connections. Place rags/towels/etc. around anything that could get dripped on. Make sure there's enough coverage and absorption so that the fluid doesn't bleed through. Set out all your tools, a couple clean towels to wipe your hands, new brake fluid, etc. before you start. Also cover the fender, and be careful of your belt buckle against the paint.
2. Clamp the reservoir feed to the MC before removing. **If you have braided stainless lines, and don't want to risk leaving a mark on them, just drain more fluid from the bleeders to empty the line and the reservoir as CraigS mentioned. Or quickly remove and raise the MC end of the reservoir feed above the level of the reservoir, plug and secure like EdwardB mentions above. Avoid jerky movements that may sling fluid on things.
3. Once enough fluid is drained, close the bleeders and remove the master cylinder. Be careful to avoid drips and spills, you'll have some, but try to orient the MC so it doesn't just spill on everything when removing it. (I wrap them in a towel). Make sure everything is covered well to protect the fender from spills and scratches Ensure your hands are clean of fluid. Keep a clean rag handy to wipe off your hands as necessary. Pull the cylinder free of the car. It's likely that you'll continue to get small drips so keep the rags in place. ***Note of caution. It's easy to forget, and you may not even notice there's fluid on your hands, so careful touching stuff.
4. Inspect the area and wipe up/clean/remove any spilt fluid and replace the rags as necessary. If you have the rags in a good location it's unlikely that you'll have any damaging spills, but double check it anyway.
5. Prior to installing the new MC, inspect it for metal shavings/debris/dirt/etc.. You can also use compressed air (like a computer duster can) but careful not to damage any seals. Ensure the threads are in good shape and not nicked/damaged. Inspect all connections and flares for nicks/bends/cross thread/etc. in the car also. Clean them all and remove any sealers or debris lodged in the threads of existing fittings. Be careful not to introduce foreign material into the lines. If required, use the appropriate thread sealer on any NPT fittings.
6. It's optional, but many find it helps to bench bleed the new MC. I've found it more beneficial for MC's with internal reservoirs and when there's antilock brakes involved, but not so much with simple systems like these. Although it will definitely not hurt. Just be careful of drips and spills when putting the thing back in the car.
7. Banging around with wrenches and such can loosen stuff you wouldn't expect. Double check all connections not removed during removal of the MC. Make sure they are properly tightened and no evidence of leaks. These fittings may be more accessible prior to reinstalling the MC, so check them first.
8. Reinstall the the MC (I like to wrap them in a towel if they've been bench bleed to avoid drips). Reconnect brake lines and reservoir line. Expect it to drip a little. Clean the connections of any fluid and place a paper towels to absorb any leaks. NOTE, put a little drip of oil between female fittings and the back of the tubing flare, just a tad. This lubricates and helps prevent damaging the solid lines when tightening the fittings. I put a drop of oil on my fingers and lightly rub it on the back side of the flare.
9. Place paper towels around each connection and rags underneath. The paper towels will help show leaks better than cloth.
10. Fill the reservoir and bleed the brakes as normal starting with the one furthest from the master cylinder. Tapping the brake lines a little may help dislodge any stubborn bubbles. But be gentle, not so hard that you leave dents or bend anything. Make sure to keep enough fluid in the reservoir during bleeding and do not let it run dry. It's likely you'll have to add some a couple times. If your brake fluid is old, or discolored, continue to bleed until the new clear fluid comes out bubble free. Do not let the reservoir run dry on you.
11. Once bleed and valves closed, inspect for leaks/spills that may have occurred during bleeding. Repair them, clean up, add some paper towels around all connections and pump the brakes to get a good hard peddle and hold it in for a bit. If you have a helper, ask them to look for leaks while the pedal keeps pressure in the system. This is a pressure test of sorts. It increases and holds pressure in the system and will help identify any leaks not already noticed. Also check the bleeders to make sure there are no leaks there, and all brake line connections throughout the system.
12. If the pedal doesn't hold tight, tap the lines to dislodge bubbles, fill the reservoir and bleed some more.
13. Check the paper towels for signs of drips or leaks and repair as necessary.
14. You're done, wash the fluid off and go play, have a beer & celebrate. Ask an obnoxious neighbor (or your deadbeat brother-in-law) to run it around the block for you a few times to see if the brakes work. If you have a leak after all this, bang your head. It fixes nothing, but surprisingly makes you feel better. Same thing if you hear a crash. LOL
Last edited by RBachman; 09-21-2019 at 05:51 PM.
FFR MKIV ordered 12 July 2019. IRS, Wilwood Brakes, 18" Wheels w/MT tires, power steering, EFI, Heat. 347 Dart w/TKO-600 by Mike Forte, Holley FI, MSD coil and CD box. All new, no donor build.
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Senior Member
Thanks all for the replies. I drained the system last night and are now waiting for the Amazon truck to bring the new MC.
Build 1: Mk4 Complete Kit #9312 Ordered 1/27/18, Delivered 3/24/18, CA SB100 Registered 9/11/19 - Gen 2 Coyote TKO600, IRS, Power Steering, Wilwood Brakes, 17" Halibrand.
Build 2: Gen3 Coupe Complete Kit #309 Ordered 1/25/21, Delivered 6/9/21 - BluePrint GM 427 LS T56, IRS, AC, Power Steering.
Album Here
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Senior Member
Got it all back together and enlisted the females of the house to pump the brake pedal No leaks from what I can see so far and I swear the car drives faster now
Build 1: Mk4 Complete Kit #9312 Ordered 1/27/18, Delivered 3/24/18, CA SB100 Registered 9/11/19 - Gen 2 Coyote TKO600, IRS, Power Steering, Wilwood Brakes, 17" Halibrand.
Build 2: Gen3 Coupe Complete Kit #309 Ordered 1/25/21, Delivered 6/9/21 - BluePrint GM 427 LS T56, IRS, AC, Power Steering.
Album Here
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Senior Member
Cool. You have some magic in there somewhere!
FFR MkII, 408W, Tremec TKO 500, 2015 IRS, DA QA1s, Forte front bar, APE hardtop.