Hello. I'm replacing a left rear caliper on my 05 TL. When I'm done I'm going to bleed and flush to replace all the brake fluid. Is it advisable / necessary to leave the master cylinder cap on when doing the flush and bleed? By the way, I'm also replacing the rear brake hose. Any advice on cracking the upper connection to the small hard line? is only one 10mm wrench required? I can't seem to figure where to grab hold on the old flexible line unless that stays secure and you just twist the 10 mm hardline coupling out.

 

 

Thanks for the reply. A crazy question but if I leave it uncapped won't fluid come out when I pump and depress the brake pedal when I'm bleeding and flushing the master cylinder?

 

siphon some of it out with a turkey baster!

 

Not a crazy question at all, considering that's also what a lot of people think and assume as well. Despite the popular belief "fluid takes the path of least resistance", the reservoir cap doesn't hold back any pressure; you could theoretically drive around without the cap installed because the fluid in the reservoir is never pressurized (under normal operating conditions), even when pressing the brake pedal.

Due to the design of the master cylinder, when pressing the brake pedal only pressurizes the fluid between the master and the calipers, while simultaneously shut off/block the flow of fluid from the reservoir into the brake line system which is why it doesn't come out the reservoir when pressing the pedal. And as mentioned, retracting the piston in the caliper WILL make fluid come out the reservoir since you're not usually pressing the brake pedal at the same time to block the flow of fluid.

 

If you are going to replace the brake fluid, I suggest using a turkey baster and removing the old brake fluid in the master cylinder until the fluid line is JUST above the minimum line. Then re-fill the cylinder with new fluid. perform your bleeding process until there are no air bubbles and the fluid coming out of the caliper is fresh-looking.

However, never let the fluid go BELOW the minimum line as this will introduce air into the brake lines and you will have to start all over.

In some situations, it may take 4 re-fills before fresh fluid comes out of each caliper, so make sure you have enough new fluid to perform this process the correct way.

Just my two cents...

 

I'd recommend getting at least two liters of DOT4 brake fluid for the flush so you can be pretty liberal in the flush process. I flush mine until the fluid coming out is clean. DOT4 is relatively cheap from Walmart. Better than DOT3 but not much more expensive. DOT5.1 is like, twice the price, and not really necessary for street cars.

 

If you're just replacing the caliper, I would assume that there would be no need to fear that the master cylinder would overflow since you don't need to compress a new caliper.. in fact you'll be LOSING fluid when replacing a caliper lmao.

Assuming you work in a decently clean garage, you can leave the MC uncapped. Makes it quick to pump the brakes to get rid of old fluid, then put fresh fluid into the MC when it's low.

The only time you need to worry about the MC overflowing is if you have a lot of fluid in the MC already, and you go to replace all the pads, but you never mentioned if you were doing that or not

common sense goes a long way for this job pumping brakes and then see the MC getting low? fill it back up. compressing pistons to replace pads and see MC almost overflowing? take some fluid out. working in a hurricane where large debris is gonna fly around? choose a different day

 

Thanks so very much for all the helpful replies.
One last thing... since I am replacing the caliper that is last in the bleed sequence ( LR), would it only be necessary to bleed that brake line and caliper, or would I still need to bleed all four?

 

Technically, you should only have to bleed that one brake line. However, while you're already in the thick of it, I think it would be a good idea to do all four. Put some fresh fluid in there!

 

Just remember, when the caliper and line is being replaced, fluid will continuously run out until the replacements are installed, so the only way that the LR would only need to be bleed is if the line and caliper can be replace without fluid going low in the master cylinder.

 

Thanks. And just to be sure.... after caliper and line replacement I will be beeding /flush system fully using the one man bottle& hose method lf,rf,rr,lr.....proper procedure to is crack bleeder , get in car and pump pedal 8 or so times , get out and check for clean fluid/ no air bubbles/ refill master cylinder / repeat next caliper? Am I incorrect or missing something ?

 

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I recommend bleeding your lines with an assistant. While they are pumping, you can see for yourself if clear fluid is coming out and if there any air bubbles still present. It will make your job a lot easier.