My mechanic friend came over to help me bleed my brakes. I had previously bled them using a vacuum bleeder but wanted to make sure. We did the rear brakes no problem had a nice firm pedal, but when trying to do the front I lost the pedal. It seems like there is no fluid going into the master from the reservoir because no fluid comes out of the caliper and there is no pedal. I was wondering if that means that my new master is not functioning. There are no leaks anywhere. Thanks much.
Iâm gonna ask a really basic questions, which master?
All reservoirs topped up?
Remember, weâve got a simple master/slave setup between the pedal and the split system brake master cylinder for the calipers.
I believe it is the top one with out the brake booster
When I have had that exact situation I found that a simple pressure bleed was the thing to overcome it. Once that gets things bleeding you can finish with a pedal bleed if you like.
âI believe it is the top one with out the brake boosterâ
Itâs been too long since I last messed with the brake hydraulics, so bear with me if what I write doesnât quite align with what you are seeing. Iâm probably wrong.
OK, here goesâŚ
The pedal drives the âprimaryâ master. That forces fluid into the primary slave and twigs the valve for the brake booster.
The primary slaveâs mechanical output is applied to the rear piston (via the brake booster) of the brake master cylinder. Pressure in the back half of the brake master cylinder (once the rear pads make contact) moves the front piston to pressurize the front hydraulics.
So, total loss of braking would indicate a primary/master and slave problem. Open the bleeder on the primary slave and see if the brake pedal will pump fluid down there.
Then repeat bleeding the rears then trying the fronts.
Possible other problems include blown seals in the brake master or a broken spring between the pistonsâŚ
Also look for blown lines.
(Personally, Iâve never liked vacuum bleeding. When Iâm alone, I use the collection cup and slowly pump the pedal. But NOTHING beats a well-trained assistant in the cockpit!)
How-do-you-do a pressure bleed? BTW, both masters and slave are new
âHow-do-you-do a pressure bleed? âŚâ
Apply about 2-3 PSI of compressed air to the top of the reservoir. Crack each bleeder (farthest to nearest) in turn. Refill reservoir after each caliper is cleared.
I donât enjoy the process. Getting a good seal to the reservoir and depressurizing each time is annoyingâŚ
How the heck did you get it to sealed to the reservoir?
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âHow the heck did you get it to sealed to the reservoir?â
THAT is the $64 question!
Commercial setups for modern US spec vehicles have a steel backed rubber plate with a hole in it and C-clamps. A garden sprayer is used to pressurize.
My guess on an E, would be to use a section of radiator hose and a hose clamp to seal to the top of the bottle. Then connect the a hose from my compressorâs regulator (set to barely flowing).
(Again, not a fan.)
Charles,
There is lots in the archives about this. A DIY pressure bleeder can be made from a bicycle inner tube and is very effective. Just search the archives. Here is one such thread:
-David
The inner tube idea is brilliant. How affective is the pressure bleeder technique?
Very normallyâŚ
Itâs always worked for me. Just remember that to pressure bleed the 4.2 Brake system you will need to pressurize each reservoir in turn, and then bleed the corresponding brakes.
I will give it a try, thanks everyone for your help
Charles,
Pressure bleeding is effective, in my limited experience although I think a significant benefir is that it is also easier than a pedal method if you have no buddy (or nobody) to help!
The tire tube method sure looks simple, but I havenât used it.
If you happen to have a radiator pressure tester, you may have a fitting that will work on the fluid bottles. Thatâs how I do it.
I am modifying an old reservoir cap by drilling a hole through it and sealing the rest of it with epoxy. The thing thatâs making me crazy is that I donât even understand why all of this has to be done. It is usually a simple process to bleed the brakes and it seems to have become a real PITFA. I guess it just all goes along with owning an old jaguar
OK so I pressurize the brake reservoirs Not as much fluid came out as I would expect even when pumping the brakes and having my friend help me. So now I have a firm pedal but there seems to be about an inch and a 1/2 to 2" of free play before there is resistance. So I donât know if itâs just not bled completely or if there some other reason for that much play in the pedal. When bleeding we did not see any air in the lines and the break is firm and not mushy but it still seems kind of low. Any thoughts would be appreciated
Yup, youâve got âissuesâ.
As we all know air in the brake hydraulics causes a mushy, soft pedal.
Excessive free play is something mechanical.
How well mounted are the rear calipers? Have a buddy press the brake pedal while you watch for wiggling that indicates a worn pin.
Check the front calipers too.
How are the bushings in the pedal box?
Are all the bolts holding the myriad of master, slave and boosters all properly tightened?
Any slop or slack in the linkage?
Personally, I still think one of the springs inside the brake master cylinder is broken or partially collapsed.
I have checked everything, all the calipers are brand new and it appears as though the play is in the master cylinder. I have to push the pedal down approximately 2" before it has any resistance. The master cylinder is also new.