Never tried to do this on SS braided lines. Maybe someone else can chime in.
Unbreak my Brakes
- Thread starter orttauq
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Never tried to do this on SS braided lines. Maybe someone else can chime in.
orttauq
SILVER Star
- Thread starter
- #42
Well I have replaced:
Master Cylinder
All 4 calipers,
All 4 rotors, pads, and related hardware
All 6 rubber lines with OEM Toyota
ABS and LSPV deleted
AND the pedal still sinks slowly...not all the way to the floor but almost. I checked the brake rod per the FSM and it is as it should be. I have bled the brakes both by the old fashion way of one pumping the brakes while I open the bleeders starting RR, LR, RF, then RF. I have used my one person vacuum bleeder (post #29), and now just ordered the Motive Power Bleeder mentioned earlier by @bloc.
Also now the pads drag on the rotors but I do not see any method to hold them on the pistons (either in the old parts that came off nor in the kit that came with the new calipers...
Master Cylinder
All 4 calipers,
All 4 rotors, pads, and related hardware
All 6 rubber lines with OEM Toyota
ABS and LSPV deleted
AND the pedal still sinks slowly...not all the way to the floor but almost. I checked the brake rod per the FSM and it is as it should be. I have bled the brakes both by the old fashion way of one pumping the brakes while I open the bleeders starting RR, LR, RF, then RF. I have used my one person vacuum bleeder (post #29), and now just ordered the Motive Power Bleeder mentioned earlier by @bloc.
Also now the pads drag on the rotors but I do not see any method to hold them on the pistons (either in the old parts that came off nor in the kit that came with the new calipers...
Rivman1243
SILVER Star
sounds like the only part left to replace is the booster
Booster won't cause a slowly sinking pedal. That's a classic master cylinder symptom.
Rivman1243
SILVER Star
I understand that I was just being facetious
Dave 2000
Not all Land Rovers are useless!
The calliper pistons should retract ever so slightly when the pedal is released, and then the pads do not drag but, if the booster push rod is a few thousandths too far out, then the master cylinder piston will maintain a slight pressure on the system preventing the retraction.
Re the pedal drop, it sounds as if the booster is simply helping you compress air that is trapped in the system, once air is in it can be a PITA to get out.
regards
Dave
Re the pedal drop, it sounds as if the booster is simply helping you compress air that is trapped in the system, once air is in it can be a PITA to get out.
regards
Dave
Dave 2000
Not all Land Rovers are useless!
I agree the booster is fine, but the rod protrusion can be the cause of dragging brakes. Also if there is air present this too could stop the master 'pulling back' on the fluid. I use a pressure bleeder a couple of times a month on customers car and found it quite effective, sometimes though the good old manual method works better, you can give the fluid (and air) a good 'shove', good luck with this.
regards
Dave
regards
Dave
orttauq
SILVER Star
- Thread starter
- #49
I get what everyone is saying about the air in the system but I have two 80s and I did the brakes on my first one a couple of years ago; just calipers and pads. Bled it using my vacuum bleeder and never gave it a second thought. Did I just get lucky that it bled okay? It is a new not reman master but I guess it could be bad.
Anyway thanks for all the input.
Anyway thanks for all the input.
If you are in the vehicle without the engine running and pump the pedal several times until it is firm and at the top of the pedal travel then hold pressure does the pedal still drop slowly? If yes then I would get another master cylinder. If no I would lean toward air in the lines. Did you bench bleed the MC prior to install?? I know this has been asked a couple times already but I dont think we have gotten an answer. I only ask because it can be a real PITA to get air out of a MC without bench bleeding.
Air in the lines isn't going to make the pedal height drop slowly. Bubbles compress quickly and stay compressed with pressure.
The only thing that is going to make the pedal continue to drop slowly is a leak somewhere. If it isn't leaking outside, it is leaking inside, which could only be the master cylinder. Look for turbulence in the MC reservoir while the pedal is dropping slowly for confirmation.
The only thing that is going to make the pedal continue to drop slowly is a leak somewhere. If it isn't leaking outside, it is leaking inside, which could only be the master cylinder. Look for turbulence in the MC reservoir while the pedal is dropping slowly for confirmation.
Air in the lines will cause a very soft brake pedal until the system is pressurized, usually 2-3 pumps of the pedal(depends on the amount of air in the lines. Thats the only reason I mentioned air in the lines being a possible cause of the issue. If its air the pedal will not drop after 2-3 pumps but those 2-3 pumps can be described/misinterpreted as a dropping pedal, i've heard it described this way too many times not to ask for specifics.
We agree about the dropping pedal only being fluid loss of bypass. Im just trying to make sure the OP is describing it correctly.
orttauq
SILVER Star
- Thread starter
- #53
Ok here goes...
Engine off pedal is very firm. Pump the pedal a few times and pedal get to point it will not move--this is like every car I have ever owned. Once the boost vacuum is depleted it is like a 1954 brake system...all manual.
Foot on pedal start engine pedal moves down a fair bit and become very soft.
Pump pedal up and pedal height rises to original position of before engine start BUT then sinks back down-as I have said before not quite to the floor but almost.
I can repeat this over and over and it never does not return to close to floor slowly.
As mentioned by @Pin_Head I have looked for fizzy bubbles in reservoir that indicate a MC leak or air in the MC and looks clear and free of air.
Also note that after days of parked in garage I removed the vacuum line/check valve and booster was still holding vacuum so those parts are good.
At this point (about 2 weeks ago) I replaced every brake part except the hard lines, bled the system several times (I have almost a gallon of flushed brake fluid) but once back together and bled again it still has the issue of pedal sinking.
Engine off pedal is very firm. Pump the pedal a few times and pedal get to point it will not move--this is like every car I have ever owned. Once the boost vacuum is depleted it is like a 1954 brake system...all manual.
Foot on pedal start engine pedal moves down a fair bit and become very soft.
Pump pedal up and pedal height rises to original position of before engine start BUT then sinks back down-as I have said before not quite to the floor but almost.
I can repeat this over and over and it never does not return to close to floor slowly.
As mentioned by @Pin_Head I have looked for fizzy bubbles in reservoir that indicate a MC leak or air in the MC and looks clear and free of air.
Also note that after days of parked in garage I removed the vacuum line/check valve and booster was still holding vacuum so those parts are good.
At this point (about 2 weeks ago) I replaced every brake part except the hard lines, bled the system several times (I have almost a gallon of flushed brake fluid) but once back together and bled again it still has the issue of pedal sinking.
Yeah, it's either the master cylinder or you're leaking brake fluid somewhere. I'd get a new master (not reman).
bloc
SILVER Star
Edit: now looking at pics of toyota MC piston parts my (now deleted) comment on fluid not necessarily going back into the reservoir appears to be wrong.
Let's think through this.
Only two reasons your pedal won't be firm.
1. a leak
2. an air bubble
as mentioned, an air bubble will typically compress then the pedal will get firm. pedal won't continue to travel smoothly. Before pedal does get firm, you won't have adequate brake pressure. With a (small) leak you will get just as much brake pressure/performance as no air, but the pedal will continue to move as leaking fluid gets pushed out of the system slowly.
So, sounds like a leak.
Leaks can be in three general places.. Internal to the MC, in a line somewhere, in a wheel cylinder.
Anywhere in a line or wheel cylinder will cause you to lose fluid. Literally every stroke of the MC is pushing that volume of fluid out of the system, with no way to push it back in.. so, with continued pumping fluid MUST be hitting the floor somewhere. The dust boot on a wheel cylinder can hold some fluid and hide this, but once it fills up it will definitely start leaking.. they can't hold enough pressure to push the fluid back around the wheel cylinder seal.
A leak internal to the MC will simply allow the fluid to go around the seal in the piston and stay in the MC bore, conveniently connected to the MC reservoir. There is a seal on the back of the MC around the piston pushrod which keeps the fluid from leaking out the back..
so as mentioned by others, with the symptoms you describe it appears your MC is still bad.
These would help you diagnose the MC but they are $20 and not very useful otherwise: 4Crawler Offroad Products - Brake Line Plugs
Let's think through this.
Only two reasons your pedal won't be firm.
1. a leak
2. an air bubble
as mentioned, an air bubble will typically compress then the pedal will get firm. pedal won't continue to travel smoothly. Before pedal does get firm, you won't have adequate brake pressure. With a (small) leak you will get just as much brake pressure/performance as no air, but the pedal will continue to move as leaking fluid gets pushed out of the system slowly.
So, sounds like a leak.
Leaks can be in three general places.. Internal to the MC, in a line somewhere, in a wheel cylinder.
Anywhere in a line or wheel cylinder will cause you to lose fluid. Literally every stroke of the MC is pushing that volume of fluid out of the system, with no way to push it back in.. so, with continued pumping fluid MUST be hitting the floor somewhere. The dust boot on a wheel cylinder can hold some fluid and hide this, but once it fills up it will definitely start leaking.. they can't hold enough pressure to push the fluid back around the wheel cylinder seal.
A leak internal to the MC will simply allow the fluid to go around the seal in the piston and stay in the MC bore, conveniently connected to the MC reservoir. There is a seal on the back of the MC around the piston pushrod which keeps the fluid from leaking out the back..
so as mentioned by others, with the symptoms you describe it appears your MC is still bad.
These would help you diagnose the MC but they are $20 and not very useful otherwise: 4Crawler Offroad Products - Brake Line Plugs
Last edited:
orttauq
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- Thread starter
- #57
Well I bled almost 2 quarts through the system using the Power Bleeder and old school pedal action but the pedal still sinks to the floor. I took it out for a drive and I still can't get it to stop short in anyway let alone lock up the tires.
I have seen someone here in Kirkland, WA with a nicely built 80 but now can't find them on Mud...I would like to just see how their brakes are.
I have seen someone here in Kirkland, WA with a nicely built 80 but now can't find them on Mud...I would like to just see how their brakes are.
Brake hydraulics are a closed system. There has to be a leak if the pedal slowly sinks to the floor. Since it isn't leaking on the floor, it has to be the MC leaking back into the reservoir or you aren't describing the problem correctly.
I would send the MC back as a defect and put another one on.
