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Lost brake pressure after m/c change

3K views 27 replies 6 participants last post by  102ndcar 
#1 ·
Today I used the eezibleeder and the two person method at the same time to bleed brakes because the eezibleeder alone wasn't doing much or anything at all alone after the master cylinder install. I bled brakes and everything seemed fine, had pressure. Got car re assembled this afternoon (had to put new rear panel delete together and re install wheels, change the push to start assy module).. anyway a few hours passed, started car and when I did I had foot on brake pretty sure and the pedal went straight to the floor again.. any ideas?
 
#2 ·
did you empty the system prior to changing the m/c?

Obviously you've got air somewhere, if you didn't empty the rest of the system its in the m/c, if you did empty the system- candidates are m/c, and front caliipers if you didn't completely remove them from the hub.

have you rebled yet to see if more air comes out? Did you "bench bleed" the m/c as suggested in the other threaad you posted?
 
#5 ·
You're saying when the engine starts, pedal goes to floor, but with engine off, it's fine?

That is usually sign of brake booster issue, but there are better ppl on the site for that diagnosis. (Never had an issue w/that.)

But, as I don't believe in automotive coincidence:


How to Bleed Brakes:

Note that many people disagree with my method, so judge for yourself.

Taught to me by semi-famous Toyota engineer, who built championship winning cars and bikes.

1. Get Sears brake bleed kit (canister, hoses, adaptors for bleed valves) and their hand vacuum pump. Kits there have both components. Inexpensive.

2. Pour a little b/f in canister, hook up hoses and use the tightest adaptor you can.

3. Pump vacuum to 20-25” with bleeder valve closed.

4. Tap caliper with small hammer or similar. This releases the air bubbles clinging to the caliper into the stream. WHATEVER method you use, DON’T skip this step.

5. Open bleed valve.

6. When vacuum is almost (but not completely) gone, close bleed valve.

7. Check level in master cylinder. Do this often.

8. Repeat as needed.

Benefits:

*Never got a firmer pedal using any other method.

*Requires only one person. Your wife/so will thank us both.

*You will not be pushing the piston in m/c into the rough area normally unused, thereby not prematurely wearing that seal. (Clutch m/cs are always used to full range.)

Note: On my Elise, I needn’t even remove the wheels.

Yeah, yeah, people use pressure bleeders, but my racecar mechanic friends don’t like these.

Yeah, I know about speed bleeders.

The above is my opinion. No responsibility for screw ups, injuries, maiming or deaths.

Take it, leave it. OK with me.
 
#7 ·
So after the issue I had, I rebled brakes and the car seemed normal. I went to the Kemah car show, approx. 30 minutes from Galveston and back with no issues. This morning I woke up early to attend the Lamborghini festival in Houston and we made it to exit 10 on i45 when I noticed it felt like my car was struggling to maintain power, it felt heavy. I pulled over at the next exit and it seemed like my brakes were locking up.

I unplugged the abs from each wheel and then turned car on, had gf hold brake and I bled right rear wheel. The car for whatever reason unseized all four wheels, at least it seemed? I was able to cruise down the service road back home with no issues, yes I left abs unplugged. I wasn't far from the house and I drove slow. The brakes seemed to be operating normally but obviously something is wrong. When I got it home, I just drove slowly around the neighborhood and after about 20 minutes they seized up completely and I had to let the car cool off to drive it back home. Is this a caliper issue, abs issue, do I need to continue bleeding brakes again due to possible air in system? Also I have some fairly cheap pads but I don't think that would cause the car to completely seize over and over?
 
#12 ·
That is a booster or apply system issue. You have one of the following problems:

The brake pedal is applied or not fully releasing due to interference at the top end of stroke.

The master cylinder is applied due to an incorrect x dimension (booster output rod is too long for the installed master cylinder).

The booster is self applying or not fully releasing due to a damaged power piston possibly due to some very high braking force in the past.

The reason you are getting brake seizing is due to constant drag on the brakes due to a light apply. As the system heats up everything expands with the heat and the master cylinder is applied so the pressure at the caliper increases because the brake fluid has nowhere to go. When you opened a bleeder you released the fluid pressure and that allowed the wheels to unlock. Don't ask how i know, lets just say it happens with prototype parts once in a while.

The fact you just installed a master cylinder makes me think booster x dimension but check and make sure the brake pedal does not have something like the brake light switch holding it applied.

Sent from AutoGuide.com Free App
 
#8 ·
I'd guess ABS accumulator, but it's a guess.
 
#10 ·
Not likely your fault. I em'd a friend who had the same problem and am waiting for answer as to the cause.
 
#13 ·
Similar to what is stated above, your master cylinder piston is not retracting all the way. When you release the brakes the piston in the master cylinder should be sliding back to reveal the port that connects to the fluid reservoir. If adjustments are too tight the piston will not be allowed to travel all the way back. Like what was stated above, using the brakes will heat up the fluid. It will expand. The brakes will start to drag and get hotter. As they get hotter the fluid expands more until you get to the point of lockup.

When installing/adjusting a master cylinder there needs to be a little bit of free play in the peddle before engaging the master cylinder push rod. This allows the piston to fully retract.
 
#15 · (Edited)
This sounds reasonable and the above stated. I'm not quite following you on the peddle play, how do I go about making sure of this and adjusting the m/c? Also when I first installed the m/c I put it on and it had resistance so I had the gf hold it while I put a nut on each side going to the booster. When I tightened down, I heard a small pop sound. I didn't think anything of it, just assumed parts were meshing together. Now that im having issues I wonder if I broke something ? It sounded like two pieces of metal hitting each other. :confused:
 
#14 ·
Alas, my friend was of little help:

It was never definitely determined. Lotus replaced all the brake parts on order from the higher ups in England after I had continued sh*t fits. Most of the pundits including your buddy from Toyota and my present car tech,Bill Thomas, felt it was probably the ABS system.
 
#22 ·
I just watched your master cylinder install video. That part where you have to push on the master cylinder and it springs in and out, and you have to hold it in to start the nuts, that is your problem. Lucky you got it to bleed at all because it is applied as far as you pushed it into the booster. The old one did not look like it came out that way. Part is wrong or built out if spec. If the old one came out that way (hard to tell in the video) then the booster was applied or broken. I am still concerned about the pop noise you heard, might have broke the booster power piston.

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#25 · (Edited)
So obviously I am new to brake systems, can someone tell me what is broken inside the brake booster and what it does and how I probably caused this to happen? Does this mean my old m/c might not have been bad and this part of the system was already broken or did I just mess it up by installing m/c incorrectly? I'm getting the vibe I did it, so feel free to lay it on me.
 
#27 ·
That is the input rod and power piston assembly. It did not slide into the master cylinder when you installed it. The pop you heard was when it snapped. I am actually amazed and a little concerned that you were able to drive it at all. The booster needs replaced, the master cylinder may have rear seal damage and may need the input cup replaced so it will nest into the booster. See if there is any brake fluid leaking at the back of the master cylinder. If not then maybe ok but better if you can get a seal kit. The old master cylinder input cup may be able to be swapped into the new master. Take the old master cylinder and give it a pull and see if it comes out nice. Sh*t happens, chalk this one up to experience and now you know what not to do next time.

Sent from AutoGuide.com Free App
 
#28 ·
You actually made me laugh when you said you were amazed haha. I'm just glad the mystery up to this point is over, my next question is do people cross reference the p/n off parts like the m/c and booster so it can be purchased locally or is this an actual Lotus part? I will have to go down tomorrow to see whats entailed in actually removing the booster, as once again, I've never done it before. I will also check my manual :facepalm:smile2:
 
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