Clarification on brake repair options please

[Africaster]

Symptom :Been experiencing gradual pressure loss at the brake pedal whilst at a stop … very disconcerting to suddenly realize you are inching forward whilst daydreaming. Pedal will eventually go to the floor at longer stops … a full single pump reverts to rock hard.

Apparent solutions: There seems to be 2 alternatives … (not considering the $3k replace everything solution unless no options remain) … 1 is to rebuild the master cylinder for $75, the second is replace the pump motor and accumulator for around $800.

Question/feedback request: Is a solution path identifiable based on the above symptom … and if yes, what is the recommendation?

Appreciate the guidance all

Cheers
Brad

 

[JunkCrzr89]

Diagnose before you start throwing money at it. Start with evacuating the accumulator and then see how long it takes for the pump motor to stop running. Sinking pedal is a typical system of failing/leaking MC, so the $60-70 rebuild kit might help, but you need to check for brake fluid leaking down the firewall inside the cab.

 

[thibaut]

Hi,
I have the same issue but I have previously replaced the accumulator and pump. I also have replaced the rubber brake lines for braided type.
Next one on the list is the piston rebuild kit.
In the winter when A/C isn’t used the problem isn’t apparent.
You should check the pressurisation time on startup (ignition on, time for the brake pump to fully pressurise system). I am getting 25 sec which is normal.

Best

 

[Jdfern]

I would inspect the brake lines, if there are no leaks visible, then bleed the brakes all around. A little air in the system will cause problems.

Good Luck

 

[KliersLC]

That certainly presents like a leaking master cylinder--of note, sometimes they leak internally and there won't be any leakage into the cabin. So definitely go with the cheaper option.

One thing you might consider doing is rebuilding the booster motor while you have it out. I bought a rebuild kit on ebay for ~$160 and will be tackling that tomorrow. I'll post my thoughts on the process when done, but initial look at the parts is promising.

 

[2001LC]

It's important to know what you're doing when dealing with brakes. Otherwise you'll risk life at worst, waste money at best.

Not flushing brake fluid regularly, moisture builds up in it. Moisture reduce boiling point of fluid, which drops hydraulic pressure. It also causes damage to rubber seals and metal components. i.e. brake lines and caliper pistons.

I'd inspect:

• Fluid level. (read instruction on reservoir)
• Fluid condition. (clue) (dark is not good)
• Inspect for staining internally in reservoir. (clue) (any especially dark, is not good)
• Count number of pump on brake pedal until accumulator evacuated (key off). <24 like new, 40 may be end of life for accumulator (clue).
• Time booster charge time (until pressure, shuts motor off) (Battery needs to be over 12.5 volt, the higher the volts the fast motor turns). 28 sec like new, over 40 sec. issue; like weak motor, air in system, excessive moisture, damage seals, leak in system, bad pump.
• Inspect for leaks immediately after aggressive use of brakes, done parked with key on; Inside cabin at master boot, firewall, around master, all flare nut, hard lines, flexible lines, bleeders, calipers piston boots.

Tip: a common signs of bad seals, and or pistons. On cold mornings the brake alarm comes on during first few minutes of brake use. As brakes used, fluidid heats, heating seal expanding them. Then alarm shut off.

BTW: For better or worst: I've gone to using only Toyota brake fluid. Not even Toyota or Lexus does that, they use bulk.

 

[Africaster]

It's important to know what you're doing when dealing with brakes. Otherwise you'll risk life at worst, waste money at best.

Not flushing brake fluid regularly, moisture builds up in it. Moisture reduce boiling point of fluid, which drops hydraulic pressure. It also causes damage to rubber seals and metal components. i.e. brake lines and caliper pistons.

I'd inspect:

• Fluid level. (read instruction on reservoir)
• Fluid condition. (clue) (dark is not good)
• Inspect for staining internally in reservoir. (clue) (any especially dark, is not good)
• Count number of pump on brake pedal until accumulator evacuated (key off). <24 like new, 40 may be end of life for accumulator (clue).
• Time booster charge time (until pressure, shuts motor off) (Battery needs to be over 12.5 volt, the higher the volts the fast motor turns). 28 sec like new, over 40 sec. issue; like weak motor, air in system, excessive moisture, damage seals, leak in system, bad pump.
• Inspect for leaks immediately after aggressive use of brakes, done parked with key on; Inside cabin at master boot, firewall, around master, all flare nut, hard lines, flexible lines, bleeders, calipers piston boots.

Tip: a common signs of bad seals, and or pistons. On cold mornings the brake alarm comes on during first few minutes of brake use. As brakes used, fluidid heats, heating seal expanding them. Then alarm shut off.

BTW: For better or worst: I've gone to using only Toyota brake fluid. Not even Toyota or Lexus does that, they use bulk.

some interesting results:
1. Fluid level a hair above full, clear liquid seen through reservoir … gels with PO mentioning replacing calipers and the like but definitely not anything MC related … guess he realised something was up and took path of least resistance.
2. Pedal pumping with key out … stopped at 70 pumps … pedal hard with little travel and no sign of weakening at all.
3. Ignition to On … buzz lasted 19s, no second run … fluid dropped to slightly below full
4. Aggressive pumping, very little pedal travel, a warning tone during pumping, buzz lasted 6s after last pump, no sign of leaks anywhere, fluid level may have dropped a hair … will leave it overnight and check fluid level.

Thoughts hugely appreciated
Tx
Brad

 

[KliersLC]

some interesting results:
1. Fluid level a hair above full, clear liquid seen through reservoir … gels with PO mentioning replacing calipers and the like but definitely not anything MC related … guess he realised something was up and took path of least resistance.
2. Pedal pumping with key out … stopped at 70 pumps … pedal hard with little travel and no sign of weakening at all.
3. Ignition to On … buzz lasted 19s, no second run … fluid dropped to slightly below full
4. Aggressive pumping, very little pedal travel, a warning tone during pumping, buzz lasted 6s after last pump, no sign of leaks anywhere, fluid level may have dropped a hair … will leave it overnight and check fluid level.

Thoughts hugely appreciated
Tx
Brad

The pumping with the key out requires some effort...like panic stop effort or riding with your teenager pushing your foot through the floorboard effort. You'll know when you've exhausted the available pressure. The good news about that result is that it seems to show that your system has and holds good pressure.

One note is that the duration of the alarm is not the same as the time it takes to bring the system up to full pressure. In order to get a correct time, you'll need to repeat steps two and three, but have an assistant turn the key on while you place your hand on the booster motor. It will run for 14 seconds (IIRC), momentarily shut off, and then run again until it reaches full pressure--it may do the momentary off thing more than once, just depends on how long it takes.

However, it seems to be functioning fine based on what you've described.

 

[Africaster]

The pumping with the key out requires some effort...like panic stop effort or riding with your teenager pushing your foot through the floorboard effort. You'll know when you've exhausted the available pressure. The good news about that result is that it seems to show that your system has and holds good pressure.

One note is that the duration of the alarm is not the same as the time it takes to bring the system up to full pressure. In order to get a correct time, you'll need to repeat steps two and three, but have an assistant turn the key on while you place your hand on the booster motor. It will run for 14 seconds (IIRC), momentarily shut off, and then run again until it reaches full pressure--it may do the momentary off thing more than once, just depends on how long it takes.

However, it seems to be functioning fine based on what you've described.

Thanks for this … and the results are interesting as they seem to point towards a fully working system in terms of pressure until measured against @2001LC’s analysis of # of pumps vs health of system … ie fewer pumps to empty the reservoir indicates healthy … and I was not holding back on the pumping effort (seat was groaning)

2001LC …

• Count number of pump on brake pedal until accumulator evacuated (key off). <24 like new, 40 may be end of life for accumulator (clue).

will give bleeding a bash but that also has 3 options … #1 bleed at MC … #2 bleed at calipers … and there is a mention of using Techstream as well … which one to follow in this circumstance? Appreciated Brad

 

[2001LC]

some interesting results:
1. Fluid level a hair above full, clear liquid seen through reservoir … gels with PO mentioning replacing calipers and the like but definitely not anything MC related … guess he realised something was up and took path of least resistance.
2. Pedal pumping with key out … stopped at 70 pumps … pedal hard with little travel and no sign of weakening at all.
3. Ignition to On … buzz lasted 19s, no second run … fluid dropped to slightly below full
4. Aggressive pumping, very little pedal travel, a warning tone during pumping, buzz lasted 6s after last pump, no sign of leaks anywhere, fluid level may have dropped a hair … will leave it overnight and check fluid level.

Thoughts hugely appreciated
Tx
Brad

Sorry your not doing right or not explaining right.

To check fluid you did read what's stated on reservoir as to how. "Key off, pump pedal 40 or more". Than check level". The number of pumps on pedal are firm at first, than pedal drops lower. That "drop" is somewhere between 20 and 40> pumps. Count how many and report. Further pumps of pedal just insure you've evacuated accumulator. That is what pumping does, i.e. evacuates accumulator. Key off keeps pump motor from running on. How many pumps on pedal until it drops out?

Then, check level. What's the level? Should be at max line and no higher.

Then turn IG key ON (do not start), time how long pump motor runs from moment key turned to on, until self shut off. This is booster motor running the pump. It stops once system has pressure it needs, this is filling accumulator.. How long did pump run?

Pumping pedal with key on, will set off alarm. Good test to see/hear if alarm works. It should as ABS brakes are never to be pumped. Each pump reduce pressure. To rapid and motor/pump can't keep up/ Alarm sounds.

 

[2001LC]

Again. If you don't know how to work on our brakes, don't!