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Brake master cylinder

Started by Dipper, April 3, 2025, 14:28

0 Members and 1 Guest are viewing this topic.

Dipper

Hi all, I've just bought a mk3 and the brakes are terrible. I'm guessing it's the master cylinder. Is there anywhere I can purchase a repair kit rather than replace it completely? I can only seem to find one for the clutch cylinder.

boor

Before you go down this road, I'd suggest to check the calipers first, as usually that's the weak spot - sized caliper sliding pins and caliper pistons.
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Carolyn

Helo and welcome to the club. 

It's great to see you getting stuck in.

It's is so rare for the brake master cylinder to be faulty, to the point that it almost never happens.

Sticky slider pins are the first port of call.  Clean and lubricate with 'Ceratec' or similar silicon grease.

Afer that check for glazed brake pads and stuck pistons.

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Call the midlife!

Just to add to the list, have you any idea how old the brake fluid is? Your description of "terrible" doesn't give us too many clues but if the fluid is old it could have an amount of water in it which won't help.
60% of the time it works everytime...

Joesson

#4
@Dipper

Hello and welcome.
Sorry to hear of your braking concern, you have however made the first step in finding a resolution by joining this Forum.
If you were to better define "terrible" more specific advice,  I'm sure, would be offered.


Dipper

Hi Joesson, thanks for the reply. Brake travels about 75% before braking begins. Also is it possible to just buy off the shelf "O" rings for it, or does the rubber compound have to be special to deal with the brake fluid?

Dipper

Quote from: boor on April  3, 2025, 16:52Before you go down this road, I'd suggest to check the calipers first, as usually that's the weak spot - sized caliper sliding pins and caliper pistons.
Hi Boor, calipers and pads have been changed, disc's are poor and have got them on order. If that doesn't fix it then I need to source a replacement.

Dipper

Quote from: Carolyn on April  3, 2025, 17:20Helo and welcome to the club. 

It's great to see you getting stuck in.

It's is so rare for the brake master cylinder to be faulty, to the point that it almost never happens.

Sticky slider pins are the first port of call.  Clean and lubricate with 'Ceratec' or similar silicon grease.

Afer that check for glazed brake pads and stuck pistons.



Thanks for the reply Carolyn,calipers and pads replaced, will be changing disc's when they arrive.

Dipper

Quote from: Call the midlife! on April  3, 2025, 18:10Just to add to the list, have you any idea how old the brake fluid is? Your description of "terrible" doesn't give us too many clues but if the fluid is old it could have an amount of water in it which won't help.

Hi, thanks for the reply, will change it when replacing disc's.

Joesson

#9
Quote from: Dipper on April  4, 2025, 13:40Hi Joesson, thanks for the reply. Brake travels about 75% before braking begins. Also is it possible to just buy off the shelf "O" rings for it, or does the rubber compound have to be special to deal with the brake fluid?

It is not unusual to have brake problems with our cars and as the comments above advise they can affect various elements of the system. These problems typically relate to usage/ age and maintenance/ lack of.
Some Members will try piecemeal maintenance or replacement until the system improves. Others, such as yourself, go for major component replacement.
As said little has been mentioned of master cylinder problems but it should not hurt in any way to give it some TLC.
With any hydraulic system there is a specified fluid and compatible seal material similarly specified throughout the system. I do not know what this is, but some research should find the answers.
Toyota could likely supply the correct size and specification of seal but may be more costly than from a specialist supplier.
Please be aware that the correct/ compatible seal material is essential. Incorrect material/ fluid can cause the seals to harden or swell either leading to inefficient operation.
With  75% of movement before any action that can indicate  poor adjustment of the calipers. These being self adjusting the test is , with engine running press the brake pedal slowly and firmly 10 to 20 times. You should notice an increase in resistance. That should reset the calipers. If no improvement it could be that seals are very worn, typically indicated by leaks. Seized cylinders. Or past  its best brake fluid.
Not mentioned in this post is the handbrake operation. That can cause some concerns.
I suggest you check the cables for free movement and the cable ends for their OE rubber shroud protection.
Assuming the cables are OK take time to read on here ( in How To ) about checking the setting of the calipers. (Mine were correctly aligned out of the box).
Very good luck with your endeavours and let us know how you progress.

Ardent

Any history to suggest brake fluid has been changed. Recommend every 2 years.

Beachbum957

#11
There can be many causes of a long brake pedal as suggested.  But even with careful assembly, maintenance, and adjustment, there can be differences. 

We have a 2002 and a 2003 MR2.  The 2003 has always had more pedal travel than the 2002, even though both have a nice firm pedal once the brakes begin to apply.  Both brake systems are set up the same with SS lines, fresh fluid at least every 2 years and pressure bled, carefully lubed sliders on the calipers, the parking brake working smoothly and adjusted by the book, and with similar pad wear.  The 2003 did get a new master cylinder, the pedal adjustment checked, and the brake booster push rod even adjusted.  Yet the 2003 still has more travel.

The only thing that made any noticeable difference was carefully following the parking brake adjustment procedure in the manual.  The brakes work great on both cars, so we just accept there is a difference.

Dipper

Quote from: Joesson on April  4, 2025, 19:05It is not unusual to have brake problems with our cars and as the comments above advise they can affect various elements of the system. These problems typically relate to usage/ age and maintenance/ lack of.
Some Members will try piecemeal maintenance or replacement until the system improves. Others, such as yourself, go for major component replacement.
As said little has been mentioned of master cylinder problems but it should not hurt in any way to give it some TLC.
With any hydraulic system there is a specified fluid and compatible seal material similarly specified throughout the system. I do not know what this is, but some research should find the answers.
Toyota could likely supply the correct size and specification of seal but may be more costly than from a specialist supplier.
Please be aware that the correct/ compatible seal material is essential. Incorrect material/ fluid can cause the seals to harden or swell either leading to inefficient operation.
With  75% of movement before any action that can indicate  poor adjustment of the calipers. These being self adjusting the test is , with engine running press the brake pedal slowly and firmly 10 to 20 times. You should notice an increase in resistance. That should reset the calipers. If no improvement it could be that seals are very worn, typically indicated by leaks. Seized cylinders. Or past  its best brake fluid.
Not mentioned in this post is the handbrake operation. That can cause some concerns.
I suggest you check the cables for free movement and the cable ends for their OE rubber shroud protection.
Assuming the cables are OK take time to read on here ( in How To ) about checking the setting of the calipers. (Mine were correctly aligned out of the box).
Very good luck with your endeavours and let us know how you progress.


Thank you again Joesson, as I said earlier, the disc's are quite bad and are being replaced shortly, the calipers and pads have been replaced.

Dipper

Quote from: Ardent on April  4, 2025, 21:58Any history to suggest brake fluid has been changed. Recommend every 2 years.

Will be changed when disc's are replaced. Thank you for the input.

Dipper

Quote from: Beachbum957 on April  5, 2025, 12:06There can be many causes of a long brake pedal as suggested.  But even with careful assembly, maintenance, and adjustment, there can be differences. 

We have a 2002 and a 2003 MR2.  The 2003 has always had more pedal travel than the 2002, even though both have a nice firm pedal once the brakes begin to apply.  Both brake systems are set up the same with SS lines, fresh fluid at least every 2 years and pressure bleed, carefully lubed sliders on the calipers, the parking brake working smoothly and adjusted by the book, and with similar pad wear.  The 2003 did get a new master cylinder, the pedal adjustment checked, and the brake booster push rod even adjusted.  Yet the 2003 still has more travel.

The only thing that made any noticeable difference was carefully following the parking brake adjustment procedure in the manual.  The brakes work great on both cars, so we just accept there is a difference.

Thank you for the reply, I'll bare that in mind and hopefully the new disc's will give an improvement.

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