24 replies to this topic

[postve]

Need yer help guys - replaced metal brake master cylinder with plastic one x 2 - bleed the system - 3 times myself, 2 times by my mechanic - same issue - pump pedal 3 times it gets hard, release and goes spongy?! Also replaced both rear brake cylinders as well???

What the heck are we doing wrong!!

1293 engine - 1978

Bench bleeding picture for reference

[Tornado99]

Have heard the rear brake pressure regulator can be a problem to bleed properely. Has a vacuum bleeder been used?
What I have read on these forums is if you apply pressure from pedal for bleeding rears it can trigger the pressure reg device such that no or not much pressure reaches rear cylinders, so not enough fluid gets through the reg to bleed it fully.
A gravity bleed, with no pressure from pedal or a vacuum bleeder at rear cylinder means the reg stays fully open letting max fluid through to get air out.

[postve]

Have heard the rear brake pressure regulator can be a problem to bleed properely. Has a vacuum bleeder been used?
What I have read on these forums is if you apply pressure from pedal for bleeding rears it can trigger the pressure reg device such that no or not much pressure reaches rear cylinders, so not enough fluid gets through the reg to bleed it fully.
A gravity bleed, with no pressure from pedal or a vacuum bleeder at rear cylinder means the reg stays fully open letting max fluid through to get air out.

So basically open the rear bleeder nipples and let fluid drip out ?

[Maccmike8]

Ive still got an initially soft pedal after replacing some worn out parts.

To get around the pressure regulator I opened all the bleed nipples and got pumping until fluid was coming out of all the nipples at once. Then I went around each one conventionally. Still not perfect though.

[absx2]

I`m guessing you are not using a http://www.minispare...|Back to search that would originally been fitted to your car unless it was late registered.

If not try opening the rear bleed nipples on at a time then get an assistant to quickly press the brake pedal to the floor and hold it there until you do the nipple up.

This way the http://www.minispare...|Back to search can`t close the circuit off.

It`s also quite possible that the brand new master cylinder needs a quick strip and clean as occasionally the small washer seen here http://www.minispare...|Back to search

can stick to the back of the seal and that stops the brake fluid being pulled through to replace the space.

So basically that`s the non return valve so if it`s stuck to the back of the seal the brake master acts more like a clutch cylinder and the pistons are pulled back when you release the pedal.

I would try that as a last resort and a gravity bleed followed by a couple of stabs will hopefully do the trick.

 

Also check your flexi hoses if you are using them as they can collapse and or swell inside and give similar issues.

[Tornado99]

Have heard the rear brake pressure regulator can be a problem to bleed properely. Has a vacuum bleeder been used?
What I have read on these forums is if you apply pressure from pedal for bleeding rears it can trigger the pressure reg device such that no or not much pressure reaches rear cylinders, so not enough fluid gets through the reg to bleed it fully.
A gravity bleed, with no pressure from pedal or a vacuum bleeder at rear cylinder means the reg stays fully open letting max fluid through to get air out.

So basically open the rear bleeder nipples and let fluid drip out ?

,

Yes, that's the way it works. Use a bit of hose on nipple to direct fluid drips to catch bottle. Keep reservoir topped up. Close once no more. Bubbles or dirty fluid. Can open more than one circuit at same time. Give them 15-25 minutes per wheel minimum for complete fluid change. Works great for me when doing yearly fluid changes.

Heres a video describing method and why it is better from old systems:

https://youtu.be/5Mkj2fRmTws

[cal844]

I've never had an issue bleeding brakes, make sure any brake calipers (if fitted) have the bleed nipples to the top, the same applies to a brake cylinder.

I've never used a pressure or vacuum bleeder, always the two man method.

I generally loosen the nipple before pumping the pedal, give it 10 slow pumps, then tighten with the nipple down.

Bleed order on a RHD car
Passenger rear
Drivers rear
Passenger front
Drivers front

Hope this helps

Cal

[nicklouse]

Never had to bench bleed a single line MC ever they are so simple.

 

I would  say the you need to set the rear brakes correctly.

[postve]

[attachment=214701:brake.jpg]

I`m guessing you are not using a http://www.minispare...|Back to search that would originally been fitted to your car unless it was late registered.

If not try opening the rear bleed nipples on at a time then get an assistant to quickly press the brake pedal to the floor and hold it there until you do the nipple up.

This way the http://www.minispare...|Back to search can`t close the circuit off.

It`s also quite possible that the brand new master cylinder needs a quick strip and clean as occasionally the small washer seen here http://www.minispare...|Back to search

can stick to the back of the seal and that stops the brake fluid being pulled through to replace the space.

So basically that`s the non return valve so if it`s stuck to the back of the seal the brake master acts more like a clutch cylinder and the pistons are pulled back when you release the pedal.

I would try that as a last resort and a gravity bleed followed by a couple of stabs will hopefully do the trick.

 

Also check your flexi hoses if you are using them as they can collapse and or swell inside and give similar issues.

Sounds like a good plan and I did a gravity bleed and all worked well yet issue persisted.  Yes, to your question above on the limiter, and see attached photo of what I currently have or at least last guy had in car. I have two brand new MC, swapped and same issue - lol - selling one soon.thoughts on my image - maybe disconnect and check that?

[postve]

Never had to bench bleed a single line MC ever they are so simple.

 

I would  say the you need to set the rear brakes correctly.

Good reco Nick and adjusted and set as per spec - should barely move after adjustment - issue persists.  Agree with bench bleed, I always do this type in car but was desperate so pulled out and bench bleed anyways

[postve]

I've never had an issue bleeding brakes, make sure any brake calipers (if fitted) have the bleed nipples to the top, the same applies to a brake cylinder.

I've never used a pressure or vacuum bleeder, always the two man method.

I generally loosen the nipple before pumping the pedal, give it 10 slow pumps, then tighten with the nipple down.

Bleed order on a RHD car
Passenger rear
Drivers rear
Passenger front
Drivers front

Hope this helps

Cal

Agreed and did that Cal, and interestingly enough one of the nipples  - 7.5 discs at front - last owner had mechanic install incorrectly - at bottom, but, it still should work as it has for the last 6 years - not sure that is my issue but one all the same.

[postve]

Ive still got an initially soft pedal after replacing some worn out parts.

To get around the pressure regulator I opened all the bleed nipples and got pumping until fluid was coming out of all the nipples at once. Then I went around each one conventionally. Still not perfect though.

Thx Mike, mine is brutal - takes three pumps and no way in hell would I drive this fast behind other cars and certainly not on the highway.  All this is compounded with my new Super charger - which runs amazing by the way - so brakes being spot on is absolutely critical for my life's sack.

[postve]

Have heard the rear brake pressure regulator can be a problem to bleed properely. Has a vacuum bleeder been used?
What I have read on these forums is if you apply pressure from pedal for bleeding rears it can trigger the pressure reg device such that no or not much pressure reaches rear cylinders, so not enough fluid gets through the reg to bleed it fully.
A gravity bleed, with no pressure from pedal or a vacuum bleeder at rear cylinder means the reg stays fully open letting max fluid through to get air out.

Good point and did gravity bleed today - which was spot on - issue persists

[postve]

 

 

Have heard the rear brake pressure regulator can be a problem to bleed properely. Has a vacuum bleeder been used?
What I have read on these forums is if you apply pressure from pedal for bleeding rears it can trigger the pressure reg device such that no or not much pressure reaches rear cylinders, so not enough fluid gets through the reg to bleed it fully.
A gravity bleed, with no pressure from pedal or a vacuum bleeder at rear cylinder means the reg stays fully open letting max fluid through to get air out.

So basically open the rear bleeder nipples and let fluid drip out ?

,

Yes, that's the way it works. Use a bit of hose on nipple to direct fluid drips to catch bottle. Keep reservoir topped up. Close once no more. Bubbles or dirty fluid. Can open more than one circuit at same time. Give them 15-25 minutes per wheel minimum for complete fluid change. Works great for me when doing yearly fluid changes.

Heres a video describing method and why it is better from old systems:

https://youtu.be/5Mkj2fRmTws

 

thx Torn - followed to the letter, fluid looked great, issue persists - I am thinking - absx2 - reco. on flex lines could be a potential issue...not sure how I can test these other than replace - cheap anyways

Edited by postve, 28 September 2021 - 07:59 PM.

[postve]

As a side note, replacing the front and rear brake hoses anyways as no idea when they were last done - sanity anyways and good to do.

Just confirmed today existing brake hoses are @20 years old - waiting for new ones to arrive tomorrow.

Edited by postve, 29 September 2021 - 10:57 AM.