Brake booster test

Hi guys,
I just did a brake booster test on my RB30 GQ Patrol.

I used the test procedure from Haynes repair manual.
I attached the procedure as a PDF file here.

Here are the results.
If I follow the numbers as in the Brake Booster Check in the document.

21)With the engine stopped, depress the brake pedal several times
The travel distance should not change
Travel distance does change.. Travel distance decreases on each pedal depress. After around 5 presses or so, the brake pedal gets really hard and doesn't go down much. This happened when I did the test in different times(day)
The car was left alone over night or all day before I did this part of the test

22)With the brake fully depressed, start the engine- the pedal should move down a little
when the engine starts.
Yes, test performed as above.

23)Depress the brake, stop the engine and hold the pedal in for about 30 seconds -
the pedal should neither sink nor rise.
Yes the test performed as above

24)Restart the engine, run it for about a minute and turn it off. Then firmly depress the brake
several times - the pedal travel should decrease with each application.
Yes. the test performed as above.

So, other than the very first part of the test( No 21), the test performed ok.

How do I interpret this test result, guys?
Do I have a brake booster or vacuum line issue(either intermittent or permanent)?

Thanks in advance for any assistance.

Mate,Travel distance does change.
If you had a booster vacuum leak it would change the idle RPMs (petrol engines only) every time you put foot on the brake.

When you say

Quote:

---

Travel distance does change.

---

does that mean you can push the pedal down further or less? To me there seem nothing wrong unless you have intermittent problem.

If the engine is not running and all vacuum pressure has been exhausted and the pedal travel changes repeatedly then the problem is in the hydraulic section not the boost/vacuum.

Ignoring the first issue all the other ones suggest no issue in the brake booster section.

If your pedal "sinks" with no booster vacuum applied and pressure maintained then you have possibly master cylinder issue.

Regards

Quote:

---

Originally Posted by Rumcajs

Mate,Travel distance does change.
If you had a booster vacuum leak it would change the idle RPMs (petrol engines only) every time you put foot on the brake.

When you say does that mean you can push the pedal down further or less? To me there seem nothing wrong unless you have intermittent problem.

If the engine is not running and all vacuum pressure has been exhausted and the pedal travel changes repeatedly then the problem is in the hydraulic section not the boost/vacuum.

Ignoring the first issue all the other ones suggest no issue in the brake booster section.

If your pedal "sinks" with no booster vacuum applied and pressure maintained then you have possibly master cylinder issue.

Regards

---

I meant I can push the pedal down less and less until it gets hard(the no 21, first part of the test).
This is how it reacts every time I do the No 21 test when the engine is cold and not running.
Since, there shouldn't be any vacuum in the booster and vacuum lines, I'm puzzled with that reaction
of the brake pedal.
I must insist, I was depressing the pedal moderately hard.

You are pumping your brakes, this means that there is air present or fluid is badly contaminated. This is hydraulic issue not the brake booster circuit.
When was the brake fluid last time changed? You need to check/bleed the hydraulic circuit.

Regards

Quote:

---

Originally Posted by Rumcajs

You are pumping your brakes, this means that there is air present or fluid is badly contaminated. This is hydraulic issue not the brake booster circuit.
When was the brake fluid last time changed? You need to check/bleed the hydraulic circuit.

Regards

---

I had to replace the front righthand side caliper hose & rebuild the caliper late last year.
I rebuilt the caliper first when one of the slide pins jammed.
I used the same pin, but polished inside the pin hole and pin with valve grinding grease.
Then the caliper hose was leaking, so I had to replace that as well.
I've never replaced brake oil, only topped it up during those leaky times.
I blocked the brake oil hose at the center of the front brake line to do the repair.
Then I bled the right hand side only(I couldn't see the need to bleed the other side at that time).

Do I need to clean the brake lines by draining all the oil?

You didn't finish the job right, always bleed whole system especially when replacing hose/s rebuilding caliper/s.
I suggest that you do complete brake fluid replacement with proper bleeding procedure or in the interim just bleed the whole system first.
The brake fluid should be replaced every 2 years, it is also good practice to replace it too when replacing/rebuilding any part of the hydraulic system.

Regards

Quote:

---

Originally Posted by Rumcajs

You didn't finish the job right, always bleed whole system especially when replacing hose/s rebuilding caliper/s.
I suggest that you do complete brake fluid replacement with proper bleeding procedure or in the interim just bleed the whole system first.
The brake fluid should be replaced every 2 years, it is also good practice to replace it too when replacing/rebuilding any part of the hydraulic system.

Regards

---

Crxp!!! Ok, cool. If I understood correctly, there's an apparent gunk build up inside the brake lines.
And I need to flush the brake lines properly.
I had no idea the brake fluid need draining and replacing like that.
When I was bleeding the van, there was lot of gunky dark brake fluid coming out of it,
so I bled the whole thing, taking my time.
I didn't think Patrol needed that, 'cos I drive it all the time, but apparently that's not the case.

So, I shouldn't use the old brake oil at all, right?

Thanx mate

as above Dom,
best way to go is buy a BIG bottle of brake fluid
undo the nipple on the passenger rear
pump ALL the fluid out (into a container) - just keep pumping the pedal and keep going for a bit after the Master Cylinder is empty

when your happy, add new fluid
keep pumping
when thats empty
fill up again, and get a mate to help you bleed the brakes properly
none of this Supercrap "self bleeding kits"
get a mate on the spanner
3 pumps on the pedal, holding pedal on the third pump - let the fluid out - pedal goes to floor, mate locks bleeder nipple, pump again, and again and again
(I always go for 3 or 4 times per wheel, until new clean fluid is coming out )

ALWAYS start at the nipple furthest away from Master Cylinder
so
passenger rear
drivers rear
passenger front
drivers front

if your getting AIR or crappy old fluid - keep going until its clean new fluid with NO air

Quote:

---

Originally Posted by Bigcol

as above Dom,
best way to go is buy a BIG bottle of brake fluid
undo the nipple on the passenger rear
pump ALL the fluid out (into a container) - just keep pumping the pedal and keep going for a bit after the Master Cylinder is empty

when your happy, add new fluid
keep pumping
when thats empty
fill up again, and get a mate to help you bleed the brakes properly
none of this Supercrap "self bleeding kits"
get a mate on the spanner
3 pumps on the pedal, holding pedal on the third pump - let the fluid out - pedal goes to floor, mate locks bleeder nipple, pump again, and again and again
(I always go for 3 or 4 times per wheel, until new clean fluid is coming out )

ALWAYS start at the nipple furthest away from Master Cylinder
so
passenger rear
drivers rear
passenger front
drivers front

if your getting AIR or crappy old fluid - keep going until its clean new fluid with NO air

---

Cool, thanx mate. Obviously I did a dodgy job last time.
It's time to get my butt cracking this time. :D
Cheers

I would not waste time to pump the system empty first, just empty/evacuate the reservoir and top up with new fluid and keep bleeding/pumping until new fluid comes out, regularly topping up reservoir with new fluid that way you avoid creating unnecessary air locks as well which will actually speed up the job .

Don't mix different grade brake fluids though.

Regards

Quote:

---

Originally Posted by Rumcajs

I would not waste time to pump the system empty first, just empty/evacuate the reservoir and top up with new fluid and keep bleeding/pumping until new fluid comes out, regularly topping up reservoir with new fluid that way you avoid creating unnecessary air locks as well which will actually speed up the job .

Don't mix different grade brake fluids though.

Regards

---

Ok cool, thanx mate.
I guess I'll be stashing away the old brake oil for future wound healing applications. :D


BTW, the vehicle is dual fuel & it idles only around 600ish when cold started.
Fast idle is not working on both fuels when cold at the moment.
Not sure the reason.
I just noticed, when cold started and when I press the brake pedal hard, rpm drops by around 150-200.
Once it's warmed up, I can't see any significant change of RPM when brake pedal is pressed hard.
Does this mean, I still have some issues with the vacuum lines(vacuum level)?!
I was suppose to properly test the vacuum level using vacuum tester.
I can't find the damn thing. Still looking for it.
I'm still suspicious about the vacuum system.
It didn't do well with the cigarette smoke test(my previous thread).
I need to do a proper vacuum test soon.
RPM drop happens when I press the pedal hard, probably meaning a small vacuum leak,
either in the booster or other parts of the vacuum lines??!!

Any thoughts?

Thanx

Nope, leak in the vacuum should raise the RPMs not drop them. At idle when throttle flap is closed there is limited amount of air getting in so if there is vacuum leak when you apply the brake that acts like slightly opening the throttle bumping the revs up.

If you had a leak it would also run out of vacuum while engine is off on first application of the pedal too.

Of course doing proper vacuum test would eliminate the guess work but I don't think you have a problem from what you described.

Cheers

from your description yes bleed the brakes but wouldnt worry too much about vacuum leak in booster. it sounds ok. my old laser used to do the same.

Quote:

---

Originally Posted by Rumcajs

Nope, leak in the vacuum should raise the RPMs not drop them. At idle when throttle flap is closed there is limited amount of air getting in so if there is vacuum leak when you apply the brake that acts like slightly opening the throttle bumping the revs up.

If you had a leak it would also run out of vacuum while engine is off on first application of the pedal too.

Of course doing proper vacuum test would eliminate the guess work but I don't think you have a problem from what you described.

Cheers

---

Thanx mate. I'm learning something new and important everyday.
Just did the test(21) with booster and other vacuum lines disconnected. The brake pedal still moves less and goes hard after few presses. So, I reckon the hydraulic issue is pretty obvious, putting aside any other issues.
Carby need a good look again to find out the reason for low cold idling rpm issue.
I haven't touched the distributor yet, to see if it has any issues.
I reckon 600 is bit too low.
If I adjust the cold start rpm to around 800 using the fast idle screw on the carby,
it idles really high once it's get warmed up, so it's no solution.
I'm guessing the problem must be somewhere else.
Cheers
Dom

Quote:

---

Originally Posted by garett

from your description yes bleed the brakes but wouldnt worry too much about vacuum leak in booster. it sounds ok. my old laser used to do the same.

---

Yes. Brakes hasn't been that great for few months. Especially, I felt a drop in brake response since I
switched to 235/85s from 225/75(super tiny tyres).
Also, it's obvious, my caliper rebuild job was done half hearted, 'cos I apparently didn't do the proper bleeding
& draining. Other thing is that front rotors haven't been machined for a while as well.
I reckon all these things add up.
Thanx mate

I've been wondering. I haven't touched the hydraulic system of the clutch for as long as I had the car.
Do I need to drain the hydraulic(brake) oil from the clutch, refill with new oil and bleed it?
Thanks guys

I think my brake booster is shot. When I press on the brake pedal and then start the engine, it doesn't go down any. The pedal is pretty far to the floor, if that gives anyone an idea as to whats wrong. I tried pumping the brake pedal and then turning the key, but nothing again.I have armored mercedes, Is there a way to test the vacuum line? can I just pull it off the booster and feel for air? I'm just learning how the vacuum system works so please excuse my ignorience.

Quote:

---

Originally Posted by dom14

I've been wondering. I haven't touched the hydraulic system of the clutch for as long as I had the car.
Do I need to drain the hydraulic(brake) oil from the clutch, refill with new oil and bleed it?
Thanks guys

---

Well, the reservoir is right next to the other one so why not? Yes it is advisable to do the clutch side too at the same time.

B/R

Quote:

---

Originally Posted by Rumcajs

Well, the reservoir is right next to the other one so why not? Yes it is advisable to do the clutch side too at the same time.

B/R

---

Ok, cool. thanx mate.

This is the advice given to me by the forum member "garett" regarding bleeding brakes properly.
This was a PM conversation between him and me.
I'm posting it here, as I find it's pretty useful for anybody.

"just mentioned that as i'm guessing it's not new, old masters tend to go rough where you dont use them and if you press it all the way it can destroy the seal and the pedal will sink( pedal slowly goes to the floor while holding pressure on the pedal), as stated every 2 years, i would recommend a dot 4 from a new/ish container. brake fluid absorbs water, even from the air. this will lower its boiling point and give brake "fade""

"empty the master res. refill with clean fluid get a mate to depress brakes then open nipple starting with the rear one at a time. lock off nipple pump brake ( dont go past usual braking as this may damage ur master). repeat for all wheels. do not let the master res. empty out."

Quote:

---

Originally Posted by Bigcol

snip...3 pumps on the pedal, holding pedal on the third pump - let the fluid out - pedal goes to floor, mate locks bleeder nipple, pump again, and again and again
(I always go for 3 or 4 times per wheel, until new clean fluid is coming out )

---

Put something behind your brake pedal Dom. If you push the pedal to the floor, the piston will be travelling further than normal and you could damage a seal etc if there is any pitting there. Fwiw, I've used a vacuum bleeder before and it worked well for me.

EDIT: Didn't see this in your last post Dom, which mirrors what I've said above.

Quote:

---

Originally Posted by Bigcol

snip..ALWAYS start at the nipple furthest away from Master Cylinder
so
passenger rear
drivers rear
passenger front
drivers front

---

The brake bias valve has been left out of the above and must be bled. From what I remember reading, it should be done first. Then PR, DR, PF, DF.

Quote:

---

Originally Posted by Throbbinhood

Put something behind your brake pedal Dom. If you push the pedal to the floor, the piston will be travelling further than normal and you could damage a seal etc if there is any pitting there. Fwiw, I've used a vacuum bleeder before and it worked well for me.

EDIT: Didn't see this in your last post Dom, which mirrors what I've said above.



The brake bias valve has been left out of the above and must be bled. From what I remember reading, it should be done first. Then PR, DR, PF, DF.

---

True. I think the vacuum bleeder is worth the money you spend on it. Master cylinder is way too expensive to damage it.

Does the bias valve has a bleed nipple?

some do, some dont

depends on what yours looks like Dom

Quote:

---

Originally Posted by dom14

True. I think the vacuum bleeder is worth the money you spend on it. Master cylinder is way too expensive to damage it.

---

a proper Vacuum bleeder is the correct way

the cheap and nasty one with a ball bearing in the end of a tube from Supercrap is shyte

G`day Guys
Bleeding the system with a new or recon master is a simple job but needs two people.
One on the pedal and one at the wheels. doesn`t really matter which where you start , but first bleed the master. Fill the master and REPLACE the cap,person on the pedal pushes pedal to floor (do not bang the pedal down, just push it down easy) only once, holding pedal down. person on the spanners cracks the pipes at the master, once air and fluid stop flowing retighten tube nuts, now person on the pedal releases pedal SLOWLY over a time of around 5 seconds. DO NOT pump.Repeat until all air is expelled and only fluid comes out.WARNING the fluid does squirt all over the place so a cover of rag and plenty of water around is necessary. IF the fluid gets on paint work wash it off strait away with flowing water.. OK master bleed now to the wheels, dosen`t matter where you start but farthest away is not a bad place to start. Person on pedal pushes pedal down and holds it down, spanner man opens bleeder and waits until air and fluid stops flowing, shut bleeder then person on pedal, SLOWLY "5 seconds "releases pedal,then waits another 10 second before pushing pedal to floor again. Repeat until only fluid comes out at the bleeder. Repeat process at each wheel and then you should have a good hard pedal.DO NOT bleed brakes with the engine running. Now with a reasonably amont of pressure on the pedal start the motor and the pedal should drop a small distance, this indicates that the booster is working.
If there is a bleeder on the load sensing valve bleed this before doing the rears.
OK reasons for NOT pumping pedal. the seals in the master are designed to collapse when the pedal is released and any air in the reservoir side of the piston will be dragged into the pressure side, but releasing it slowly gives the reservoir side time to recover, once the system is air free it can operate at any speed. The same problem happens with drum brake system where when bleeding, a quick release of the pedal can and will draw air into the wheel cyls especially if they are old. Another thing I do is to clamp of all the hoses apart from the wheel being bled, this stop back and forth movement of fluid apart from the wheel being worked on. WARNING DO NOT CLAMP BRAIDED HOSES.
Hope this is of some help.

Quote:

---

Originally Posted by pearcey

G`day Guys
Bleeding the system with a new or recon master is a simple job but needs two people.
One on the pedal and one at the wheels. doesn`t really matter which where you start , but first bleed the master. Fill the master and REPLACE the cap,person on the pedal pushes pedal to floor (do not bang the pedal down, just push it down easy) only once, holding pedal down. person on the spanners cracks the pipes at the master, once air and fluid stop flowing retighten tube nuts, now person on the pedal releases pedal SLOWLY over a time of around 5 seconds. DO NOT pump.Repeat until all air is expelled and only fluid comes out.WARNING the fluid does squirt all over the place so a cover of rag and plenty of water around is necessary. IF the fluid gets on paint work wash it off strait away with flowing water.. OK master bleed now to the wheels, dosen`t matter where you start but farthest away is not a bad place to start. Person on pedal pushes pedal down and holds it down, spanner man opens bleeder and waits until air and fluid stops flowing, shut bleeder then person on pedal, SLOWLY "5 seconds "releases pedal,then waits another 10 second before pushing pedal to floor again. Repeat until only fluid comes out at the bleeder. Repeat process at each wheel and then you should have a good hard pedal.DO NOT bleed brakes with the engine running. Now with a reasonably amont of pressure on the pedal start the motor and the pedal should drop a small distance, this indicates that the booster is working.
If there is a bleeder on the load sensing valve bleed this before doing the rears.
OK reasons for NOT pumping pedal. the seals in the master are designed to collapse when the pedal is released and any air in the reservoir side of the piston will be dragged into the pressure side, but releasing it slowly gives the reservoir side time to recover, once the system is air free it can operate at any speed. The same problem happens with drum brake system where when bleeding, a quick release of the pedal can and will draw air into the wheel cyls especially if they are old. Another thing I do is to clamp of all the hoses apart from the wheel being bled, this stop back and forth movement of fluid apart from the wheel being worked on. WARNING DO NOT CLAMP BRAIDED HOSES.
Hope this is of some help.

---

Hi Pearcey,
I've been wondering. From what I've heard so far, bleeding the master cylinder is very important to make sure the brake's are working properly.
Yet, there's no bleed nipple on the master pump. It's not that easy to bleed the master pump without making a mess, even when bench bleed it.

Why haven't they put a bleed nipple on them? I'm wondering!

Quote:

---

Originally Posted by Bigcol

a proper Vacuum bleeder is the correct way

the cheap and nasty one with a ball bearing in the end of a tube from Supercrap is shyte

---

How about this one?

http://www.ebay.com.au/itm/Brand-New...4AAOSwstxVTgGF

Quote:

---

Originally Posted by Bigcol

a proper Vacuum bleeder is the correct way

the cheap and nasty one with a ball bearing in the end of a tube from Supercrap is shyte

---

I just realized, a cheap bicycle pump or a balloon pump with a long enough transparent vacuum hose attached to it,
is also a good makeshift vacuum bleeder.

G`day Dom.
Yep bleeding the master is a bit messy, but it`s only done once every few years , not like changing the the oil filter every 6 months.
Only problem with brake fluid is it removes paint in a very short time, hence plenty of water.
Bleed nipples on the master are an added expense that serves no real purpose so the factory leaves them off.
There are a few older cars and trucks with them but these are on masters that are very hard to get at and would have made bleeding at the factory a lot easier and less time consuming (which equals money saved)

Quote:

---

Originally Posted by pearcey

G`day Dom.
Yep bleeding the master is a bit messy, but it`s only done once every few years , not like changing the the oil filter every 6 months.
Only problem with brake fluid is it removes paint in a very short time, hence plenty of water.
Bleed nipples on the master are an added expense that serves no real purpose so the factory leaves them off.
There are a few older cars and trucks with them but these are on masters that are very hard to get at and would have made bleeding at the factory a lot easier and less time consuming (which equals money saved)

---

Yeah, the brake oil leak from the master cylinder has ruined the paint on the brake booster and the body, which has caused rust as well. I had to respray the whole area with metal care paint to avoid any further damage.
I understand the master cylinder get bled once every few years, but that's enough to damage the paint if I drop some on the paint.
Yes, of course, plenty of wet rags should prevent from brake oil getting onto the paint.