Brake booster test

[dom14]

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.


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

[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

[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.

[dom14]

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

[dom14]

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

[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

[Cillian21]

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.

[Rumcajs]

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

[dom14]

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.

[dom14]

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."