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Discussion Starter #1
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.
I followed 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 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.
 

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Step 21 is quite vague, because in theory the distance travelled should remain the same. The problem is though because the engine is off, you have no vacuum, hence no assistance from the booster after a few presses. This is why it's concieved that it travels less when the engine is off. If you really stamped on it, it should go the same distance as when the engine is running.

Having read your results though, your booster sounds like it is working perfectly fine.
 

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Discussion Starter #3
Step 21 is quite vague, because in theory the distance travelled should remain the same. The problem is though because the engine is off, you have no vacuum, hence no assistance from the booster after a few presses. This is why it's concieved that it travels less when the engine is off. If you really stamped on it, it should go the same distance as when the engine is running.

Having read your results though, your booster sounds like it is working perfectly fine.
Yes, I think the booster's fine. But, the results of above step 21 is not exaggerated.
The pedal travel less and less distance until it gets rock hard.
So, I reckon I may have some other issues with the hydraulic system.
I've been told to drain it completely and bleed it thoroughly.
 

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Having re read it, there may be a step before step 21 that has you bleed any vacuum you may have, so in that scenario the pedal travel wont change at all. Then in step 24 after running the engine, you create enough vacuum for the booster to work for a couple of presses after the engine is off. (so essentially from the extract you've provided, step 21 and 24 are the same step).

Whats the exact problem you're having? Is it going rock hard after a few presses with the engine running?
 

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Discussion Starter #5
Having re read it, there may be a step before step 21 that has you bleed any vacuum you may have, so in that scenario the pedal travel wont change at all. Then in step 24 after running the engine, you create enough vacuum for the booster to work for a couple of presses after the engine is off. (so essentially from the extract you've provided, step 21 and 24 are the same step).

Whats the exact problem you're having? Is it going rock hard after a few presses with the engine running?
Let me check. I'll be back in a minute.
 

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Discussion Starter #6
I just checked. The brake pedal goes hard after few depresses, regardless of there's vacuum or not. To confirm, I disconnected booster vaccum hose and couple other vacuum hoses before I did the test(21). So, by the looks of it, I have some other issue with the brake system?

About the problem, brakes aren't that great at the moment.
Especially after I switched to 235/85s from 225/75(too tiny), I feel like there's a lot less brake response.
I did a caliper rebuild late last year on front right, which I only bled that side.
Apparently I need to do a proper drain and bleed when I do such repairs.
I didn't know that.
Always did the quick and slack solution of bleeding the repaired side, only.
Other reason for testing brake as above 'cos the cold start rpm is as low as 550-600rpm.
I was suspecting booster has slight leak and causing the vacuum to drop.
I can't find my vacuum tester, so I've been doing other types of vacuum tests like this one.
 

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Discussion Starter #7
The problem is that when I adjust the cold start rpm to 800ish via the fast idle screw in the carby,
it idles too high once it gets warmed.
This is why I was suspecting, some kind of vacuum issue.
Having said that, I haven't had a good look at the distributor, yet.
 

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I still think your booster is working fine. There's a one way valve on the booster, so once you disconnect the vacuum lines it should still hold a vacuum. Which it does. Which is good.

With the engine is running, press the brake pedal several times. If it goes harder after a few presses in quick succession then there is air in the system somewhere (most likely the front right). You will need to follow the proper procedures and bleed the system properly.

If the pedal stays the same travel and firmness then there's no air in the system.

I know from personal experience the carby's on those RB30's can be a pain in the buttocks. I was never able to get mine run nicely when cold. I ended up using the throttle lock to keep the revs up until it warmed up.

You might be better to see if you can get this thread moved over to the GQ section, as more GQ experts will see it there and someone might be able to help you better. But as far as the booster goes it sounds like it is working fine so you will need to start looking elsewhere.

CHeers
 

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Discussion Starter #9
I still think your booster is working fine. There's a one way valve on the booster, so once you disconnect the vacuum lines it should still hold a vacuum. Which it does. Which is good.
Yes, from the help I got so far, everybody agrees the booster is fine.
As you indicated the problem is somewhere else.

With the engine is running, press the brake pedal several times. If it goes harder after a few presses in quick succession then there is air in the system somewhere (most likely the front right). You will need to follow the proper procedures and bleed the system properly.
Yes, that's what happened when I performed that test.

If the pedal stays the same travel and firmness then there's no air in the system.
It doesn't on the cold pedal depress test. So, I reckon that indicated hydraulic issue,
rather than a vacuum issue, as I initially wrong suspected a booster vacuum issue.

I know from personal experience the carby's on those RB30's can be a pain in the buttocks. I was never able to get mine run nicely when cold. I ended up using the throttle lock to keep the revs up until it warmed up.
Yes, they are real PITA. I have a back up carby, but that one's not perfect either.
The one on the motor at the moment is better.

You might be better to see if you can get this thread moved over to the GQ section, as more GQ experts will see it there and someone might be able to help you better. But as far as the booster goes it sounds like it is working fine so you will need to start looking elsewhere.
Yes, I agree the booster is working fine.
Not too sure about the GQ section, I feel there are less and less hits in the GQ section
over the years. Carby's are even rarer these days.
But, following your suggestion, I'll see if I can move this thread to GQ area.

Thanx for taking time to help me mate.
Cheers
Dom
 

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Discussion Starter #10
I can only see a way to duplicate this thread in GQ section.
I don't seem to be able to move it.
I think the forum admin considers thread duplication as a serious crime! :D
Can you admin guys move this thread to GQ section, please?
Thanx
 
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