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Discussion Starter #1
Hey guys,

Ive been having this problem for a while now, just wondering if it's happened to anyone else. When on a hillclimb, if I have to stop to pick another line or reverse back down, i seem to lose all vacuum assist in the brakes getting a rock hard pedal, pushing the pedal barely pulls me up so I have to resort to the handbrake. I basically only do climbs now that I know I'll get up 1st go as it's a little scary, even descending nose first down a rocky hill running in 1st low, it still seems to not have any vacuum as soon as i feel for some brakes so it's not like I'm wasting it without enough rpm to let the vac pump build up pressure. On flat ground day to day driving I've never had a problem with my brakes they are strong and consistent, all calipers have been rebuilt and all lines are new. It did it with the original alt/vac pump, that has been replaced with a whole new unit about 12 months ago and still does it, so leaning towards booster but i thought that would make it happen all the time not only on steep inclines.

Anyway sorry bout the rant hope someone can give me some insight
cheers, Brady
 

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Right Turn Clyde
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Are you getting just one pump of the pedal or getting a few more before it goes hard?
Do you have a boosted clutch as well?
 

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Discussion Starter #4
Depends eighty8 sometimes I'll get 6 pumps sometimes none, and yeah it's a boosted clutch which occasionally has similar problems

and gqtoy excuse my ignorance but where abouts is the valve?? Is it the little black cylinder where the vacuum hoses run?
 

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mine did this as well turned out to be the clutch booster, try unplugging the vacum line from the clutch booster and blocking the line off so you only have the brakes in the system. Clutch will just be a lot heavier to use. I drove mine around for about 12mths before i fixed the booster.
 

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Discussion Starter #7
Alright mate next time I go out 4wding I might try that, then I can look at replacing the booster, might replace both while im at it, did you go genuine or get yours rebuilt??
 

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They all do it, it's just a diesel thing. I have twin vacuum tanks, but I'm going to replace one with an old fire extinguisher to use as a larger tank. I don't have the booster type clutch, but I do have a factory vacuum rear locker (not that it takes much vacuum to work).

Loosing vacuum under braking is normal. It's just that diesels don't create vacuum quick enough at low RPM- the vacuum pump is just too slow at idle. I installed a vacuum gauge which is quite useful. I can see how much vacuum is remaining which is handy when reversing down steep hills like you said. Generally I can pump the pedal about 4-5 times before the vacuum is too low to be effective.
 

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Discussion Starter #9
I know they'll lose vacuum quickish but this seems really instant and only on big inclines whether it's the first touch of the brakes or not, however if it does turn out to be normal I'll be trying to sort out some way of fixing it haha, no real fun
 

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Sorry mate, not sure about the TD42 set-up. I expect that it's somewhere between the vac pump and the boosters. On the petrol models it's a small in-line cylinder, not much bigger than the hose.
 

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Right Turn Clyde
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As Patrol_Mav has said its a diesel thing, unfortunately. If you can get 4 or 5 pumps thats about right. I have what Patrol_Mav has said, a small fire extinguiser as an extra inline tank. I reckon I get an extra few pumps on the pedal but its not a huge improvement. I'd like to replace the small bottle with a larger unit to see if that makes any more of a difference, might make this the next little project.
A few things you can check first are all the vac hose connections, the rubber becomes hard and loses its seal, replace the factory spring clamps with hose clamps if needed.

Also check the small a/c idle up hose, it can fall off without you realising, effectively being a big vaccum leak.
cheers.
 

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Discussion Starter #12
Where does the a/c vac hose go to? I'm too comfy to go check hahaha, thanks for everyones replies I might look into getting a slightly larger tank fabricated
 

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i had mine rebuilt about $130 ish from memory. The alternator vacum pump is useless. I removed the motor in my Patrol aprox 12 months ago to fix a damaged crank after the balancer spun and destroyed the keyway, while i had the motor out i converted it from the vacum alternator to the later model vacum pump on the block. Since then i have no further issues at low revs with loss of vacum. Not a cheap option if paying to do it. On the upside i can fit any alternator that will fit as i no longer need a vucum pump on the alternator.
 

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Discussion Starter #14
Im guessing there arent any bigger vac pump assemblies that can be fitted to the alternator??
 

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naturally asthmatic
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I've been there a number of times and it is blood scary when that brake goes hard and you are looking at sky. Here are few solutions.

1) For a quick and easy fix, use the idle-up to set idle at 1000-1200 rpm before starting the hill.
2) Increase the size of your vacuum tank(s)
3) Clean or replace faulty check valves
4) Add a 12V (or 24V for Safari) vacuum pump (nice to have back-up)

The mechanical pump addition would also work fine. However, I'd rather have the electric vacuum pump then the mechanical one as it leaves that spot open for an endless air set-up, or in my case, a 12V alternator for my 12V needs.
 

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Be careful about how much you increase the size of the vacuum tank, at some point it will possibly become dangerous due to the time needed for the pump to create a "new" vacuum.
( think about the time taken to charge a small air tank as opposed to a large one)
 

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naturally asthmatic
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I fail to see how it would be more dangerous. If you have a leak in your vacuum system, then you will have to wait longer to get vacuum. Just like an air compressor system, adding volume allows you to go with increased demand over what your compressor will put out. I have another 20L tank I add to my current shop air compressor when I know I need more capacity than my compressor can provide. Ask any trucker what they would prefer to drive, a truck with 20L air tanks or one with 60L air tanks. If you have a vacuum leak, your best bet is to fix it.
 

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bit cold out it seems
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most GQs being as old as they are should really get their vacuum pumps refreshed and all hoses replaced to combat leaks. Probably also a good idea to replace the standard vacuum tank, if i remember rightly it is plastic??
 

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The mechanical pump addition would also work fine. However, I'd rather have the electric vacuum pump then the mechanical one as it leaves that spot open for an endless air set-up, or in my case, a 12V alternator for my 12V needs.

er you should be able to fit it no problems

i have on mine

power steering
alternator
air cond compressor
endless air
super charger

the mechanical pump runs off the block its not belt driven, i have my power steering pump mounted below my injector pump and the vacum pump fits in between. endless air hangs off the alternator which was a crappy design due to aweful brackets supplied by endless. I made my own which i have plans for somewhere which im quite happy to share. the ones i made up you can remove either the air or the alternator with out removing both.
 

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I fail to see how it would be more dangerous. If you have a leak in your vacuum system, then you will have to wait longer to get vacuum. Just like an air compressor system, adding volume allows you to go with increased demand over what your compressor will put out. I have another 20L tank I add to my current shop air compressor when I know I need more capacity than my compressor can provide. Ask any trucker what they would prefer to drive, a truck with 20L air tanks or one with 60L air tanks. If you have a vacuum leak, your best bet is to fix it.
I agree, IF you have a leak that you are aware of you would be mad not to fix it, the issue here may not be caused by a leak, it could simply be caused by too many brake applications at idle which the vacuum pump cannot keep up with,in this case a larger vacuum tank could be handy but only to a point. i am just suggesting to take care with how big you go.
If you empty the air tanks on a truck the brakes will lock on (assuming you haven't overheated them to the point where they are useless anyway) but if you empty a large vacuum tank by the time you build up vacuum again it could be too late.

Or to look at it another way if a truck loses air overnight thru a small leak the brakes will not release until you build up air,small tanks = short time large tanks = long time,either way no danger.

But if your nissan loses vacuum overnight thru a small leak and you roar off up the road for a short distance and come to a stop sign a small tank will have already "charged up" a large tank may not have. = POSSIBLE DANGER.
 
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