[scott12]

Hi All,

Had an air leak from the freewheel diff compressor on my '03 GV - wouldn't pump to pressure.

I have cleaned the rust off of the dump valve in the compressor (and cleaned / flipped over its o-ring to present a better seal) per fordems good tech thread which has improved things dramatically (pumps to pressure in 1 - 2 seconds), however -

When blocking the output pipe from the compressor it will hold pressure for 15 seconds before losing enough pressure to operate again for a very short while until it regains pressure, and over the cycle continues.

Is this the normal operation (i.e. loses pressure every so often) or will this cause problems (e.g. jump out of 4wd while driving and possibly do some damage) ?


P.S. I'm not real keen on grinding off the diaphragm housing to look for other potential leaks if losing pressure after a while is the normal operation.

[scott12]

Well maybe my thumb (which was blocking off the compressor outlet) is not as air tight as I'd like to think -

Just connected all the hoses back up to the diff and it maintains pressure for over a minute without dropping the 4wd light.

Still keen to know whether a slow leak will cause loss of 4wd tho ?

[foonji]

Are you talking about the 4wd light flashing once every 15-20 seconds?

[steak_knife]

scott12 wrote:

Hi All,



P.S. I'm not real keen on grinding off the diaphragm housing to look for other potential leaks

It's not, it should hold pressure, the actuator in the front diff may be buggered if you can't find an external leak..

[scott12]

steak_knife wrote:

It's not, it should hold pressure, the actuator in the front diff may be buggered if you can't find an external leak..

Note - when I was testing the compressor (situation at my first post), I used my thumb to close off the outlet port, this is when I had the compressor cyling on / off (and 4wd light doing same) every 15 sec or so.

Per my 2nd post, since re-assembling everything and re-connecting air hoses to front diff - all good 4wd light stays on no problem (although i get bored of watching the 4wd light after a minute and then turn off the ignition), so it is holding pressure for as long as I get bored looking at the 4wd light and pumps pressure straight away - I'm thinking it's now fixed.

[steak_knife]

[scott12]

Oh, nearly forgot,

will a momentary pressure loss (e.g. 1 - 2 seconds max) cause a loss of 4wd ?

or will the gears hold in no worries if they're contantly under load ?

[steak_knife]

scott12 wrote:

Oh, nearly forgot,

will a momentary pressure loss (e.g. 1 - 2 seconds max) cause a loss of 4wd ?

or will the gears hold in no worries if they're contantly under load ?

yes....

Sorry to burst your bubble, but it's a vacuum pump...

[fordem]

As long as it's not constantly cycling on & off every few seconds, I would ignore it - the design allows a certain amount of "leak down", so when the pressure drops below roughly 6psi the pump runs for a seond to top it back up, usually before it looses enough pressure to disengage the freewheel clutch.

You can get an idea of how much it's leaking from the time interval between pump cycles, which by the way coincides with the light flashes - the light goes out everytime the pump turns on - so a wink out every 4 seconds isa serious leak, but a wink out every 4 minutes is liveable.

One last thing - Stekky - it's not a vacuum pump - put a gauge on it, or check your manuals (Section 7E) - 5.4~8.25 psi, 38.0~58.0 kPa.

[scott12]

Thanks fordem,

for your good tech thread, very informative - mine was a case of rust on the dump valve, didn't have a rotary tool so I scraped off the rust gently with a knife and polished with 1200 paper.

The o-ring under the dump valve was rust pitted on the inside / perfect on all other sides, so I cleaned it up and flipped it over to give a good seal on the dump valve.

Yes its holding pressure very well now, (tested for over 3 minutes without depressurising once - that'll do me).

I'd expect the hysterisis of the pressure switch would be such as to prevent loss of 4wd during that re-pressurision, many thanks for your input.

[foonji]

Guess I better check over mine then! Didn't realise the light going out was the pump going on, and mine goes every 15 sec or so.

[steak_knife]

fordem wrote:

As long as it's not constantly cycling on & off every few seconds, I would ignore it - the design allows a certain amount of "leak down", so when the pressure drops below roughly 6psi the pump runs for a seond to top it back up, usually before it looses enough pressure to disengage the freewheel clutch.

You can get an idea of how much it's leaking from the time interval between pump cycles, which by the way coincides with the light flashes - the light goes out everytime the pump turns on - so a wink out every 4 seconds isa serious leak, but a wink out every 4 minutes is liveable.

One last thing - Stekky - it's not a vacuum pump - put a gauge on it, or check your manuals (Section 7E) - 5.4~8.25 psi, 38.0~58.0 kPa.

Sorry boss.....

[gravity_powered]

It's a vacuum pump if you connect your gauge to the intake rather than the outlet

My pump seems to have shit itself in the last week or so. Getting 6 psi with te pump running straight into the gauge but not shutting off when it gets up to pressure. I suspect the pressure switch is not playing the game.

I Discovered it when I tried to pull out a Prado bogged in the neighbors front yard...

[scott12]

gravity_powered wrote:

It's a vacuum pump if you connect your gauge to the intake rather than the outlet

My pump seems to have shit itself in the last week or so. Getting 6 psi with te pump running straight into the gauge but not shutting off when it gets up to pressure. I suspect the pressure switch is not playing the game.

I Discovered it when I tried to pull out a Prado bogged in the neighbors front yard...

Before I pulled mine apart it would pump air no problem but would not stop running (and 4wd light would flash every second or two), not because the pressure switch was faulty but because the dump valve was leaking.

Follow fordem's good tech thread, once you have pulled the internals out of the unit, if it's like mine you'll see a large build up of rust on the metal dump valve. Clean off rust, renew o-ring and check operation.

[bailey08]

I didn't even realise I had a problem till I read this, light was flashing 90 times a minute but 4WD worked fine.

Thanks Fordem for the great write up. cleaned the rust off the dump valve and now works perfect

Thank you.

[fordem]

You're welcome - it was just my contribution to an outstanding forum that has given me sooooo much.

[steak_knife]

fordem wrote:

You're welcome - it was just my contribution to an outstanding forum that has given me sooooo much.

Group hug!!!!!

[gravity_powered]

I did a bit more investigating tonight. The pressure wasn't quite getting to 6psi as I first thought. 4 psi was as high as it got.

I Pulled the square cap off, and pulled the solenoid valve/ pressure switch assembly apart. Everything looked fine so I put new o-rings in and put it all back together. I got the pump running with the cap still off, even when putting extra force on the valve shaft the pressure still wasn't rising any higher.

I then cut the top off the cylinder and pulled the diaphragm out. Under the intake flap valve in the center of the diaphragm I found a stray bit of plastic swarf. I cleaned it up, put it back together and tried it again holding the top on the cylinder by hand and bingo! Getting up to 6 psi and cutting off!

Now I just have to glue the top back on.

[fordem]

gravity_powered wrote:

The pressure wasn't quite getting to 6psi as I first thought. 4 psi was as high as it got.

Those symptoms are very similar to the ones I had.

Quote:

Under the intake flap valve in the center of the diaphragm I found a stray bit of plastic swarf.

Are you sure it was swarf? I want to believe there was originally a little foam filter in the rectangular space shown in the picture below - and that the foam disentegrates and gets sucked into the intake flap valve.

Quote:

Now I just have to glue the top back on.

That can be tricky - the diaphragm acts as a gasket, and you need just enough force to compress the diaphragm to get a good seal, but not enough to distort the plastic so that it leaks.

I used Devcon Plastic Steel, but any good epoxy should work - and a couple of woodworking spring clamps - it took me two tries and I had to grind the plastic steel away and reapply.

[gravity_powered]

fordem wrote:

Are you sure it was swarf? I want to believe there was originally a little foam filter in the rectangular space shown in the picture below - and that the foam disentegrates and gets sucked into the intake flap valve.

Not sure exactly what it was but it was definitely more solid than foam.

fordem wrote:

That can be tricky - the diaphragm acts as a gasket, and you need just enough force to compress the diaphragm to get a good seal, but not enough to distort the plastic so that it leaks.

I used Devcon Plastic Steel, but any good epoxy should work - and a couple of woodworking spring clamps - it took me two tries and I had to grind the plastic steel away and reapply.

I used a bead of silicone sealant around the underside of the lid. It is holding pressure fine, we'll see if it lasts long term.