Brake Air Regulator or blow off valves?

[Diana Alan]

I have a problem of too high pressure in my Mk3 brake air system.  The pressure goes up to around 120psi and the buzzer and warning light come back on.

The problem is that I don't have the manual for the 6BB1 compressor and I get the impression from the Inter RPS that the regulator is a part of the Inter compressor or at least there is an unloader in the IH compressor.

Can anyone brief me on the IH system and or the Isuzu side and where I should be looking for an air pressure regulator or blow off valve?

There is what appears to be a blow off valve after the gate valve for the tyre inflation hose connection.  But I rather think that after a gate valve is the wrong place of a regulator.  

[Richard Farrant]

The problem is that I don't have the manual for the 6BB1 compressor and I get the impression from the Inter RPS that the regulator is a part of the Inter compressor or at least there is an unloader in the IH compressor.

Can anyone brief me on the IH system and or the Isuzu side and where I should be looking for an air pressure regulator or blow off valve?

Hi Diana,
According to the manual for the Inter, the unloader valve was part of the compressor, but the governor valve that controls it is mounted separately by looks of it.
Check this link out and go to page 33 onwards of the pdf:
http://www.wbo2forum.com/ex-army/aaco-serv-man-part-1-A-D.pdf

regards,
Richard

[Ravvin]

Hi Diana.
I think you will find the problem is your tyre inflation vale. That is also the line that supplies the air back to the governor/unloader.

I think the handle of the tap has to point towards the back of the truck for the governor to get air. If you point it straight out, you get air out the valve to inflate tires, so the hole in the valve spindle has to be a 90 degree passage. This also cuts air to the governor/unloader and is how you build pressure to test your blow-off valve on the back of the reservoir

If the handle points towards the front of the truck, I don't think there is a through-passage for the air and the governor will never shut of the air flow.

Easy enough to test. Build up to about 60psi and shut the engine down. Carefully crack the flare nut on the left side of the tyre inflation valve. Should be a big rush of air if the handle is towards the back of the truck and none if it points towards the front.

Another issue I have read of is that these compressors can get a build up of carbon that blocks the unloader mechanism. This is from oil working past the rings and apparently it's pretty easy to pull down and rebuild these compressors. It would pay to have a chat to Restless Rover if you need to do this, as I know he has rebuilt a few of his and will have a good idea of any tips or traps.

Greg.

[Diana Alan]

Thanks Greg and Richard

I need to sort this out before the weekend as were packing up for our AAVA annual camping weekend at Camden Park House and my truck is carrying the gear. ATM the truck is wrapped up in silver tarps like a Christmas present and the plan was to sort out this issue this week.  (It also has my copy of the service manual inaccessible inside the cab)

Now I have some starting points to investigate. 

[Ravvin]

I found a pic of the valve on the 6x6 with the handle pointing to the back of the truck, so that is the correct position for normal running. I have the one off the 4x4 in a tin at home, so I will pull it apart this afternoon and check the positioning of the holes, but I am pretty sure I'm right about it blocking the airflow to the governor if turned to point forwards.

There is a small cam-shaped washer on the bottom before the split pin that is supposed to stop the spindle turning too far. The valve spindle in mine was a bit worn and it would have leaked, even if there weren't so many holes and missing sections of air pipe on my truck. The cam was too low to contact the stopper point on the valve body, which allowed it to turn right around.

After I pulled it apart, cleaned all the paint off and reassembled it with an extra washer between the split pin and cam washer, it would only turn 90°.

Greg.

[Diana Alan]

I think you may have solved the issue, the tap was pointing at the Schrader valve for the tyre hose.  I've turned it to the correct position and will e running the vehicle tomorrow so will let you know the result.

[Ravvin]

Yep, that's the problem.
In that position, the compressor will never cut out. It's also used to test the air system and over-pressure relief valve.
The section below is the info I found on testing the system.
Unfortunately, I cant find who originally posted it as I think it was in the Inter section on the AULRO site, and I can't search there to find the original poster to give credit for it.

AIR SERVICE FOR ALL INTERNATIONALS MK3 - F1 ETC
________________________________________
Over the past month or two there have been several posts regarding brakes on ex army Internationals MK3-MK5 s. These vehicles as we know all have air over hydraulic braking system and air has a lot of moisture in it, one of the army’s routine orders was that the air tanks be drained daily or as soon as the vehicle was finished with for the day and the drain valve left open. It was part of a driver’s daily servicing to do this and I have seen drivers punished for not doing so as it was a safety aspect of maintenance as water causes rust within the system and rusted parts in a braking system will and have caused accidents. The army devised a program whereby an air service it would show up any faults or weakness in the air part of the braking system this test was done on a monthly basis when a non technical inspection was performed by transport NCO or a driver under supervision of an NCO and a record kept of the report for a period of 12 months.
THE AIR SERVICE
1. Ensure the safety valve on the end of air tank is free by pushing it in and moving it from side to side
(This is located on the rear of air tank located inside the left hand chassis rail).
2. Ensure the dust cap is fitted and tight on the tyre inflation outlet and open tap
(These are located on the left hand side of chassis just above spare wheel)
3. Start engine at about 60 PSI check safety valve again.
4. Let air system build up to 180 psi at this point the safety valve will release air let it do so a couple of times.
5. Go to rear of truck and open the service tap of the trailer coupling.
(Air pressure on the gauge should drop to 60 PSI and maintain this pressure while the engine is running).
6. Close the above valve.
7. Open the emergency line to trailer
(Air pressure should drop to approx 35 PSI and maintain this while engine is running).
8. Close all taps and the tyre inflation valve ( as in No2)
9. Let air pressure build up to 120 PSI (Normal operating pressure) push the tell tale rod/ rods on the brake booster/s in then fully apply the foot brake once.
(This will tell you if a brake adjustment is required)

The above will show up any leaks or weak spots due to rust in the air system and ensure that the tractor protection valve is working correctly.
The tractor protection valve is located in the towing brake system so that if a trailer breaks away and causes a sudden loss of air pressure the driver has one full application of the foot brake DO NOT PUMP BRAKES which will bring the vehicle to a stop.
The tractor protection is found on a 4x4 in the right hand chassis rail just in front of the right hand rear wheel and on a 6x6 R/ rail again between the intermediate axle and the rear axle .

[Chazza]

...
Unfortunately, I cant find who originally posted it as I think it was in the Inter section on the AULRO site, and I can't search there to find the original poster to give credit for it.

...

I am 99% sure, that it was posted by Hodgo; who I hope is still a member, his posts were always worth reading,

Cheers Charlie

PS If you own an International, or might do so one day, then cut and paste Hodgo's information into a Word doc and keep it forever, before the next forum upheaval.

[Diana Alan]

Well the reposition of the tap did naught.    The over pressure still comes on around 120psi.

Worse still after unwrapping and taking the truck for a short drive around the paddock, as I descended a steep bit I found I had no brakes. eeek glad it has a maxibrake on the park brake system, I don't think I could have pulled hard enough to stop the truck.  The annoying thing is that I had all the brake hydraulics overhauled with stainless steel sleeves only last year. On inspection I found that the brake fluid has bubbled off the paint on the RH rear wheel, but it couldn't be seen till I drove it out from next to the container.  After taking off the wheel and drum I find that I've also done a hub seal as the brakes are covered in oil.

Are the hub seals still available?

[Ravvin]

The rear/inner seals are available and a common size. I can't find the actual part number for the ones I bought, but the replacements are a standard 2 lipped seal. 5.125" outer, 3.875" shaft and 1/2" thick. I think they were about $15 each.

I am betting that your diff breather is blocked. Pressure built up and pushed the oil past the front seal and into the grease-packed bearings, then pushed the mixed slurry out through the rear seal. I make sure I park with the axles level now, so the oil sits down in the bottom of the diff, not across one side against the hub. Think that's why mine leaked badly a few months after I parked it when I first got it.

Refit the hub, do up the hub nut and the outer nut with seal. Put a straight-edge across the seal lips and the face of the hub between the axle studs. The seal lip should be about 1mm higher. If it doesn't protrude, you could put a spacer between the lock washer and nut with the seal to push it out a bit to make better contact with the inner face of the axle flange.
If the seal on the outer nut looks worn or torn, let me know. I might be able to help. I have a couple of original seals but they are rock hard. I think you are supposed to soften them in oil before use, but didn't want to do that unless I was going to use one.
Actually, a better idea. If you need one, I'll pull the whole nut and seal off the MK3 and send it to you. You can send me yours back once you are going again and I will try out these NOS seals. Let me know if you want to try that.



As for the air pressure issue, the overpressure valve is supposed to release at 150psi, not 120. The valve is very basic, pretty much just a spring and ball bearing. The spring might be getting a bit weak. You could pull it out and stretch it a bit, I suppose.
If you loosen the flare nut on the left side of the tap, (towards the front of the truck), you should get loads of air hissing out. If none, the passage in the tap is clogged. If there is plenty of air, the governor/unloader unit might be carboned up. Page 42 of the MK3 Service manual mentions that. Explains how it all comes apart.

If you need a digital copy of the Workshop manual, grab it here..International MK3 Service Manual

Greg.

[Diana Alan]

Hi Greg

Its not the valve that' coming that's coming off at 120 psi its the pressure warning light and buzzer coming on.  So annoying I've fitted a toggle switch in the buzzer circuit, but not much I can do about the light in the gauge. I think I have to go right through the air system because I lose air very quickly after I shut off the engine.

Would over pressure also blow out the seals in the wheel cylinder too??

Will follow your advice re the bearings and seals.

Thanks for the offer of the manual, I have an original copy although its sitting in the passenger's footwell of the truck 50km from where I live hence I don't have it at home. To research over night.

[Ravvin]

The manual says the brake unit is designed to work with a pressure of 85 to 105 psi. I wouldn't think a bit extra would cause that much difference at the wheels though.

As for the buzzer/warning light, I didn't realise it came on if the pressure was high. Mine doesn't come on at all, but I haven't traced the wiring back yet, or checked the bulbs in the dash. That's a fair way down the list still.

The leaks are annoying. I couldn't tell where mine was leaking while it was running and it drained too fast once stopped. I screwed a fitting into the air socket under the dash and hooked it to my 240v compressor and ran the regulator at 60 psi. For me, the leak was a small hole in one of the steel pipes that runs down the chassis rail to the tracta protection valve between the rear wheels.
I don't think the MK3 and 4 have this fitting though. The manual says it is for filling tires and pressurising diffs for deep water crossings. Sounds like a good way to blow your seals out. You could pressurise yours through the tire inflation port, with the tap turned 90°, as if you were filling a tire. That should let you hear where it's leaking.

Greg.

[Chazza]

Rotten luck Diana 

Some soapy water in a can and a 1" paintbrush is a good way to test for air-leaks; use dishwashing detergent. A squirty bottle can be handy if you can't reach the fitting with a brush.

Good luck!

Cheers Charlie

[Diana Alan]

Thanks for the tip Charlie.

I've managed to borrow a hub nut spanner so should have the hub off later this morning.

In relation to the wiring, my wiring was a nightmare as some of the wires on the terminal block between the screens had become disconnected and were coved in olive green paint so no reading the code.  Behind the switch panel were numerous scotchloks for taps to flashing beacons and sirens plus a number of cut off original wires.

My only solution was to sit in the drivers seat with the wiring diagram on the engine cover, the switch panel hanging down and the same with the instrument panel and test each wire one by one with a continuity meter.  In the end it was well worth the trouble, although the blinkers have subsequently stopped working but I suspect the problem to be in the stalk.

Hi Ho Hi Ho its off to truck I go! 

[Bluebell One-eight]

I don't think the MK3 and 4 have this fitting though. The manual says it is for filling tires and pressurising diffs for deep water crossings. Sounds like a good way to blow your seals out. You could pressurise yours through the tire inflation port, with the tap turned 90°, as if you were filling a tire. That should let you hear where it's leaking.

Greg.
[/quote]The air hose fitting is also on the Mk3 & 4, the diffs are pressurised through a regulator at 1 or 2 PSI,  just enough to keep water out of the housings and the air is supposed to be turned off as soon as the truck leaves the water. An LPG regulator would be ideal if any one wants to do this. It would be a good idea to tap the air from somewhere else, rather than this fitting. The diff breather would need to be restricted during operation, because the air supply would be exhausted fairly quickly.  The soapy water idea is brilliant because it makes plenty of bubbles and lots of noise, and it can be squirted into places that are out of view and it will leave no doubt there is a leak when you can't see it directly. It will also detect very slow leaks as well.