Air Suspension and Compressor - technical help needed

[Ghost-Who-Walks]

Hi Brains Trust

I have a MY10 D4 with 320k kms on the clock. Still going strong, and keen to keep it for a while longer.
It has the original Hitachi compressor in it, which I've tried to look after over it's life (3 or 4 dryer overhauls, plus 2 compressor overhauls).
I've replaced the seals in the front valve block (at least 5 years ago), and replaced all 4 struts about the same time.
In general, my air suspension system has been relatively trouble-free given it's age and the lack of parts I've had to put into it.

I started getting the "Normal Height Only" warning a few months ago which was getting more frequent. I asked the service people to have a look and they just said I should put an AMK compressor in (for ~$2500). I decided I'd try a full overhaul of the compressor and components before replacing the compressor, as it still works fine and doesn't seem like there are any actual faults with it.

Work completed:
I replaced all the seals in the front, rear and centre valve blocks (rear one is a pita to get the airlines reinstalled)
I did a compressor and drier overhaul (using X8R kits), and replaced the non-return valve.
It was all done at the same time (all parts out, overhauled and replaced on the same day).

Result:
Everything seemed to work fine. Despite my misgivings, I didn't introduce any leaks and the compressor continues to run well.
But...

However:
I think there is an issue around the compressor and/or relief valve (farting/venting). Which is why I need your help...

Symptoms:

Compressor starts and runs when it needs to, then cuts out when it reaches pressure.
The previously quiet little "Disco fart" is now a really loud pressure relief event. Short, sharp relief, but sounds like much higher pressure that is being released (it's much louder anyway!).
Sometimes it seems like too much pressure is released and the compressor cuts back in to build pressure again. Mostly this will only happen once or twice after starting the car, but sometimes can turn into a loop of run-cutout-vent-run-cutout-vent-run.... until the temperature protection cuts in and then gives me the "Normal Height Only" warning. The warning only comes up once a month or so, but the compressor is DEFINITELY running more often and for longer due to the above 'venting' issue.


My thoughts:

The little metal wafer thing installed in the compressor (maybe called a 'valve' in the cylinder head) - I'm not sure I put this in the right way, when I reinstalled it. It has a perforated hole in one side and a flexible wafer on the other side. I think the hole and flexible wafer are in the right spots, I think I may have just installed it "upside-down" from the way it came out.
The little vent line from the compressor (which I think goes onto the drier) - this was not connected at the compressor end before I reinstalled the compressor to the car, so I had to try and wiggle it in once the compressor was already on the car (very tight little spot, hard to get to, hard to see). If that vent has was not connected, could this be a cause/contributor?


Even while I write this, I think I just need to pull it all off and put it all back together again.

But if someone has a detailed understanding of how the compressor and pressure systems work, when it vents, where and why - I thought I might be able to get an understanding of where the issue is before I pull it all apart again!

Note - there are no leaks, dropping on any corners etc. It's only the 'long running and venting' that are issues.

TIA

Rob

[Ghost-Who-Walks]

This is the best image I could find online of the little 'wafer valve' thing...

[Ghost-Who-Walks]

And this is the Air Suspension schematic...
Looking at this, I think the wafer thing is item 23.
I don't know what/where item 20 (Pilot Exhaust Valve) is on the compressor. Maybe that's the non-return valve I changed?

[PerthDisco]

I’m on 3rd or 4th rebuild also. I have two Hitachis on the go of 2008 vintage.

One tip I have discovered the hard way is eventually (100% guaranteed) the big end bearing fails which is the part you never and can’t service. It starts to seize and slow the compressor down and eventually you pop the fuse or cook the relay or both or worse destroy the unit. This sends you down a rabbit hole on the slow to fill error code.

So, I discovered this available ex Tasmania (never seen anywhere else)

Air Suspension Compressor Repair Kit for Hitachi Compressor (https://www.british4wd.com.au/air-suspension-compressor-repair-kit-for-hitachi-c)

This is an absolute must bargain as you solve 3 problems at once

Big end
Worn out cylinder bore
Worn out piston seals

Worth every cent. Do it every rebuild.

Repairing the piston rings with the kit is a bit of a joke I’ve found and by 10 years your bore is flogged out also.

Also clean the motor and brushes internals as per the 4x4airseals video. The motors seem indestructible.

After this the backbone of the Hitachi is then 10/10 as new plus a few gaskets and o rings. Minimising current draw is important.

You can see if the wafer plate is correct from the dust shadow on it but I don’t think it fits incorrectly due to the shape.

Those head bolts are tricky. Try and put them in the same holes as they are self tappers and align to the thread they’ve already cut. Hard to get snug otherwise.

Don’t forget the gasket under the cylinder also.

Pilot exhaust valve is the solenoid on the side which activates the main valve. Disassemble and clean as per videos.

https://youtu.be/9Fot3RLQc3Q'si=R-LpHOELoJVP9oWj

I clean and blow out everything but have never replaced the exhaust valve ring seals only the bottom plug. The videos are useful as you do each component.

Always replace the external quick connect internal orings

Mine farts a lot as well but I put this to the latest software update. I definitely notice the noise more now anyway.

You can operate the unit no problems without the rear intake and fart hoses fitted if you want to contrast and compare.

Silicone grease on every o ring.

I’ve also put a few wraps of Teflon plumbers tape to help the o ring where the dryer fits on the unit as the play builds up here to avoid any leaks in this high pressure zone.

Must have the updated cap you get in the XR8 or air seals kit.

Run and soapy water spray the hose to the centre valve block before installing cover to check for leaks in the cap and hose area.

I’ve also had the big electric plugs chafe a hole in the high pressure line coming out of the unit as it’s all jammed in the cover. There’s joiners and spare hose kits you can cut off and add a new piece which gives a clean end where it goes into the cap. I now wrap my electrical plugs with some bubble wrap to keep everything chafe free.

Having two units allows careful and patient rebuilds rather than the panic when you’ve tried to get it fixed and running fast guaranteeing a glitch.

About $200 for a good rebuild is definitely worth it and they are a better unit than the AMK I reckon.

[PerthDisco]

[emoji638][emoji639][emoji[emoji6[emoji640][emoji638]][emoji640][emoji640]][emoji[emoji6[emoji640][emoji638]][emoji640][emoji6[emoji640][emoji638]]][emoji640][emoji6[emoji640][emoji638]]]This is the best image I could find online of the little 'wafer valve' thing...

The wafer or flapper valve is a shiny thin stainless plate that sits here. It has an o ring above and below it. A fiddle to get together but silicone grease keeps o rings from falling out.

It’s the defacto inlet valve allowing suction then compression by the piston.

[Ghost-Who-Walks]

I’m on 3rd or 4th rebuild also. I have two Hitachis on the go of 2008 vintage.

One tip I have discovered the hard way is eventually (100% guaranteed) the big end bearing fails which is the part you never and can’t service. It starts to seize and slow the compressor down and eventually you pop the fuse or cook the relay or both or worse destroy the unit. This sends you down a rabbit hole on the slow to fill error code.

So, I discovered this available ex Tasmania (never seen anywhere else)

Air Suspension Compressor Repair Kit for Hitachi Compressor (https://www.british4wd.com.au/air-suspension-compressor-repair-kit-for-hitachi-c)

This is an absolute must bargain as you solve 3 problems at once

Big end
Worn out cylinder bore
Worn out piston seals

Worth every cent. Do it every rebuild.


Ah, that's great info, thanks for that! I might order that and then pull the compressor apart and refit (and ensure all my bits/pieces are correctly assembled)...

Also, I've never pulled the motor or the exhaust valve apart. Those 4x4AirSeals video's are the first time I've seen that done. Gold!!!

I'll order the Exhaust valve kit and the replacement cylinder, piston, big-end - pull it all out and finish the overhaul I started a month ago!
After seeing that, I feel like I've definitely only done half a job!!!

Thanks heaps.

[PerthDisco]

Ah, that's great info, thanks for that! I might order that and then pull the compressor apart and refit (and ensure all my bits/pieces are correctly assembled)...

For your sanity slot the top hole in the mounting bracket to make 1 thing a little easier

[Ghost-Who-Walks]

For your sanity slot the top hole in the mounting bracket to make 1 thing a little easier

Yep, did that the first time I took it out!! 🙏🤣

[loanrangie]

You can get that piston and cylinder kit on Amazon and even less on AliExpress.

I'm on my original Hitachi with just one rebuild and now on 252k.

[PerthDisco]

You can get that piston and cylinder kit on Amazon and even less on AliExpress.

I'm on my original Hitachi with just one rebuild and now on 252k.

I think the 2nd and 3rd and 4th rebuilds get shorter due to bore slop and other factors hence doing it well each time pays off

[PerthDisco]

Ah, that's great info, thanks for that! I might order that and then pull the compressor apart and refit (and ensure all my bits/pieces are correctly assembled)...

Also, I've never pulled the motor or the exhaust valve apart. Those 4x4AirSeals video's are the first time I've seen that done. Gold!!!

I'll order the Exhaust valve kit and the replacement cylinder, piston, big-end - pull it all out and finish the overhaul I started a month ago!
After seeing that, I feel like I've definitely only done half a job!!!

Thanks heaps.

The exhaust valve kit strongly recommends not changing those black rings unless absolutely necessary but there is a plug bung at the end that’s easy to change.

Get the kit with the cylinder seals also always good to have the lot.

I blast contact cleaner throughout and motor and have a small air compressor makes a big difference to these jobs.

I wet and dry that wafer with 2000 just to tidy up.

It’s never shown well but you pry the metal collet out of the quick air connectors and inside there’s an o ring you fish out. Change these they are in the kit.

[loanrangie]

I think the 2nd and 3rd and 4th rebuilds get shorter due to bore slop and other factors hence doing it well each time pays offReplacing the piston and cylinder will go a long way to making them last for sure.

[discomatt69]

I am at only 142,000km original everything with the air suspension
I was just going to buy new everything if I decide to play crank roulette, how long should I expect the compressor last and what’s the cost difference between replacement and rebuild ?

[loanrangie]

I am at only 142,000km original everything with the air suspension
I was just going to buy new everything if I decide to play crank roulette, how long should I expect the compressor last and what’s the cost difference between replacement and rebuild ?

You will have an AMK compressor so you can only service the drier as parts aren't available unlike the Hitachi, rebuild about $250 to replace everything available versus $700 plus for a genuine Hitachi.

I would look at a service kit now before you start having any issues.

[discomatt69]

You will have an AMK compressor so you can only service the drier as parts aren't available unlike the Hitachi, rebuild about $250 to replace everything available versus $700 plus for a genuine Hitachi.

I would look at a service kit now before you start having any issues.
For the sake of 450 difference I would just buy anew unit
i Will look at getting the dryer beads replaced and get a whole new unit ina few years if I still own it
I am thinking a couple more big trips before replacing the whole lot if I keep it

even with replacing the bags and compressor with new it’s still cheaper than aftermarket suspension every 8-10 years from brand new
i never have a never understood how some rave about how good their 4wd is when they throw away brand new suspension to replace it at a cost of 1000’s to get a decent set up them claim LR air suspension to be expensive and unreliable

[loanrangie]

Those estimates are for a Hitachi, double that for the amk but the service kit is cheaper as there are less replaceable parts.
So more like 4 x the service cost to replace.

[Tombie]

Bloody hell....

I got 12 years out of the first AMK, so just threw in a new one...

[veebs]

I swapped my Hitachi out for an AMK, as at the time, the Hitachi's were considered inferior to the AMK unit.

Annoyingly, I had the mechanic do it, so I didn't keep the old part for repairs. That said, I will probably simply follow Tombie's lead, and replace the whole damn thing when it goes.

[PerthDisco]

Buying yourself ex UK it is around $1000 delivered Hitachi or AMK but the service guys seem to turn it into a $2k+ job buying at local stealer prices plus labour so the $200 to rebuild the Hitachi properly every 8 - 10 years is worth it.

There is no rebuild option on the AMK other than desiccant which I tried on my mates 2015 D4 to no avail then swapped to a new one. That was last year so they got 8 years. It was faulting for a good 6 months prior to me getting involved.

[~Rich~]

Buying yourself ex UK it is around $1000 delivered Hitachi or AMK but the service guys seem to turn it into a $2k+ job buying at local stealer prices plus labour so the $200 to rebuild the Hitachi properly every 8 - 10 years is worth it.

There is no rebuild option on the AMK other than desiccant which I tried on my mates 2015 D4 to no avail then swapped to a new one. That was last year so they got 8 years. It was faulting for a good 6 months prior to me getting involved.

You can service more than the desiccant on the AMK.

Land Rover Discovery 3 / 4 Archives - 4x4 Air Seals (https://4x4airseals.com/product-category/landrover/discovery34)

I gave mine a new set of O-Rings / Desiccant as a regular service also serviced all the Valve blocks too, I'll do it every 50,000k.

[loanrangie]

Buying yourself ex UK it is around $1000 delivered Hitachi or AMK but the service guys seem to turn it into a $2k+ job buying at local stealer prices plus labour so the $200 to rebuild the Hitachi properly every 8 - 10 years is worth it.

There is no rebuild option on the AMK other than desiccant which I tried on my mates 2015 D4 to no avail then swapped to a new one. That was last year so they got 8 years. It was faulting for a good 6 months prior to me getting involved.

New genuine hitachi is $745 on amazon with free delivery and about 30 mins to fit.

[loanrangie]

You can service more than the desiccant on the AMK.

Land Rover Discovery 3 / 4 Archives - 4x4 Air Seals (https://4x4airseals.com/product-category/landrover/discovery34)

I gave mine a new set of O-Rings / Desiccant as a regular service also serviced all the Valve blocks too, I'll do it every 50,000k.


You cant replace the main wear items like piston/cylinder, cylinder liner or piston seal though.

[shack]

We are running a Dunlop copy of the Hitachi, it's been in the car 6 months and has been faultless so far.

It cost $535 au plus freight, I bought a number of things so I don't know what the freight would have been.

This isn't a recommendation, just a report of how it's behaving.

[veebs]

Buying yourself ex UK it is around $1000 delivered Hitachi or AMK but the service guys seem to turn it into a $2k+ job buying at local stealer prices plus labour so the $200 to rebuild the Hitachi properly every 8 - 10 years is worth it.

There is no rebuild option on the AMK other than desiccant which I tried on my mates 2015 D4 to no avail then swapped to a new one. That was last year so they got 8 years. It was faulting for a good 6 months prior to me getting involved.

Yeah, I got one delivered ex UK, but as the car was in for something else anyway, I just had them install it for me. I've since become a more typical Land Rover owner, and service myself :)

[DazzaTD5]

I have found the Hitachi ones to be the more reliable unit and being Japanese you can get the service kit and parts.
The AMK to me seem more unreliable with no parts.
I have also pulled them apart to find all the inside of the motor totally stuffed.

But saying all that, I have given up and have supplied many customers with a knock off Chinese amk for $300 fitted and saying lets see how long we get out of it.

[loanrangie]

I have found the Hitachi ones to be the more reliable unit and being Japanese you can get the service kit and parts.
The AMK to me seem more unreliable with no parts.
I have also pulled them apart to find all the inside of the motor totally stuffed.

But saying all that, I have given up and have supplied many customers with a knock off Chinese amk for $300 fitted and saying lets see how long we get out of it.

My old man put a Maxspeedingrods chinese AMK in his 2009 ML350 Mercedes 2 years ago and so far no issues, 1/3 the cost of a genuine.
He also just put in the same brand rear air struts so we'll see how long they last.