[AHC] High pressure values: what to do? (1 Viewer)

[tibo123]

Hello,

I am new on this forum but I knew it for long time and like multiple threads being discussed over there

I own a 2005 HDJ 100 (vxe - European specs). I really like it.
I actually bought it because on 2011 I took part to the Mongol Rally in a used ambulance. The plan was to drive the ambulance from the south of England to Mongolia.
Unfortunately, the gearbox failed and we had to give up in Kazakhstan (Astana). One guy we met there offered to store it in the backyard of his house and to keep an eye on it. Since then, it is waiting for me (and for a new gearbox...).
This was the reason why I bought my LC100.
I plan to salvage it during summer 2013 so I try to prepare the journey and to service properly the Toyota.

I have bought the 35-dollar diagnostic plug (discussed in many threads of I8mud) to assess the condition of the AHC (amongst other systems).

Thanks to Techstream, it appears that the pressures are as follow:
- From low to N: Front: 7.6MPa-g ; Rear: 6.4MPa-g
- From N to Hi: Front: 10.1MPa-g ; Rear: 7.5MPa-g

Based on the values given by Toyota's specs (6.9MPa [+/- 0.5MPa] for the front suspensions and from 5.6 to 6.7MPa for the rear ones), it seems the pressure from low to N position are almost within the limits but, the pressure when the suspension lift up the car from N to hi position seem much higher the limit.

What would you do?

It seems the accumulators are in good condition (difference in oil level is visible between low and hi position, as per Toyota specs).

Would you mind changing the rear springs and tighten the torsion bar?

Please find hereafter 2 printscreens from Techstream:

From Low position to N:

From N to Hi position:

In addition there is a parameter (RL after height adjustment) which keeps displaying 0 mm, would think a sensor needs to be replaced?


Thank you

tibo123

 

[Dinosaur]

To reduce the front pressure, you just have to tighten the torsion bars (30mm bolts, try about one full turn). Also, keep left and right sides level (measure from wheel hub to fender). You only check from Low to Neutral, ignore the N to H values. I had rear pressures a little high and out of spec. I replaced the rear springs which were 6 years old. Did not make much difference to the pressures (7.1 to 6.9) and was kind of a pain. Yours look ok, so I would leave them alone. I don't know about the RL value of 0mm.

 

[tibo123]

Thank you Dinosaur for your clear explanations.
I will try to slightly tighten the torsion bar.

tibo123

 

[tibo123]

I have tighten both torsion bars (1 full bolt turn on both sides).
Unfortunately it doesn't change much the pressure values (-0.2 MPa at the front, +0.2MPa at the rear)


Now the pressures are:
- Front: 7.4 MPa (Toyota specs: 6.4 - 7.4MPa)
- Rear: 6.6 MPa (Toyota specs: 5.6 - 6.7MPa)

The pressures are right on the upper limit.
Is there a way to reach the lower Toyota limit?

I plan to use my LC in a journey to central Asia. I would like to carry a scooter (200kg), other camping gear and 2 to 3 guys (including the driver).
The LC is 100% stock. I will not carry the 3rd row seats.
Do you think it would be feasible with AHC?

 

[PADDO]

You will lower your front pressure 0.2MPa per turn, as you found. Keep adjusting till you're happy with your readings, another turn or two should do it.

 

[tibo123]

ah ok! But will it increase the rear pressure by 0.2MPa per turn?

 

[PADDO]

ah ok! But will it increase the rear pressure by 0.2MPa per turn?

No, but you may see a very slight increase in rear pressure when you bring the front into spec. Benefit of having the front pressure set close to nominal would seem to far outweigh any small increase in rear pressure. Crank your TBs another 1.5 or 2 turns, they won't break, and retest.

 

[dealmaker]

If the AHC fluid has not been flushed, doing so might help bring down the values a little bit. Al least thats what it did for me.
https://forum.ih8mud.com/showpost.php?p=8197097&postcount=104

 

[tibo123]

I will try to tighten a bit more the torsion bars and flush the hydraulic system.
Since I need to carry heavy load, uHu suggests to replace stock springs by stiffer ones.
I have no clue on which ones I could buy. Any suggestion?

 

[uHu]

stronger coils is a bit tricky, as the ahc versions will be too weak and the non-ahc versions to strong (normally). The ahc needs to see the right pressure in order to work. Best option might be air bags (Although it adds another point of failure, they seem to hold up very well. Just make sure it is well tested and checked again befor departure)

 

[tibo123]

Ok, so the air bags fitting seams to be the best option.
Do you have some on your HDJ?

Regarding the torsion bars tuning (and in order to give my feedback on it), I have finally tighten it by 1.75 turns which now gives the following pressures:
- Front: 6.6 MPa (Toyota specs: 6.4 - 7.4MPa)
- Rear: 6.4 MPa (Toyota specs: 5.6 - 6.7MPa)

 

[peeaa]

Measure your (rear) pressures and try the ride quality/comfort with your heavy load first and think about the air bags only after that.

I had high pressures and dead spheres on my 100k 2006 LC. Replaced the spheres (which does not have impact on pressures) and cranked the torsion bars to get the front pressure in specs.

Then I installed Airlift 1000 airbags (model 60728). They definitely help with heavy load but I was still not satisfied with them. Without load they did not really change the AHC normal pressure unless inflating them to quite high pressure, which in turn made the suspension uncomfortable.

This could probably be fixed by putting spacers (inch or so) on top of the air bags. Also a bit higher model (with same diameter) of air bags could be a solution as well. Now the bags were so low that they started to carry load only after some compression on the coils, which in turn was compensated by AHC leading to high normal pressure.

Another problem with the air bags was that when putting AHC on high, the air bags were useless, as they lifted with the coils so that they were about 1-2 inch away from the bottom plate and carrying no load. And when lowering back to normal, the hose connection of the air bag got stuck to the hole on the bottom plate ripping the air hose off (hole diameter was according to instructions).

Overall I would say that the air bags are a good choice for extra load with normal suspension where the height remains the same, but not necessarily a very good idea with AHC.

I got my normal pressure on rear back to specs by adding 30mm spacers to the rear coils. Significant improvement in ride quality and comfort, but I don't know how it behaves with heavy load (what you were asking)

 

[tibo123]

Thanks for your feedback of the airbags and your advises.
Actually, I would need these airbargs to relief the ahc and reduce the risk of failure.

Maybe a higher model than yours, as you suggest, would be even more efficient and would allow more flexibility.
Do you keep an air compressor on board or do you adjust the air bag pressure just time to time?

I think the accumulators (or spheres) and in particular the membranes are still in good shape. I have read on Toyota service manual that in order to check whether the spheres are ok or not, you have to check the hydraulic oil level difference when your LC is in Low and Hi position. If it is more than 7 marks on the scale (on the hydraulic oil tank), it is ok. If it is less, the spheres are shot.

 

[peeaa]

Yep, higher model or spacer (rubber/plastic) on top is the way to go at least with AHC. And bear in mind that in high position they don't really support AHC, only on normal. Air bags don't really fit too well in the same sentence with words "flexibility" and "long travel of suspension".

In my opinion air bags are good (or at least ok) to carry load, especially if the load varies, but for constant load (bumpers, extra tank etc) I would try to find suitable coil springs.

I did not have a dedicated compressor for the air bags (took them off after a month or so). I routed the air hose and installed the valve to the left rear pillar between tailgate rubber seal and tail light and inflated either with my garage compressor or portable compressor which is usually in the trunk anyway.

That way it is ok to use, but if you want a high end solution you need a small compressor behind the panel and a remote pressure gauge in the dashboard.

 

[tibo123]

Thanks.
My LC has no mods and I don't intend to carry heavy loads at all time.
From what you wrote me, airbags seem to be what I need.

 

[hkeller]

OK. I Finally got access to Techstream. It is Version 9.00.025. However, I can't get to the AHC screen. Any know how to help me? Thanks,

 

[hkeller]

OK. Figured it out. The software defaults to he Toyota UZJ-100. You have to manually select the LX470.

 

[MSABRI786]

Yep, higher model or spacer (rubber/plastic) on top is the way to go at least with AHC. And bear in mind that in high position they don't really support AHC, only on normal. Air bags don't really fit too well in the same sentence with words "flexibility" and "long travel of suspension".

In my opinion air bags are good (or at least ok) to carry load, especially if the load varies, but for constant load (bumpers, extra tank etc) I would try to find suitable coil springs.

I did not have a dedicated compressor for the air bags (took them off after a month or so). I routed the air hose and installed the valve to the left rear pillar between tailgate rubber seal and tail light and inflated either with my garage compressor or portable compressor which is usually in the trunk anyway.

That way it is ok to use, but if you want a high end solution you need a small compressor behind the panel and a remote pressure gauge in the dashboard.

Can you pls tell me which spacer to buy?