AHC Problem (1 Viewer)

[tom.]

I have changed accumulators, changed AHC fluid again and ... there is no big difference in ride quality Car is a little bit softer on big bumps but if tarmac become rough I can feel everything. Whan I am changing the height setting from ‘low’ to ‘high’, the oil level in the AHC reservoir is 13 graduations instead 8 graduations before. I would like to go to Toyota and ask them to check pressure of shock absorbers, adjust sensors and check their wirings. I need also to try another car with good suspension to drive and compare to mine.

Ps. If someone want to change accumulators use Fan Spanner 32/36mm. No need of grinding. If it will be difficult to unscrew hit accumulators firmly few times.

 

[tom.]

I have been in Toyota and checked shock absorbers pressure, it is to high. It can be adjusted by adjusting torsion bar but I do not know if I should tighten t-bar more or loosen it. Does anyone know?


Ps front 83mm, back 71mm is correct.

 

[uHu]

Where is the the pressure too high? Front or rear?
If at the front, you can adjust the TBs.
That the pressure is too high means that the Torsion Bars do not do their part of the job, so you have to tighten them, so that they will take more of the load. That way the AHC system will not have to pump in so much pressure in order to get the correct height.
Just remember to jack up the front to take the load off the TBs.

 

[Joe422]

Tom, did you ever get the AHC problem sorted out? What was the solution for you?

Thanks~

 

[tom.]

I have changed accumulators, checked sensors, shocks pressure, set everything (t-bars, sensors, car height) to correct specifications, fitted new tires (pressure front 30, back 32), changed AHC fluid four times and suspension works like before. The ride is harsh and it is only noticeable on expansion joints/cracks, potholes. On 40+mph speed and bigger road imperfections everything seems to be Ok. Maybe there is some air in system but I went through 5 cans of Toyota AHC fluid. Maybe tires should absorb this but they do not. I am using PIRELLI Scorpion ATR.

 

[uHu]

Tom,
did you ever do a comparison test ride?

I wish I was closer to your location.

 

[tom.]

I have tried one as a passenger. But the driver, Toyota mechanic, was driving above 40mph and did not want to slow down. At that speed ride was similar to mine. I am going to try another car in few weeks.
Thanks uHu.

 

[tom.]

After I have changed accumulators, opened and checked sensors, checked shocks pressure, set everything (t-bars, sensors, car height) to correct specifications, fitted new tires (pressure front 30, back 32), changed AHC fluid many times , I finally found out what the problem was.


Very loose front wheels bearings. Funny, isn’t it?

 

[GOR100]

After I have changed accumulators, opened and checked sensors, checked shocks pressure, set everything (t-bars, sensors, car height) to correct specifications, fitted new tires (pressure front 30, back 32), changed AHC fluid many times , I finally found out what the problem was.


Very loose front wheels bearings. Funny, isn’t it?

Tom, one thing that hasn't been mentioned in the discussion on your suspension is the spring rates. Do you know if they have been changed from standard?

One of the "fixes" for the standard suspension where the AHC weighs the system and then goes down to LOW has been to fit up heavier springs. The heavier springs then, in my own case, completely overpowered the shocks. They gave an extremely poor harsh ride. It cost me another set of Toyota shocks too, which I realise now were OK.

I used three separate spring rates before I finally went for Firestone air suspension. It is now fantastic again, like the standard springs for when I am not weight carrying, and when I am, I can just dial in a little more air pressure to compensate. I do the adjustment based on the distance between the bottom of the wheel rim and the underside of the guard at the rear. I can now use the AHC again as it should work, the dial in for the suspension rates and all.

The standard Toyota springs in the rear for AHC systems are very light wire - they looked about 15mm-16mm wire

Cheers

 

[Adolf]

AHC sucks. I went through every scenario one can think off, but the best was to replace it for a proper Offroad suspension. I will never look back.

My 2c worth!

 

[GOR100]

AHC sucks. I went through every scenario one can think off, but the best was to replace it for a proper Offroad suspension. I will never look back.

My 2c worth!

AHC is a good on-road suspension and a pretty capable off-road one too. In standard form doesn't handle a lot of weight, and that is the way Toyota designed it. Not everybody wants to hamper their agreement with their insurer by doing a complete replacement.

Your opinion in this case would be the same if you didn't apply 2c with it

 

[Adolf]

AHC is a good on-road suspension and a pretty capable off-road one too.

Well I agree partially, but how many do really keep their vehicle stock after they have seen so many nice offroad accessories on other 100's ?!

My opinion is, that the AHC was merely designed for better ground clearance, but not for long term offroading!

 

[Texasoil]

When heavy duty springs are fitted, the pressure in the ACCUMULATORS must be reduced. This is because the gas charge was set for standard springs and the resulting oil pressure in the shocks. With stiff springs, less pressure in the shocks-right. But, now the accumulator gas charge is too high for the lower pressure oil to enter--hence--NO SHOCK MOVEMENT at first. Takes a larger bump to raise pressure to 'the absorbing point. Solution is either add vehicle weight or tell me to make up a set of lower pressure accumulators for you. Cost LOTS less than the L2000 pounds mentioned earlier, about half that.

If I am not advised about the stronger springs, I will not lower accumulator pressure because I , like most people, can not read minds nor assess things from across the oceans. Were I so capable, perhaps I could have for-seen the financial meltdown and avoided losing over $200K in the US stock market with all 5* rated stocks.

 

[1loudLX]

so if I've added a few, ok more like several hundred extra curb weight pounds, stiffer springs and no adjustment to the pressures needed?

 

[hoser]

I used three separate spring rates before I finally went for Firestone air suspension.

Just curious which springs you used and when doing so, did you check the system pressure and adjust the height sensors accordingly?

 

[ejike]

Ohh..Hoser you know you can't bring up AHC height adjustment when i'm trolling the forums..... Please drop all knowledge of how to perform the proper height adjustments and pressure calibrations

 

[hoser]

ejike, I am not an expert with the AHC system and would rather not give misinformation. However, I have played with my suspension some and do know that replacing the springs without adjusting the sensors will result in an over-sprung ride. Using any of the existing non-ahc springs out there will also result in some lift.

In your case, you only changed one height control sensor. You should not need to mess with the T-bar height adjustment, just adjust the height control sensor (the linkage). Start with the same height as the opposite side. To get real accurate, you would need to take either take it to Lexus/Toyota who has a scan tool that shows the AHC pressure or buy a brake pressure gauge. But eyeballing it and driving it would probably be good enough for most.

 

[ejike]

Well Spoken