Nose Dive when braking hard (1 Viewer)

[Quade]

Hey Guys

I used to own a year 2000 100 series which had shocks and springs
When I braked hard, the car would squat.

I've upgraded to a year 2005 with AHC, and when i brake hard the car nose dives.
When i Accelerate hard, the front end lifts quite a lot and steering is VERY light

I initially thought it was the suspension
So i've done this
new AHC shocks
new Fluid
New front and rear accumulators
New rear AHC springs

What I have not done:
The bit that connects to accumulators
The AHC pump

I've also tried playing with the settings for hard/soft suspension in the car.... i do notice a different with this, but only if its on max
I generally drive on one or two up from softest setting

Any ideas what it could be?

 

[DirtDawg]

Well for starters, you can replace parts all day long, but have you checked your neutral pressures? The system can be in perfect shape, but if not meeting stock parameters, can still act weird.

 

[Quade]

Here is the screen... Not sure what I need to look at?

 

[geanes]

Front Pressure Sensor and Rear Pressure Sensor. They shouldn't read "0"

Front should be 6.7-6.9
Rear should be 5.7-6.7 I believe

Drop AHC to Low, then raise to Neutral with Techstream attached and take your reading then

 

[Quade]

Sorry for the delay, I have been oversea

So here are the results after going from hi, to low, to Neutral and letting it sit for a few mins with engine running

I also noticed there were some error, also attached

do the neutral pressures look wrong?
What do I need to do to fix?

 

[Julian Stead]

Your front pressures are to low, I would try and wind back your torsion bars, you might find then that your system struggles to maintain height as the fault codes relate to a weak pump, don't just take my word on that though you will have to check that for yourself. As mentioned in other threads you need to measure your height and adjust to spec, then get your pressures and get them as close as you can get them on the front by adjusting your torsion bars, for the rear you may need to get springs or spacers to dial it in. Have you over adjusted your torsion bars to compensate for the nose dive?

 

[Julian Stead]

Ps. Just clear them fault codes as they might of just been produced because of the work carried out, make sure there is no air left in the system by doing another round of bleeding from the accumulators. I notice you have got new springs, did you get the right colour one. In the uk the are purple or pink, stupid colours as they look the same, but purple band is what is fitted to 99%. Different colours in the US I believe.

 

[Quade]

Ok, heres the update

I cleared the fault codes
As we didn't know which way to turn the torsion bar nut, we tried 3 turns one way, which dropped pressure on front from
4.9
to
2.7

I then put reset the the nut to the beginning and went 3 turns the other way and it went to
7.9

So using this technique, it seemed one whole turn adjusted by 1 Mpa-g, so i dialled it back by just over 1 turn which should have given me in the region of 6.8
However, tech stream reads them both as 0, and also crashes (see attached with 0)

I also note after i cleared the codes, one came back which is also attached...perhaps this was from me messing around.

Since the above tests, i put the car in Hi, but it dropped to N and now the OFF yellow light is flashing.... this has happened before and it usually goes away after a day!

what the heck is going on!!

 

[Julian Stead]

Like I mentioned, if your pump is weak I am not surprised you had problems after turning your torsion bars down.

 

[Hokie LX]

To properly test the pressures you need to drop the truck to low, then up to N and take the readings, otherwise it won't read correctly. You don't need to go to high at all.

 

[Julian Stead]

To properly test the pressures you need to drop the truck to low, then up to N and take the readings, otherwise it won't read correctly. You don't need to go to high at all.

You don't need to go to high, but it still should be able to with no problems. There is another thread with this same issue. My theory is that the AHC system isn't able to produce enough pressure to run the system. It worked previously due to the torsion bars being over sprung, intern reducing the stress on the AHC. So more mechanical spring rate less AHC load, but this brings its own problems as the OP is experiencing.

I have never experienced this in person so it is just my thought, maybe @uHu or @PADDO would have come across this, as they seem to be the AHC guru's on here with a lot more experience than myself.

 

[Hokie LX]

You don't need to go to high, but it still should be able to with no problems. There is another thread with this same issue. My theory is that the AHC system isn't able to produce enough pressure to run the system. It worked previously due to the torsion bars being over sprung, intern reducing the stress on the AHC. So more mechanical spring rate less AHC load, but this brings its own problems as the OP is experiencing.

I have never experienced this in person so it is just my thought, maybe @uHu or @PADDO would have come across this, as they seem to be the AHC guru's on here with a lot more experience than myself.

My truck has AHC and I have gone through testing and correcting pressures and troubleshooting issues so I'm fairly familiar with the system. Agreed that he should be able to go into high but it isn't necessary to test pressures.

My next suggestion once the OP gets his pressures in spec is to check his sensors because I have had my truck kick me out of High or not allow me to change heights when my rear height sensor was failing. When the sensors begin failing they cause some funky stuff to happen including constantly trying to level itself.

 

[Quade]

Thanks guys

Is there a test to see if the sensors are failing?
I do occasionally see the car leveling itself, but not often

I'm not sure what to check next, I guess I need to read the values on techstream before going any further?

 

[PADDO]

To properly test the pressures you need to drop the truck to low, then up to N and take the readings, otherwise it won't read correctly. You don't need to go to high at all.

To properly and accurately test the system, particularly one like the OPs which clearly has problems, you really should begin with the full on board AHC inspection procedure - starting with checking the fluid level in the reservoir; checking the height deltas and timing to reach H and L and then checking pressures. Build a more complete picture of what’s working and not working, what’s known to be good or questionable etc and use valid evidence to progress the fault finding. For example if it takes too long to raise to H this could be because the pump output pressure is low or air entrained in the fluid is compressing or there is binding in the suspension or the vehicle is trying to go too high or it’s too heavy or a hydraulic line has been crushed or the height accumulator is playing up or there is a dead Wildebeest wrapped around something..... could be any number of things. And please note that the correct way to read the rear pressure with Techstream is with the systems temperature sensor disconnected. Peeps do get different rear values with the temp sensor disconnected as opposed to just raising from L to N and taking those values as true and accurate. To me, something obviously isn’t right when the OP cranks the TBs a couple of turns and concludes that one turn equates to 1MPa variance (its 0.2MPa variance per turn on both sides in a functional system). That’s just bad/questionable data.

Essentially I am not particularly confident in the validity of simple L to N pressure readings taken off a system that obviously isn’t functioning properly and has one or more fundamental problems. Also, @Quade techstream says you’re testing with the diff locked, if correct is that how you normally operate?

 

[Quade]

thanks all
I just tried now again with PADO feedback but when i start the car the OFF light is on constantly, and its in N

PADO, I did not have the DIFF locked, but when i started the car after, the DIFF light was on for 1 second, which i did think was strange!

Perhaps I have an electronic gremlin as the fuel gauge has stopped working and its showing empty / not showing correct reading

Let me get that sorted asap and then get back on this


Thank you all for the advise so far!

 

[Quade]

Ok I got the fuel gauge fixed, and it turns out the OFF on the dash was as simple as holding the button for a few seconds

I've attached the latest reading from tech stream (not sure how to disconnect the temp sensor)

I also dropped the car to low, waited a min, and then hit the up button
the N light stopped flashing after 30 secs
I did hear the pump still working for a while afterwards, but did not notice any height different while it was still whiring away

I'm guessing 30 secs is too long?
What would you suggest I try next?

 

[PADDO]

Standard time to physically raise from L to N should be 15 seconds or less and it can take a few more seconds for the ECU to accept the feedback and that it’s now at N, the N stops flashing then. 30 seconds seems a little bit slow if you’re on flat level ground, wheels pointing straight ahead and you’re not carrying additional weight. The pump continues to run until the height accumulator is recharged and that’s what you’re hearing when the N stops flashing but there is no more leveling changes. You’ll get a pump time out error code if it tries to run for +100 seconds. If you search “temperature sensor” posts by me you’ll see what needs to be done, you simply pull the connector and run the L to N test.

I don’t like the variance in your height sensor feedbacks, assuming you’re on flat ground. What are your physical vehicle heights measured at each corner when at N? Pressures and physical heights and weights go hand in hand so it’s beneficial that this info is provided to put things into context, it’s guessing otherwise.

With all the work you’ve had done I’d honestly start with a fluid change and bleeding, dropping it all the way to the bump stops to expell as much old fluid/gas as possible and making sure the height accumulator is bleed too. No hydraulic system functions properly if the working fluid isn’t up to it. Changing out “shocks” is intrusive (and usually pointless unless they are trashed) and can introduce lots of air if not done properly by pre flushing and pre filling prior to installation and setting the system back to work. Are the new coils you had fitted the correct ones for your vehicle?
You can reset your steering angle back to 0 degrees by ensuring your wheels are pointing straight ahead and pulling the battery neg terminal for a while (I do 20 mins, some 10 mins) to reset ECUs and clear memories. You might get a VGRS flashing light but that will go away when you drive it next in a straight line above about 30mph for a few seconds, can’t recall exactly what the spec says so just drive it and it goes away quite quickly.

 

[Quade]

Hi Paddo, Sorry for the delay in replying,
I had a couple of hours spare today so had another look while pulling the TEMPERATURE SENSOR plug

I struggled initially as the OFF light kept flashing when i pulled the 2 wire plug closest to firewall
as my car is right hand drive, and the temp sensor wasn't next to firewall, it was furthest away (ahc fluid is on right hand side when looking into engine bay from front of car)
Anyway, I pulled the other one (the 2 thin wires not 2 fat wires) and I got the temp sensor error code so all was good

I was on flat ground, with wheels pointed forward, I noticed the steering angle was crazy too late, so I pulled the battery AFTER the tests and s
creen shots (sorry if that messes things up)


I took a bunch of measurements, from floor to wheel arch, and from top of centre cap lip to wheel arch, as shown:

Here are the measurements in CM

Front Left Floor: 86.0 Cap: 46.5
Front Right Floor: 84.7 Cap: 45.8
Rear Right Floor: 87.8 Cap: 48.6
Rear Left Floor: 88.2 Cap: 48.2


Here is the tech stream settings before pulling the temp sensor:

After pulling the temp sensor, dropping to L and going back to N

Regarding the rear springs, they were genuine toyota black thin ahc springs
As i remember there were 2 options with different heights
48231-6A750 or 48231-6A770 (i think)

I've no record of which one i got, but I gave my chassis number as part of the process

Does the above information give you any other ideas of what it could be? or what to try next?

Thanks

 

[PADDO]

For heights it’s customary to measure from the actual wheel hub center to the fender bottoms and you should be getting something close to 500mm front and 520mm for the rear, if you want stock height and pressures referenced back to this. It does appear you’ve got some cross lean at the front and this should be adjusted out via torsion bar adjustments. Then reset your front pressure to 6.9MPa as it’s way too low at 6.1 which is over sprung and under dampened. The rear at 7.4MPa is too high which is impinging on dampening as well. Makes you wonder if the correct coils were fitted, there is some binding and resistance or what? Fitting 30mm coil spacers should lower that rear pressure about 0.5MPa.