Definitive list of AHC maintenance items (5 Viewers)

[tjb]

I’ve searched and read a lot, but I can only find this question but no answer. Apologize if I missed it somewhere.

If new rear springs have no effect on rear pressures, where do you look next?

——

Background:

I bought new OEM rear springs to try to bring my rear pressure down from 7.0, but gained exactly nothing (it appears) from doing so.

I did get to 6.9 front and 6.7 rear on the first three reads a few days ago. Today, I got 6.9F, 7.2R. Pulled the temp sensor for three more and got 6.9F/7.1R.

Cranked the torsion bar one full turn each and got 6.7F/7.1R.

I’ve swapped the front sway bar links and bushings out, but done nothing with the rear aside from the springs.

Not terribly out of spec but thought I was going to get a good bump from the spring swap.

 

[PabloCruise]

I’ve searched and read a lot, but I can only find this question but no answer. Apologize if I missed it somewhere.

If new rear springs have no effect on rear pressures, where do you look next?

——

Background:

I bought new OEM rear springs to try to bring my rear pressure down from 7.0, but gained exactly nothing (it appears) from doing so.

I did get to 6.9 front and 6.7 rear on the first three reads a few days ago. Today, I got 6.9F, 7.2R. Pulled the temp sensor for three more and got 6.9F/7.1R.

Cranked the torsion bar one full turn each and got 6.7F/7.1R.

I’ve swapped the front sway bar links and bushings out, but done nothing with the rear.

Not terribly out of spec but thought I was going to get a good bump from the spring swap.

Not sure how your rig is built, but I would try the King springs and check pressure.

 

[tjb]

Not sure how your rig is built, but I would try the King springs and check pressure.

All stock.

Just not sure I understand what could be causing the tiredness in the back if the springs are new.

 

[uHu]

Height, weight and coilsprings; that's what decides the rear pressure. What is your height, and do you read the pressure exactly as per the FSM? (Remember there is no pressure sensor for the rear pressure, only an algorithm for calculating it from the pump pressure, so it has to be done the right way)

 

[tjb]

Height, weight and coilsprings

I used the "center of the hub to bottom of the fender" method rather than the FSM to measure height.

Front:
19 1/4 Driver side, 19 5/16 Passenger in front (1/16" lean to driver side)

Back:
20 1/4 driver side, 20 5/8 passenger side (3/8 lean to driver side)

I did the low to normal on a level garage floor, using TechStream, waited for numbers to settle after the pump finished. I averaged each of three readings. (Today I did two of the three readings with the oil temperature sensor disconnected (per the FSM), did not really notice much of a change.)

I'm stock, but I removed the back seats and I have an SS1 sleep platform in the back with a Persian rug on top of it. Everything else was out of the vehicle (except me and some papers). I had a full tank of gas (less the gas the 9 miles between the gas station and the garage burned).

 

[PabloCruise]

What are your front pressures?

 

[tjb]

What are your front pressures?

Started at 6.9 but cranked them down to 6.7 to see if that might drop the rear. Didn’t.

 

[Snow Wagon]

If you aren’t carrying any extra weight or towing on a regular basis, I’d just add 30mm spacers and call it a day.

 

[ChuckB]

I added new rear springs and Slee 30mm spacers. I actually think I over compensated when running day-to-day. I carry nothing abnormal onboard, just seats and people. With weight added, rides like it should.

My techstream numbers are probably a few pages back. You should be able to the see the difference pre-fluid flush with old springs and new fluid/springs/spacers.

 

[tjb]

I may end up trying spacers, but I'm really trying to figure out what can cause a stock machine to have high rear pressures besides the springs. It doesn't seem like there's that much left to be "tired".

 

[trdcorolla]

I may end up trying spacers, but I'm really trying to figure out what can cause a stock machine to have high rear pressures besides the springs. It doesn't seem like there's that much left to be "tired".

Did you disconnect the AHC temp sensor when you were checking the rear pressures? That's what the FSM says to do. My pressures read 1.0 less with the temp sensor disconnected.

 

[tjb]

Did you disconnect the AHC temp sensor when you were checking the rear pressures? That's what the FSM says to do. My pressures read 1.0 less with the temp sensor disconnected.

Yes, for two sets of three readings each yesterday. That was my first suspicion when my new OEM springs did not buy me very much pressure reduction. But it made no appreciable difference compared to my first set of three readings with the temp sensor in.

Moreover, I got quite a bit more pressure than yesterday with the temp sensor in (7.2 Rear) and with the temp sensor out (2 times, 7.1 Rear) my first set of three readings a few days earlier (6.7 out).

 

[uHu]

I see only 2 options: Either the new springs are weak or the pressure measurement is off. There could be a faulty pressure sensor, or something wrong otherwise with the TechStream readout. One way of making sure is to get a pressure gauge to attach to the bleed plug, like the t0yota LSPV-gauge-kit.
The Lexus springs I believe are weaker than standard LC AHC springs, and the LC ahc springs come in 3 flavours, pink, purple and brown. The pink is known to give high pressure, and the brown (strongest) end up in the middle of the range with an empty car, even when new.

Btw, are the insulators and spacer in place on the coils?

 

[2001LC]

I used the "center of the hub to bottom of the fender" method rather than the FSM to measure height.

Front:
19 1/4 Driver side, 19 5/16 Passenger in front (1/16" lean to driver side)

Back:
20 1/4 driver side, 20 5/8 passenger side (3/8 lean to driver side)

I did the low to normal on a level garage floor, using TechStream, waited for numbers to settle after the pump finished. I averaged each of three readings. (Today I did two of the three readings with the oil temperature sensor disconnected (per the FSM), did not really notice much of a change.)

I'm stock, but I removed the back seats and I have an SS1 sleep platform in the back with a Persian rug on top of it. Everything else was out of the vehicle (except me and some papers). I had a full tank of gas (less the gas the 9 miles between the gas station and the garage burned).

I'd start by making sure the tall newer OEM coil spring on LH.
Than do 1 or 2 CCW turn of RH T-bar adjuster. Dropping RH front, raising LH rear.
Then I'd adjust rear height sensor to drop rear ~1/4", putting more load on springs. Shooting for 3/4" rake.

This assume: Good sensors, globes and clean fluid. No Frame damage!

 

[tjb]

I see only 2 options: Either the new springs are weak or the pressure measurement is off.

Thanks, that’s my gut too but I am happy to hear it from someone with more experience.

Btw, are the insulators and spacer in place on the coils?

I replaced one spacer (which was in fine shape, and came off easily), but left the other when it proved harder to pull off. The insulators came pre-installed with the new OEM springs, so I’ve got a couple of new ones available to whoever wants my old springs.

I did feel that it was easier to slip off the old springs over the bottom mount than it was to slip the new ones over it, but that could have been a mirage related to its positioning as I worked them on and off.

One way of making sure is to get a pressure gauge to attach to the bleed plug, like the t0yota LSPV-gauge-kit.

This has felt like my next move, thanks.

 

[tjb]

I'd start by making sure the tall newer OEM coil spring on LH.
Than do 1 or 2 CCW turn of RH T-bar adjuster. Dropping RH front, raising LH rear.
Then I'd adjust rear height sensor to drop rear ~1/4", putting more load on springs. Shooting for 3/4" rake.

This assume: Good sensors, globes and clean fluid. No Frame damage!

I’m certain that the tall spring is in the right place, as I triple checked it and left the part labels on them until after they were installed. Famous last words.

Wait, there’s a way to adjust the rear torsion bars?

 

[2001LC]

No rear T-bars. No rear control arm(s) adjuster(s).

But as you drop right front by 1 CCW turn of RH T-bar, the left rear will go up. This will help too level the rear, to get 3/8" lean out. You need to play with this a bit. Maybe 1 CW of LH and 2 CCW of RH T-bar or more.
Shoot for readings closer to:
19 1/4 LF, 19 1/4 RF. - Frt 6.8
20 3/8 LR, 20 3/8 RR. - Rear 7

1 1/8" is more rake than needed. If you turn both the t-bar adjusters more, say 4 CW each, to take out rake. It will put more load on t-bar, which you'll be then taking weight off front hydraulics. That would drop pressure in front below 6.7, which is below what's considered optimal.

Rake 1 1/8 is good a amount of rake, which will not hurt. But you can get away with 3/4", and not get HWY wondering from to little rake.

So at this point I'd adjusted rear height senors lowering rear end. This will reduce rake (front to rear) and rear pressure reading. By lowering rear with sensor adjustment (sliding arm), you increase load the coil springs will carry, thus reducing load hydraulics (AHC) carries. With new spring and good globes, you should be able to hit ~5.8 in rear.

I like my ride so that from comfort to spot mode, I can feel the difference clearly without bounciness in comfort!

Tip: To measure rear hub to fender height. I use the chrome bar (hub cap removal tool from tool bag) and a magnetic level. I attach the level to the chrome bar. Then place end of bar in center of rear axle hub. Then measure from fender well to level. This just helps get a consistent measurement for one side to the other time and time again.

 

[2001LC]

Rear sensor is adjusted by loosening nut, then moving arm up or down in slot of bracket. I've seen the bracket on control arm bent by road debris. This can damage sensor, sensor arm or bracket. Also when install LH coil spring without compressing spring first. This can put a great deal of force on sensor arm and brake line, as we push down the LH side rear end to pop in spring.

 

[nothappening]

First, thanks to everyone who contributed. 2006 with 188k here.

Starting heights from wheel center hub to fender (I made the mistake of taking my measurements with the vehicle off):

Driver's Front: 19 3/16"
Passenger's Front: 19 1/2"

Driver's Rear: 20"
Passenger's Rear: 20 1/2"

I turned the driver's side torsion bar bolt 1 turn clockwise, and the passenger's side torsion bar bolt 1 turn counter-clockwise.

New heights:

Driver's Front: 19 5/8"
Passenger's Front: 19 3/4"

Driver's Rear: 20"
Passenger's Rear: 20 5/8"

I decided this was close enough on the front for cross leveling since it has been recomended to be within 10mm and at this point we're under 5mm difference. Moving on to Techstream to get the pressures.

Average over three readings:

FR Height Control Sensor: -0.1
FL Height Control Sensor: -0.1
RR Height Control Sensor: -0.2
Front Pressure Sensor: 8.0
Rear Pressure Sensor: 6.8
Accumulator Press Sensor: 10.5

According to the theory of 0.2 MPa change per revolution of the torsion bar bolt, I turned both driver's and passenger's side torsion bar bolt 6 times clockwise to reduce the pressure.

Average over three readings after 6 revolutions:

FR Height Control Sensor: -0.2
FL Height Control Sensor: -0.1
RR Height Control Sensor: -0.2
Front Pressure Sensor: 6.7
Rear Pressure Sensor: 6.4
Accumulator Press Sensor: 10.2

Then I read that the car should be idling when the measurements are being taken, so I measured my heights again from wheel center hub to fender:

Driver's Front: 19 1/2"
Passenger's Front: 19 3/4"

Driver's Rear: 20 3/8"
Passenger's Rear: 20 1/2"

I didn't have an exact science. I held the end of the tape measure as close to hub center as possible and my father read the distance to the fender, some deviation should be expected. I figure I'm close enough on heights to spec, and now my pressures are pretty good.

At what point is it advisable to get new rear springs and spacers? It doesn't seem an immediate concern for me at the moment, my pressures are all pretty good. I have no history on the springs though, and can only assume they are original. I have 8-9 graduations on the resevoir when I checked it a few weeks ago after a AHC fluid replacement.

Anyway, thanks again for the tips guys, it was exactly as I expected from the posts here. The vehicle felt slightly more composed, and handled bumps a little less harshly. I'm not sure I would have noticed if the procedure had been done without my knowledge, that's to say, it didn't make a big difference but it feels good to know I've got it in a good state.

 

[tjb]

I'm going to mess with this a bit today, try to reduce lean, reduce rake and reduce pressure on the fronts.

Rear sensor is adjusted by loosening nut, then moving arm up or down in slot of bracket.

1. Is this a 1:1 correspondence, i.e. moving 1/4 inch down lowers the rear height 1/4 inch?

2. Is it odd that I had zero issue getting the springs in in my 06 LX without doing anything other than removing the lower shock bolt? I didn't even unscrew the brake line from the attachment. I had planned to, but proceeded without by watching everything closely as I very slowly lowered the axle, nothing (brake line, breather line, height sensor) seemed even close to reaching a stress point.