AHC mini lift
- Thread starter CrusrDug
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wildsmith
SILVER Star
Don't know the cause but mine does the same I think, it adjusts itself quite often and if I stop on a slope it pumps itself up at one end 
Did you leave the engine running for at least two minutes once you had stopped on a flat surface? The AHC will level out a stopped vehicle after a short period, no more than couple of minutes or so, usually much less. You should notice it when stopped at lights on an uphill road. If you didn't wait for the AHC to level out, the extra 1/2" is the effect of higher oil pressures in the AHC during operation.
The oil pressure in the AHC goes up quite a lot during even a short drive. For example, when I had the front pressures adjusted to L450/R480 psi, and went for a short gentle drive with the gauges on, stopped the engine on return and checked the pressures immediately. They were both sitting at 700 psi, and had been up to 800 psi on the drive (the gauge keeps the maximum pressure reading). When I started the engine again and did the Normal to Low to Normal sequence, the pressures were back to 500 both sides. It was higher than before the drive because I had been teaking the TBs. I found for fine adjustments that a short drive was needed to get the AHC to settle at the pressure it should be, and this drive did the job, equalising both sides.
The highest pressure I measured was on a short drive in the High postion, when the gauge got up to 1550 psi. The is a gentle drive downhill on my road, up another hill, then back again. Less than a kilometre. The AHC is supposed to max out at 2500 psi for normal operation, or something like that, which should give you an idea of the pressures involved. I don't know the maximum pressure the pump can generate, or at what pressure the bypass valve operates though.
That is a feature designed into the AHC. It is supposed to try to level the vehicle, for your comfort, if you stop on a slope. Mine does it when I stop on a slope all the time, such as at the bottom of my driveway. That is why you must do all AHC measurements on a flat surface.Don't know the cause but mine does the same I think, it adjusts itself quite often and if I stop on a slope it pumps itself up at one end
In other words guys, what you are seeing is normal.
- Thread starter
- #24
Thanks. I figured as much, but when I was at the gas station today it was rather "stinky" looking.
So, I tried to get the 1/4 in difference in the front equalized by making the heim joint shorter on the DS. I shortened it as much as I could without cutting the bolt.
It increased BOTH sides by 1/4 inch
I thought they were independent of each other???
So, I tried to get the 1/4 in difference in the front equalized by making the heim joint shorter on the DS. I shortened it as much as I could without cutting the bolt.
It increased BOTH sides by 1/4 inch
I thought they were independent of each other???
Well they are indepenent, but still bolted to the same rigid frame. Maybe there is a slight twist in your chassis? Perhaps that is why the TB and heim joint were adjusted the way they were.
If you do get the fronts to be equal, you might find that the rear heights have a slight difference, since raising the front left side is probably going to drop the rear right side a little.
Mind you, I had difference up to 5 mm before my latest adjustments, and now most are within 1 or 2 mm at all height positions (Low, Normal, High), so I guess it is possible. Only the rear is a little more out, being 4 mm difference in the High position.
I didn't attempt to adjust the height of any corner during my adjustments. I just equalised the pressures at the fronts using the TB adjustment. Yes, you can get different pressures left to right. I saw difference up to about 40 psi during adjustments. I suspect they were due to stiction in the system though, and they evened out after test drives and lowering and raising the AHC.
If you do get the fronts to be equal, you might find that the rear heights have a slight difference, since raising the front left side is probably going to drop the rear right side a little.
Mind you, I had difference up to 5 mm before my latest adjustments, and now most are within 1 or 2 mm at all height positions (Low, Normal, High), so I guess it is possible. Only the rear is a little more out, being 4 mm difference in the High position.
I didn't attempt to adjust the height of any corner during my adjustments. I just equalised the pressures at the fronts using the TB adjustment. Yes, you can get different pressures left to right. I saw difference up to about 40 psi during adjustments. I suspect they were due to stiction in the system though, and they evened out after test drives and lowering and raising the AHC.
wildsmith
SILVER Star
I didn't word my reply very well, I know why when I park on my drive the AHC jacks the front end up, a lot, it's just very annoying when I pull off the drive again and have to drive nose in the air until at some point it will decide I've been stopped long enough to adjust it back again I think the extra front end weight probably makes this issue more pronounced and can't quite work out if a stiffer i.e. none AHC OEM TB will make any difference to this because the combined spring rate should be just the same 
I think the extra front end weight probably makes this issue more pronounced and can't quite work out if a stiffer i.e. none AHC OEM TB will make any difference to this because the combined spring rate should be just the same
Hmm, the AHC should re-level itself pretty quickly once you start moving. Mine doesn't wait until I've stopped for a period after leaving a sloped position. I don't know why yours would delay.
I don't think changing the TBs would result in a change of behaviour of the AHC, with respect to leveling the vehicle. TBs with a different spring rate would change the way the suspension works, since not only could you tighten up the TBs more, taking more of the supporting load, but the range of oil pressures required for different heights would change. The oil pressure range would be smaller for a given suspension movement, compared to the OEM TBs.
I did notice a stiffening up of the suspension when I tightened the torsion bars, but it was probably just going back to the original stiffness. Possibly lower oil pressure allows the dampening valves to work better, giving a stiffer ride. Actually, my AHC is now running at below oil pressure spec, so I probably have a stiffer than original ride, which is fine by me.
I don't think changing the TBs would result in a change of behaviour of the AHC, with respect to leveling the vehicle. TBs with a different spring rate would change the way the suspension works, since not only could you tighten up the TBs more, taking more of the supporting load, but the range of oil pressures required for different heights would change. The oil pressure range would be smaller for a given suspension movement, compared to the OEM TBs.
I did notice a stiffening up of the suspension when I tightened the torsion bars, but it was probably just going back to the original stiffness. Possibly lower oil pressure allows the dampening valves to work better, giving a stiffer ride. Actually, my AHC is now running at below oil pressure spec, so I probably have a stiffer than original ride, which is fine by me.
- Thread starter
- #28
My FSM for a 2006 LC has the same exact numbers for TB spec as yours. The TB's don't have different spring rates do they? I know there is a right and left, but isn't that just orientation so the torsion resistance is correct? I was thinking maybe I have a left hand bar in the right, but that would mean (i think) that the bolt head would be farther above the bracket than below it if I'm thinking correctly.
There's a spec for a reason and now I think I have a deeper problem I have just uncovered. I should do a poll for people with AHC and see how many TB adjuster "bolt heads" are below the bracket.
I guess it would be a reasonable assumption that a 2006 LC with AHC would have the same TBs as a 1998 LX with AHC. After all, Toyota use the Lexus brand to develop new stuff for the Toyota brand, so the design of the fancy bits such as the AHC on the LC come from the LX.
Yes, I believe that the left/right issue is to do with the way the bars are made, and the orientation of their spring attributes. Someone may have put a left hand bar in the right. You would have to pull it out to check I think. Regardless, you really need to measure the left and right pressures to get things correct. Yes, the hydraulics are connected left to right when the wheels are straight, but I still saw pressure differences left to right. Theoretically, I guess, the truck could stand level on one torsion bar and the AHC, but that would likely twist the frame. I think the TBs need to be relatively close in their adjustment, with the difference down to the slightly different spring rate in individual bars.
BTW I found measuring the distance of the bolt head below that bracket a pain, since it was hard to get a good view of the situation when the LX was on stands, and I was on my back underneath it. In the end I used a straight edge across the bracket, and the wire extension of a Vernier Caliper to get an accurate measurement. That way I didn't have to try to guess a straight line across the bracket, or take the reading under the LX. I just locked the caliper and slid out from under to read it. Worked well. I mention this because the point of view of those photos give a worse impression than it is, I think.
Yes, I believe that the left/right issue is to do with the way the bars are made, and the orientation of their spring attributes. Someone may have put a left hand bar in the right. You would have to pull it out to check I think. Regardless, you really need to measure the left and right pressures to get things correct. Yes, the hydraulics are connected left to right when the wheels are straight, but I still saw pressure differences left to right. Theoretically, I guess, the truck could stand level on one torsion bar and the AHC, but that would likely twist the frame. I think the TBs need to be relatively close in their adjustment, with the difference down to the slightly different spring rate in individual bars.
BTW I found measuring the distance of the bolt head below that bracket a pain, since it was hard to get a good view of the situation when the LX was on stands, and I was on my back underneath it. In the end I used a straight edge across the bracket, and the wire extension of a Vernier Caliper to get an accurate measurement. That way I didn't have to try to guess a straight line across the bracket, or take the reading under the LX. I just locked the caliper and slid out from under to read it. Worked well. I mention this because the point of view of those photos give a worse impression than it is, I think.
- Thread starter
- #30
I saw what looked to be part numbers on the outside of the bars. I think it was 60040, but there was an L and R on each respective bar, so now I'm confident they are correct.
I found the same thing taking measurements of the bolt head. Especially with the one below the bracket! It will be interesting to see if I get a big response on the poll I put up and to see the results of TB/AHC relationship.
I adjusted the right TB to spec yesterday to see what it would do and I got a crazy LEFT hand pull. Needless to say, I put it back.
I found the same thing taking measurements of the bolt head. Especially with the one below the bracket! It will be interesting to see if I get a big response on the poll I put up and to see the results of TB/AHC relationship.
I adjusted the right TB to spec yesterday to see what it would do and I got a crazy LEFT hand pull. Needless to say, I put it back.
The pull to the left may just mean that you need an alignment done with that setting. But I don't know. I'm no expert on wheel alignment. In fact, it is a bit of a black art to me!
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- Thread starter
- #32
I think I need an alignment bad. This thing jumps around over bumps and the front tires squeal under acceleration
- Thread starter
- #34
Still have it adjusted for lift and am doing the alignment tomorrow.
- Thread starter
- #36
Alignment today was an eye opener
Before L
Camber .3
Caster 2.0
Toe .26
Before R
Camber -.4
Caster 1.5
Toe .19
After L
Camber .2
Caster 2.1
Toe .04
After R
Camber .2
Caster 2.4
Toe .04
Total Toe before was .45 and spec is -.10 to .30
For you techies- My Cross SAI is a little out, but I didn't notice that until I got home. Before it was -.01 and now it is .8 with .5 being the upper limit.
It's driving much better! I asked him if my minimal lift would do that and he said no. He said it was out before the lift and is evidenced on my tires. Les Schwab tire did say something last time I was in, but I knew I would be jacking with it so i didn't care. Funny how it seemed to drive fine before the lift but still out of whack
Truck is still riding rough and was actually riding rough before I started this, so next up is checking my AHC pressures after replacing the fluid and bleeding the system.
Before L
Camber .3
Caster 2.0
Toe .26
Before R
Camber -.4
Caster 1.5
Toe .19
After L
Camber .2
Caster 2.1
Toe .04
After R
Camber .2
Caster 2.4
Toe .04
Total Toe before was .45 and spec is -.10 to .30
For you techies- My Cross SAI is a little out, but I didn't notice that until I got home. Before it was -.01 and now it is .8 with .5 being the upper limit.
It's driving much better! I asked him if my minimal lift would do that and he said no. He said it was out before the lift and is evidenced on my tires. Les Schwab tire did say something last time I was in, but I knew I would be jacking with it so i didn't care. Funny how it seemed to drive fine before the lift but still out of whack
Truck is still riding rough and was actually riding rough before I started this, so next up is checking my AHC pressures after replacing the fluid and bleeding the system.
How easy is it to move the sensors to the top of the sliders?
Will do, thanks!
Old thread, I know but I'm looking to do the same with mine. However, as my LX (recently purchased 05 w/ahc) will be used for HWY travel, more than trail, I am looking for .5-.60' gain in the front, not a level out. Not sure which method to take: adjust sensors, then TB's; adjust sensors only or any other method? With the small amount of lift (basically to support droop with TJM) is there a pressure issue? The AHC really throws me for a loop. Purchased this for more of a daily driver. I really like the AHC as it allows for extra height, when needed, while retaining MPG for highway travel. only 120k miles and the AHC checked out perfect so ripping it out, at this point, would be heavy on the pocket book. Any expertise would be great!
