Measure AHC Pressures with Airbags (1 Viewer)

[mojaveoverland]

Spent all day installing a set of Firestone airbags and 30mm spacers on the 99 LX470. Saw a lot of feedback about the Air Lift bags going through the bottom, so just turned the Firestone bags upside down and seems to work so far unless I’m missing something about why they would need to run out the top as called for in the instructions.

Anyway, part of the reason for my install is to lower my AHC pressure and I’ve done a lot of searching and can’t figure out how to measure AHC pressures with the bags installed. If I inflate them above a few PSI, it would seem like the vehicle wouldn’t go into Low and I couldn’t measure the neutral pressure via techstream.

What am I missing?

I plan to tow quite a bit and would probably need to inflate the bags to 20-30 psi to maintain neutral pressures, but I have no idea how to measure them if it won’t go into Low because bags are inflated. Yet I see lots of posts recommending this method to help with pressures. Can’t figure this one out.

ps ride seems much smoother so far after install and excited to check pressures to see how much the spacers helped

 

[ramangain]

If you set the bags to ~5psi you can go into L sans spacers installed. When hitched/towing, you should set bag PSI to retain stock N ride height. Don't sweat the pressure measurements, not possible when inflated.

 

[mojaveoverland]

If you set the bags to ~5psi you can go into L sans spacers installed. When hitched/towing, you should set bag PSI to retain stock N ride height. Don't sweat the pressure measurements, not possible when inflated.

Makes sense. I was hoping to use the spacers to bring rear neutral pressures down to spec and then airbags if I needed a bit more pressure reduction, but now this doesn’t sound possible since I won’t be able to measure pressure by going L—>N with the bags inflated + spacers.

 

[ramangain]

By the nature of the bags, they inflate and grow to add some not-too-compressible material between the coils. Downside is that they also grow vertically and raise the truck a bit themselves, making pressure tests impossible (can't sink to L setting). The bags are VERY handy for hitching heavy loads to reduce trailer jack cranking when it supports weight. Folks find their own process for this (I know i did)

 

[mojaveoverland]

By the nature of the bags, they inflate and grow to add some not-too-compressible material between the coils. Downside is that they also grow vertically and raise the truck a bit themselves, making pressure tests impossible (can't sink to L setting). The bags are VERY handy for hitching heavy loads to reduce trailer jack cranking when it supports weight. Folks find their own process for this (I know i did)

In that case I plan to deflate the bags completely, measure pressures with the new spacers and get them in spec, then inflate to ~5psi for normal driving and 20-30psi when towing.

 

[ramangain]

That should work

 

[ramangain]

FWIW I found my bags never held 5-7PSI over time when using my AHC to lower the rig to get in and out ... normal city and highway driving included. Some folks can keep 5-7PSI over a long period of time, but I never discerned if they actively use the AHC as well when keeping the bags inflated to such a low pressure. I always chalked it up to non-optimized barbs at all of the nipple locations, but have zero interest in chasing it down on my rig. Maybe one day when the rear axle needs to get dropped again .....

 

[mojaveoverland]

FWIW I found my bags never held 5-7PSI over time when using my AHC to lower the rig to get in and out ... normal city and highway driving included. Some folks can keep 5-7PSI over a long period of time, but I never discerned if they actively use the AHC as well when keeping the bags inflated to such a low pressure. I always chalked it up to non-optimized barbs at all of the nipple locations, but have zero interest in chasing it down on my rig. Maybe one day when the rear axle needs to get dropped again .....

I’ll report back in a few weeks of driving with 5psi in them. Since I won’t (can’t with spacers and bags) be going into low, perhaps they will hold this low pressure longer.

 

[ramangain]

Bumpstops are gone, correct?

I don't run spacers but I can get my rig to L with a few psi in the bags.

Will the rig go to L with deflated bags?

 

[mojaveoverland]

Bumpstops are gone, correct?

I don't run spacers but I can get my rig to L with a few psi in the bags.

Will the rig go to L with deflated bags?

I cut the bump stops down to just the top portion (maybe 1-1.5”) per the instructions that came with the airbags. I could take them out but then I think there’d be a gap between the airbag and top at Normal height. Haven’t tried deflating completely yet and going to L.

 

[ramangain]

Ah, OK. I know the Airlift instructions (used to) call for total removal of the bump stops. The Firestone flavor may need the partial bump stop in order to protect the nipple in the normal installation method (protect the air nipple)?

Either way, differences. Could be apples to oranges at this point. I run the Airlift system, so most things should be equivalent, but probably not all.

That bump stop chunk and the lightly inflated air bags may just be enough to keep the system from dropping down to L under its own weight. That's my working suspicion.