Where to Find Leak in Firestone Air Bag in Coil

Updated 04/08/2025 | Published 04/07/2025

Question:

One of my coil rite bags on my FJ Cruiser leaks at the bag fitting 2.5 years on install,1400 miles Ive tried re cutting air tube and it still will not seal, and it is a real pain to work on with bag inside the coil spring. I hate the thought of ping the axle again to replace the bag if one is available. Any suggestions?

asked by: Charles H

Firestone Air Bag
(click to enlarge)

Expert Reply:

Hey Charles, sorry to hear about the leak. What I would do before doing anything too complicated is for sure narrow down where the leak is. You can do this by spraying soapy water on the bags and the line and where the leak is you'll see bubbles.

expert reply by: Jameson C

Charles H.

4/8/2025

Thanks for the advice. I rechecked with soap and the bag fitting is definitely leaking, and I think I know why. I've been maintaining the minimum 5 lbs pressure in the bags and the vehicle has been in for routine service multiple times. They lift the fj at the frame which extends the rear coil springs. With pressure in the bags the coils grab the bag and put major pressure on the air fitting damaging the seal. With zero pressure, the bags just dangle on the air line. When going in for service let off all pressure in advance. My problem, and lesson learned. Is it possible to purchase a replacement bag? Thank you.

Jameson C.

4/8/2025

@CharlesH I'm glad you figured out exactly where the leak is and what caused it. I wish we offered a replacement bag for that kit but at this time we can't get it. I'd reach out to Firestone directly and ask them for a replacement bag for the 4135 kit. [email protected]