Fiat 500 (2008-2015) Seat Back Recline Knob Strengthener / Repair

Background I recently bought a used Fiat 500 and the driver's seat adjuster wheel/knob to adjust the tilt of the seatback wasn't working. I pulled the knob off carefully using a trim removal tool and noticed the plastic socket that grabs the metal splines was split. Looking up the cost of a replacement I found the knobs were between $20-$40 AUD without shipping.

So I designed a small donut shaped strengthener (Donut of Strength :)) that fits between the outer and inner collars to hold the inner collar back into round and the snapped piece in place. It is a simple piece but took a bit of fiddling to get the dimensions spot on so thought I'd share it. Total cost if you print 2 of the Donut/Collars plus both helpers is about 50cents.

Design and Fitment The design is a tight fit but should only need tapping in lightly with a hammer, I've also designed two assistance pieces a Mounting Helper which can be printed in PLA to help gently tap the piece in and a rough replica of the splined chair piece to help hold any broken pieces in place if you need to for gluing. recommend using a slow curing glue so you can remove the internal piece before the glue fully sets.

As you can see from the photos mine was bent outwards so I just gently aligned the piece using a small screwdriver to bend it back into alignment and then inserted my Donut of Strength (Orange Collar) over the top. Make sure you align your broken piece or the Donut of Strength can catch it and snap it off. I thought I would need glue and my internal support piece but I didn't end up needing any glue. If you do use glue this is a one-way insertion getting the Donut of Strength out once its in would require a drill and a fair bit of patience which combined with glue could get messy fast so if you don't need glue don't use it, if you do use glue go with something slow setting like a 24hr epoxy.

A little more detail on installation - I pushed my orange Donut of Strength in by hand until it just cleared the outer clip ring. At that point I grabbed the Mounting Helper and used it to gently tap the Donut of Strength down until it was snug. It dosent take much to tap it down a hammer, spanner or heel of a shoe would do. Put the adjuster knob on hard surface to support the tapping but place something cloth, tea towl, microfiber cloth or tshirt between the adjuster knob and the hard surface to help protect that front surface.

I added the part to my passenger seat knob as well while I was at it, better a small preventative part now than being on a longer trip and the knob breaks on someone trying to adjust the seat.

Printed Parts

- Donut/Collar Strengthener (Orange in my pictures so you can easily see it) - Print in ABS or PETG Min (0.2mm, 3 walls, 30% infill)

- Mounting Helper (Yellow Optional if you have a short length of 20mm dowl use that) - PLA (0.2mm, 3 walls, 20% infill)

- Metal Chair Spline replica (Yellow Optional print if you need it) - PLA (0.2mm, Hollow if you like)

- Print all vertically

Thoughts If your central hub is totally destroyed my part could be used as a starter design for a piece to fully replace the centre so my onshape files are here . Do not use my Internal Glue Helper piece as a true to life replica its very much a rough model to just be an internal glue support not a sub-mm accurate replica :).

Long hand URL - https://cad.onshape.com/documents/c2a8b7ef73b362c185334ea4/w/2e6ec6abc01305880874eb53/e/c9198b7cf654e21c89d96224?renderMode=0&uiState=6a85287c53d5e08a2e6f4d25

This might work on the 2015+ I just don't have access to that model car, but the dimensions of my donut/collar are:

- Internal hole diameter- 12.65mm

- Outer diameter - 22.35mm

- Height - 13.9mm