Project Snicket, Seat Diaphragm Replacement

No one likes either a saggy unsupportive seat, or one where you literally sit on wood. The Mini had both, and it was time to fix it.

The first, obvious step, is to remove the seats from the car. In a Mini this is super easy, with just two bolts at the front to remove.

Once out, I took the driver’s seat into the house and began pulling it apart. This is what I started with. A very hard, unsupportive seat that was bodged with wood.

The diaphragm is the large black rubber part with the holes in it in the above photo. This is used kinda like a big sprung net that allows some support and spring for your bum when the seat is sat in, making the seat comfortable. To replace the diaphragm you need to strip the whole base down. This isn’t too hard to do, as long as you’re careful.

First you need to remove the vinyl cover. This is held to the frame with the black metal clips. These have two little tangs on the top side of them (the side you can’t see) that dig into the material and hold them in place. I used a flat blade screwdriver to carefully pop them off. Some were a bit harder to remove, so I used needle nose pliers to gently wiggle the clips free of the material

I found this froggy rag stuffed inside the cover of the seat. Not sure if it was added to help bolster it, or just randomly stuffed in. Should make a good rag in the garage.

With the clips removed, gently peel the cover back. Take care that it might be slightly stuck to the pinky-red material wrapped around the base, so carefully peel the cover free

If the original diaphragm is as stuffed as mine, and no longer attached to the frame, the foam and diaphragm can be pulled out. If your diaphragm is still attached to the frame you will need to unhook the metal hooks from the frame. My diaphragm was stuck to the foam. I’m not sure if its meant to be stuck to the foam or not, but it was a pain to pull away without damaging the foam.

A random chunk of hard rubber was stuffed into the back of the cover. More bodged “fixes”.

With the foam off the seat you have access to the top of the frame. This allows you to hook in your new diaphragm hooks or springs. In my case I’m using a newer style diaphragm with springs, and not the rubber. This should hopefully last another 38 years.

This came with instructions which were good to show how to attach the springs, which although isn’t hard to do can be a pain the first couple of times. You don’t want to get it wrong as the springs are fairly strong. They also have a different type of hook on each end of the spring, the less curved hook goes in the frame.

The new diaphragm fitted. One issue I noted was that the front and rear springs are too long for this seat and aren’t under tension. They stay in place OK because of the foam, but they can fall out until the foam is in place properly (and it looks like one even fell out before this photo)

One thing I stuffed up first time, and it isn’t mentioned in the instructions, is that I didn’t slip the loop of vinyl through a spring before fitting to the diaphragm. This loop is at the back of the seat base

I had to strip the foam out again, and remove the two rear springs and slip them through the loop before reattaching.

And the completed diaphragm, with the clips reattached. Unfortunately one of the clips broke in half during assembly, so I’m short one.

The seat isn’t back in the car yet, but already its 120% more comfortable. Like a good Mini seat, it has that slight suspension spring when you sit in it. I’ll do the passenger’s seat tomorrow. That one has no wood in it, so it was almost like sitting on the floor when you fall through the frame.

Parts Used

CZH3508MS – SEAT DIAPHRAGM 59-92 FULL WIRE STRAP WEBBING x2

Please note these parts are specific to my car and may vary. Please check before ordering.