Removing Isobarik woofers

[colinegreen]

Hello PFM -

I am pretty far into a restoration project of late 70's Isobariks. One speaker has all the drivers and internal XO's removed, and the varnish stripped. I was even able, using the drill-a-hole-in-the-bottom technique posted elsewhere on PFM (thank Neil James for the tip) to remove the inner B139 on the first speaker.

The second speaker is proving more challenging. I cannot get the front woofer out. The mastic is holding on too tight. The amount of force on my pry bar is excessive and will damage the wood surrounding the hole, or bend the woofer frame. I tried the cross threaded screw idea which worked to some extent on speaker #1, but on #2 they do not hold and pop out every time.

One of the corner bolts also will not come out. This one seems to have been "threaded" into the wood, not anything more solid. I can turn it with a socket, but it just turns in place and does not come out, and there is no way to get under it to push it out. I am assuming the threads are not engaged in the wood and it will just spin forever with not spin out of the hole as the others did. But as it is not threaded into anything, it is not preventing the woofer from coming out.

Is it worth experimenting with Goo Gone or some other solvent in the crack between the frame and the baffle to try to dissolve the mastic?

Any other approaches experienced people can suggest?

I hope I do not have to drill a hole through the bottom just to get the front one out.

 

[hp1]

All of the isobariks that I have rebuilt have used t nut inserts for the bass unit fixings ,so the spinning bolt on yours means trouble.
Do they have hex headed bolts or Allen headed capscrews? You will need to drill the head off either, but the capscrews can be 12.9 hardness and very difficult to drill.
To remove the bass drivers the best way is to tap a thread into the chassis of the driver through the fixing hole ,screw in a bolt and use a load spreader / nail drawer .

 

[JemHayward]

Your rotating bolt may mean that the T-nut is loose the other side. Try pulling on it with pliers to see if you can re-seat the T-nut and then screwew it out. Removing the bolts is only half the issue. I used some large screw extractor bits, a bit like these:https://www.amazon.co.uk/DazSpirit-...tractor&qid=1595435587&sr=8-9&tag=googhydr-21
and laid lots of wood on the cabinet to take the force, and then hammered the long end of my crow bar with a lump hammer. I also warmed the mastic with a hair drier, but not sure that helped much. Came away with quite a bit of MDF attached to the driver with mastic.

 

[colinegreen]

Your rotating bolt may mean that the T-nut is loose the other side. Try pulling on it with pliers to see if you can re-seat the T-nut and then screwew it out. Removing the bolts is only half the issue. I used some large screw extractor bits, a bit like these:https://www.amazon.co.uk/DazSpirit-...tractor&qid=1595435587&sr=8-9&tag=googhydr-21
and laid lots of wood on the cabinet to take the force, and then hammered the long end of my crow bar with a lump hammer. I also warmed the mastic with a hair drier, but not sure that helped much. Came away with quite a bit of MDF attached to the driver with mastic.

Thanks to you both for the help. The woofer on speaker one released its hold surprisingly easily, once I got up the courage to apply some force. Trying the thread tap next.

 

[hp1]

If you are making a tool as I did to tap and pull the units ,be sure to make it long enough to pull the rear unit out also. I used a 12.9 capscew with flutes ground into the sides then welded the head to a T handle. Just screw it into the speaker chassis and pull like ..c.