Fed up with having to stand on the brakes to haul it to a stop, mostly due to only pulling 11-12in vac during idle and cruise. So last week I ordered a new hydroboost from the USA and it arrived at the end of the week. So I've spent today making it fit.
The recon/new hydroboosts don't come with the output or input pushrods so I had to make those to suit. They also dont have the special star washer to lock the spring in for the output rod. I managed to find a large washer which served the same purpose though. I picked the cheapest hydroboost with the external accumulator I could find, happened to be from a 1980 C30 truck. They are all more or less the same, though there is some variation in the piston sizes and accumulator pressures. This one is the same as an astro van though under a different part number....
It also came with no mount plate, so I cut one from some 1/4" steel. I needed to add some 5/16" spacers so that the nut on the hydroboost cleared the hole in the firewall. I then put some strip caulk around it before bolting to the firewall. The booster used an input pushrod retained by an O-ring, I managed to find one the right size in the end. I also had to remove the brake switch actuating plate as it was bolted to the upper hole in the pedal where I needed to connect the pushrod. But there was enough adjustment on the switch to just actuate it with the pedal itself.
The most expensive bit of the conversion was the hoses and adaptors. But it's good stuff, rated to 7000psi burst pressure! Like big braided brake hose, PTFE inner with braided outer.
Last job was to top it off with fluid and bleed it through. Took nearly 3 quarts to fill it all back up again. I still have a few things left to finish off, like a new bracket for the prop valve, change the return hoses to braided to match the pressure hoses, and refit the subframe brace (which does still fit!). I also should add a filter in the system somewhere as I'm reliably informed the hydroboost will benefit from one.
Loads more access around the firewall now too, which should make future maintenance easier. The short drive up and down the yard seems to indicate the brakes are much improved!