Joined: Sat Aug 19 2006, 05:03PM
Location: Ontario, Canada
Posts: 2919
I finally bought a (reman) '73 disc booster to "complete" the disc brake swap in my hardtop. I have a console shift, so I don't need to worry about the larger diameter of the booster interfering with the (column) shift linkage. The original '66 drum booster is 8" diameter; the single-diaphragm '73 booster is 10" diameter.
I thought this would be a straightforward bolt-in swap. No. Where the 73 booster goes through the firewall, there is a shoulder on the booster which is larger in diameter than the hole in the firewall. I need to get out my dremel and open-up the hole by about 1/8" all around. Fortunately, most of what I need to grind is on a steel plate that is bolted to the firewall, so can be done out of the car.
Anybody else encounter this problem? I think Ross had a '73 booster on one of his cars for awhile, but I don't recall reading this caveat in his disc brake conversion FAQ.
Cheers, Mike <span class='smallblacktext'>[ Edited ]</span>
Joined: Sat Aug 19 2006, 05:03PM
Location: Ontario, Canada
Posts: 2919
That is odd. According to rockauto.com, the same booster fits all C-body disc brake applications from 1971-73. It's Cardone #5473700. The one I received looks just like the one in the picture on Rock Auto:
Possibly the rebuilders installed a dust boot that is a thicker rubber than the original, and that's causing the binding. If it were not for the dust boot, the shoulder on the booster would probably just fit through the opening. <span class='smallblacktext'>[ Edited Fri Apr 03 2009, 11:57AM ]</span>
Joined: Tue Oct 11 2005, 01:33AM
Location: Calgary, Alberta
Posts: 5893
While you've got the booster out, measure and compare the push rods on the new and old units. Seems I recall reading that there are differences in rod length that you normally wouldn't notice until you start to drive with the new brakes.
I had the same issue when I swapped out mine in my 68 Fury. I went from power drums to disks. The booster I got from AutoZone was for a 68 with front power disks. It was the only one I could find anywhere for less than $175. ($105) I did not have to grind out my firewall though. I did just the mounting plate and all is good! The booster I got is not one with an adjustable rod so I didn't have to mess with it and it works fine.
Joined: Thu Nov 24 2005, 07:29PM
Location: So Cal.
Posts: 1111
I had to grind the firewall and the mounting plate. I had the plate done at a friend's shop on a mill but the firewall was a different story...
What I did was made a wooden template with the mounting plate as a guide, then bolted the wood to the car and used a hole saw to cut through the firewall.
The pushrod is indeed longer so I had to modify my brake switch bracket in order for the switch to sit back farther. This is something I would like to fix properly but for now the brakes work GREAT!!!! I honestly don't notice that the brake pedal is much farther out but that's probably because I forgot how far in it was since the car was apart for so long.
Joined: Fri Oct 07 2005, 12:03PM
Location: Central Ky.
Posts: 1575
Well, here's the one he got for the 65....
I know he ordered one for a 71 but who knows what they gave him. Got it from a local CarQuest about 4 years ago. Looks looks like a Dual-Diaphragm one.
Joined: Thu Mar 22 2007, 08:13AM
Location: In the workshop
Posts: 1063
I had exactly this problem when I did my conversion. When I looked closely, I noticed that the hole was double plate, and the rear plate was more of a ''D'' shape that a circle. Dremelled this out, tried again, but the booster still wouldnt fit. Ended up doing the same 1/8" diameter increase.
In a way, I am surprised that this problem has not been mentioned before, though in another way, I'm not. I suspect that its more a question of tolerances. Some cars are to the max plus side, others the max minus, and its the latter ones that have the problems.
