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I’m in the process of replacing the master cylinder on my recently purchased ‘61 Dynamic 88. The master cylinder is seized. Right now I’m leaning towards replacing the single pot with a new single pot, making sure the emergency brake functions and inspect all components...... but while I’m doing a master cylinder replacement I can’t help but think I should just install a dual reservoir master cylinder. So the question, if I went to a dual reservoir, would I be able to use the stock brake booster? Any suggestions on a kit or the master cylinder to buy?
If it's possible, I would suggest replacing all wheel cylinders, rubber hoses, and metal lines. If the master was seized there was probably water in the system and the lines and wheel cylinders are probably also rotted out.
The pushrod should be in line with the bottom two studs. I'm not sure if the spacing on the studs matches the traditional GM master cylinder bolt spacing. Your other problem is that you need to find an M/C with the correct pilot outside diameter where it fits into the booster, since that needs to be a vacuum seal with an O-ring on the stock M/C. The stock M/C is a 1" bore, so the new one will need to be the same. Frankly, given the issues of matching an M/C to that booster, it's likely easier to use a matched M/C and booster combo.
If you get a matched booster, MC combo you could install a dual master. You can get a 66-67 Cadillac or 67+ Oldsmobile dual master for FRONT and REAR Drums (NOT front disk rear drums). Then you have to change your T fitting on from 4 ports to 3 ports for your front brakes and a 2 port to connect to your rear brake line, and a new brake line from the master to one of the fittings. I'd still consider replacing all the lines, wheel cylinders and hoses.
it's likely easier to use a matched M/C and booster combo.
Agreed. You may not have space to mount a big Moraine unit there but the street rod crowd should have you covered. 9" booster/mc package is common in that world and IIRC many look similar to your original Bendix unit.
Look at it this way. GM itself offered a dual mc retrofit package for 62-66 cars and it was still in the parts system as late as 1974. Who would know it wasn't one of those?
I just put a dual MC on my 61. I did have to replace the power booster as the one on my car had the piston for the MC built into it. I went with a universal fit 7" dual diaphram street rod style booster I got off of Amazon for less than $70. I used a 62 Cadillac Master Cylinder (Any GM MC should really work) and the only thing I really had to "modify" was I needed to make a 1" spacer between the booster and the firewall and use a longer adjusting screw coming out of the booster. I split my lines front and rear with no proportioning valve. At the same time I replaced all the shoes, wheel cylinders, hardware and all the rubber lines. Car stops great now. I hope this helps.
I used a 62 Cadillac Master Cylinder (Any GM MC should really work)
GM dual circuit master cylinders have two styles, deep and shallow pushrod hole. The 62-66 Cadillac M/C has a deep pushrod hole. The 67-up M/Cs have a shallow pushrod hole. The M/C has to match the length of the pushrod coming out of the front of the booster. Some aftermarket M/Cs have a deep hole and come with a spacer that can be inserted to use it with a booster that needs a shallow M/C.
Note that the M/C on the left in this photo has the insert in the deep hole to convert it to use with a booster that needs a shallow hole.
December 14th, 2020, 05:38 PM
