I tried putting this question in the "Brakes" section....but no one answered. Maybe someone can help here.

What exactly does the correct master cylinder look like for a 1970 W30 with manual front discs? The master cylinder on my 72 W30 with manual front discs is original and is:
Dual Bale
Two indentical ROUND domes
No bleeder screws on side
But the 72 chassis service manual doesn't show the master cylinder for non-powered front discs and the ones it does show are single bale units. If I assume nothing changed between 70 and 72 I'm thinking my 70 master cylinder should look like my 72.

From the 442.com FAQ it says for 70 w/man disc brakes the MC should be a 1" bore with dual bales, so that jives with what my 72 has, but again, looking at the 1970 Olds Chassis Service Manual it only shows illustrations of single bale units. Looking online the replacements with 1" piston and 2 bales come with and without bleeder screws above the brake lines that go into the master cylinder. And some top caps have 2 identical round domes and some have oblong domes of different sizes.

Based on what I'm reading I'm thinking the MC on my car now is most likely not the original one (it is a single bale unit with the different size oblong domes with bleeders on the side of the unit) and I'd like to get the correct one when I replace it in the near future. Anybody have an original 70 W30 with manual discs that can clear this up???

Thanks for any help you can provide.

regards,
bob

 

The Nov 72 GMPD parts book and the Illustrration Manual aren't definitive but it seems you should have the single bail, two round bulges on the cover, Moraine master cylinder. The other choice is Bendix. Check a parts house to see what style/s are available. I have had good luck with John Andreotti <andreotti@ottsfrictionsupply.com>
I got a Centric replacement for the Moraine style 67 master cylinder. It looks correct except for having bulges above the brake line ports where they could put bleeders but didn't.

 

With any 67-72 manual brake A body, be sure to re-install the pushrod retainer (cup shaped) on the back of the master cylinder, protruding through the firewall but with the flared end in the cylinder and too big to go through the firewall. Without it, the pushrod can come out and you have no brakes. The Chevy S10 has a similar retainer but I don't know if it interchanges. I haven't been able to find a current source for the 67-72 part, 5452525.

 

Bobb,
This is one where I believe the assembly manual is not "correct". The master that appears on every original manual brake 1970 W30 and W31 that I have come across, is a square single bail, with two bleeders, coded "EB" on the front half moon machined surface. I am not the orginal owner of my cars and others that I have researched, so I cannot state with certainty that they left the Lansing plant that way and I stand to be corrected. I have found the same coded master on power brake applications on other Oldsmobiles and Pontiacs as well.

 

Inline tubes has what They say is the real deal.