I have 68 olds delta 88 with the original master cylinder and brake booster. It just recently sprung a leak between the master cylinder and booster. Should I replace both or just the master cylinder ? . Also I noticed they sell master cylinders for power brakes and manual brakes 1” or 1-5/8” on rock auto. I have no idea which one to get . Car has drum brakes all the way around .

https://www.rockauto.com/en/catalog/oldsmobile,1968,delta+88,7.5l+455cid+v8,1213513,br ake+&+wheel+hub,master+cylinder,1836

 

Just rebuild your existing master cylinder, very easy to do.

 

Brake fluid leaking into the booster can cause damage. It's probably smart to have the booster rebuilt. Be sure the seal between the booster and M/C is also replaced. These can be difficult to source. I've found that the Corvette repro vendors are the best source. Here's another potential source.

As for which booster, you have power brakes. Why would you get anything other than a master cylinder for power brakes? The bore controls both the amount of force required at the pedal and the fluid volume that goes to the wheels. The power brake M/C typically has a larger bore because the booster reduced required pedal pressure.

 

Thank you both for the information . Any leads on a rebuild kit ? Struggling to find one . Also , if this just started leaking between the master cylinder and booster could it be as simple as replacing that seal?

would the AC Delco one work or do I need the 1-5/8” specified one ?

 

First, the seal between the booster and M/C is a vacuum seal for the booster. If you have brake fluid coming out the back of the M/C, that means that the seals on the piston on the M/C are bad. Since the booster contains vacuum from the engine, leaking brake fluid tends to get sucked into the booster if the M/C leaks. If the leak is recent, the booster is probably OK, but you really don't know how long the M/C has been leaking.

Read that listing for the M/C again. 1 5/8" is not the bore of the M/C, it's the depth of the hole for the pushrod in the back of the M/C - the listing says "depth pushrod". GM power boosters come with one of two length pushrods between the booster and M/C. The long one requires the deep pushrod hole in the M/C, the short one requires the shallow pushrod hole. All 1967 Olds power brake M/Cs use the shallow pushrod, so any listing for the deep pushrod is wrong. The bore for a power brake M/C is 1.0" for power drum brakes and 1 1/8" for power disc brakes. This is listed in the 1967 Chassis Service Manual. Yes, in this case the 1.0" bore is the same for manual and power drum brakes. The factory part number for the power brake master cylinder is 5458521. If you go to the Part Number Search tab on RockAuto and type in the OEM number, you get the correct Raybestos MC36234 part number. Yes, this comes with the rubber boot for a manual brake application, at least as shown in the photo. Since both manual and power brakes use the same 1" bore, don't worry about that, just don't use it.

 

White Post in VA or Karp's in CA are two reputable rebuilders to get your components rebuilt and you know they will fit properly without issues. Inspect the steel brake lines while doing the job and soak all bleeder screws multiple times with penetrating oil.

A '68 Delta, what an awesome ride...Good luck!!!

Pictures?

 

Thank you for that info Joe but the car is a 1968 and I noticed you said 67 . Is this Info still valid for a 68.

here’s some pictures

44,000 all original miles . Great grand father bought it off the show room floor new .

 

Yeah, sorry for the mixup, but 67 and 68 use the same P/N master cylinder for drum brakes, so the info still applies.

 

Nice lookin 88 good luck with your brakes.

 

I have original rebuilt Drum Masters available code CT.

 

Just as a point of reference, I had the same problem on a 1966 Starfire. Replaced the master and the new one leaked too, had to rebuild the booster and replace the second master.

 

The booster won't cause the master to leak. That's just a crappy replacement part.

 

So I bought that raybestos mc36234 m/c but it did not come with the oring . Does anybody know where I can get one ?

 

I'm not sure what you mean by "o-ring". If you are talking about the seal between the M/C and the booster, I provided you links to two vendors up in Post #3.

 

Update .

I finally got around to getting the master cylinder off . Had to soak all the bolts in PB and put a little bit of heat on them but they all came off without issue . Here are the pictures of what it looked like the second it came off . I bought that new rubber boot piece off the corvette website says for 64-67 corvette but they look nearly identical . Should this work ? Let me know what ya think . Thanks guys .

Also, I cleaned up that rubber piece ( in hand) and it looks fine . No obvious rips or tears and still very malleable . Should I reuse it or use the new corvette one ?

 

The repro seal will work fine.

 

Awesome .

Does this rubber bushing on the rod effect the sealing ? Could this cause the leak ? Or did the leak come from within the M/C do you think ?

 

There's no liquid in the booster. That plastic bushing only seals vacuum in the front cavity of the booster. A brake fluid leak can only be caused by worn seals in the master cylinder. If possible, clean that bushing as well as you can before reinstalling the seal. Have someone press on the brake pedal to push the rod out to where you can get to it (being careful not to over-travel the booster since the M/C is not in place). After cleaning, a light coating of silicone grease on that bushing will help preclude wear on the seal.

 

Great information thank you