Upgraded master cylinder, crappy pedal now...

[81_El_Homewrecker]

You made sure you didn't trip the combination valve switch during bleeding, right? Sometimes, if this happens, the pedal gets hard as a rock and you only have 1/2 your brakes.

I don’t think so. It stops about as quick as it did previously but the pedal feels much harder. It’s also worth noting my brakes had an obnoxious amount of air in them previously. I just don’t like that I can’t lock the tires up in a panic, makes me feel like I’m leaving stopping power on the table. It also doesn’t throw all its weight forward or squat like only half the brakes are working

it sounds like others have used the larger dual b-body booster and have had good results.

 

[TURNA]

You want to lock up the tires??

 

[L92 OLDS]

Part number?

If memory serves me I pulled it off a low mileage 1990 Caprice. You need the push rod from the Caprice but everything else bolts up.

 

[69hurstolds]

If memory serves me I pulled it off a low mileage 1990 Caprice. You need the push rod from the Caprice but everything else bolts up.

That would be p/n 18006566 or equivalent. B-body master cylinder is p/n 18013426. Not that it matters.

Most G-bodies came with the dual diaphragm boosters too if they were Delco units. Nothing magical about that. Probably just the rod length.

 

[JAMCAR223]

You didn't say if you had 4 wheel discs... If so, did you change your prop valve to a disc/disc valve? BTW, disc brakes are not typically designed to "lock up"

 

[81_El_Homewrecker]

You didn't say if you had 4 wheel discs... If so, did you change your prop valve to a disc/disc valve? BTW, disc brakes are not typically designed to "lock up"

Yes I have discs all around, but did not change the prop valve because it was not causing drag on the rears. Others advised to not change too many things in one go, and since the prop valve isn’t holding residual pressure on the rears I’m leaving it alone.

 

[81_El_Homewrecker]

You want to lock up the tires??

Not intentionally, but I figured that was a good gauge of how solid the brakes are? Maybe there isn’t much wrong with mine then...hard to gauge haha

 

[69hurstolds]

The point is you don't WANT rear brake lockup if you can help it. When you do that, you effectively are not in control. That's why the "proportioning" or more technically, pressure limiting valve to help minimize shoe lockup.

EDIT: I see you have discs all around, so never mind. Except you still don't want them locking up in a panic stop if you can help it. You can get rid of that metering valve for the front then and just put a plug in there. You don't need the fronts acting any slower with discs in the rear. You don't need to do it now, but after you figure out your braking issue with the master cylinder.

 

[TURNA]

disk disk needs disk disk

 

[81_El_Homewrecker]

Just want to update everyone in case others are having similar issues. I installed the 2000 Blazer master cylinder and had a pedal that was too hard. So I installed a dual diaphragm booster from a 1990 Caprice. Pedal is wonderful now! Extremely responsive and firm but not hard like a lack of vacuum, just what I wanted. Thank you to everyone for the help and advice!