C5 master cylinder on C3 question.

[Twin_Turbo]

The pushrod fits just fine, however the 77 uses the later style short pin, the early models had the long pin, for the deep hole MC same as used in the manual (and what kept it from falling out of the MC)

Larry, that's fine. The rod pulls out like that, it's kept in by the MC. That's why the early non power MCs (and those years power ones too as they used 1 an the same) have the deep hole in the piston. That kept the manual rod setup from falling out.

 

[69427]

The pushrod fits just fine, however the 77 uses the later style short pin, the early models had the long pin, for the deep hole MC same as used in the manual (and what kept it from falling out of the MC)

Larry, that's fine. The rod pulls out like that, it's kept in by the MC. That's why the early non power MCs (and those years power ones too as they used 1 an the same) have the deep hole in the piston. That kept the manual rod setup from falling out.

Well, that makes sense. After I sent the previous post I went back out to the garage and plied the seal out of the booster with a small screwdriver. Popped right out. And, holy crap, there's a boatload of difference in the piston recess hole depth between the 69 m/c and the C5 m/c. I made some measurements, and it looks like I'd have to shorten the rod by about 1.300 inches, along with drilling and tapping it. Looked like it was going to be a slow dull process. But hey, I appreciate the info that the later rod is shorter. I would have assumed that all C3 brake stuff was the same through the model run. Now I just have to locate a later rod.
Thanks again, TT. I do appreciate it. :thumbs:

 

[69427]

Did the power brake booster change in '77? I was just scanning ebay for some stuff, and they keep listing boosters for 68-76 applications. Obviously the pushrod changed, but what about the booster?

 

[turtlevette]

Did the power brake booster change in '77? I was just scanning ebay for some stuff, and they keep listing boosters for 68-76 applications. Obviously the pushrod changed, but what about the booster?

I heard there was a double diaphram. If i would have known that i would have told autozone i had a 77 when i replaced mine 10 years ago.

This is where Gene comes in and says his face hits the windshield with a hydroboost.

 

[69427]

Did the power brake booster change in '77? I was just scanning ebay for some stuff, and they keep listing boosters for 68-76 applications. Obviously the pushrod changed, but what about the booster?

I heard there was a double diaphram. If i would have known that i would have told autozone i had a 77 when i replaced mine 10 years ago.

This is where Gene comes in and says his face hits the windshield with a hydroboost.

Well, according to the pictures, mine is the Bendix dual diaphram booster.

Regarding HB, outside of a boatload of pad taper wear when driven hard, my stock brakes (and the assist level) have always been first rate on this car. My only complaint was I always had to remove the pads and file them level again (high wear at the piston areas, and lower wear between the pistons, causing a crown in the middle of the pad) before each new track day due to the excessive pedal travel caused by the crown/taper wear.

 

[Yellow73SB]

What size fittings are on the proportioning block?

Also as far as the pad taper, isn't that what the j56 stiffeners are for? I'm going to make some eventually

 

[69427]

What size fittings are on the proportioning block?
They're two different sizes, but I don't recall what at the moment. If someone doesn't pipe up with the info I'll try to measure them the next time I'm out in the garage.Also as far as the pad taper, isn't that what the j56 stiffeners are for? I'm going to make some eventually

My particular problem would have been solved if the pad backing plate was thicker and didn't flex. At the end of a half dozen track sessions the pads weren't flat, but had high wear on the leading and trailing edges where the pistons applied force, and the pad material essentially was only contacting the rotors in a short vertical slice in the pad middle, until the pistons pushed out further (under braking) and flexed the backing plate into a curve which caused the friction material on the pad to "straighten out" against the rotor.

 

[69427]

'77 and later pushrod shape. ???

TT,

What did the pushrod look like in your brother's car? My initial plan was to just substitute a later pushrod, but one of the pictures in a vendor's catalog indicated that the later pushrod has a different seat shape on the rear, booster side. If that's so, I'll have to change plans, and just shorten the original pushrod. What can you tell me about the later item?

thanks again,
Mike

 

[mrvette]

TT,

What did the pushrod look like in your brother's car? My initial plan was to just substitute a later pushrod, but one of the pictures in a vendor's catalog indicated that the later pushrod has a different seat shape on the rear, booster side. If that's so, I'll have to change plans, and just shorten the original pushrod. What can you tell me about the later item?

thanks again,
Mike

Go HB and fix the damn thing...but if you insist, I remember pulling that shaft out, and shortening it....measure careful...you only get one attempt...the booster did not loose vacuum from pulling it, as I recall......been a LONG time since I did that, but it's simple to get outta there....looks like a intake valve for a lawnmower....

:bounce:

 

[Twin_Turbo]

You can't swap pushrods between older and later style boosters, you need the later booster or shorten your existing pushrod

 

[69427]

TT,

What did the pushrod look like in your brother's car? My initial plan was to just substitute a later pushrod, but one of the pictures in a vendor's catalog indicated that the later pushrod has a different seat shape on the rear, booster side. If that's so, I'll have to change plans, and just shorten the original pushrod. What can you tell me about the later item?

thanks again,
Mike

Go HB and fix the damn thing...but if you insist, I remember pulling that shaft out, and shortening it....measure careful...you only get one attempt...the booster did not loose vacuum from pulling it, as I recall......been a LONG time since I did that, but it's simple to get outta there....looks like a intake valve for a lawnmower....

:bounce:

Nothing to fix, Gene. This thing has always had a firm pedal and stopped on a dime. I'm changing master cylinders to take six pounds of weight off the front end, and to also have a master cylinder that doesn't continuously look like shit because paint won't stick to a brake fluid soaked piece of cast iron.

 

[69427]

You can't swap pushrods between older and later style boosters, you need the later booster or shorten your existing pushrod

Hey, I appreciate the quick response. Looks like I'll start work on shortening the original pushrod.

Thanks again!

 

[69427]

It's in.

Got the master cylinder installed. I made a small gauge out of sheetmetal to set the pushrod depth/length, so I think I'm pretty close to what will work out, pedal-wise. Won't know for sure until I get the body mounted again. One thing concerns me. I would be willing to bet there's a 50% chance I'll have to section the reservoir to reduce the height by about a half inch. It's going to be stinking close (cap/hood spacing) the first time I try to close the hood.

 

[69427]

Got the lines run from the master cylinder to the junction block today. The front line was straightforward, I just needed to cut and flare one end of a metric line to fit the junction block. The rear line was a bit of a headache, mainly the lack of availability of the fitting nut that screws into the master cylinder. I managed to get a pair of lines off a parted out C5, and just ended up using the rear circuit line nut. Fortunately, the guy I got the lines from was a good guy, and I managed to purchase them for a very reasonable price. I put the original fitting nut on the new line, and then just reflared the opposite end with the standard double flare. Now, the only remaining brake work is the flex lines to/from each caliper. (I'm also hoping that the m/c cap is going to clear the underside of the hood. LOL)

 

[Twin_Turbo]

It'll clear the hood just fine.

 

[69427]

It'll clear the hood just fine.

One thing that I'm curious about. Is the later booster different in shape or length? It just seemed like the m/c was positioned slightly lower in your brother's car than it is in mine.

Once again, thanks for all your help.

 

[Twin_Turbo]

The MC is in the center of the booster and the length is roughly the same for both models.

 

[Twin_Turbo]

Looks to be in about the same spot: