[NeighborsComplaint]

I wanted to replace my brake booster brackets with a “reduced angle” set to place my master cylinder closer to horizontal. As it is now w factory brackets, the reservoirs hardly hold any brake fluid due to the way it is tipped up.

Since I going solo on this, are the factory brackets held by bolts requiring a second set of hands under the dash or are they pressed/welded studs?

[Scarebird]

There is more than enough fluid there for your brakes.

The angle is there for the different geometry required to go thru the firewall hole without interference versus the manual master and it's different pushrod location; changing this angle may upset this relationship.

[Schurkey]

Originally Posted by NeighborsComplaint

now w factory brackets, the reservoirs hardly hold any brake fluid due to the way it is tipped up.

WHAT VEHICLE?
Incorrect master cylinder/reservoir?

[NeighborsComplaint]

Originally Posted by Schurkey

WHAT VEHICLE?
Incorrect master cylinder/reservoir?

1971 GTO w. disc-disc conversion. Typical 1-1/8" bore GM/Corvette master cylinder. Master cylinder is tilted back so far that the fluid barely covers the floor of the reservoir over the secondary reservoir vent and replenishment ports. On hard acceleration, I can only assume the fluid climbs up the back of the reservoir even further, uncovering them even further. SDtab the brakes and air is induced into the system as the brakes are applied before the fluid can move forward.

The stock style (disc/drum) has deeper, narrower reservoirs, in the GM disc/disc master, they are large and shallow and makes me think they it is more sensitive to the angle of the master resulting in a low fluid level.

The reservoirs are barely half full because of the nose up angle. Once bled to an acceptable pedal feel and travel, the pedal gradually gets spongey and develops excessive travel. I have no external leaks and can get a good pedal by bleeding but after successive stops, it goes right back where it was. I've replaced the master with the same (1-1/8" bore) and it acts the same. I don't have a pic of the reservoirs, but the fluid level is at the top at the back of the reservoir and barely covering the floor at the front of the primary and secondary reservoirs.

Here is the angle at which the master is inclined. Yes. it's the same as stock but the master cylinder needs different geometry because of the shallow reservoirs.

[Scarebird]

What if you got rid of the Corvette master and put in the proper square-type master?

I would agree about the shallow issue.



https://www.rockauto.com/en/moreinfo...t=1836&jsn=670

[242177P]

If it's just a capacity thing, have you looked into
the truck master cylinders? I've seen these taller
ones on so-called "restored" cars so many times
it isn't even funny. The bail wire retainers are like
an inch(?) longer but they use the same cap.

[Scarebird]

I never liked the pot-bellied pig masters - now I wonder how many others have the same issue you are having?

This is the 1968-82 booster with master, note how it is designed to mount horizontal...

[NeighborsComplaint]

Yup. This problem has been recurrent ever since I did the disc/disc conversion. Every time I bleed the master, it stops normally for a while and goes right back to it’s old tricks.

As regards the OEM master, I’m told it won’t work with rear discs, too much fluid to move. Also, the 1” bore will give a stiffer pedal and longer travel which I want to avoid.

I bought reduced angle brackets made for this scenario but it looks like a complete pita to get to so I’m just going to throw on a stock dis/drum master and see. It can’t be any worse than what I’m dealing with now and the deeper reservoirs are made to accommodate the mounting angle. Thanks for the idea. Bet it works out fine. I can that changing the angle might bind the pushrod.

[Scarebird]

OEM master will work fine - this nonsense about "not moving enough fluid" is bull****.

I have the 1/2 ton manual master on my 4 disc setup - works perfectly.

[JLMounce]

More expensive than you are really talking about, but MP Brakes sells a bell crank master/booster combo that keeps everything level.

https://www.mpbrakes.com/booster-mas...F42BA75F8932B2

[NeighborsComplaint]

Originally Posted by Scarebird

OEM master will work fine - this nonsense about "not moving enough fluid" is bull****.

I have the 1/2 ton manual master on my 4 disc setup - works perfectly.

Yeah, I see it actually has the 1-1/8" piston so there's no reason it shouldn't work with disc/disc.

[Schurkey]

Originally Posted by NeighborsComplaint

As regards the OEM master, I’m told it won’t work with rear discs, too much fluid to move.

Not a matter of the volume of fluid moved during braking. The issue is the volume of fluid held in the reservoir over the life of the brake pads.

As brake pads wear, the pistons travel farther out of the caliper bores. This means there's a greater amount of fluid in the calipers. That fluid comes from the reservoir.

IF (big IF) the system is competently-designed, AND working properly, the reservoir holds enough fluid so that the pads can completely wear-out, pistons extended to their farthest normal displacement, plus a little extra for "safety". In fact, THAT is your warning that the pads need service--when the reservoir is intolerably low on fluid (but not "empty".)

Of course, when dough-heads at places like Spiffy-Lube fill the brake reservoir, they defeat this "warning sign".

Using a drum-brake reservoir with disc brakes means the reservoir will have to be re-filled occasionally, and the fluid level will have no relation to the amount of pad wear.

Originally Posted by NeighborsComplaint

the 1” bore will give a stiffer pedal and longer travel which I want to avoid.

Longer travel, yes. But easier-to-push, not stiffer.

[Goatracer1]

You got your master cylinder bores backwards. The 1 inch bore will give you a more responsive pedal requiring LESS pedal effect than the 1 & 1/8 master cylinder will.

[NeighborsComplaint]

Originally Posted by Goatracer1

You got your master cylinder bores backwards. The 1 inch bore will give you a more responsive pedal requiring LESS pedal effect than the 1 & 1/8 master cylinder will.

Longer stroke required for the same equivalent swept volume ...

[NeighborsComplaint]

Originally Posted by Scarebird

OEM master will work fine - this nonsense about "not moving enough fluid" is bull****.

I have the 1/2 ton manual master on my 4 disc setup - works perfectly.

Good plan except the hood wouldn't close.

Np damage, I'm smart enough to run a string line fender to fender if it even looks close.

[Scarebird]

It would not close with a manual master?

[NeighborsComplaint]

No. Stock master on my dual diaphragm booster.

[Scarebird]

Remember, the hood "humps" up quite a bit where the master is.

Try some wadded up aluminum foil on the master then slowly close the hood to see if there is indeed lack of clearance.

[HWYSTR455]

Pretty sure the brackets on an OE booster are riveted onto the booster, so you can't just change them.

Repop boosters have the studs to use different brackets. But the OE 'replacement' type boosters' brackets are still riveted to the booster.

The booster mounts to studs that are attached to the steering column & pedal bracket under the dash.

True that by changing the angle of the booster the rod angle could/would be incorrect, but you can solve that by drilling another hole in the pedal. You have to be thoughtful of the pedal ration when doing so. If pedal feel is undesirable, you can always play with the master bore size.


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[HWYSTR455]

Another thing to remember is that an OE drum front to rear brake line is smaller in diameter than a disc line. (Volume).


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