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-   -   Suspect front brakes doing all the work? (

db flyer 07-30-2018 09:43 AM

Suspect front brakes doing all the work?
I just installed a new master cyl. with a bigger 1-1/8" piston, which also required a different pedal rod setup and adjustment. I have disc on front and drums on rear. Both front and rear are new within 300 miles. I have a higher pedal for braking now but not any difference in stopping power. However when I come to a slow stop I get what I call a groaning noise that sounds from the front as I put more pressure on brakes. Could this be a rod adjustment to the pedal? Thanks for any help. Duane

68NovaSS 07-30-2018 12:04 PM

Are your rear shoes adjusted properly? I assume you have a proportioning valve in the system, otherwise your rears would be locking up early. Isa this a power brake system?

If this is a large bore GM master cylinder, they have a different depth rod 'seat' in the rear, do you have the correct length for your MC?

db flyer 07-30-2018 12:16 PM

Thanks for the reply. my 56 chevy is not power brakes, and I do have a proportioning valve, and rear shoes are new and are adjusted properly.
Do you think adjusting the piston pedal rod so that the brake pedal will
go lower to floor will go deeper in cylinder and maybe help?

OneMoreTime 07-30-2018 02:01 PM

A good test is to take the car onto a gravel parking lot and dynamite the brakes at a low speed. The lockup marks left in the gravel should be about the same length if the brakes are working evenly. Then out on the road course you can do this at some higher speed to see if your adjustment of the proportioning valve is close to correct. Having a higher pedal upon replacing a master cylinder is normal to me as the new cylinder is acting a bit quicker than the old worn one.


db flyer 07-30-2018 02:21 PM

Thanks for that brake/gravel test of proportioning valve. I had wondered if the valve may be adjusted wrong, as I had trouble with rears locking up and just tweaked the valve until rears did not lock up, but maybe went too far with the knob. I assume turning the valve clockwise decreases fluid to rear?

68NovaSS 07-30-2018 07:03 PM

1 Attachment(s)
Here's a page from SSBC's installation manual regarding adjustment.

db flyer 08-02-2018 02:44 PM

Interesting update on my brake situation. I did check out the link you sent on proportional valve adjustment, and turned valve in both directions to each stop,
and made no difference at all. Appears as though the valve does not work at all, even though it did when I installed it 5 years ago. I put my brake pedal down with a bar resting against seat and confirmed rear brakes were locked also made sure fluid was present at master cyl. to rear brakes and at P. valve.
Also raised rear or car and ran engine in drive and confirmed wheels stopped as I applied brakes. Went out for a road trip and tested stopping at many stop signs with no rear brakes grabbing seamed fairly normal. Seems like P. valve
does not work which seems strange that rear brakes are not grabbing no matter the valve adjustment ?

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