Master cylinder push rod to short

[Ed P.]

Installed new master cyl today and I have to much free play in pedal. Went to adjust rod and it was only threaded into clevis two turns. Master cyl dimensions match old unit and also match other threads I found on the subject. Pedal bumper is in place and the rod is 4.12 inches long and the clevis looks original. I estimate that I am about half inch short on the rod. Any ideas or will I have to make a new rod. Clevis was also installed in the upper hole. Manual brakes. Thanks Ed

[Edward J.]

Re: Master cylinder push rod to short

Ed, When looking at the master cylinder rear piston- do the pistons have the same distance the resting position new and old ? may have to pull rubber boot back if theres one present.

[Ed P.]

Re: Master cylinder push rod to short

Yes I measured both M/S and the dimensions are almost identical. Problem was there before I replaced M/S. Ed

[Edward J.]

Re: Master cylinder push rod to short

Ed, is there any way maybe the pedal support where attached to body may have some movement to bring pedal closer, I have never removed one so its just a question. at this point there may be something thats causing the extra space between cylinder and push rod.

[Gene M.]

Re: Master cylinder push rod to short

Ed,
I suggest to try an aftermarket longer rod and see if you can make the correct adjustment. Be sure to leave a bit of clearance "free pedal" as the power brake unit needs full release to avoid dragging on brakes.

I do not recall if the 4.12 is the original rod length.

[Ed P.]

Re: Master cylinder push rod to short

Now that you mention the support for the pedal. This is a 66 that has a 67 steering column installed so maybe I need to look closer at the whole assy. mounting. The 4.12 dimension I have on the rod appears to be correct. I found a reference in the archives that confirmed this dimension. Thanks Ed

[David L.]

Re: Master cylinder push rod to short

The M/C push rod used on 63-66 Corvettes with standard brakes is GM # 3819077 in Gr. 4.658.
Enclosed is a sketch with dimensions.
Dave

[Ed P.]

Re: Master cylinder push rod to short

Well there is my problem then that explains it all thankyou very much. Ed

[Joe M.]

Re: Master cylinder push rod to short

The bracket sometimes bends and can throw off your measurements

[David L.]

Re: Master cylinder push rod to short

Ed,

Here is a photo (on left) of the original 3819077 rod (meas. 4.17" long), 9419815 nut, 3819078 clevis, 3817879 pin, and 3817880 retainer from my 1966 Corvette. Refer to the 1966 AIM (UPC 5, sheet A2).

I also have similar assemblies from a 1963 & 1964 Chevrolet as well as a 1964 Chevy II where the rod and clevis are much longer. I also have a 3812970 rod from a 64 Corvair that measures 4.41" long. See photo on right.

Dave