1951 Super Sedan master cylinder conversion to dual chamber

[bioposi]

Hi, Jacob,

Thank you for your experience feedback, you saved me from a newbie mistake.

Now I understand why there was no proportioning valve in the original design. The shop manual refers to an unbalanced brake power in favor of the front wheels. Buick's engineer did a great work as they built this by design. It is key to understand how it works and how a hack can change the car behaviour on the road.

So, I'll have to add a proportioning valve to the rear circuit, so the rear braking power can be adjusted.

Many thanks !

[telriv]

If you use the PROPER drum/drum master cylinder I still say NO proportioning valve is needed. I've ALSO done plenty of these type conversions. YOU NEED THE PROPER M/C NOT A DISC M/C. Using a disc M/C is usually where you run into the most problems. Like I mentioned previously if you use the larger width shoes front & rear it will almost feel like power brakes WITHOUT the power assist.
Just my thoughts.


Tom T.

[bioposi]

Hi Tom,

I understand and agree to your statement. The Wilwood MCs I selected applies to 'actuate four wheel or dual caliper axle brake systems'. Not being a native English speaker, I am not sure to fully capture what this statement means. I retained these models because I felt I could adapt them to my project.
It is not clear to me what are their correct field of application, maybe you could help me on this ?

I believe that the 53/47 braking power ratio between front and rear has to be kept to secure the behaviour of the car. Once separated with the Wilwood dual MC, adding a proportioning valve on the rear circuit should help at this while keeping the stock brake system. Worst case, maybe it could be left wide open, like if there was no valve at all ?

Thanks for your help!

[LONG]

on my 52 special I stole the shoes and drums from my 50 super parts car. If I remember correct, the 52 special had 1-3/4" shoes and the 50 Super had 2" shoes. on my car this seems to have made a big difference.

[telriv]

Keeping that ratio your talking about has been designed in by Buick with smaller wheel cylinders & brake shoes. In all honesty I feel/think the ratio is actually higher because there is MUCH more weight up front. When you step on the brakes kinda hard the rear has a tendency to rise up which REMOVES weight from the rear. This is why the rear brakes have more of a tendency to lock up. Now if you installed larger wheel cylinders OR brake shoes or both in the rear I would say to add the valve. You could add the rear adjustable valve & if there is NO problem you have the option of opening it ALL the way keeping the stock performance. If NOT you can adjust it down. While you have the system open it wouldn't hurt to JUST add it.
Again, just my thoughts for the subject at hand.


Tom T.

[bioposi]

Hi all,

The car has still the stock brake drums and shoes currently. I just replaced the original master and wheel cylinders by new components, so still compliant with the genuine specs. The Wilwood MCs has the same 1" bore size and 1.1" stroke, I assume that the pressure power they have will be equivalent to the original MC.

[telriv]

If the original M/C bore is 1" then ALL should be OK>