1951 Super Sedan master cylinder conversion to dual chamber

B

bioposi

Member
Hi All,

I would like to improve the brake system to augment the safety on my Super 1951 Riviera Sedan in moving from the single chamber master cylinder to a dual one and a proportioning valve. This in the objective to separate front and rear brake circuits to still have brake power, should one fails. Apart from that, I plan to keep the rest genuine, being drum-drum.

What would be your part of choice to achieve that for the MC and valve ?

I went to some online supplier but choice is very large and i don't know what would be the best pick.
Thanks in advance for sharing your recommendations.

Bio.
 
Thanks Tom for the information !

Now that you point me at that detail, I'd never figure out that there's no proportional valve in the original setup ... However, as I look for safety, it was also the automatic circuit closure feature in case of a leak of a circuit that I considered.
Ok, even if proportional valve is not required, I assume that I should find the best MC fit for that new application. Maybe you have a recommendation for a model ?
Thanks.
 
Bio, I am answering this not for info on a master replacement, but as a FYI. Why do you think you have to have something to warn you that one side of the braking system is not working??? Isn't a lower than normal brake pedal a BAD sign that something is wrong??? As for the master I can only suggest & give examples. You must use your imagination & fabrication skills to your advantage. I had a customer with a '48 Plymouth Woody Wagon. I won't go into the long story of why. Just that he wanted power brakes & a dual master. Many of the experts said it couldn't be done the way I wanted. A CHALLENGE!!! I ended up using his ORIGINAL master as the support, gutted it. Ran the actuating rod for the NEW master/booster assembly & mounting it reverse of normal. The master was below the floor boards so I added a remote fill for the master.
It's been more than 10yrs. since this has been done & NO problems or associated issues.
I've done a lot of conversions & it's mostly ALL common sense. I would be happy to try & guide you through the process, but you MUST have an open mind & fab skills.


Tom T.
 
Tom,

You're right, there's no reason why a soft pedal would not been enough to see that something goes wrong. I just don't want to feel that once running at high speed on the highway under heavy traffic :D. My basic idea is to duplicate the setup of my '77 Corvette but without the booster and the prop valve. I assume that a dual chamber MC should do the job, having front and rear circuits separated by the dual connections of the master cylinder.

Now I know that numerous cars continues to run perfectly with the original setup and for the time being, I am going to overhaul mine with brand new parts. I was just wondering if such modification would had ever been addressed and how. I still expect to give this setup a try for a potential improvement of safety.

Tom and all, thanks for the support.
 
Way back when I did an upgrade to my '55 Special. It originally had 12"x2" fronts & 12"x1 3/4" rears. What I did was to use a '63 Riviera as a parts car. I swapped over all the riv. stuff to my '55. 12"xx2 1/4" front & 12"x2" rear. This was BEFORE dual masters came about. The brakes were SO much better I couldn't believe it. Even if your system has the same size brakes as the riv. an upgrade would be to the finned aluminum drums with your original brakes if they are the same size. Another upgrade would be to put front drums & shoes on the rears also.
Just more thoughts & combinations.


Tom T.
 
A plan for the dual master cylinder installation on the '51

Well, it took me time but I think I have a plan.

I identified two models of a tandem master cylinder from the Wilwood disc brake company (260-8794 and 260-7563) with the following benefits:
- they are relatively compacts,
- one is shorter in length than the other, as integration should be easier, it would become my best bet,
- they offer remote reservoir capability which will be my setup (to check the level of the fluid),
- the two separated brake line outlets are placed below the body of the master cylinder. There's plenty of space to adapt connections to the car's brake lines,
- they comes with their 3.38"x5/16-24 pushrod.

Plan is to fabricate a bracket to mount the Wilwood MC in place of the original one, connect the pushrod to the car pedal and run two custom-made brake lines from the MC outlets to the brake lines of the car.
I expect to reuse the original tee, as it supports the pressure stop light switch, to connect the two front wheels while plugging the former connection for the rear brake line. Then, adapt and connect the rear brake line directly to the new MC.
Doing this, I should have separated the front and rear circuits (my initial objective) while keeping the genuine stop light switch system.

I have plenty to do on the car before I'll be able to do this but I expect to work on it. For skilled members like we have here, I believe this would not be such a big challenge (but for me, it is :) ).

-Bio
:wavey:
 
I'm working on making a bolt in, firewall mounted brake kit for the 51 Buick. I did it on my 56 and it works great. I plan on using the same idea- remove the firewall driver side cover, have steel cut out from 10 gauge on a plasma table and use a generic $90 GM booster and $50 master cylinder.


Also, you DEFINITELY want a proportioning valve. Splitting the system into front and rear circuits means pressure will now be able to be different. The stock system only works without a proportioning valve because front and back can not have different pressure by design. the different size wheel cylinders effectively acts as a proportioning system. Once you put a modern master cylinder on there, two circuits that have different size wheel cylinders receiving the same volume of fluid will give the rear (smaller diameter) wheel cylinders significantly more pressure. A proportioning valve corrects this. I put 20k miles a year on my buick and I've had several different brake systems so this comes from experience.

Also, drum brakes might have enough stopping power but I've found that under more aggressive or emergency situations they get a little squirmy and inconsistent. if you're changing lanes going 70 and have to slam on your brakes you better have both hands on the wheel. Not to mention you have to get under the car and adjust the shoes way too often. Just my experience.


BhEeiYS.jpg
 
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 ! :hurray:
 
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.
 
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!
 
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.
 
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.
 
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.
 
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