Cheers all,

after a great summer with my Starfire here in Europe, I am planning & implementing some upgrades. One of them is to convert my brakes to a dual master cylinder setup, as it was recommended by some of you, e.g. @cfair. Thanks much for this hint, I will follow your recommendations!

I ordered the Cadillac master cylinder from Rockauto (M36373), waiting it to get delivered in a week or so. I prefer this one versus the universal ones since it is more slim, has brake line ports towards the engine only and is a direct fit on the original 9" brake booster.Overall, I hope this configuration will give me maximum space towards inner fender and horn relay/battery terminal.

Here my first (bunch of) question(s) related to installing a (Cadillac) dual master cylinder:

• Did anyone make such a conversion to the Cadillac master cylinder already, keeping the stock 9" brake booster and the original drum brakes on all wheels?
• If yes, were there any tricks needed?
• How satisfied are you with the booster support / pedal force?
• Did you experience any issues with brake force distribution between front & rear? If so, what did you do about it? E.g. did you use any fixed or variable brake proportioning valve?
• Also, I would totally appreciate any photos of such a setup

Then, from having driven the car well during this summer with the original single master cylinder setup, I would wish less pedal effort / more booster support. Since also the dual master cylinders feature a bore of 1", I expect pedal travel and force to be identical with the original setup. I also already checked the booster, it keeps the vacuum well and works when engine is running (it's a remanufactured one installed by the previous owner). So I start to think of replacing the brake booster with a 8" dual diaphragm one, still in combination with the Cadillac dual master.

Here my second bunch of questions related to installing a dual diaphragm brake booster with the Cadillac dual master cylinder:

• Did anyone already do such a changeover to a dual diaphragm booster? If yes, which one?
• How is space situation with this configuration in the engine compartment, including brake lines, power steering hoses, inner fender, etc.?
• How satisfied are you with pedal power? Is it fine, or too much/sensitive and potentially to easy to lock the wheels?
• Did you have any issues with the master cylinder pushrod length? What length did you use? Was a proper pushrod included in the master cylinder contents?
• How did you connect the booster lever to the brake pedal? (brake pushrod) Did you buy any special components, or was it even possible to reuse the original pin from the 9" booster?
• Again, all pics you might have I would be happy to study :-)

I know, the questions are quite specific, still I would appreciate any discussion. Anyway, when proceeding with my project, I will report it here with pics in order to give back to the great ClassicOldsmobile community.

See you, Steffen



my original 9" brake booster with the brake pushrod



Master cylinder pushrod

 

Steffen,
Many thanks for tagging me on the post. I’m away from home today, so I can’t take photos, but here are some details which may help. I have 2 such cars configured with the front disk/rear drum set up. Each is a little different. Overall, this is a critical (maybe the most critical) safety system. Cut no corners. Everything has to be very high quality or someone can get hurt or killed.

Some research is required. I believe that GM used a 1 1/8” master cylinder bore for most of their disc/drum (front/rears) system in the early 70’s. It’s been a long time since I did the research so please confirm that independently since my memory may be wrong. What I remember is that the cylinder bore for disk/drum systems is different from drum/drum systems. What I would do is check out recommendations here, then check Pontiac, Buick and Cadillac forums for the most common measurements and go with that. But since you have the Caddy part coming, that may be complete. I really, really like the fact that you chose the engine-side hydraulic output. I had to bash/beat/reshape my driver’s side inner fenders to make the dual master fit since they’re so long. I’d do it your way if I were to do it again.

The thing to look out for with the engine side outlets is heat coming from the exhaust manifold. You might want to put some kind of heat shield between the exhaust manifold and brake lines to keep the fluid cool.

With my convertible, I used an early 80’s clear plastic top master cylinder because I wanted to keep an eye on the fluid level. I believe it came from an 80’s Pontiac Fiero which has a vertical firewall like our 60’s Big Oldsmobiles. Many GM cars through the years don’t have a vertical firewall so the top of the master cylinder leaks since it’s not horizontal. I believe my convertible has an original size brake booster, but I remember finding or repairing these is a pain because they are an unusual size. As you’re learning, a different size one may work, but you may have to experiment with the diameters and depth to get it to work right. My diaphragms are both single to my knowledge, not dual, but dual may work better if it fits. I don’t know.

Also be aware that these boosters can eventually wear out and turn into what seems like an engine vacuum leak, but is really a booster vacuum leak…

You definitely want to get an adjustable proportioning valve, like the ones from Wilwood, to adjust the front/rear braking force. I can’t remember which you want to lock up first, but I mounted my valves with on the driver side frame rail after the brake proportioning value, just under where your left foot would go. Not too far from the emergency brake frame holes. Think about whether you want the **** to face down for easy adjustments, or up so no one messes with it.

If Joe P jumps in on this conversation, do listen. He is almost never wrong on questions like these. If he & I conflict in our answers, go with his.

On the push rod, you may have to go custom on the length, or you may be able to reuse the existing one. I believe you can buy adjustable ones, but I’m not sure. I had my work done by my favorite mechanics who are pros’ unlike amateur me. For a long time I’ve been paying for 90% of safety related work since I have no formal training and what I think are limited skills.

I suspect you have already figured out you will need to switch to 15” wheels. Somewhere around here I have a post on my latest tire/wheel combination for my ‘66 starfire which I like very much.

If I find some pictures in my computer which detail or show my brake setup, I’ll post them here later.

Best of luck. This is one of my favorite modifications to my cars ever. Well worth the effort.

Chris

 

Hi all,

update: My Cadillac master cylinder arrived, I did a mockup today which I want to share with some pics. Since the engine is out of the car currently, I have plenty of space but no secure information if later it will fit. But I believe it will work since the new master cylinder is no big bummer.

@cfair Chris, thanks very much for your comprehensive feedback, this is super valuable input for me. Fully agree with all your comments. Since did an apprenticeship (however at the metric guys over at Mercedes-Benz here in Germany) and then worked for several years as a car mechanic, I do all the stuff on my own. Also, because my office job cannot give the same satisfaction like accomplishing such stuff which I do on the car. I will keep the drum/drum setup since I figured out from your post (and from checking ebay and other marketplaces that it will be super difficult to get suitable parts).

I also checked using a proportioning valve, especially I currently have a small issue that my rear brakes lock up slightly before the front locks up. However I trace this back to my current wheels which are significantly more wide in the rear (245/40R18 on the front, 275/35R20 in the rear). Since I anyway want to replace the wheels with something like 245/65R15 for all four corners, I will now first try without a proportioning valve. I hope that the same tire width will give me factory brake performance again (but of course with the improved safety due to the dual master).

I also decided to be on the safe side and order a new brake booster, for now a 9" single diaphragm, same as factory. Will now wait for the missing parts which I order from the US. This will take about two weeks, then I'll post an update here again (with new booster, brake lines installed and potentially also the engine reinstalled so that the complete mounting situation can be seen).

Cheers, Steffen


Original brake booster with original style single circuit master cylinder on the bench.



Original brake booster with Cadillac dual circuit master cylinder on the bench.



Front view of original single master cylinder in engine compartment (no brake lines attached, only mockup)



Side view of original single master cylinder in engine compartment (no brake lines attached, only mockup)



Front view of Cadillac dual master cylinder in engine compartment (no brake lines attached, only mockup)



45 degree view of Cadillac dual master cylinder in engine compartment (no brake lines attached, only mockup)

 

Hi again,

sharing two pictures below which roughly show the mounting situation of the original single circuit master cylinder. I am positive that the Cadillac master cylinder with its ports towards the engine will work, Just may need to remove aftermarket wire looms from previous owner, and cautiously route power steering hoses and check engine starter harness for good clearance...

CU, Steffen


Original mounting situation of power steering hoses / aftermarket ignition wire looms / original single master cylinder



Original mounting situation (picture 2)

 

I'm not too sure these photos will help, but here's what my '66 Starfire looks like with the dual master cylinder.

Please excuse the home built outside air induction hose.



Hoping this top view will help


Chris

 

Hi @cfair , sorry for the very late answer, but many thanks for the pics! There can never be enough information about the setups of others. Your master cylinder setup looks great!

I needed quite some time to make progress on my installation, since it's also winter here and my Starfire space is not heated. So I took a long break.. But even if now it's also cold, I am already eager for spring and for getting the car on the street again...

Steffen

 

Took me a while and several orders since I decided to go for an universal 8" dual diaphragm master cylinder from Classicindustries. Unfortunately the booster provided several ugly surprises:

• Most of the mounting bolts were metric: Booster to firewall (M6); booster to master cylinder (M8) and booster pin for master cylinder (M5)
• The bolt for the brake pedal clevis was 1/2-20, and the clevis adapter set did not contain a fitting clevis
• The brake booster did not contain a long master cylinder actutation rod, so I had to manufacture one myself

So, I had to make several major changes. See the pics below:


Original 1/2-20 bolt of universal brake booster, too long for Starfire...



Booster taken apart, then I shortened the thread. But still no fit...



This is how I shortened the thread and applied a long nut to extend it with a fitting clevis...



Master cylinder actuation rod, self constructed...



Master cylinder acuation rod, installed.



Mock up installation for bending new brake lines...



Vertical view....



Front view. engine and several other parts are not installed at the moment

 

For reference, the parts I used:

• Dual master cylinder (Cadillac style): MC36373
• Dual diaphragm brake booster: OER PB1083A
• Push rod kit 1: 154235 (from classicindustries, no suitable pedal clevis for Starfire!)
• Push rod kit 2: SUM-760125 (from summit racing, for pedal clevis only)

If you plan to change to a dual master cylinder, I would recommend not to use the universal brake booster but keep the original 9" single-diaphragm one. Only buy the Cadillac master cylinder. This will bolt directly to the factory brake booster, and also the actuation rod has the right length already. You just need to change the brake lines for the dual circuit setup, and bleed it. That's it.

 

Steffan,
Your set up looks great. I would love to drive it to see how it feels - perhaps different from my setup, perhaps not.

Dual master cylinder is obviously safer than the single master cylinder Oldsmobile offered in 1966. Your upgrade is simply better. Well done!

I love your engine-side (not fender-side) brake hoses. I went the other way and don't like it quite as much -- it was painful to bang out the inner fender to make room for my fender-side brake lines. Not clean. With you solution, the risk is that engine exhaust heat boils the brake fluid, but I love the fact that you did not need to bend/massage/reshape the inner fenders like I did. I believe you will not have a problem. If you feel something strange or soft in your brakes after a long drive, consider the heat effects of your driver's exhaust manifold on your engine-side brake lines. It will be fairly simple to fabricate an insulation cover and bolt it to the exhaust manifold or below the brake lines to keep them cool if there is a problem. With luck you will not have a problem.

Thank you for posting your solution whether it is in mm or inches, for the future use of people here.

Cheers
Chris

 

Hi all,

Short update: After having installed the engine today in my car, I finally also could see clearance situation for the master cylinder setup. I am really happy with it, has way enough clearance to the engine and all surrounding components. In two weeks I plan to fire up my engine, then I'll also be able to check the dual diaphragm booster behavior and pedal feel. For now, I attach some pics for reference.

@cfair : Thanks again for your pics, I they were of great help for reference. I think both setups feature the same great level of safety and functionality. Cool!

See you, Steffen

P.S.: Please ignore the wrongly routed starter motor harness, this is already fixed.


Car with installed engine



Booster + dual master



brake line routing detail view 1


Brake line routing detail view 2



Great clearance so far, power steering hoses still to be installed but should not be an issue

 

Hi all,

next update: installed the power steering pump and hoses today. Clearance still very nice. Check the pics...

Cu, Steffen