Power vs manual disc
 

So my '66 has power disc front/rear conversion from Master Power Brakes. 9" booster with 1 1/8" master, single piston calipers, EBC green pads all around. Brakes work ok, but its almost impossible to get a wheel lock if needed (front or rear). With marginal vac at 13-14" you have a "one pump" hit on the booster. I've completely flushed, bled and tested pressures (right at 950-1000 psi) and pretty much eliminated any of the components including proportional valve. I don't want to run a vac pump or canister, not in the program. The only thing I still need to do is replace the flexible brake lines that are now 15 years old since replaced.

How many have converted back to a properly setup manual system? How do you like it? I'm thinking lose the booster, change the master & go braided lines all around. This would clean up the firewall not to mention easier valve cover access.

I went with manual 4 wheel disc. With the new style master cylinders it works great. 0 issues, I can lock the brakes no problem. ( don't ask how I know this LOL) I do have braided lines too. I have a CCP master.

This is the link, polished too!
http://www.classicperform.com/NewPro...V-1/MCPV-1.htm

It's 260% lighter also! It weighs less than nothing!

George

That 9" booster does not give a whole lot of assist esp with low vacuum.A 9" DUAL diaphragm booster like the 79-81 TAs give a lot more boost.

If you have 13"of vac, then booster should work ok. Friends car has about 10-11" of vac, no problem, drag races with it.

Another friend had a 67 GTO with factor disc brakes, factory booster; he fitted the later GM floating calipers; brakes were good, but not great.
Then he swapped the 1 1/8"m/c for a 1" m/c & now has great brakes.

I had a '67 lemans with drum brakes, no power assist. I liked the feel of the system xcept for the fading of the drum brakes. On the current GTO (drums) I installed an 11" booster and felt it didn't add much. I'm converting to front disk and not using the booster to see how it feels. The booster really crowds the engine bay at the valve cover and firewall; I'd rather have it open.

george

No issues locking up my manual discs with a 69 Firebird chassis and 1" bore mustang m/c.
I run out of tire grip before braking power.

We re-did the complete manual 4 drum braking system on our '66 Tempest, including wheel cylinders, lines, shoes, drums, springs, everything. I was surprised at just how well it stops and the pedal feel. I can lock them right up when I dynamite the pedal. Haven't done that much highway driving, though.
It seems like there is a new thread every about people being unhappy with their power disc brake conversion. It's got me wondering if I want to do a stock conversion or go with the hydroboost or an aftermarket performance booster. I sure don't want to be disappointed after all that work.

Is there a recommended performance or high quality brake shoe if you wanted to keep its stock with drums?

I have been fighting with my brakes forever...

Started with Manual 4 wheel drums

Converted to 69+ Front Discs w/ 7/8" Wilwood master...... kept it manual , never could lock em up, and just would not brake hard enough in a panic....

Finally gave in and installed a 9" booster, and 1 1/8" Wilwood Master...... brakes much harder now, but still will not lock them up.

I would prefer Manual if I could get the proper braking pressure...... But I am considering Hydroboost also....

I feel your pain...... wish I had an answer....

I'm leaning towards removing booster, swapping all the rubber lines for braided, hawk pads and going manual with 1" bore master. Car was manual to start with so pedal already has hole for correct stroke. This should increase pressure at the calipers with smaller bore by a couple hundred lbs.

I used to run a 1-1/16" bore 2nd-gen F-body manual master and prop valve on my '64 Tempest, stopped great and would lock up the 12" 1978 B-body single-piston discs whenever necessary. I kept the stock 9.5" rear drums.

Moving up now to C6 Z06 Corvette 14" 6-piston and 13.4" 4-piston discs and will be using a 15/16" bore '77 Malibu manual master. Will use the same F-body prop/combo valve (gutted) combined with a Wildwood adjustable prop valve.

How I configured the master and prop valve:http://forums.maxperformanceinc.com/...6&postcount=12

Manual brakes work just fine, they give you great pedal feel and more ability to modulate your braking action.

These guys make some claims. They've been around for some time but I've not seen one review.

http://musclecarbrakes.com/bib6472gto.html

The special matrix shoes & stiffer springs work very well. Have installed 2 pair on each of two local customers early GTO's., which also had nice thick original style brake drums. Have a pair of the special matrix shoes on the rear of my T-37 & am finally installing a pair on the front (after I pulled the concours power disc setup I installed for previous owner). Instead of buying their cry'oed new braked drums, which aren't correct for a higher point restoration correct, I've taken two pair of nice clean thick original '71-72 front drums along with 2 pair of rear drums to local cry'o shop.

There are TWO fundamental OPERATING differences between drum & disc brakes:

[1] Disc brakes require a LOT more line pressure than drum brakes [ the reason that a proportioning valve is used with disc/drum cars, to reduce pressure to rear drums ], all else being equal.

[2] GM type drum brakes have a duo-servo action, where one shoe gets 'wedged' into the drum during braking & this force is transmitted via the star wheel adjuster link into the other shoe. Result is much better braking for the same line pressure & is a 'freebie' you get with drum brakes.

Disc brakes are self adjusting, use less parts & are generally less maintenance.

Think about why trucks/buses still use drum brakes...

Local cry'o shop, huh? Sometimes I'm envious of the depth of resources you guys have down there.

I worked at the Denton, TX Peterbilt truck plant and I know that on the newer generation model Peterbilt and Kenworth heavy trucks they are 95% disc brakes on the front because they were able to get better stopping distances and heat dissipation. There were only a few odd-ball trucks that came down the assembly line with front drums and it was because they were cheaper and the application didn't need the extra stopping distance the discs gave.

I'm planning the brakes for my 69 GTO now. I'm going to go manual with the Corvette 1" bore MC. If the pedal is too stiff I'll find a 7/8 bore MC. The power brakes on my 79 TA were not bad, but never felt like they had great stopping power. Pedal feel was very inconsistent too.

I too am disappointed with the "feel" my 9 inch booster conversion left me with. It will not lock up the front wheels and the feel is very inconsistent. I called tech support from Summit because I bought it from them even though it's a CPP kit and the tech was very straight forward in his answer. He said they use the cheapest pad possible in these kits like even lower grade than basic part store stuff. I put ceramic pads on it and it got better. I haven't had the chance but I'm gonna get some hawk pads and see if it makes a difference

I like my manual disc set up with the 15/16" 1977 Malibu MC and braided lines. Brake feel is excellent - very linear. If I push light I get light braking. If I push hard they lock up. I have 18" vacuum but wanted the simpler system.

Did you do front disc/rear drum? I am starting the process of converting from manual 4 wheel drum to manual front disc/drum. I took the 72 Lemans for a maiden voyage this week, and I think only one wheel had working brakes.

Did you use a prop valve of any kind?

Squidward-
I don't have much advice on going manual disc/drum because I have 4 wheel disc. My 1968 Firebird started out with power 4 drum brakes.. I upgraded to power front disc with GM single piston calipers and 11" rotors off a 1972 Nova. I didn't change the MC or the prop valve and it worked pretty well.
Tom

Thanks Tom. When I did my power disc/drum convo on my FB I went with a factory disc/drum prop valve. I wasn't sure if doing a manual setup would require additional consideration.

Adding another data point to this older discussion:

My drum/drum MC was a POS. It was rusty, crusty, and leaking. I could not get any kind of reasonable pedal pressure.

After doing some reading here and elsewhere, I'm going to try a 1" MC. I have a Raybestos new MC36424 on the way, $36 ride included. It has 1" bore, big reservoir for the front/small for the back, 9/16 fitting for the back, 1/2 for the front. Looks to be a drop-in. Rest of the system is Scarebird front disc, factory drum. We shall see...

Standard celebrity. If you have a part number, that would be cool. I wanted to find max of 1", and not have to flare any tube. Flare nuts are 1/2 and 9/16. Trying to keep it basic.

Yup. The big reservoir for the front (actually nearest the firewall) is 1/2. The rear brake reservoir is 9/16. If this was my FB with a prop/dist block under the mc, I'd flare some tubing. But since this is my Lemans, the block is way down on the frame by the header tube. Yuck. That's why I am trying to work with something available.

I have front disc/rear drum manual brakes in my car which was originally a power brake car. Stops great with no issues, more room under the hood, and less weight. I can't figure out what the big deal is with power brakes.

OCM, what size bore are you running on your m/c? And are you running a combination valve or a proportioning valve plumbed inline to your rear brakes?
Thanks

All stock parts, I'm not road racing.

So all you did was remove the booster? Maybe move the pivot on the brake pedal?

If you can't lock up the system, something is either wrong with it, or it's not well spec'd for the vehicle or what you do with it. People run in to this issue a lot when going to fancy high dollar stuff and wonder why their car doesn't stop well. It's not that the parts are crap, it's more likely that the integration in the system is not where it needs to be, or there's simply a problem that hasn't been addressed.

with 13" of vacuum your boost should work okay. It may be a bit firm, but if the system as a whole was operating correctly, you should be able to lock up the wheels. Your pressure at 950-1000 psi is likely okay for drums, but not really adequate for disc brakes. You really want that to be around 1200 psi. Then you get to the braking pressure you want through changes in piston area, effective rotor radius, pad coefficient and tire rolling radius.

Here's a good calculator that allows you to input the specs for your system, car etc. And it'll tell you what kind of line pressure you need to achieve optimal braking. Remember that although being able to lock the tires gives confidence, it does not produce the most rapid deceleration. That occurs at the point where the tires are on the edge of their coefficient of friction. Most tire manufacturers provide this information on their websites or product catalogs, so you can reference that for the type of tires you're running.

If I had to point in one direction though, I'd say your master cylinder is not sized properly.

Prompt, It was done by the previous owner and according to PHS came with PB

Ok. Thanks.

I bought a CPP disc brake kit mostly for the lifetime warranty and the fact that it uses readily available factory parts. I was pulling 20 inches of vacuum before the motor let go and I still couldn't lock them up. Car was originally a power drum car and it would lock them up but it would also swap ends with you LOL. I have never liked this brake setup and will probably switch to manual or hydroboost when the cars back on the road

OK, here is a question:

I just replaced the manual MC. It has a 1" bore. Front is Scarebird disc, rear is drum.

I am trying to decide what to use for my prop valve. Should I get the full adjustable combo/prop valve, or get a single inline rear valve? I am leaning toward the single inline, like this:
https://www.summitracing.com/parts/sum-g3905/overview/

The existing distribution block is down at the frame on my 72 Lemans near a header tube, so re-plumbing would be a PITA. Any thoughts on if I shouldn't use the single inline?

Thanks.

Does the stock manual 4 wheel drum prop block do any pressure biasing, or is it just routing fluid pressure? I still have the stock distribution block in use, but if I am reading you correctly, putting in an adjustable inline valve to the rear should work to get some good biasing.

Cool, thanks for the edumucation. Single inline rear valve it will be!