parts help please - 68 w/ manual disc brakes

[68bowtie]

i've been searching on the forum, but i can't find all the details i need. so i'm hoping you guys can get me pointed in the right direction on which parts to buy.

the boring background... 68 c10 with 5-lug drive train. new factory 71-72 front disc brakes and original 12-bolt rear drums. it's got an old booster setup that i assume is from the same 71-72 donor but not sure. the brake lines are in pretty rough shape so i am looking to buy all new brake lines. while i'm at it (yes the notorious slippery slope), i plan on replacing the master as well.

i've read some posts on here that it's possible/safe to go manual disc/drum or disc/disc with no booster. i like the idea of cleaning up the engine bay so i'd like to go that route. i'd like to buy a master, prop valve, and all new brake lines that will be suitable for the disc/drum setup i have now, and ideally the parts i buy now would still work if i upgrade to rear discs later. if i have to swap the prop valve at that point that's no big deal, but i'd like the master and brake lines to work either way if it's possible.

any first hand advice you guys have (or suggested part numbers) would be appreciated. i've been shopping around for parts and it's VERY overwhelming. from what i've read, i believe i need 3/16" brake lines all around, and a 1" master. are there other criteria to look out for besides brake line diameter and master plunger size? i have no idea what to look for in a prop valve.

[SS Tim]

For what it is worth Chevy built the base 71-72 C/10s without power brakes. The J70 booster was optional but also required with some options like any of these: A/C, P/S, 402 BBC, Aux Battery, Step Bumper, Four Speed Trans and more.

IMHO, based on your signature, you should have power brakes if running factory disc brakes. To delete a booster just to clean things up doesn't make much sense to me nor sound too safe in today's driving enviroment full of inattentive idiots with ABS.

[Rickysnickers]

I would also suggest running a power booster of some sort. There are others that are more learned than I am, but this is just my opinion. 3/16" brake line is perfect. If you are thinking about rear discs as a future upgrade, I would do it now while you are getting your parts together. The reason being, if you run a disc/drum now and convert to disc/disc, then you will most likely want to change out the prop. valve. They are designed to be disc/drum or disc/disc.

FWIW, I would suggest that you get you full disc system and run a 7/8" Wilwood master with an 8" dual diaphragm power booster. You should be all set with that.

[68bowtie]

no question #1 goal is safety. that's why brakes are one of the first things i'm tackling. but if i can delete the booster and have a safe/functional system i would like to.

my truck was factory a/c big block with manual drum/drum brakes. i would think manual disc/drum would be better (with a correctly designed system). i've read several individuals on this site have had good experiences with this setup, but i'm just not sure the exact parts combinations they had. for example for it to work properly do i need big fancy brakes, which require big fancy wheels (not the route i'm going). hoping for some first hand experience, and i may give it a shot. if i don't like the results i can always add the booster. i appreciate all kinds of feedback.

[68bowtie]

Originally Posted by Rickysnickers

I would also suggest running a power booster of some sort. There are others that are more learned than I am, but this is just my opinion. 3/16" brake line is perfect. If you are thinking about rear discs as a future upgrade, I would do it now while you are getting your parts together. The reason being, if you run a disc/drum now and convert to disc/disc, then you will most likely want to change out the prop. valve. They are designed to be disc/drum or disc/disc.

FWIW, I would suggest that you get you full disc system and run a 7/8" Wilwood master with an 8" dual diaphragm power booster. You should be all set with that.

thanks, that's helpful. i think the rear discs will not happen now due to funds. with disc/drum would you still recommend the same 7/8" and 8"?

[kehstr]

Originally Posted by SS Tim

To delete a booster just to clean things up doesn't make much sense to me nor sound too safe in today's driving environment full of inattentive idiots with ABS.

That just want to sit and text on their phone, and don't pay attention to what is going on around them

[midniteblues]

my 67 and my kids 67 both run manual disc/drum.
they both have a 71-2 5 lug swap front and rear.
71-72 had slightly bigger rear breaks than 67-70.
All parts were store bought locally(for ease of replacement).

The manual disc/drum set up works damn well in my opinion.

Now if your building to haul and tow I would certainly use power breaks. I don't like that huge Booster in my k20 but it's gonna stay.

[SS Tim]

Originally Posted by 68bowtie

...my truck was factory a/c big block with manual drum/drum brakes. i would think manual disc/drum would be better (with a correctly designed system)...

Understand your truck didn't have a booster originally. The J70 booster was not required at the time with any specific option during the 68 MY that I can find. However many were dealer installed with a simple GM kit.

However I would simply like to point out that the 71-72 power disc requirements were GM blanket to meet then design and performance standards.

Some people may find the unboosted performance acceptable even with a heavy or forward bias option load. However one would have to ask, does the entire family of drivers feel the same and will they be as safe?

Finally there is a mechanical advantage inherent with the drum brake design that increases their effectiveness that disc brakes do not have. They are simply fixed ratio hydraulic clamps.

[Rickysnickers]

Originally Posted by 68bowtie

thanks, that's helpful. i think the rear discs will not happen now due to funds. with disc/drum would you still recommend the same 7/8" and 8"?

Well, I will qualify that by saying that I have four wheel disc on my truck, 1957. It has a 7/8" Wilwood master and power booster. You may want to look into what size would be best for a disc/drum combo. I attached a couple of web pages for you.

If you want to stay manual w/the disc-drum set up then it seems the best bet would most likely be a 1" bore master cylinder and then use a disc/drum prop valve and you should be all set.

http://www.wilwood.com/TechTip/TechFaqs.aspx

http://www.markwilliams.com/braketech.aspx

http://www.mbmbrakeboosters.com/inde...ters&Itemid=10

[Mike C]

My thoughts on master cylinders for a driver is to use what GM used. If you want to go manual disc, get a 71-72 manual disc master. Same on power. If you go 4 wheel disc, then I would run a mid 70's Corvette 4 wheel disc master and prop valve.

[68Gold/white]

I believe that the attachment points (on the brake pedal arm)for the booster pushrod or the m/cyl rod (on manual brakes) is different. The manual brakes needing more leverage because there's more effort (as in from your leg!) for manual brakes, the booster obviously needs less effort, and might even be touchier if the push rod is mounted to the same place as manual brakes.

My 67 came w/ manual drum brakes, and my 68 came w/ power brakes, I plan to check the 67 soon to verify. I don't know if all the brake pedals had 2 holes drilled in them, for manual or power brakes...
If so, the manual brake push rod would be closer (as in higher) to the pivot point to get better leverage.

I plan to convert both my 67 and 68 to manual disc (5lug) when they get back on the road.

In my opinion, rear disc is not needed, it IS a better deal, but just having factory front disc brakes is 1000% better brakes, period!!!

If there's something better about drum brakes, I am clueless as to what it is. Drum brakes fade faster, need adjustment, even with automatic adjusters, wear fast, especially on the front, and can be a doozy to get stopped when wet. No worries about these issues with disc brakes...

[fwayne]

Regarding the bore size of the Master Cylinder. All things equal, a 1" MC will offer less brake pressure compared to driver effort than a 7/8". It's basic physics. When you compress Hydraulic Fluid It's the ratio of the input vs output. The smaller in diameter the input, the higher the pressure, but the tradeoff is the lower the volume for a given pedal travel.

So...Manual brakes tend to have smaller diameter Master Cylinders, while boosted versions can afford the larger version. Using the smaller diameter will require less pedal effort, but consequently more pedal travel. So go 7/8" for manual, 1" for boosted.

If you get it backward, you'll have a rock hard pedal, brakes will come on quickly but you'll have to stand on them to stop. If you get it backward in a boosted setup the pedal will be mushy or even hit the floor before brakes work.
Be careful matching to aftermarket calipers, they can vary wildly on caliper piston size or number of pistons, the ratio can get out of whack very easy.

[68bowtie]

this is excellent info, thanks everyone for the input. i'm not sure exactly what parts i'm going to use, but i will be doing a manual disc/drum setup, as close to factory specs as i can get with all the parts. 3/16" brake lines, disc/drum prop valve, and something around 7/8" to 15/16" master.