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Factory disk brakes, upgrade worth while? General recommendations.
Looking to put an old project back on the road. Been off the road for 10 years while finishing college, having kids, moving across country 3 times etc. It is a 72 Supreme and has disk brakes that are presumably factory brakes. Rears are still drums. Does anyone make larger calipers and rotors for a factory disk car or so I need to do a "conversion" kit with new spindles?
Is it really even worth going to bigger calipers and rotors with factory disks as a starting point?
Rear conversion to disk anything I need to be wary of or just grab a low-mid level kit from summit/jegs for a 72 A Body and go? If I remember way back 20 years ago this has an odd rear end. 8.5 ten bolt, but not Chevy C-clip style.
The car is currently running and can move under its own power but before doing much else I want to ensure the brakes are working as good as possible with an end goal of this finally being a bit of a near daily driver "pro-touring" type car. Occasional autocross, maybe a track day on a road course, just for fun, not trying to win or set records.
Long list of **** to do but I think brakes are a logical next step after getting it running and driving. Bigger disks or not, all of the rubber is getting replaced, new fluid, etc. looking to pull the trigger on stuff within two weeks.
Last edited by 72_supreme; March 25th, 2024 at 04:35 PM.
If you're going to autocross and track the car, then better brakes might be worthwhile. If it's gonna be a daily driver, then the factory brakes should be sufficient. Personally, I'd focus on a lot more things other than brakes.
If you're going to autocross and track the car, then better brakes might be worthwhile. If it's gonna be a daily driver, then the factory brakes should be sufficient. Personally, I'd focus on a lot more things other than brakes.
Hey man glad to see you around still. -ozzy4ever on ROP many many years ago.
Daily here in Atlanta is plenty of near panic stops on interstates from 80 to 20mph for no reason and idiots on cell phones so I feel like upgrading the rear drums to disks is almost a necessity. It's upgrading or keeping the factory disk thats the real question. Life's harder with kids, this thing has near zero vacuum from a ridiculous angle cam and horrid brakes when I was single young and dumb. Never thought twice about it.
Ive got a viper to play with if I really want to corner. I just think it'd be fun to do one of the "stage 2" type mail order suspensions and drive the Olds like a kid again, but legally.
How much is a 13" dual piston really going to matter over the stock 11" single on the front I suppose is the question.
Last edited by 72_supreme; March 25th, 2024 at 06:08 PM.
Yep, I’m still kicking around. Good to see another “old timer” still at it.
I had brake issues after the last cam swap. It’s not a really radical cam, but initially the engine had a bouncy 13-ish inches vacuum and the brakes didn’t work well at all. GM HEI distributor was set up with a Moroso HEI Advance Curve kit that replicated the points setup, with 24* mechanical advance so the initial was at 10-12. I experimented a lot and ended up with the original HEI weights and center bar that gave 18* mechanical and set the initial to 18*, then connected the vacuum advance to manifold vacuum. That increased the idle vacuum to a steady 16” which was enough to get the brakes working properly. An added benefit of the increased initial timing was the engine RPM didn’t drop when when turning the AC on. Previously it would go into a death spiral until the RPM dropped so low the engine died.
Anyway, the point is if you can get the vacuum up the power brakes will work much better. The other option is ditch the vacuum booster and go manual brakes. I daily drive mine in Phoenix traffic and I am (almost) as confident with these brakes as I am with “the other” vehicle that has 4 piston Brembos on all four corners.
Last edited by Fun71; March 25th, 2024 at 07:41 PM.
I neglected to say my car has premium Raybestos pads and shoes. D52 semi-metallics up front and I can’t remember the rears. There are more performance oriented pads (and shoes ???) that would enhance the operation of the factory setup.
Yep, I’m still kicking around. Good to see another “old timer” still at it.
I had brake issues after the last cam swap. It’s not a really radical cam, but initially the engine had a bouncy 13-ish inches vacuum and the brakes didn’t work well at all. GM HEI distributor was set up with a Moroso HEI Advance Curve kit that replicated the points setup, with 24* mechanical advance so the initial was at 10-12. I experimented a lot and ended up with the original HEI weights and center bar that gave 18* mechanical and set the initial to 18*, then connected the vacuum advance to manifold vacuum. That increased the idle vacuum to a steady 16” which was enough to get the brakes working properly. An added benefit of the increased initial timing was the engine RPM didn’t drop when when turning the AC on. Previously it would go into a death spiral until the RPM dropped so low the engine died.
Anyway, the point is if you can get the vacuum up the power brakes will work much better. The other option is ditch the vacuum booster and go manual brakes. I daily drive mine in Phoenix traffic and I am as confident with these brakes as I am with “the other” vehicle that has 4 piston Brembos on all four corners.
Vacuum isn't going to be an issue anymore, I sold out to the dark side circa 2012 after smoking some mains on a 455 . Should've stuck with olds and done a turbo stroker. Had a 330 or 425 crank whatever the special sauce recipe was back then, chevy rods, diesel 350 block etc. sold it all and went LS with dreams of turbos, then got married and kids came along, project has sat with crates of parts for 3 point seat belts, vintage air, dynamat, new wiring harness etc. for 10+ years. LS with some minor work should be about 450 and pull good vacuum, which is enough for now. Found the build sheet when swapping out the gas tank for an EFI tank, sitting on top of the factory tank. Stung a bit knowing I sold the original 350 motor and trans when I was a dumb 17 year old kid swapping in the 455 back then.
I think I'll just get the rears converted to disks and leave the factory fronts alone, replace all the old lines and good pads all the way around. I'll save the money from a "big brake" type kit to help cover the badly needed interior refresh.
Last edited by 72_supreme; March 25th, 2024 at 08:24 PM.
If the current brake system will lock up all 4 wheels there isn't stopping to be gained from "stronger/better" brakes. As soon as the wheels transition to sliding friction from rolling friction stronger/more powerful brakes won't help. If you're driving situations are so severe that you are encountering heat fade that is a different story, discs will be less prone to heat fade.
I'd stay with a factory engineered brake system kept in top notch condition.
I'll add to the comments here. As others have pointed out, the braking force to the car depends on much more than just drums or discs. The biggest variable is tire contact friction to the road surface. All the brakes in the world won't do any good if your locked tires are sliding on the pavement. Once that happens, you have zero directional control. Locking the back brakes also causes loss of directional stability, which is why factory disc brake cars carefully set the front/back brake bias based on car weight, weight distribution, tire contact patch, etc. I really have to laugh at people who spend thousands of bucks to install rear disc brakes then throttle them with a prop valve so that they only provide the same braking force as the original drums. But hey, it looks good when you're parked at cruise night.
The first question is, what is the current tire package and how does that provide contact patch to the pavement. The next question is, what is the weight distribution, especially under hard braking when there is weight transfer to the front. As an example of how much this matters, the nose-heavy early Toronados with four wheel drum brakes actually used a prop valve to dial back the rear drums to prevent premature lockup. Once you understand this, THEN worry about what aftermarket brakes you need.
Daily here in Atlanta is plenty of near panic stops on interstates from 80 to 20mph for no reason and idiots on cell phones so I feel like upgrading the rear drums to disks is almost a necessity.
I understand your desire for increased braking to cope with panic stops on the interstate. However, just because you "feel" rear discs are a necessity doesn't make it so. You can expect likely worse performance than rear drums from most kits unless the manufacturer has gone to great pains to sort out the proportioning issues.
Current is 255/60r15 front 275/60r15 drag radials rear. Fairly immediate plans for 275/35r18 front and likely 305/40r18 . Current tires are ancient and radials were about done from quite a few burnouts back in the day, so as soon as this thing is mobile new tires and wheels are a must. Should be plenty of grip to take advantage of better brakes. I have no illlusions of trying to make this antique do anything then brake on par with a normal newer sedan/crossover.. I feel like that is a lot of rotational mass to slow down for brakes originally on a car equipped with 14x7 wheels and a 215 tire.
Weight distribution, while I don't have hard numbers is more rear heavy than stock. Fiberglass bumper, pin-on fiberglass hood, aluminum radiator. It's a swap car, iron block olds 560lbs, current motor, 520 or less. Add it all up probably nearing 200lbs of weight loss off the front end of the car.
I'm all ears to advice from anyone smarter than me on this particular issue, which would be just about everybody. It's basically boiling down to if i'm going to do it, now is the time. I'd rather not spend time and money and rebuild the shoes, bleed the system, etc. just to yank it all of down the road. Trying to put re-do work in the past on this whole thing.
Originally Posted by BangScreech4-4-2
I understand your desire for increased braking to cope with panic stops on the interstate. However, just because you "feel" rear discs are a necessity doesn't make it so. You can expect likely worse performance than rear drums from most kits unless the manufacturer has gone to great pains to sort out the proportioning issues.
I've seen that statement a lot over the years.
Thoughts on just something like this? Could careless about the fancy rotor appearance but seems like all new components, flush the system and get new brake lines on it would get it to at least as good as it was in 1972. Would remove complications and messing with the proportioning valve etc. https://www.summitracing.com/parts/p...331Yfu3D3qEc38
Last edited by 72_supreme; March 26th, 2024 at 10:03 AM.
I did the big brake upgrade on my car along with a wheel & tire upgrade; this was partly because my car started life as a 4-wheel drum car and nothing looks worse than drums peeking out behind 18" rims. You can buy well designed kits from Tobin at Kore3.com but I choose to "build my own" kit and purchased the parts individually. For the fronts I bought the Kore3 caliper mounting brackets used from a guy on Pro-touring.com, the C5 calipers and abutments were bought from Summit Racing on a price-match deal. The rotors are the 12.8" C5 Corvette. A lot of guys go with the 4th gen LS1 Camaro rear discs, but I found a smokin' deal on a very similar 2001 Blazer rear disc set-up. The LS1 Camaro discs are 12" whereas the Blazer discs are only 11.5" in diameter. Maybe the 12" discs woiuld look better through the wheels but the smaller Blazer discs work just fine.
My engine makes good vacuum but I wanted more stopping force than the stock 11" booster could provide so I upgraded to dual 9" booster and 1" master cylinder. My wheel and tire package is 245|45R18 front and 285|40R18 rear on 18x8 and 18x9 wheels. With the larger tire footprint in the rear, I only have the porportioning valve dialed back just a little. I don't have much driving time on the car yet so definitely need do a few panic stops to get the front-rear balance right. I live in Houston, TX where rush-hour traffic often becomes a contact sport; I plan to drive my car as much as the weather will allow so the brake upgrades made sense to me. If I lived in a more rural area I probably wouldn't have been so concerned about stopping power. Here's some pics of my stuff:
Rodney
Kore3 Caliper Bracket.
Not a big fan of the red calipers but couldn't find a good price for the black calipers.
Through the wheel pic.
Blazer rear disc.
Caliper has plenty of room inside the 18" wheel, it may fit inside 15" SSII steel wheels.
Last edited by cdrod; March 27th, 2024 at 12:45 AM.
Don't have much else to offer except to say I put a Power Stop front disc setup on my Dakota truck about 10 years back. Made in China, but at least assembled in USA. Unfortunately the metallurgy of the day wasn't quite there yet -- rotors warped after about 30K miles. Everything else was okay, and they stopped great when they were new.
Thoughts on just something like this? Could careless about the fancy rotor appearance but seems like all new components, flush the system and get new brake lines on it would get it to at least as good as it was in 1972. Would remove complications and messing with the proportioning valve etc. https://www.summitracing.com/parts/p...331Yfu3D3qEc38
This looks like the most sensible option to me.
The extra fade resistance of the premium friction materials and the drilled rotors is a plus.
It's a hairy world of disc brake conversion kits.
I find that most are poorly designed.
In fact, I haven't seen one that was properly designed.
I feel like that is a lot of rotational mass to slow down for brakes originally on a car equipped with 14x7 wheels and a 215 tire.
Just a piece of information - my Jeep Wrangler has 32 x 11.50 tires that weigh around 55 pounds each (how's that for rotational mass) and the factory rear drum brakes that were designed for 215-75-15 tires, and I have no issues driving (and stopping) in Phoenix racetrack traffic. Could it be better? Yes. But I haven't had any issues with daily driving it for the last 20 years.
Just a piece of information - my Jeep Wrangler has 32 x 11.50 tires that weigh around 55 pounds each (how's that for rotational mass) and the factory rear drum brakes that were designed for 215-75-15 tires, and I have no issues driving (and stopping) in Phoenix racetrack traffic. Could it be better? Yes. But I haven't had any issues with daily driving it for the last 20 years.
Right on, I'll just freshen up all the factory stuff. New pads, shoes, drums lines etc. and call it a day. It'll put this thing on the road that much sooner and cheaper. As long as it's better than our 4runner brakes it'll be fine enough.
March 25th, 2024, 04:19 PM
