1958 Buick Disc Brake Swap
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I've been researching doing a disc brake swap for my 1958 Buick, and this is where I'm starting to collect all of the technical info I've been able to glean. For the rotors and calipers, there are three basic approaches I've learned of plus one that is a research-in-progress, each is detailed below. There are also master cylinder, power brake booster, and proportioning valve concerns - they are listed below as well.

Anyone who hasn't tried to remove the factory master cylinder on manual brake cars or the master cylinder and booster combination on power brake cars hasn't had to deal with the obnoxious 1-3/4" nut under the dash that holds everything together. This page has good details on how to deal with it. Unless you are supremely lucky and yours is not stuck or rusted in place, and you don't have the magic factory tool, you will curse the Buick engineers who designed this way back in circa 1956... It may be keep the kids out of earshot when doing this job... You have been warned. :-)


Kit from Scarebird Mechanical

I stumbled across this place at a local swap meet and talked a good bit with the owner who is a very nice fellow. They have a decent website up with details - check out http://www.scarebird.com/ and they have their kits on eBay as well. The kit includes a custom caliper mounting bracket plus details on specific rotors, calipers, pads, and brake hoses to use. This kit does not require welding. The cost is currently $165 + shipping and appears to include any shipping fees.

The original approach they used was to use a custom caliper bracket with later model GM calipers and a set of rear brake style rotors that slips over studs mounted to your original drum brake hub. You drill out the rivets that mount the drum to the hub, mount modern style studs in the hub, and slip the rear brake rotor over the studs, just like you would do on a rear brake car. You may need to machine the hub once to get the rotor to fit over it and sit properly, but other than that one-time machining job, everything is a bolt on.

At some point, they switched their kits to using later model one piece hubs + rotors with modern roller bearings. For the 1958 Buicks they use a 1971-1976 Buick full size or Riviera rotors/hubs + bearings + calipers. The folks at Scarebird also provided me a copy of the installation instructions as a Word document. That document contains the full parts list needed to complete the swap. Their kit has pre-welded caliper brackets, and that changes things significantly from the original research I did.

Here's a picture of the caliper mounting bracket for the current kits provided courtesy of the folks at Scarebird.

Scarebird1958BuickCaliperMountingBracket.jpg (113309 bytes)



Kit from Mike Pemberton

I originally hadn't found a website for this, but Mike had posted various details online and I've emailed him a bunch for details, as well as talked to him on the phone, and he is a nice fellow. Various websites I found with Google listed his contact information - I was searching on "mike pemberton disc", "mike pemberton brake", etc. to find out more about this. The best details I found were here. I emailed him and talked to him a bit, and out of the conversation, I ended up creating and hosting a website for him - check out Disc Brake Mike for all the details. His kit includes a custom caliper bracket, plus details on specific rotors, calipers, and brake hoses to use. This kit does require welding - the caliper brackets need to be bolted up, final fitted, and welded together. The cost is currently $195 + shipping.

In this case, Mike has found a specific single piece rotor and hub setup that will work on the original spindle, and it appears no machining is required. This is good because it allows you to convert to the more modern roller bearings in place of the older (and hard to find) ball bearings. He has good coverage on various years in this era for Buicks and Oldsmobiles. Not only have I gotten one of his kits (which is yet to be installed), I liked his business enough to make him a website! :-)


I've received some email from Joe Braun who read this  page and was in the process of installing Mike Pemberton's kit plus a custom dual master cylinder and power brake booster setup on his 1957 Buick. Joe was kind enough to give me details about the swap and take a few pictures which he has graciously allowed me to post here. The photos of the master cylinder work are below. He did mention that he ended up using different hoses than what was specified because the original ones were too short in his application. He said late 70's Chevette front brake hoses were a bit longer and worked out well for him.

Joe says that the calipers and rotors went on quite easily with this kit and has high praise for the kit.

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Kit from RRS

I found this while searching about online a while ago and they used to have a decent web page about this conversion up at http://www.rrs-online.com/html/buick_discs.htm, but it's gone now. Unfortunately, it appears they have stopped selling this kit and the company has focused on early Mustang/Falcon and other Ford parts instead. Their kit had claimed 1961 and up, but I had seen reports that this kit will fit back to 1957. The kit was pretty expensive, and was shipped from Australia, but it was also the most complete of all the options. It included the caliper brackets, calipers, pads, hoses, custom machined rotors, and all hardware to complete the conversion. This kit did not require welding. The cost was $1875 and included shipping.

The only potential hitch here was the custom machined rotors. They are a wear item, and will need to be replaced eventually. Having to order new rotors all the way from Australia was a bit of a disincentive for me, and so was the price.



I found this info through a friend who was contemplating creating a kit. He claimed that the front rotors from a 1969-1978 Cadillac Eldorado or Oldsmobile Toronado (Hollander interchange #1298) and calipers for the same (Hollander interchange #177), and a custom caliper mounting bracket would get the job done. It appears many GM's of th1 19050's, 1960's, and 1970's used the same basic dimensions for their spindles (for drum or disc), so it's entirely possible that many different GM rotors and calipers will physically fit onto the original spindles. All of these would need a custom caliper bracket made, and that's the part that is hard to engineer and make yourself.


Kit Comparisons

Rotor Size

It looks like the Scarebird kit ended up with an 11" rotor, and the RRS and Mike Pemberton kits end up with a 12" rotor.

If you want a more powerful braking system that can take more abuse and stop better, going with a 12" rotor could be worth it. For me, I won't be road racing my 1958 Special, but the added braking power in a panic stop is nice to have. Your interests and mileage may vary, though, and I wanted to mention it here. For example, the later model Riv's are much heavier than my Special, and if you do any spirited driving in one of them, you may very well require the added braking power that a 12" rotor provides.


It looks like Scarebird is the cheapest, followed by Mike Pemberton, followed by the (now defunct) RRS kit. Mike's kit seems to offer the best balance overall of price vs. performance, and Mike is a car enthusiast just like the rest of us, so I really like to support that.

Part Scarebird Mike Pemberton RRS
Source Cost Source Cost Source Cost
Caliper Mounting Bracket Kit $165.00 Kit $195.00


Caliper Mounting Bracket Hardware Kit $ Kit $ Kit
Rotor Donor Vehicle $ Donor Vehicle $ Custom
Hub Integral w/ Rotor n/a Integral w/ Rotor n/a Included
Caliper Donor Vehicle $ Donor Vehicle $ 2004 Pontiac GTO
Caliper Mounting Hardware Donor Vehicle $ Donor Vehicle $ 2004 Pontiac GTO
Pads Donor Vehicle $ Donor Vehicle $ 2004 Pontiac GTO
Machine Work None? $ None? n/a Included
Brake Flex Hose Donor Vehicle $ Donor Vehicle $ Included
Brake Flex Hose Mounting Hardware, etc. Various $ Various $ Included
Inner Wheel Bearing Donor Vehicle n/a   $    
Outer Wheel Bearing Donor Vehicle n/a   $    
Bearing Seals Donor Vehicle n/a   $    
Total $ $ $1875.00


Both the Scarebird and Mike Pemberton kits use factory style single piston floating calipers from a 1970's era GM. The RRS kit used a dual piston floating caliper from a 2004 Pontiac GTO. In terms of performance, the 2004 Pontiac GTO caliper likely gets the edge, though I'd be skeptical if most folks will ever notice the difference. And it's no longer being sold, so it's not an option.



Master Cylinder and Power Brake Booster

This swap generally requires the use a modern dual reservoir master cylinder and power brake booster arrangement, which in turn requires custom brackets to mount it to the firewall. Some folks say you can get away with running the original single master cylinder, but I think that's playing with fire. You really have to keep an eye on the fluid level and add more fluid as the pads wear - disc brakes consume much more fluid behind the pistons in the calipers as the pads wear - and that's easy to forget and leave yourself with no brakes.

I believe all of the later model GM power brake boosters and master cylinders use a common mounting pattern, so fabricating mounts for one will suffice for all of them. This is important because the simple first step would be to convert to a modern dual reservoir master cylinder and power brake booster setup for drum brakes, and then to later convert to a disc brake setup, this focusing attention on one simple piece at a time. It also helps that I happen to have a complete master cylinder and brake booster setup sitting around from both a 1970 Electra with 4 wheel drum brakes and a 1973 Electra with front disc brakes and rear drum brakes, so I can afford to do this one piece at a time to verify what works and what doesn't. :-)


I've received some email from Joe Braun who read this page and was in the process of installing Mike Pemberton's kit plus a custom dual master cylinder and power brake booster setup on his 1957 Buick. Joe was kind enough to give me details about the swap and take a few pictures which he has graciously allowed me to post here. The photos of the rotor and caliper work are above.

Joe opted to remove the air plenum entirely in his conversion and replace it with a flat piece of 16 gauge steel cut to be the same size and dimensions as the base of the air plenum. Joe said that in his case, the original 1957 Buick master cylinder refused to come off until a Sawzall was used on it, so salvaging anything from the original mounting was not possible. He took this opportunity to create a custom access hole in the firewall to get at the power brake booster mounting bolts from the interior side. (I gotta hand it to him for taking the lemons life handed him and making lemonade! :-)

I would be a bit concerned about the 16 gauge metal flexing under heavy braking, but Joe said it's working fine for him so far. I've heard horror stories about fatigue cracking the firewall over time in disc brake conversions on early Mustangs, especially power brake conversions, so I'm really leery of how the power booster is installed. In later GM models, the factory tied the booster mounting directly into the brake pedal support assembly (which also holds up the steering column), and they became one large assembly with the firewall sandwiched in between the booster and the pedal support bracket. The firewall could not flex independently of the brake pedal bracket flexing or moving in relation to the firewall, an unlikely occurrence.

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Below are some scans of the notes I made on booster dimensions and how to build a custom adaptor plate to mount a later model power brake booster in the original location. I used a 1969 Riviera booster as the basis for my "later model" booster dimensions. The one possible hitch here seems to be the need for the very long pushrod for this to work. Some boosters have a threaded end on the pushrod to allow for adjustability, and I can use that to add an extension to the pushrod. The problem is that none of the Buick boosters I have laying around use the threaded end. My Suburban appears to have a booster that uses the threaded end on the pushrod, but it uses some very tall brackets to allow the booster to "stand off" the firewall to clear some things. I need the threaded pushrod end without any standoff brackets. It looks like I'll have to do some parts hunting to find one that will work right. Master Power Brakes makes aftermarket units that look good for this, but they are brand new and thus much more expensive than a remanufactured unit at the parts store - $200+ vs. $80-$100.

I compared my pictures and notes to what Joe Braun did for his 1957 Buick, and it appears that on the 1958 Buick there is much more room and that extra room makes it look like it's possible to do this without removing the original plenum as Joe did. I haven't tried it yet, so it may or may not work, but so far the planning looks favorable to not having to modify the actual firewall. If the plenum turned out to be too thick to make this work, my next ideas were to mount the booster right to the adaptor plate (and drill holes in the plenum to make it work) and thus gain another 1" to 1.5" of clearance. If that wasn't enough, next up would be to create a "recess" in the plenum that would allow the booster to sit back further - all the way to making it flush against the firewall behind the plenum if need be. This would still provide a way for some air to flow into the plenum and thus into the car for ventilation. I would still need the adaptor plate, and I would have to modify the plenum extensively, but I do have a "spare" plenum laying around so this isn't such a bad thing for me. This might not gain me much clearance, but then again, it might be "just enough" to make this work if space turns out to be really tight.

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Hydroboost Brake Booster

This is a a new idea I'm messing around with to see if it will work. Many GM trucks, especially newer ones, came with what is known as a "Hydroboost" brake booster instead of a more traditional vacuum operated brake booster. The hydroboost units use hydraulic power from the power steering pump to provide the extra braking boost. They are smaller in most dimensions than a vacuum booster, though they might be a bit longer than some vacuum boosters. They mount to their mounting plate with a single large nut, which is a possibly large advantage for this conversion - if that nut will fit into the existing triangular opening in the plenum on the '58, and I can make a custom mounting plate for it, and I can somehow create an extended mount with a nut on the end, much like was done on the original 1958 brake booster, then this could work out reasonably well without any cutting of the factory parts being required. I'm trying to get a junkyard Hydroboost unit out of an 1990's Astro van (or the like) to compare to the 1958 parts I have sitting in the garage to see what might work here.

The Hydroboost units use a standard GM master cylinder, so there are no issues there.

There is the issue of running more hydraulic hoses and using the original power steering pump in a way it was not really intended, but it could work. I've seen lots of folks say that the Hydroboost units should use ATF instead of power steering fluid, and the 1958 power steering system uses Type A ATF fluid, which has been (more or less) superseded by later Dextron ATF fluids. That means that I should be able to use Dextron ATF in the existing power steering system, and it should be compatible with the later model Hydroboost system. I would have to modify the hydraulic lines, but I can save the originals and make up new lines "just in case" I ever want to return the car to stock condition.

Here's a quick diagram I whipped up showing how the plumbing needs to be set up for the hydroboost brake booster. Basically, you run the high pressure hose from the power steering pump to the hydroboost unit first, then to the power steering gear like normal. Then, you run the low pressure return line form the hydroboost unit to a T-fitting in the original return line. If there is a cooler for the power steering gear, you do not run the return line for the hydroboost through it - there simply isn't enough work being done by the power steering fluid in the hydroboost unit for it to build any massive amount of heat that needs to be removed by a cooler, and any extra backpressure in the return line (which a cooler can cause) can cause problems with how the hydroboost unit operates.

 HydroBoostPlumbingDiagram.png (15389 bytes)


Proportioning Valve, Metering Valve, and Warning Light

First up, some terms. A factory non-adjustable unit is what most folks are familiar with, and it is more correctly called a combination valve. Why is it a "combination" valve? Because it does multiple things all in one combination unit, of course! Each function is named and detailed below. I found a good description of a typical GM combination valve on this page and on this other page. They discuss how to "gut" a factory non-adjustable proportioning valve and allow adding an aftermarket adjustable valve in-line after the combination valve, but the basic descriptions and pictures are pretty good to understand the different parts of the combination valve. After all, if you want to modify it, you better know what part of the thing to modify, right? I also found a PowerPoint slide deck explaining a bunch of this.

  • It's a proportioning valve for the rear brakes. This reduces hydraulic pressure to the rear brakes relative to the front brakes as the brakes are applied. Why? If the rear brakes lock up first in a panic stop, you'll swap ends very easily. That's bad. This is the important one and in the real world of swapping parts you pretty much always want this functionality to be present. See this page for more information. On a factory combination valve, this will usually be part of the outlet fitting assembly to the rear brake lines, though I've also seen it mounted inline after the combination valve in some cases.
  • It's a metering valve for the front brakes when you have a disc/drum combination; also known as a "hold off" valve. This delays application of the front disc brakes a fraction of a second to let the rear drum brakes catch up on low pressure brake applications. Why? Drum brakes are a tad slower to activate, and on small brake applications, especially on slippery surfaces, this prevents the front brakes from being "grabby" and locking up easily. See this page for more information. On a factory combination valve, this will usually be part of the outlet fitting assembly to the front brake lines; sometimes in a funky way, but it's usually there. On some models, particularly earlier disc brake equipped models, it's a separate part mounted after the combination valve.
  • It's a differential pressure switch for the brake warning light. A small internal valve senses when there is a large pressure difference in the front and rear brake lines - such as when one of them has developed a massive leak and is running out of fluid. When this happens, the switch activates and grounds the electrical contact for the switch. This is wired so that the "brake" warning light on the dash comes on to tell the driver "stop now, your brakes are 50% fubared!". The switch is usually self-resetting after the brakes have been applied with equal pressure front and rear. Fix the problem, step on the brakes, and if the light goes out, it's happy again. This is generally in the center section of the combination valve and it has the electrical connector on top of it.
  • It's usually also a distribution block for the front brake lines - one input connection, two output connections. Sometimes the factory will use a separate distribution block, though, and in that case it's one input connection, one output connection.

Here's a cut-away diagram of a typical GM combination valve with labels and explanations. This is taken from a 1972 Buick Chassis Service Manual, so all the credit goes to GM and not me.

GMCombinationValve.jpg (530112 bytes)

You need to be careful in understanding what folks mean when they say "proportioning valve". If they are talking about a factory non-adjustable unit, they usually mean "combination valve", and if they are talking about an aftermarket adjustable unit, they usually mean "proportioning valve". But, not always - there is some unusual and creative stuff out there on the market, so make sure you are talking about the right things.

Some folks say a proportioning valve is not needed, but that's pretty much dead wrong in any normal installation you're going to run into in a hot rod or custom application. Sure, if every component was perfectly balanced against each other, right down to the tire size and stickiness of the rubber compounds in the tires, you wouldn't need one. However, welcome to the real world of custom hot rodding where you're mixing and matching stuff together in ways never thought of by the factory engineers. You need a proportioning valve. But what one? An adjustable unit would be the best choice for performance driving, but a factory style "fixed"/non-adjustable unit will work as well for most cases. Basically, pick what you need based on your driving habits/needs/desires. Whatever the choice, it should be reasonably obvious that the plumbing between the master cylinder and the proportioning valve would need to be custom bent and flared hard-line. This is a custom install, after all! Also, if you add an adjustable unit and you manage to get the rest of the system well balanced, you may end up adjusting the valve "wide open". That's a good thing - it means you got really lucky, or that you designed your mis-mash of parts to work well together. I found a really good page explaining why in a perfect system, you shouldn't need a proportioning valve. There is also a previous page to go with that giving more background information. The guy is right in theory, but in practice of swapping parts and using things that may not be well matched but are "close enough", a proportioning valve is pretty much going to always be needed. I also found this page, which explains why you need things to be balanced properly; this is a good background primer on your braking system and how it works "in the real world".

One thing I really like about the factory non-adjustable style proportioning valves is that they are pretty much all equipped with a warning light. That adds the ability to hook up the existing parking brake warning light just like a later-model car, with only a one-wire hookup. After all, if half of the braking system fails, you really want to know about it right away via a big red light coming on inside the car. I like that for things my wife (or someday, daughter!) might drive. And in the Buick's around 1958, the brake pedal has a funky bell crank arrangement that makes the pedal sit very low to the floor, and that makes it really hard to tell if the brakes are "going away", so it's even worse. So, to all you die hard car guys that say "ditch the warning light, we're smart enough to know if the brakes feel mushy!", all I have to say is "Not only no, but HELL NO." And if you ever plan to sell your car, better hope the next idiot doesn't have a lawyer if the brakes fail... Anyways, I've heard that there are a few aftermarket adjustable units that have the warning light switch feature, but I can't get clear info on this right now. If they are out there, they are likely pricey, and frankly most folks are not going to be pushing their car that hard. You may also be able to get a factory-style combination valve that does not have the proportioning valve in it (harder to find, but I hear they are out there). You can also simply take a "normal" factory-style combination valve apart and remove the springs and such that form the proportioning valve part of the assembly - basically, "gut the factory proportioning valve". You can refer to this page and on this other page that were mentioned above for some info on gutting the proportioning valve part of a factory combination valve. If you do that, then you can mount an aftermarket adjustable valve in the rear brake line after the modified combination valve. That's more plumbing to do, but not hard. I'm going with a factory non-adjustable combination valve to start with, and maybe add in the modified combination valve and aftermarket adjustable valve later on. We'll see how creative I want to get. The factory style combination valve is needed either way, so I'll start there.

For mounting, there are many simple brackets and plumbing kits to mount the factory style combination valve directly under the master cylinder using a small bracket mounted to the master cylinder mounting bolts. That keeps it out of the way, and uses what would otherwise be "dead space" under the master cylinder. It also saves drilling new holes in the frame and/or inner fender to mount it. I like not drilling new holes in my classic; it keeps the ability to return it to stock in the future, which a future buyer might want. Some cars I might not car about that; but for this one, I do. So, under the new master cylinder is the place for the combination valve on my conversion.

If I decide to add an aftermarket combination valve, I'll just fab up some more bracketry under the master cylinder to hold it. As far as the plumbing is concerned, it's basically a funky looking union in the line, and I'm going to need one of those in the rear brake line anyway... Hmm... That's not a bad idea...


Brake Line Plumbing

All this new stuff needs some changes in the brake lines. No matter what options I go with, they're going to be pretty much the same.

  •  New brake hoses for the front calipers. Re-use the original hard line mounting points and hook them up to the new calipers. With luck, it'll all Just Work(tm) when the time comes to do this work. If not, I'll post details about what needs doing.
  •  Separate the front and rear brakes at the factory distribution block. I'll do this by removing the rear brake line from the factory distribution block and plugging that outlet in the factory distribution block with a brass plug. I need to figure out the thread size and note it here. With any luck the rear brake lines will not break when I try to remove it from the distribution block. If the feeder line from the original master cylinder snaps, that's not the end of the world as that will be replaced with all new pieces.
  •  Hook up the front brakes from the new proportioning valve to the original inlet on the factory distribution block. Simple, easy, and it will be a relatively short piece of brake line.
  •  Hook up the rear brakes from the new proportioning valve to the factory rear brake line that used to connect to the factory distribution block. As with the front brake lines, this will be a relatively short piece of brake line, but this one will need a union to hook things up. The rear brake line may need to be carefully bent out of the way so I can hook up the new line from the proportioning valve, though I'll need to be careful about tweaking on the old and possibly brittle factory lines. Instead of using a union here, I may use an aftermarket adjustable proportioning valve; if so, I'll also gut the proportioning valve part of the combination valve...



When I do this, I'll need to take pictures.

Comments? Kudos? Got some parts you'd like to buy/sell/barter/swap? Nasty comments about my web page so far? You can email Mike or Debbie.

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Page last updated 04/17/2011 04:13:36 PM