Hi everyone! I look forward to sharing pics, pitfalls and advice as I navigate through restoring my new baby, a '70 98 Holiday Sedan. 455, power everything, and the brakes that I'm sure we're the reason for the low price, lol. I'll be looking for a 4 wheel disc option utilizing the smaller 5x4.75 bolt pattern, so recommendations are welcome and my process will be shared.

This is a labor of love for me as this is a car I've wanted for many years, bringing back memories associated with it from when my my mom had one when I was a kid.

 

Welcome. Why are you looking for the 4.75" bolt pattern? As I'm sure you are aware, your Ninety Eight uses the 5x5 bolt pattern. What exactly is your problem?

 

Welcome to the site.

 

Hey Joe! My brakes are toast all around. Bad rotors, calipers, wheel cylinders, shoes, lines, etc. I want to add discs to the rear and give it all new parts all around. I intend to drive this car a LOT. I have a few sets of very nice wheels in 5x4.75 and one set in particular that I'm in love with but I'd never spend the money on them new with tires (got them used for $350 but they'd cost $2k to replace, more than I paid for the car). I know that may sound like a silly reason, but I just want to have the more common size on the car. And all new components.

 

Also since sourcing original brake parts is such a headache...

 

You're right. That's a really BAD reason to change the bolt pattern. These are heavy cars and the large bolt pattern is there for a reason. I just got Torque Thrust Originals for my 67 Delta in 5x5 and it was no issue.

You are also correct in that replacement rotors for the front of these cars are impossible to get. Try Craig at Mobileparts for NOS. Otherwise, there are later model rotors you can adapt with a little work. I'm looking at using the 11.6" rotors from a Chevy half-ton pickup, which fit right on the stock spindles. They are 1.25" thick, so you need to use the 1971-76 calipers that are wide enough for these rotors. Some mods to the caliper bracket may be required - I'm working on that now.

 

What year half ton? That's an interesting option.

 

Rotor P/N is RAYBESTOS 8004R
Calipers are RAYBESTOS RC4213 and RC4214

 

Same proportioning valve ok? Also is there a bolt up rear disk kit that will work on our cars?

 

I'm not aware of a bolt on rear disk kit.

Be aware that those front rotors are slightly smaller in diameter than the originals - 11.6" vs 11.9" or so.

 

With access to Joe Padavano knowledge, you can't go wrong.

Side note: I have a set of 14" 5x5 steelies if you are interested. They are designed for disc brakes as I intended to put them on a '65/'66 Delta or Jetstar I was intent on buying and making a street rod. That didn't materialize (yet).

 

It is unlikely that you'd notice any improvement in stopping between rear disks and rear drums - the rears do only a small amount of the braking.

I'd just replace the shoes and hardware (and the cylinders, if necessary) and see how you like it, before making large investments and changes.

Welcome to ClassicOlds.

- Eric

 

 

I thought I read somewhere that the front discs could only carry 15" or larger wheels. I'm new to the confusion of all this though, all my other GM's were easy peasy.

 

The A-body cars used 10.75" disc brakes and came from the factory with 14" wheels. The B/C-body cars like your Ninety Eight used 12" rotors and used 15" wheels from the factory.

 

Hey Joe, any luck on the use of the half ton rotors with 71-76 calipers? Did they fit?

 

Very timely question. I just tried them this past weekend. The answer, unfortunately, is not so much. Note the two photos. Note that these are factory drum brake spindles. I installed the rotor using the stock bearings, washer, and spindle nut. The first problem I found was that the truck rotors apparently have the bearings closer together than do the original drums. With the spindle nut tightened all the way to the bottom of the threads, there was still in-and-out plan of the rotor on the spindle. This could be solved easily by using a second keyed washer under the spindle nut, but this was the least of the problems.

The second problem, as shown in this photo, was the lack of clearance to the top boss on the spindle. Again, these are drum brake spindles and I expected this to be somewhat of a problem. Scarebird claims their brackets do not require mods to the spindle, but I just don't see how that can be true given the minuscule clearance.



The final problem was clearance between the rotor and the lower control arm at the ball joint. Note that the suspension on my car is currently at full droop, so clearance may get better when the suspension is at ride height, but as it was, there was rubbing. Now, this is a very non-critical area and one could either clearance the bottom of the LCA or make a very slight cut on the rotor for clearance, but again, this is not a bolt-on.



At this point I've tabled the conversion until spring. I want to try the rotors from a 1971 D88 also, but for now I've just put the drums back on. Sorry.

 

Well that just stinks, sorry Joe. I have a close friend who had been in the brake parts business for many years. I just called him and he said he'd be able to bring me to one of the warehouses he used to work at to dig through and search for comparable options, as I'll bring my complete front spindle assembly with all its parts with me. Don't know how soon I can get there but hopefully I can find something. I'll make note of backside clearances on the car ahead of time to hopefully cover all bases.

 

There are unfortunately only a handful of rotors I've found that have the correct wheel bolt pattern and bearing sizes. Note that I've shown the Raybestos numbers, but the equivalent interchange rotors have the same dimensions.

Raybestos 5032
Mid 1980s Chevy half ton with 2" rear brakes
Rotor is 11.86" OD and 1" nominal thickness

Raybestos 5006
Mid 1980s Chevy half ton with 2.75" rear brakes and 1971-76 B/C-body
Rotor is 11.86" OD and 1.25" nominal thickness
(this is the one in my photos)

Raybestos 5800
Early 1970s Caddy Fleetwood
Rotor is 11.94" OD and 1.25" nominal thickness
Currently out of stock at RockAuto

I'm wondering if I might have had better luck with the 1" thick rotor.

 

Scarebird custom makes a hub and uses a 76-79 Ford T-Bird rear disc rotor with a 69-72 Cutlass caliper .

https://classicoldsmobile.com/forums...elta-88-a.html

 

Might I have different luck with trying these rotors since I have already have a disc brake car?

 

You are correct I confused their 1961-64 kit with the 65-70 kit. Sorry for that.