Front drum to disc swap. Done on my 1964 98

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Old Aug 13, 2022 | 07:22 AM
  #1  
drjaredshelton's Avatar
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Front drum to disc swap. Done on my 1964 98

I thought I’d post my disc swap info here for anyone looking into it. There was only one previous post I could find. I bought the scarebird kit. It’s pretty expensive but very high quality. Would recommend. However I just wanted everyone to know what to expect. The kit only comes with the hubs and the brackets. Everything else has to be purchased in addition from an outside source. I used RockAuto. Scarebird tells you exactly what to order though and it all goes on perfectly. I bought cheap but everything is pretty good. I also replaced the master with a corvette one at the same time but bought that from speedway.







Old Aug 15, 2022 | 11:12 AM
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Great post-I'm doing the same thing to my 64, I have the Scarebird kit and all the parts except for the master cylinder. What year Corvette was the master from? Also, did you use any time of proportioning valve?
Old Aug 15, 2022 | 11:45 AM
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Originally Posted by midtown_towman
Great post-I'm doing the same thing to my 64, I have the Scarebird kit and all the parts except for the master cylinder. What year Corvette was the master from? Also, did you use any time of proportioning valve?
I think that any corvette up to like 1984 works, but I can't remember exactly what was in the instructions. I bought the universal 1" bore GM style for disc/drum from speedway and their proportioning valve for the same. Mine came together as a kit for a better price, but now I don't see it on their website any more as a combo though for some reason.

https://www.speedwaymotors.com/Unive...re,318857.html

https://www.speedwaymotors.com/GM-Di...lets,9878.html

I'm still having issue with the brakes not slowing me down great, but I think that might be from the lack of vacuum d/t a big cam install. I haven't verified that yet though, so I just plan on stopping well in advance, lol.
Old Aug 15, 2022 | 03:00 PM
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So many people do a disc swap and wind up with braking that is worse than when they had drums.
Old Aug 15, 2022 | 05:06 PM
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Originally Posted by oldcutlass
So many people do a disc swap and wind up with braking that is worse than when they had drums.
Because few people (including the vendors) actually understand the engineering behind their brake system. One of the biggest problems I have with the aftermarket kits that use flat plate brackets for the calipers is that they don't provide any resistance to the caliper twisting. The stock brackets have features that guide the sliding caliper as it moves in and out. Without these guides, this twisting load is carried by the two pins, which are not designed for that (they sit in rubber o-rings). This causes the caliper to bind, which results in asymmetrical loads and wear on the pads. The disc brakes aren't going to be much of an improvement if only the inboard pad is being pressed against the rotor. Of course. 99% of the cars that get these kits only drive to and from cruise night on the weekends, so there isn't a lot of load on the brakes.



Old Aug 16, 2022 | 05:10 AM
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I just priced this out for my 63 and thought the pricing was really reasonable. Glad to see someone posting about it. It is a bit intimidating thinking you have to buy mismatched parts from other vehicles and hope the instructions were clear enough and correct. Awesome post, thanks!
Old Aug 16, 2022 | 05:14 AM
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Does your speedometer still work?
Old Aug 16, 2022 | 06:43 AM
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Good info joe_padavano, I did have some of the same concerns about the kit. I'll save my old parts in case I'm not happy with the end result and I can swap it back. I do like the idea of the twin pot master cylinder. I was also wondering if the speedo will still work after the conversation.
Old Aug 16, 2022 | 08:57 AM
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The speedo is driven from the left front dust cap. So long as you reuse that dust cap, the type of brakes are irrelevant.
Old Aug 16, 2022 | 09:50 AM
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Originally Posted by joe_padavano
Because few people (including the vendors) actually understand the engineering behind their brake system. One of the biggest problems I have with the aftermarket kits that use flat plate brackets for the calipers is that they don't provide any resistance to the caliper twisting. The stock brackets have features that guide the sliding caliper as it moves in and out. Without these guides, this twisting load is carried by the two pins, which are not designed for that (they sit in rubber o-rings). This causes the caliper to bind, which results in asymmetrical loads and wear on the pads. The disc brakes aren't going to be much of an improvement if only the inboard pad is being pressed against the rotor. Of course. 99% of the cars that get these kits only drive to and from cruise night on the weekends, so there isn't a lot of load on the brakes.


What is the solution for this? I've seen the posts about how others, possibly you, have done it using other components and some machine work. But if someone were to make a conversion kit that worked as it should, what specifically would need to be done differently to take the load and remove it from the pins?
Old Aug 16, 2022 | 10:07 AM
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Originally Posted by ludothegreat
What is the solution for this? I've seen the posts about how others, possibly you, have done it using other components and some machine work. But if someone were to make a conversion kit that worked as it should, what specifically would need to be done differently to take the load and remove it from the pins?
Excellent question. There are several ways to approach this. The easiest is to just use a fixed four piston caliper. This is what most of the high-end systems like Wilwood and Baer do. Since the caliper doesn't slide, it bolts rigidly to the bracket, which CAN be a simple flat plate in that case. Of course, the fixed caliper is very sensitive to being centered on the rotor, so it requires shimming to ensure this. Not a big deal, but a step that some people overlook. The downside is that any runout in the rotor will cause piston "knock-back", where the pistons are pushed back into the caliper. This causes a long pedal throw when you first press on the brakes and is the reason why GM went to the sliding calipers in 1969.




If you want to use sliding calipers (which can be a good thing for a street-driven car), either adapt the factory style bracket (which requires cutting and welding) or use a later model floating caliper that incorporates the sliding mechanism in a separate bracket that then bolts rigidly to the spindle (or adapter bracket for a conversion). Most late model disc brakes use this latter mounting method. Note by the way that the fixed bracket used with these floating calipers is MUCH more rigid than the aftermarket flat plates, as needed to properly react the braking loads from the caliper without twisting.


Old Aug 16, 2022 | 10:14 AM
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Originally Posted by joe_padavano
Excellent question. There are several ways to approach this. The easiest is to just use a fixed four piston caliper. This is what most of the high-end systems like Wilwood and Baer do. Since the caliper doesn't slide, it bolts rigidly to the bracket, which CAN be a simple flat plate in that case. Of course, the fixed caliper is very sensitive to being centered on the rotor, so it requires shimming to ensure this. Not a big deal, but a step that some people overlook. The downside is that any runout in the rotor will cause piston "knock-back", where the pistons are pushed back into the caliper. This causes a long pedal throw when you first press on the brakes and is the reason why GM went to the sliding calipers in 1969.




If you want to use sliding calipers (which can be a good thing for a street-driven car), either adapt the factory style bracket (which requires cutting and welding) or use a later model floating caliper that incorporates the sliding mechanism in a separate bracket that then bolts rigidly to the spindle (or adapter bracket for a conversion). Most late model disc brakes use this latter mounting method. Note by the way that the fixed bracket used with these floating calipers is MUCH more rigid than the aftermarket flat plates, as needed to properly react the braking loads from the caliper without twisting.

Has anyone done a write-up on how to adapt the factory style bracket? Or any pictures of what it would need to look like?
Old Sep 20, 2022 | 08:47 PM
  #13  
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How many times you hear these guys swap over from drum to disc and they don't stop better, rebuild your drum brake system completely and it will serve you very well
Old Sep 21, 2022 | 08:41 AM
  #14  
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I was going to say ... just make sure your facrory drum setup is in good working order and save yourself a bunch of money and heartache, while maintaining similar (if not superior) stopping performance.
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