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Old December 2nd, 2015, 01:46 PM
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jimjaz jimjaz is offline
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Join Date: Jan 2013
Location: Tempe AZ
Truck: 1963 K-1000 Sub, 1963 C-1000 Sub, 1965 C-1000 Sub
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Default Re: Disk Brake Conversion

Doing a disc brake conversion on these trucks is a good idea for the reasons you mention (safety), but I would caution against the power disc option for the simple reason of potentially "locking up" the brakes in the case of a panic stop. Once the front (or rear) wheels lock up, it's game over, and you are very quickly out of control. It is hard to regain control from this, even for a very experienced driver. Your vehicle suddenly starts tracking in a direction that you do not want it to go in, like sideways. The exception would be having a power disc brake truck that utilizes the anti-lock feature found on virtually every modern car or truck made today, making these newer vehicles very safe in almost any hard braking situation. Quite honestly, I do not know if this is feasible in older trucks like ours, or even is available. If anti-lock is available, it would probably be very expensive to retrofit to a 60's truck. Don't really know, or care for that matter.
I have found out myself from doing two non-power drum-to-disc conversions conversions that power assist is not necessary if properly designed. My first was not a truck that we talk about on this forum, and the latest one is a 65 GMC Suburban that has OEM (all General Motors hardware except the front disc rotors) under the truck. Quite simply, I put a 1979 GMC (or Chevy- same hardware) under the front of my '65 that is a non-power version. One of the main benefits to doing this is having all GM parts with gobs of R&D that went into it at the factory, so any parts you might need in the future are readily available from a variety of sources. Another added benefit worth talking about is the size of the hardware increases, and you wind up with much more robust and durable (in size) upper and lower ball joints and tie rods and ends, so greater strength is achieved. Tie rods on a stock 60's truck is like the thickness of your little finger, vs. tie rods on a 73-87 GMC or Chevy truck is like the thickness of your thumb. Major improvement, and looks just like original, because in a sense, it IS original. Going aftermarket you will be adapting disc components onto the smaller 60's era ball joints.
There are several upgrades to disc front that can be readily had and installed from a variety of aftermarket competitors, just do your homework and ask questions. Nothing wrong with that. I have no experience from LMC Truck on this, but I will tell you that I purchased a power steering box adaptor kit from CPP to put a power steering box onto my 65 GMC, and found that although the cost was only $60 or so, it was junk, and I wound up throwing it in the recycle can. I wound up going with Captain Fab on power steering conversion, but I digress.
Doing what I did in swapping out the entire front suspension from 1965 drum to 1979 disc is pretty straightforward. The whole front suspension crossmember you drop out with 6 or 8 bolts total, you wind up installing a 73 to 87 front suspension into the same physical position, and all the bolt holes line up with the exception of 2 that you need to elongate to get the bolt through, and 2 that you need to drill. The important part if you go this route is finding a suitable donor truck whether it be power-assist or not, is to get ALL of the braking components from the donor truck. This includes the master cylinder on the firewall, brake lines that feed the front, and most importantly, the proportioning valve for that vehicle that feeds the front and rear brake lines. All I am trying to say here is DO NOT try to invent your own braking system. Do not think that "well.... bigger is better, so I'm going to make this line a 3/8" instead of the 5/16th" line that it was designed with." Stick with a proven and reliable design that the factory came up with at the time.
To others who may be contemplating this move, beware that the 60-63 GMC trucks use a hydraulic line off the master cylinder for the clutch, so a conversion to a later model truck's braking system will not work in this situation, and you would need to convert your clutch from hydraulic to mechanical linkage, something that can be done but with some challenges in finding the right hardware for converting this. I believe that 64-66 GMC's all have a mechanical clutch linkage, and if so, you are golden for converting your braking system- just check yours to be sure.
I am very happy with the front disc conversion that I did with using parts from a 1979 non-power brake truck on my 65. Yes, I can lock the brakes up if I want to, but who really wants to do that? Braking is one of the most important things we can improve upon from a safety perspective. Most of us really don't care how fast we can go- that is another discussion.
I kept and used my original 65 coil springs and put them into the 79 upper and lower spring pockets of the A-arms. I just made sure that I put them back onto the same side. This makes my ride height the same as it was before I started. If you leave the coils in place from whatever year donor truck you might be using, then you could potentially be looking at a different ride height up front. Just something to consider if going this route.
Happy trails, and keep on truckin!
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Jim Jantzen
Tempe AZ

63 GMC K1000 Sub restored original
63 GMC C1000 Sub original
65 GMC C1000 Sub OEM modified
72 GMC 1500 Super Custom SWB original
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