Disk Brake Conversion

[makindust]

David
I found a recent post of yours where you commented on doing a 1/2 ton to 3/4 ton conversion. Did you use a donor truck? I'm looking at using a 1978 GMC 3/4 ton as my donor, but trying to research to make sure the cross member will swap without major modifications.

[David R Leifheit]

Originally Posted by makindust

David
I found a recent post of yours where you commented on doing a 1/2 ton to 3/4 ton conversion. Did you use a donor truck? I'm looking at using a 1978 GMC 3/4 ton as my donor, but trying to research to make sure the cross member will swap without major modifications.

Yes, we had two trucks for the change.
-BUT-
One was a fairly complete and running '66 1/2 ton and the other was a chassis, cab and bed '66 3/4 ton. So everything swapped over because... well, same year.
We did not complete the swap though since someone was interested in buying the truck, and intended on replacing all the axles anyway (modern disc brakes, etc). He bought both trucks, and some loose parts I had. Funny thing is he was a Chevy guy but knew about the 305. The way he talked he sounded like he was going to hotrod the truck, but keep the 305 to be different.
I really didn't want to sell all we did, but the money was good and needed. He even paid "the kid" (who is living in a 5th wheel in the yard with his fiancee while they try to find a house) to help him haul. Worked out good all around for us.
And we (I mean the kid) didn't have to finish the swap. Just had to put it back together enough to get on a trailer.

[suburbangeorge]

Originally Posted by jimjaz

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!

I should probably read this whole thread before picking on you but what, exactly, do you have against power brakes? Converted my 1966 4WD Suburban to disk brakes and used the stock '66 booster. If any thing I have too little boost. Drum brakes are what they call "self energizing". When the shoes contact the drums the leading(I think) shoe sort of wedges in place against the drum. You need less boost to get to this point so the factory provided less boost than they did later when disk brakes became stock. Disk brakes are not self energizing and the caliper clamping on the rotor is in direct proportion to the pressure applied. Locking up is a complex combination of caliper pressure applied, rotor diameter and vehicle weight. You should talk to one of the companies who sell these conversions like Stainless Steel Brake who will ask enough questions to sell you the correct parts. Maybe your experience comes from using a booster designed for a 5000 pound truck on a 4000 pound truck? My swap was pretty straight forward as I used '73 Blazer parts on my '66 Suburban. Pretty similar weights.

[jimjaz]

Hello Suburbangeorge,

I do not have anything against power brakes other than (a potential for) lock-up. Some people will have nothing but. I prefer the look of a non-power brake setup under the hood- no gargantuan booster drum to look at or get in the way of any maintenance that one might need to do. For those that choose power brakes, there is plenty of room under the hood for a brake booster.

I like the control that you have with non-power (disc) brakes. As I mentioned in my original post, a panic stop can cause your brakes to suddenly lock up, and without the booster, locking up the brakes is, simply put, not as easy to do.

I don't need to talk to anybody about what parts I need, because I am quite pleased with what I already have, and just thought that I would share my experience with others that may be looking for input and others' experiences.

My "experience" originally came from researching and reading about automotive brake systems, and some of that which I was reading was telling me that a properly designed braking system does not need to be power-assisted with a vacuum booster, so this is the approach that I took, and by golly, all that reading and research paid off. The original goal for me was to replace the front drum with disc on my 65 Sub, and it all worked out very nicely.

You did admit that you should "probably read this whole thread" before picking on me. I wholeheartedly agree with that statement.

Cheers!

[Drewski]

I know this isn't staying in line with the conversation completely, but I just did a front disk swap In my 65 3/4 ton. Basically i only spent around $200 for the entire swap by finding some 8 lug 84' C20 disk brakes from the junk yard. Surprisingly, the 84' ball joints are the exact same size as the 65' ball joints as far as fitting into the control arms. Only the shaft that fits in to the brakes is slightly different. And that's it. I got the brakes, cleaned them up, installed the 84' ball joints and put it back together. I still have 8 lug all around the truck and now have some seriously beefy disks on the front now. I have a daughter I need to keep safe as well so I get were your coming from. I also understand that having a child can hinder finances a bit too. So maybe this is something that can help you out a bit.

[jimjaz]

Drewski, I gather from what you laid out is that 3/4T trucks use the same ball joint sizes for the 60's through the 80's. This should help out some other folk who may be considering some kind of front-end swap for better brakes using disc up front.
In my own 1/2T experience, I found that basically everything on my 65 was smaller than what the 79 donor truck had. This includes ball joints, control arms, center drag link, and also the anti-sway setup that my 65 just happened to have as factory OEM.
I'm sure you will be happy with having disc brakes up front. I am very happy with mine.

[Drewski]

Jimjaz, thanks for that info. I had no idea that a 1/2T would be so much harder. I honestly don't have much experience with the 1/2T. I would have to thank jollys write up about how he did this type of swap on his 1 ton. I read that about a year and half ago and said to my self "I bet I could do that on my 3/4T. A bit of research and a bit of a what the **** attitude got me to try it out. I was definitely pleasantly surprised. I needed to upgrade to disks because the wife is on the hunt for a camper to start hauling around. That and I live in Albuquerque were the drivers are the worst I've seen, and I've lived in 3 countries and all over the US.

[suburbangeorge]

Originally Posted by jimjaz

Hello Suburbangeorge,

I do not have anything against power brakes other than (a potential for) lock-up. Some people will have nothing but. I prefer the look of a non-power brake setup under the hood- no gargantuan booster drum to look at or get in the way of any maintenance that one might need to do. For those that choose power brakes, there is plenty of room under the hood for a brake booster.

I like the control that you have with non-power (disc) brakes. As I mentioned in my original post, a panic stop can cause your brakes to suddenly lock up, and without the booster, locking up the brakes is, simply put, not as easy to do.

I don't need to talk to anybody about what parts I need, because I am quite pleased with what I already have, and just thought that I would share my experience with others that may be looking for input and others' experiences.

My "experience" originally came from researching and reading about automotive brake systems, and some of that which I was reading was telling me that a properly designed braking system does not need to be power-assisted with a vacuum booster, so this is the approach that I took, and by golly, all that reading and research paid off. The original goal for me was to replace the front drum with disc on my 65 Sub, and it all worked out very nicely.

You did admit that you should "probably read this whole thread" before picking on me. I wholeheartedly agree with that statement.

Cheers!

So I read the whole thread and I hadn't missed anything. I'm thinking that your "lock up' experience came in an over boosted vehicle. Like my parents one time '75 Pontiac. Back in the day( early '80's) I used their car to take them to the airport. On the way back some guy cut unexpectedly into my lane. As I was used to driving an un-boosted '57 Austin Healey, I hit the brakes harder than maybe I should have and the car began to fishtail on a straight freeway. Not all boosted systems work that way. Pretty much all more modern cars have boosted brakes including those without anti-lock. My experience with a '66 4WD Suburban, using the factory drum brake booster, and maybe too large a master cylinder diameter was that I really needed to stand on the brakes with both feet to stop fast. I could do it but I wanted something with less effort if my wife needed to drive. Anyway, you guys all seem to be talking 2WD. 4WD conversion has different set of issues but booster/no booster decision should be more or less the same.

[jimjaz]

Drewski, I had to laugh about your comment on Abq drivers being the worst. We must all feel that way about where it is we live- I have that very feeling you describe about Phoenix metro. I could not survive in this place if I had to do a M-F, 8 to 5 gig and be exposed daily to all the morons around here on the streets and freeways who THINK that they have self-driving vehicles the way they text and drive. I would either have to shoot myself or someone else the way they drive around here. I think we hold the gold medal for the number of wrong-way drivers in Arizona! If I have to drive somewhere to get something done on a day off, I try to dial my travel time in between about 10AM and 2PM as the rest of the time it's like a big giant parking lot with lots of people who think that if they ride up your ars real close that this will make the person in front of them go faster. Cheers!