Disk Brake Conversion

[makindust]

Does anyone have experience using the disk brake conversion kit from LMC trucks? I have a 1966 GMC Fleetside, 351 V6, 4 speed manual transmission. I would like to convert the front to disk and keep the rear the stock drum. I have a teenager who will be driving soon and need the piece of mind that she will be able to stop the truck with the power assisted disks.

[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!

[makindust]

Jim, thanks for the reply, I really appreciate the input. I have been contemplating finding a donor truck for this conversion and now I will stop contemplating and start looking.

[d4rksp1dy]

Has anyone used the front disk convertion kit from Ecklers?

[Sonic65]

Originally Posted by makindust

Jim, thanks for the reply, I really appreciate the input. I have been contemplating finding a donor truck for this conversion and now I will stop contemplating and start looking.

I bought a fully running/driving 1975 GMC with power steering and power brakes. Dropped the 65's rear end and installed the 75's rear end. Very easy and it got me bigger drums. Dropped my 65's control arms (with brakes) and installed the 75's control arm assembly's (with brakes) right into my 65's frame. Bolts all lined up. I did change the all the bushings, ball joints etc. with Moog parts. I installed the 75's proportioning valve and power brake booster (with new master cylinder) and used all the 75's brakes lines (I bought replacement hoses) and connected everything up. I have not had any issues, although I have not had a panic stop situation. I too decided to go with OEM parts instead of a kit because the EOM parts have a lot of R&D behind them. Not only that, but it was cheaper to buy a whole truck than a kit!

[jimjaz]

Hello,

Sorry for the long delay in response, but I do not spend a lot of time on this website. I am glad to hear that you went the route you did with buying a donor truck to do your upgrades, and you are right that buying a "kit" can easily cost more than an entire truck!

Good for you!

[jimjaz]

Just a note about my reference to "panic stop"..........
You might want to try this yourself on a lonely road (or a big empty parking lot) with nobody around to see what happens when you mash down on that power brake pedal. One of the BIG things I really like about non-power is that I have GREAT control over the braking system and can lock them up if I want to with increased pressure on the pedal, but I prefer not to. It is the closest thing to "anti-lock" without all of the expense in doing this sort of modification.

R/
Jim

[Sonic65]

Originally Posted by jimjaz

Just a note about my reference to "panic stop"..........
You might want to try this yourself on a lonely road (or a big empty parking lot) with nobody around to see what happens when you mash down on that power brake pedal. One of the BIG things I really like about non-power is that I have GREAT control over the braking system and can lock them up if I want to with increased pressure on the pedal, but I prefer not to. It is the closest thing to "anti-lock" without all of the expense in doing this sort of modification.

R/
Jim

I will give it a try. I will just have to put a pillow over the steering wheel first!

[GMCNUT]

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 don't know why anyone thinks they need to do any of this above modification when GMC offered power steering and power drum brakes that work awesome to begin with. Both of my trucks have factory power brakes and factory power steering and there is nothing about modern power steering that I can think of that works better than these original 60's slave cylinder power assist units. With a rebuilt control valve and rebuilt slave cyl they don't leak and I can steer my 66 Suburban with my pinky finger its so responsive.
I do understand the value of discs over drums but you have to sacrifice your stock wheels and stock hubcaps when you do that, so the tiny gain in stopping power is simply not worth wrecking the original appearance of a totally stock truck over. Just my two cents - I never see posts where anyone is suggesting use of the factory available power parts but they are well worth considering if you ask me

[David R Leifheit]

Originally Posted by GMCNUT

I don't know why anyone thinks they need to do any of this above modification when GMC offered power steering and power drum brakes that work awesome to begin with. Both of my trucks have factory power brakes and factory power steering and there is nothing about modern power steering that I can think of that works better than these original 60's slave cylinder power assist units. With a rebuilt control valve and rebuilt slave cyl they don't leak and I can steer my 66 Suburban with my pinky finger its so responsive.
I do understand the value of discs over drums but you have to sacrifice your stock wheels and stock hubcaps when you do that, so the tiny gain in stopping power is simply not worth wrecking the original appearance of a totally stock truck over. Just my two cents - I never see posts where anyone is suggesting use of the factory available power parts but they are well worth considering if you ask me

Original power steering components are harder to find, or so it seems. Finding a bracket for the V6 has proven difficult for several members in the past, if memory serves me.

Having driven vehicles with and without power brakes... I can't honestly say there is much difference. The pedal on power brakes seems to activate easier, but stopping has been about the same. Anti-lock is always questionable, several of the vans my wives have had were rear-antilock, which never made sense because the front (steering) could lock up then and you'd lose control. Also when the anti-lock feature failed, there was no difference in driving (except the annoying light on the dash). A lumber company I worked for had anti-lock on the 1/2ton Chev pickup we used for small deliveries and "running around", you had to learn to apply brakes sooner than normal because they felt like mush (shop said they worked perfectly) and it took longer to stop. I *assume* that was the anti-lock since if you had to try to stop quick you could feel the pulsing in the pedal, and if you stopped in time it was a miracle.
Drum brakes are just as good as disc, both stop the vehicle. Manual stops you just as fast as power, it just takes a little more pressure on the pedal.
Anti-lock and power systems are also just one more component that can fail, brakes are real simple and don't really need to be made more complicated.
But that is my opinion, based on driving a wide array of vehicles over the last several years.