66 c20 disc swap questions

[jazzbum]

I've searched all over and have come up goose egg on a couple on fine points of swapping 8 lug drums for 73-87 style discs. Any light you could shed would be much appreciated.

I have a 66 c20 with drums front and rear. I want to swap to discs in front and retain the 8 lug pattern so I can use my existing wheels. I'm looking for the most straightforward way to do it. I do not have the facilities to do a full crossmember swap so I am limited to what I can do at wheel and under the hood.

I am under the impression that all that needs done to physically bolt in the 73-87 disc spindles is to put 73-87 balljoints into the 66 a arms. Is this correct?

Or would it be more straightforward to get everything from the frame out--upper and lower a arms, spindle, brakes--and bolt it into the 66? This assumes that the upper and lower arms from the later truck will physically bolt to the 66. Will they?

As for the tie rod issue that this creates, I guess I will probably use the adapter sleeves that are sold by POL and CPP and others and retain my 66 steering links and ends. The question I have here is, will the c10 adapter that these companies sell also work for my c20 steering with an 8 lug disc spindle, or are the c10 parts smaller/different? Otherwise I suppose I could swap the steering from the donor truck, assuming the widths match. Any advice here?

Also, is there a difference between the spindles found in dually trucks and those found in SRWs? I know the rotors are different, but is the spindle itself different? I seem to see a lot more dually trucks than anything else in the wrecking yards around here, so this would be good to know.

Thanks very much in advance for helping out a newb. Sorry about the novel-length post.

[Clyde65]

You can do it with a spindle and ball joints but the later model a-arm cross shafts are better and rebuildable, also the a-arm u-bolts should also be replaced.

Easier to just roll one out and roll one in and drill a couple houses.

[Clyde65]

Duallies are mostly 1 Tom in GM world so yes they are different

[Captainfab]

On the '63-'66 C20's I do not know for sure if the '73-'87 lower ball joint will press into the '63-'66 lower control arm. I have never tried it. In the past I have just changed the entire front suspension. Also on the '63-'66 C20's, you can not just change to the '73-'87 lower control arms.The '63-'66 lower control arm shafts are flat where they bolt to the crossmember and consequently do not have the saddles required for the round shafts found in the '73-'87 lower control arms. The '73-'87 C30 dually spindles are different than the C20 spindles since the calipers are different. I believe the C20 tierods are larger than the C10 tierods so I do not think the aftermarket aluminum adapter sleeves will work. I have always just used the entire later model steering linkage.

[jocko]

What are your existing wheels that you want to continue to use? I’ve never found an answer as to whether or not factory pre-1971 16, 16.5 or 17” wheels clear the caliper on a 73+ factory disk setup. I’m particularly interested in the 17” question - and wanted to ask what your wheels are. If aftermarket, you’re fine. If 66 original - I don’t know for certain they we’ll fit (clear the caliper). In the 15” world, they will not - but this is the 16 or larger world, and I don’t know if the taper on the backside of one of those wheels clears a caliper. Seems like it would come closer to clearing it at least. Anyone know?

[Chevy Fleetside]

Then there is this option. http://www.67-72chevytrucks.com/vboa...d.php?t=357610

[jazzbum]

Thanks for the replies, guys. That gets me a little closer to having all of the info I'm looking for.

As far as wheels go, mine are definitely not stock '66. In fact, they don't even match--two have outside nubs for hubcaps and two are smooth, like you might see on a 90s era pickup. All are 16" and I'm sure they probably came out of the junkyard from disc-equipped trucks. I'm just hoping to keep them to keep costs down as I get this thing roadworthy.

[jazzbum]

While I would love to be able to just roll a complete crossmember under the truck, it's just not possible. I am working on the side of the road in a neighborhood that doesn't look favorably on that kind of activity. No garage, not even a truly flat surface to use. Just not a possibility.

[jazzbum]

Ok, I finally managed to find a decent set of spindles and rotors from a 73 C20 in the wrecking yard. Unfortunately, the calipers were gone when I got there. No problem, I'll just order a set from rockauto, right? Almost.

This seems ridiculous but the new calipers don't come with banjo bolts, and I can't seem find the verifiable correct part anywhere. Anybody have a part number or size spec? Much appreciated m

[Chevy Fleetside]

Check you local parts house for calipers and banjo bolts. There are core charges for the calipers.

[jazzbum]

Calipers are on order from rockauto, but that raises a good point--being that they're reman units, there's no way to tell whether they're early or late, standard or metric, until I get them in hand. I doubt rebuilders separate early from late. I guess I'll just have to trial fit bolts at the parts store, if they'll let me.

Anybody know the right length, in any case?

[jazzbum]

Banjo bolts sorted, but now I'm trying to figure out a manual dual master cylinder for a disc/drum system that will be stout enough for the eight lug brakes.

Closest I can find that's disc/drum is 73 camaro. Has 1" bore, which should be small enough to keep the pedal from being too hard, but I'm wondering if that master going to be capable of handling the much larger hydraulic circuits and brake parts of the truck otherwise.

Yes, I do want manual brakes, personal preference. Any suggestions for a cylinder that will work? Thanks much.

[Captainfab]

Get a '73 C20 manual master cylinder along with the proportioning valve.

[jazzbum]

You wouldn't happen to have a part number, would you? Haven't been able to locate a manual 3/4 ton cylinder, only power brake type cylinders with shallow plunger hole and 1-1/8" or larger bore. I did find a 1/2 ton manual cylinder for a 73 in the LMC catalog but the fact that they list it separately from the 3/4 cylinders makes me think it may not be right in bore size or reservoir volume when matched with the larger brakes.

[Captainfab]

No I do not have a part number. I guess I should have looked before I posted. I know that the C10's were available with manual brakes. It is entirely possible that the '73+ C20's were not available with manual brakes, for a good reason.....safety. You may have to look at the '71-'72 C20 and see if there is a manual master available. And just because it isn't shown in the LMC catalog, doesn't mean it isn't available from a good local auto parts store.

[jazzbum]

Yeah, I think you might be right about that. I have looked as extensively as I know how to look into both 73+ and 71-2 3/4 ton cylinders, and found no manual units at all. There are rumors of a 73+ 3/4 cylinder but the only ones I've found that were rated for the heavier trucks are for the earlier drum/drum systems. I wonder if it might be possible to remove the residual valve from one of the ports and run discs with the earlier cylinder.

[Green chevy c20]

https://www.performanceonline.com/19...-8-Lug-Deluxe/
Here is a 8 lug kit from performance online. Install this kit in my truck and it is a direct bolt in. Everything you need is there. I have disc in front and and stock drums in the rear. It's a c20 and the braking power is insane, it stops better then my daily driver

[Short 3/4]

Originally Posted by jazzbum

Yeah, I think you might be right about that. I have looked as extensively as I know how to look into both 73+ and 71-2 3/4 ton cylinders, and found no manual units at all. There are rumors of a 73+ 3/4 cylinder but the only ones I've found that were rated for the heavier trucks are for the earlier drum/drum systems. I wonder if it might be possible to remove the residual valve from one of the ports and run discs with the earlier cylinder.

Did the same thing years ago. Sorry no part number, but do know I found a manual Disc/drum MC that worked very well for many decades. As I recall only modification was possibly to the push rod length. I also used an adjustable proportioning valve. As I recall I left my arms and just changed stuff from ball joints out ( was on a 66 ).
I was lucky to have a parts store that knew how to read a parts book. My advice is to find such a store and give them ALL your business, so they can stay around. Online and chain stores are cheap, but you get what you pay for.
Sorry to go off on a rant there, but bottom line it can be done. I also prefer manual brakes. Good luck on your project, Tom

[jazzbum]

Thanks, Tom. I'm thinking a 1/2 ton manual cylinder may actually work just fine--looks like both the caliper bore size and rotor thickness are the same for 1/2 and 3/4 ton trucks. Is it possible that you used a 1/2 ton cylinder on your rig?

Man, I'm with you on the value of a good traditional parts store. Chain stores are practically worthless for stuff like this, which is why these forums are so great. Since my go-to parts guy retired several years back this sort of project has gotten a lot more difficult. I've always happy to pay a premium for good service. Real shame you often don't have the choice anymore.

[Short 3/4]

Originally Posted by jazzbum

Thanks, Tom. I'm thinking a 1/2 ton manual cylinder may actually work just fine--looks like both the caliper bore size and rotor thickness are the same for 1/2 and 3/4 ton trucks. Is it possible that you used a 1/2 ton cylinder on your rig?

Man, I'm with you on the value of a good traditional parts store. Chain stores are practically worthless for stuff like this, which is why these forums are so great. Since my go-to parts guy retired several years back this sort of project has gotten a lot more difficult. I've always happy to pay a premium for good service. Real shame you often don't have the choice anymore.

Sorry, don't remember any more about the master cylinder, was a long time ago and as I said I relied on my parts guru. All I know is that it worked great. Unfortunately that truck went to meet its maker about a year ago, and while I harvested as many organs as I could so others could live, I know that 30+ year old MC went into the scrap pile.
I agree with you on the value of this forum. I never had much use for computers before, but I learn something new every day from these guys.
I'm thinking if the calipers are the same part # or same bore size then the MC should be the same. I can tell you I had NO problem coming to a stop on a hill while fully loaded, with those manual discs.
Sorry I can't offer more than encouragement, but I can assure you the results will be worth the effort, Tom