C20 disc brake conversion help thread

[May70]

I know the question has been posed many times, I have read through about 15 threads. The problem is many people have input on those threads and there are vast discrepancies with "what you need" I would like to clear up (I will also note most of the reply's came from people who haven't actually done the swap and dont know from experience). For what ever reason I dont see a sticky guide for this topic (for the MINIMUM requirements), so if I missed it please tell me.

Some say you must:
(1) Take the whole cross arm and everything from a donor
(2) Take just the control arms and spindles from a donor
(3) Buy the kit (expensive & simple)
(I am just talking basics right now not all encompassing)

To do 1 & 2 does not make logical since because the kit ONLY comes with spindles to be used with stock control arms. Why would you take anything else besides the spindles from a donor and go through all the hassle to do that if all you need are the spindles, even more so for the whole cross member??????? Common sense here is screaming people dont know what they are talking about so they do (1) take the whole cross member (more than they need). Someone has to have a better answer than that or maybe I am just totally missing a key concept here. I know there are many ways to do this (1 & 2 might work) but why would you put in all that extra effort and money when you dont have to? Someone please dumb this down for us common folk.

I have a completely refinished frame with fully rebuilt front end drum brakes. Its all painted, new ball joints, completely rebuilt and ready to be taken to the alignment shop (the whole nine). I've decided to convert it to disc brakes, so I want to know exactly the (minimum) parts that I need to swap over to prevent unnecessary work and expense. I have refinished upper and lower control arms, spindles off a 75 c20 and brand new hub assembly's. I am already partially frustrated because I went to the hassle of getting the donor frame and refinishing all that based on what I now believe to be inaccurate information. Also I am highly considering throwing discs on the back, which I recall the kit being about $600-700, so I am not going to reinvent the wheel for that price (half of the front conversion).

I am going to reply to this thread with exactly what I end up doing so please reply if you have done this swap already and know from experience. Too many of these threads the OP never said what they ended up doing to make it work. A complete part list will be provided when I finished. I highly appreciate the feedback.

[HO455]

The reason folks replace the entire front crossmember with a C10 square body crossmember is not only do you get disc brakes but you also get rubber bushing mounts for the lower control arm which give you improved ride quality over the bronze bushings that came factory on 72 and earlier trucks. Most everyone wants less NVH. And you can run 5 lug wheels. So as you can see there may be more than item on the agenda when making the decision as which route to go.

From your post am unsure if you are wanting to stay with a 3/4 ton front end ,(8 lug) or do you want to run a 5 lug wheel?
And finally have you seen this thread?

http://67-72chevytrucks.com/vboard/s...d.php?t=456889

[Andy4639]

I bought the whole front end of a 86 3500. I had plan to swap the whole deal. Now I'm thinking to install new upper & lower ball joints which by the way per 3 web sites I looked at are the same for both years. I'm sure the 67 Ramp truck could use new ones anyway.

Then pull the spindles and brakes off the 86 and install on the 67. I'm staying 8 lugs. Use the 86 tie rods and the sway bar and center link. That's my plan as of now but will be interested in hearing what other's have to say.

[Sheepdip]

I just did a C-30 DRW I'm sure there is some good info here you could use. I also see absolutely no advantage to changing out a perfectly good front cradle.
http://67-72chevytrucks.com/vboard/s...light=sheepdip

[RichardJ]

What is the purpose of this thread?

In your build thread, you said you bought this '77 frame and complete front disc brake setup. Now you are saying it's a '75 frame?
You disassembled the new disc setup, painted and replaced many of these parts with NEW parts from Napa.

I do want you to answer my question above, but your confusion and probably mine is that you said you read 15 other disc brake threads.
A lot of those threads you read may be from guys that cobbled together a disc setup from a combination of aftermarket parts and GM parts from more than one year vehicle.

The complete '77 disc setup is a complete system designed by some pretty good engineers.

Be sure and use the complete '77 brake line setup including Combination Valve mounting location.

[May70]

Originally Posted by RichardJ

What is the purpose of this thread?

In your build thread, you said you bought this '77 frame and complete front disc brake setup. Now you are saying it's a '75 frame?
You disassembled the new disc setup, painted and replaced many of these parts with NEW parts from Napa.

I do want you to answer my question above, but your confusion and probably mine is that you said you read 15 other disc brake threads.
A lot of those threads you read may be from guys that cobbled together a disc setup from a combination of aftermarket parts and GM parts from more than one year vehicle.

The complete '77 disc setup is a complete system designed by some pretty good engineers.

Be sure and use the complete '77 brake line setup including Combination Valve mounting location.

I am not sure what difference it makes since my understanding is 73-87 would have been the same. The only new stuff I have purchased from Napa are the hub/rotor assemblys and calipers which I would have needed anyway? To answer your question though, I was later told (after that post) its actually a '75 cross member and all the front suspension swapped over onto a 69 frame. I got it from a multi pass down situation, and the previous owner messaged me the correct info. So yes its a '75 crossmember disc setup, what difference is that from a '77?

The purpose of the thread is to figure out what options people have to do this and what are the differences are in those options (while at the same time understanding why you would choose one option over another). There are a ton of people who have had an end result of disc brakes but the reasons of different methods arent common knowledge.

HO455 understood the purpose of the thread clearly, his post answered it and explained why. Apparently the reason someone would choose to swap the cross member and all is because of the improved ride quality (rubber bushings) that the later models had. If that is indeed true, then common sense would tell me that there is no advantage in using the squarebody control arms if you are not going to use them with the squarebody crossmember (contradictory to numerous posts on this forum!).

What HO455 said is not a well known fact and hasn't been highlighted on any thread I read prior to this (obviously). The fact so many people don't fully understand the specifics and what the advantages are for each option is why this thread exists. Honestly to pass on knowledge is why the whole forum exists to begin with (so ????).

My takeaway from HO455's comment is at this point I should go ahead and prepare the '75 cross member as well. That way I can swap the crossmember and its entirety to my frame to gain the improved ride quality.

I wish this forum utilized 'sticky' functions more or some way of organizing threads like the one HO455 referred to. That is an incredible guide (Richardh
notice that even that extensive thread does not mention anywhere why you would choose a certain option over another). There are simply too many threads to find one post inside thousands of threads. Hopefully when this thread is done it will lessen the chance of someone being confused like I have been on this topic.

Case in point; Sheepdip also stated "I also see absolutely no advantage to changing out a perfectly good front cradle". Thanks to HO455 we now know the reason why it is an advantage.

[Sheepdip]

HO455 understood the purpose of the thread clearly, his post answered it and explained why. Apparently the reason someone would choose to swap the cross member and all is because of the improved ride quality (rubber bushings) that the later models had. If that is indeed true, then common sense would tell me that there is no advantage in using the squarebody control arms if you are not going to use them with the squarebody crossmember (contradictory to numerous posts on this forum!).

If you keep your original cross member and use the 75 control arms as a complete unit (they bolt right to it) you get the rubber bushing ride everyone is concerned about. That being said I still see no advantage to swapping the cross member

[May70]

So another interesting development. I found a youtube and now I see the rubber bushings you are referring to (I was thinking of the rubber seals on the shaft I saw when disassembling mine).

The previous owner of the doner frame told me that all of the front suspension was off of a '75 as I mentioned above. Now looking at this picture, my 'donor' control arms look like the top, not the bottom.

So does that mean the control arms arent from a squarebody? I am confused

https://www.youtube.com/watch?v=Yrzym6L_KPw

[HO455]

The C10 squarebody's went to the rubber bushings in 73. The C20's stayed with the bronze bushings for much longer. If your spindles are 8 lug then it is quite possible you do have squarebody parts. Probably the easiest way to help confirm would be to check the rotor size. This thread will help.

http://67-72chevytrucks.com/vboard/s...d.php?t=319487

Another small reason to convert to the later crossmember is it has all of the brake lines/hoses and the associated clamps and they are all in the correct locations. As opposed to putting disc brakes on a 67 drum brake truck crossmember where the lines and clips are on the behind the spindles and having to find a longer brake hose that will work. Thus the conversion to disc brakes with larger rotors becomes a bolt in modification with the possible exception of the brake line from the master cylinder.

[May70]

Conversion complete minus brake line routing.

In Summary:

In the C10 series, Squarebody disc brake setups are often swapped over for two main reasons; to gain disc brakes and to gain the (believed) improved riding quality of the newer bushing style (seen in. Since 71-72 disc brake setups are much harder to find and more expensive, that gives us a really good alternative. Since there are significantly more C10 restorations going on than C20 restorations, we naturally have less information and experience to rely on.

I have read all over the internet and been told by some however I have not been able to source any factory 73-87 ¾ ton truck with the newer bushing style (seen in the previous picture referenced). I have looked at numerous parts websites and all show the same lower control arm bushing style (3/4 ton series) from 67-87. Reproduction manufacturers show the same. This leads me to believe, if someone has seen them on a c20 from 67-87 they must have been swapped over from a C10 (or a 88+ if those were still being used). I believe the newer c10 bushing style would not have the material strength properties the c20 assembly has, also leading me to believe they would keep the early style through 87. That all being said; Unless your control arms need to be replaced, I have found no need or benefit what-so-ever to swap control arms.

Bare minimum to pull for a swap:
If you have a cheap source or a 73-87 frame available, the only thing you need off it are the spindles (WITH THE CASTLE NUTS) and dust covers. You can find these pretty cheap if you shop around or go to a junk yard. I picked up a whole frame free. I know eBay has sets for like $300 but I would stay with original equipment if you can find it.

What you will need off the old drum brake equipment:
Some upper ball joints have a thin plate that goes on the lower side of the control arm. If yours has that plate when you remove the upper ball joint make sure you keep it and put it on with the new ball joint. Keep the tie rods so you can ball park the distance you need to set the new ones. That’s how a lot of people get them ‘close enough’ to drive up to the alignment shop.


Thought process:
This isn’t rocket science however most people doing this job have little to no experience. In cases like this, it might as well be pretty close to rocket science. Let’s dumb this down. Say you weren’t doing this swap and you were just replacing warn out suspension parts on your current truck. Odds are you would probably ride up to the parts store and tell them the year and model of your truck. That’s pretty much all you have to do with a conversion, with some exceptions to match the year truck you have different parts from. With a swap you have parts needed from different years, so knowing what year stuff you have is important. The beauty of this job is that certain parts are compatible with each other. This doesn’t take any fabrication, only knowledge.

Tie rods connect the spindle to the steering equipment that transfers your action of turning the steering wheel to the wheels (real simplified explanation). There is an inner and an outer tie rod and a linkage that connects the two together. The outer tie rod is the one furthest away from the center of the truck (connects to the spindle) and the inner is the one closest to the center of the truck (connects to the steering linkage). Say your frame is a 67 and the spindles you got were off a 75. You would need 67 inner tie rods and 75 outer tie rods, because remember the outer tie rod connects to the spindle you got from a 75. If you buy a 67 outer tie rod, it will not work. Now the funny part, because the years have different thread sizes you can’t just use the typical linkage to connect the two, you need a special made linkage with two different size threads. Performance online sells them (which I will list below) and I’m sure others do also. So, what’s left? Ball joints (yes you need new ones for the new spindles), hub assemblies and calipers. Ball joints are easy, you need them to match the year of the spindle. The hub assembly is also straight forward, you just need a hub assembly to match the year of the spindle it sits on. The hub assembly encompasses an inner and outer wheel bearing, inner bearing seal, dust cap, rotor and studs. If you buy the hub assembly new it is well worth it, it comes with bearing races already pressed in and studs. So, you just need to buy bearings, inner seals and dust caps for that year hub/rotor assembly. See the pattern? Oh, you will also need different lug nuts to match the new hub assembly.

Tools needed:
-Basic tools (assuming you have done some minimal automotive work).
-Press or a master ball joint press kit (the big one with all the extra size adapters) or you can take the control arms completely off and to a shop (big pain though).
-Impact gun for the spindle castle nut (makes it way easier).
-Breaker bar (ball joint nuts where you can’t get an impact to).
-A way to compress a spring. I used a jack under the lower control arm and a ratchet strap over the upper control arm to the jack. My spring compressor wouldn’t fit in this application and I wasn’t going to buy another one. Just a safety note: these springs are under a ton of compression, be very careful. Dropping a control arm without compressing the spring can cause it to fly out and kill you. It is very dangerous. Do your research.
-Grinder to remove old upper ball joint rivets and likely an air chisel with a punch attachment to push the stud out of the hole.
-Grease gun with high temp wheel bearing grease to lube everything up when you’re done.

Parts List (my donor spindles were from a 1975):
Spindles/spindle nuts and dust covers 73-87.
Hub/rotor assembly (x2): (1975) Napa part 4885679
Calipers (L/R): (1975) Napa parts SE4587 and SE4586 (Note: there is a core fee)
Inner bearing seal (x2): (1975) Advance Auto part 8974S (National Oil Seal)
Inner bearing (x2): (1975) Advance Auto part 15103S (National Bearing)
Outer bearing (x2): (1975) Advance Auto part A35 (National Bearing)
Dust Cap (x2): (1975) Advance Auto part 13997

Performance Online (tie rods, linkages and ball joints.
Inner Tie rod (x2): POL uses the 1965-70 outer tie rod end as the inners. POL part ES358L.
Outer Tie rod (x2): POL uses the 1971-87 outers for the outers. POL part ES409R.
Tie rod linkage (x2): To be used with POL (POL ES358L & ES409R, 5/8” to 11/16”), part HPAS6570.
Upper Ball Joint (x2): (71-87) POL part FA681.
Lower Ball Joint (x2): (71-87) POL part FA997.

Cost:
$175 from POL on tie rods and ball joints, $100 on KBS paint kit, $300 at napa on hubs/rotors/calipers, $70 at advanced auto on bearings seals and dust covers. All I needed was spindles from a square body which I got for free. Maybe 45 bucks on grease and some other random stuff I bought. So $700 total and that was buying the highest quality bearings/tie rods/ball joints I could get. To buy the same kit online would have been $1200 for 8 lugs and I wasn't too confident in the quality or sending some random website 1200 bucks.

Special note:
Factory 15" steel wheels will fit over the rotors but you cannot install the calipers until you get larger wheels.

[Big Kev-O]

What about the front brake hose? Do the drum brake hoses fit the disc calipers? I thought the disc calipers used banjo style hoses.

BTW I'm sure somebody will find your parts list useful. I just had to return the Timken wheel bearings I purchased from RockAuto because they were to small. They have Set3 & Set5 bearing listed as compatible with C20s but they are actually for C10s. Now I have the correct National bearing you listed. I also found out C20 Brake boosters and Master cylinders are not the same a C10 despite many listing selling them as one in the same.

[May70]

I will update with the rest of the brake info once I complete it. I haven't gotten that far. Ive been trying to finish a floor pan install for a few weeks now. A lot of wheels turning here

[May70]

I tested a few different hoses and determined the best route was to drill out a hole on the front side of the upper control arms (how they come factory with discs) and use O'Reilly Part numbers (BH86550 / BH86551). Much happier with these than some of the others I found on the forum - zero contact and the hose isn't bending back over itself.

This thread covered the discussion on brake hose selection and re-routing.

https://67-72chevytrucks.com/vboard/...d.php?t=832601

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Obviously it is likely that if you are going to this effort of modernization you will also be looking at upgrading to power steering (if you do not already have it). I decided to abandon my power assist setup and took the square body donor PS gear, pitman arm and center link. PS gear seals were shot, after three rebuild kits with the wrong seals. Three weeks of messing around with it, I said screw it and ordered a red head gear.

Selection of the gear was based on two things:
Quick vs standard
O ring vs flare fitting style

I chose the standard ratio box with the o ring style fittings as that will be directly compatible with the ls style pump fittings. Read head gear PN#2856 (3 Turn): 1980-1991 Chevrolet gear.

More info on gear/ratio selection here:
https://67-72chevytrucks.com/vboard/...d.php?t=836032 (Ratio thoughts)
https://67-72chevytrucks.com/vboard/...d.php?t=833856 (Rebuild kit mismatch issue)

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If you are installing a power steering unit onto a 1967 frame, those frames do not have a dimple which compensates for the power gears more obtruding size. Therefore you either have to dimple the frame or offset the gear. Offset is arguably minimum (less than 1/4 inch) and I had already finished painting my frame so I opted for for the spacers. Grumpy did caution the implications, which some may consider acceptable. Geometry is offset, which leaves one direction of turn less aggressive. As long as you have a good front end guy I don't see this being an issue. I have tested this and I am not worried about it.

Core support bracket will also have to be slightly trimmed.

More info here:
https://67-72chevytrucks.com/vboard/...d.php?t=836267

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Pitman arm is a Moog K6143

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Correction to this-
"Special note:
Factory 15" steel wheels will fit over the rotors but you cannot install the calipers until you get larger wheels."

I had read that somewhere and just believed it (mis-information). My stock 15" wheels have no issue with calipers bolted on.



Hope this helps.