1970 K20 drums to disc conversion
 

Hello Everyone, this is my first post and needing some help. From the little bit of looking around I have seen that most people choose to do an axle swap for this conversion. When doing a search for parts I have also pulled up what looks like conversion kits that are making for this year model now? Anybody know if the axle swap is the only way to go or do the conversion kits work? Thanks!!!

Re: 1970 K20 drums to disc conversion
 

Just a little more information and numbers. The BOM stamped on the long axle is 603036-9 and the drum is a Budd 95478.

Re: 1970 K20 drums to disc conversion
 

You should have the open knuckle housing so you should be able to swap all the knuckle out disc brake parts and axles onto your housing. But if your donor has same gear ratio, then swapping whole thing no more work IME.

Re: 1970 K20 drums to disc conversion
 

Thanks Mike! Would any of the later year model K20's (71,72, etc) with disc brakes work for the knuckles out?

Re: 1970 K20 drums to disc conversion
 

My 67 K10 has a 70 K10 front axle with drum brakes. The only bolt in disk setup for that axle would be out of a 71. 72 and up axles have a different inner axle length and diameter. Not sure if the K20s had the same differences, but you may want to do a little more research for the K20.

There are a few threads discussing the 70 disk conversions. For my K10 I also confirmed the axle differences using the DANA information based on the BOM.

I’ll see if I can find a thread and post the link here.

Re: 1970 K20 drums to disc conversion
 

You have the 1970 aardvark axle, first year open knuckle and last year drum. I ended up getting a newer axle. You can pick from an assortment of front axles that are a straight drop in. if you get a newer axle you may have to change or adapt the soft line for metric and maybe change the lug nuts. I recommend new mounting u-bolts. That's it for the axle( You can pull the Residual pressure valve out of the front reservoir of the master and call that good too!) anything beyond that (for the axle) is an unnecessary exercise IMHO.

My two cents, worth the price paid! :smoke:

Re: 1970 K20 drums to disc conversion
 

Thanks Guys! I believe you have answered my question for me, looks like axle swap it is! Now just need to find to find the donor axles. I haven't had much luck looking online, maybe have better luck at some of the salvage yards or U-pull its close to me.

Re: 1970 K20 drums to disc conversion
 

I'd forget the rear disks since they really add nothing. Look for a 71 and up to 87 (up to 91 burb) K20 front diff.

Re: 1970 K20 drums to disc conversion
 

The only reason I thought of changing both is that the rear axle is a 1 ton (original??) and I have very large spacers already on the back. If what I have read is correct, the disc will add 3" overall length over what I have now on the front. I believe the current gear ratio is 4.09 or.10? I just thought it might be easier to do both rather then trying to match the gears on the donor axle.

Re: 1970 K20 drums to disc conversion
 

I’d start looking thru craigslist in your area for a 3/4 or 1 ton front axle with 4:10s. Keep in mind that if you swap both with the tire size your running I wouldn’t stray to far numerically lower from 4:10 other wise it’s gonna turn into a dog off the line pretty quick. Also with swapping the rear end if you go to a 73-87 rear your limited to 1 ton single rear wheel(not 3/4 ton) being mostly bolt in.(need to change one shock mount) 1/2,3/4, 1 ton dually will all need perches and shock mounts moved.

Re: 1970 K20 drums to disc conversion
 

This is about as close as I can find on craigslist, is it possible to change the front axle to an 8 bolt fairly easy or should I just keep looking?


https://houston.craigslist.org/pts/d...371289618.html

Re: 1970 K20 drums to disc conversion
 

My 2 cent
Doing the same swap now on my 67 k20
The blazer axle my have 3.73 gears very common
Look for another 71-87 3/4 ton
May be easier to find whole truck and scrap what you don't need
I'm using a 76 axle set d44 front and corp 14 rear
Payed 400 for the rust bucket
Good hunting

Hey, I have a 1970 GMC K20 that I’m just about to swap out the rear end for a newer GM 10 bolt Corporate rear end with disc brakes. I’’m looking for a newer front axle to swap out the “aardvark” axle out, and if I’m reading this correctly, I don’t have to replace the brake booster and cylinder?? Is that correct?

Thank you for any reply, I realize this is a pretty old post
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Re: 1970 K20 drums to disc conversion
 

Just out of curiosity why are you putting a half ton axle in a K20?

Haha, my bad. It’s a 14, not 10. Got all my numbers jumbled up. I’m not downsizing at all. Trying to upgrade actually, and make sure my brakes can stop my heavy steel flatbed and a 10,000 pound trailer with trailer brakes. I’m trying to get it up and running right now, then start upgrading and replacing everything, starting with the wiring, then rebuilding....everything. Currently looking at a Dana 60 to replace my Dana 44 front end
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Re: 1970 K20 drums to disc conversion
 

That’s more like it! Those aam disk brake 14’s are pretty sweet I’ve got 2 of them my self. That and a 60 should be bomb proof. Just an FYI somewhere around ‘11 or ‘12 (can’t remember the exact year off the top of my head) or so they changed the wheel bolt pattern to a metric pattern. Before then the bolt pattern is the same as our trucks. Maybe in another thread you could post some pictures of your progress we love pictures around here! With your goals in mind I think I’d suggest going with a hydraboost setup and a disk disk master cylinder personally. I’ve got the hydraboost on mine and it’s one of the best mods I’ve done to it so far. If your curious on how I did it, there’s pictures on the last few pictures in the link in my signature.

Re: 1970 K20 drums to disc conversion
 

I’m trying to get a new thread started, but I’m a REALLY new member, and don’t have a computer. So it’s a challenge haha. Anyway. I’m putting this axle in today and ran into two things that I don’t think I saw in your thread. What was the soft line that you used from the stock hard lines to the rear axle? I’m looking at two different setups and am a little lost.

Re: 1970 K20 drums to disc conversion
 

Sorry I should have been more specific, my truck has an old school drum 14 bolt in it. I’ve got two of the aam rears in the shop for a later day. On the main 67-72 discussion page there is a link you can click that says new thread. Click that and you can start another thread. It’ll probably get more traffic than this one. I can help you on the line honestly.

Re: 1970 K20 drums to disc conversion
 

I would check this dude from Fort Worth out, seems cheaper and much easier than finding a donor these days.....

https://youtube.com/playlist?list=PL...Vg-BELo4e3_vxa

Re: 1970 K20 drums to disc conversion
 

3 yr old thread....