70 drum to disk - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jbailey · 11-01-2013, 04:57 PM

Ok have you ever read so much you just confuse your self more?

That is where I am at so thought I would throw it out there make sure I am on the right track.

I have a 70 with a power booster and M/C can I use for disk in the front and drums in the rear. My original plan was to buy a new booster and M/C but if I can reuse mine why not?

So can I just buy the proportioning valve for a disk/drum one? And could I use the adjustable one that mounts on the frame rail near the rear brakes?

I have been doing a restore on this truck and just got the cab back on the frame and hoping to start putting back together.

Here is a link to my build
http://67-72chevytrucks.com/vboard/s...d.php?t=600795

And thanks for the help

Longhorn 70 · 11-01-2013, 11:17 PM

I did my C20 front Drum to Disc. I did change the master cylinder for a 71 with disc brake cylinder. The disc/drum cylinders do have a bigger bore. Truth be told the original one did work OK but not as well as the new bigger bore.

I had to shorten the pushrod in the booster as the drum/drum master had a deeper cylinder bore. The didtribution block should be changed to a proportioning valve for disc/drum. In the first pic you can see the new proportioning valve. Note that if you have a C20 or C30 you cross the brake lines from the master. You leave them uncrossed if you have a C10.

The second pic is what the disc install ended up looking like. If I had to do it again I definately would!

You'll like the better stopping power especially in deep water. Good luck buddy. And Welcome to the board.

jbailey · 11-02-2013, 09:40 AM

Thanks for the info.

Just to be clear I should replace the M/C and the proportioning valve? I will do some research on the push rod I am sure its explained on this site some where.

any one have experience with the proportioning valve that mounts on the frame rail near the back? just wondering if that would be better because it is adjustable.

**WIDESIDE72** · 11-02-2013, 01:44 PM

Yes you need to change mc and prop vale when switching from drum to disc. I have never messed with the brake rod when doing this but the two i did already had power brakes. I used the existing boosters i both as well

jbailey · 11-02-2013, 06:52 PM

Got it. Keep booster and replace M/C and proportioning valve. Thanks

ReeseBobby · 11-03-2013, 05:43 PM

I didn't replace the M/C when I did mine on the K20. I might eventually but it's fine so far. You could always try it as is.

11-01-2013, 04:57 PM	#1
jbailey Registered User Join Date: Dec 2012 Location: Valley Springs CA Posts: 28	70 drum to disk Ok have you ever read so much you just confuse your self more? That is where I am at so thought I would throw it out there make sure I am on the right track. I have a 70 with a power booster and M/C can I use for disk in the front and drums in the rear. My original plan was to buy a new booster and M/C but if I can reuse mine why not? So can I just buy the proportioning valve for a disk/drum one? And could I use the adjustable one that mounts on the frame rail near the rear brakes? I have been doing a restore on this truck and just got the cab back on the frame and hoping to start putting back together. Here is a link to my build http://67-72chevytrucks.com/vboard/s...d.php?t=600795 And thanks for the help Attached Images

11-01-2013, 11:17 PM	#2
Longhorn 70 Registered User Join Date: Dec 2012 Location: Chandler AZ Posts: 1,149	Re: 70 drum to disk I did my C20 front Drum to Disc. I did change the master cylinder for a 71 with disc brake cylinder. The disc/drum cylinders do have a bigger bore. Truth be told the original one did work OK but not as well as the new bigger bore. I had to shorten the pushrod in the booster as the drum/drum master had a deeper cylinder bore. The didtribution block should be changed to a proportioning valve for disc/drum. In the first pic you can see the new proportioning valve. Note that if you have a C20 or C30 you cross the brake lines from the master. You leave them uncrossed if you have a C10. The second pic is what the disc install ended up looking like. If I had to do it again I definately would! You'll like the better stopping power especially in deep water. Good luck buddy. And Welcome to the board. Attached Images __________________ 1970 Longhorn, Front Disc, 350/4 bolt, 882 heads, HEI, Edelbrock, 700R4, HO-52/4.11. 1996 Corvette, Collector Roadster, LT4, 396, 450RWHP, 6sp, 4.11/Dana44/posi 5 point roll bar And let us not grow weary of doing good, for in due season we will reap, if we do not give up. Gal 6:9 Last edited by Longhorn 70; 11-01-2013 at 11:30 PM.

11-02-2013, 09:40 AM	#3
jbailey Registered User Join Date: Dec 2012 Location: Valley Springs CA Posts: 28	Re: 70 drum to disk Thanks for the info. Just to be clear I should replace the M/C and the proportioning valve? I will do some research on the push rod I am sure its explained on this site some where. any one have experience with the proportioning valve that mounts on the frame rail near the back? just wondering if that would be better because it is adjustable.

11-02-2013, 01:44 PM	#4
WIDESIDE72 Senior Member Join Date: Aug 2008 Location: Cedar Park, Texas Posts: 7,494	Re: 70 drum to disk Yes you need to change mc and prop vale when switching from drum to disc. I have never messed with the brake rod when doing this but the two i did already had power brakes. I used the existing boosters i both as well

11-02-2013, 06:52 PM	#5
jbailey Registered User Join Date: Dec 2012 Location: Valley Springs CA Posts: 28	Re: 70 drum to disk Got it. Keep booster and replace M/C and proportioning valve. Thanks

11-03-2013, 05:43 PM	#6
ReeseBobby Registered User Join Date: Apr 2013 Location: Portland, OR Posts: 38	Re: 70 drum to disk I didn't replace the M/C when I did mine on the K20. I might eventually but it's fine so far. You could always try it as is.



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