'70 drums -> '78 discs (8-lug) - The 1947 - Present Chevrolet & GMC Truck Message Board Network

jkeady · 10-09-2009, 02:34 PM

Hi all, I poked around to see if this had been discussed but didn't find anything specific. Hopefully I'm not dredging up something that's been discussed a million times.

I've got a line on a pretty complete '78 3/4 ton front end for a disc brake swap on my truck ('70 3/4 ton with power drums). It's got calipers, caliper brackets, rotors, spindles, A arms, and the front cross member.

My question is: is this a good swap? Other questions:

Cross member: will the new one bolt up to my frame, or will I have to drill?

Steering: I assume that I'll need to at least get new outer tie rod ends... will they just bolt up and be good to go?

Master cylinder: I assume I'll need a new one, will the '78 3/4 ton disc M/C bolt up to my current booster?

Springs: will my '70 springs work?

Wheels: I'm still running stock size 16.5" rims; good to go there, right?

Any other thoughts?

Thanks in advance for your input, folks.

Josh

LONGHAIR · 10-09-2009, 02:48 PM

It will bolt up, for the most part. Two holes will need to be drilled, but the others line up. As for the master cylinder, yes it will need to be replaced. Booster, I just don't know. The only time I ever did this, the drum truck didn't have power brakes to start with, so it was a full swap from the donor.
We swapped the tie rods and all, so I don't know about yours fitting the drum spindles?...same with the springs.
Yes, the 16.5 wheel will fit with the caliper.

jkeady · 10-09-2009, 03:18 PM

Thanks. I assume the reason that I can't just do a spindle swap is because the spindles use ball joints that won't work in my A-arms and the A-arms won't work on my cross member... right?

Longhorn Man · 10-09-2009, 04:45 PM

while i can never rememberr the details of this, I can say a crossmember swap is simple if you plan on already having the motor out.
While the 16.5 rims will clear, they won't bolt on. The 70 and older 8 lug trucks were 1/2 inch stud, in 71 they went to 9/16ths.

jkeady · 10-09-2009, 06:13 PM

Cool, thanks for the feedback. This is exactly what I needed to know.

I'll skip it for now and make this a Spring project. Too much other stuff to worry about now.

10-09-2009, 02:34 PM	#1
jkeady Registered User Join Date: Apr 2004 Location: Salem, OR Posts: 127	'70 drums -> '78 discs (8-lug) Hi all, I poked around to see if this had been discussed but didn't find anything specific. Hopefully I'm not dredging up something that's been discussed a million times. I've got a line on a pretty complete '78 3/4 ton front end for a disc brake swap on my truck ('70 3/4 ton with power drums). It's got calipers, caliper brackets, rotors, spindles, A arms, and the front cross member. My question is: is this a good swap? Other questions: Cross member: will the new one bolt up to my frame, or will I have to drill? Steering: I assume that I'll need to at least get new outer tie rod ends... will they just bolt up and be good to go? Master cylinder: I assume I'll need a new one, will the '78 3/4 ton disc M/C bolt up to my current booster? Springs: will my '70 springs work? Wheels: I'm still running stock size 16.5" rims; good to go there, right? Any other thoughts? Thanks in advance for your input, folks. Josh __________________ Josh '70 Custom Camper / 20 Last edited by jkeady; 10-09-2009 at 02:36 PM.

10-09-2009, 03:18 PM	#3
jkeady Registered User Join Date: Apr 2004 Location: Salem, OR Posts: 127	Re: '70 drums -> '78 discs (8-lug) Thanks. I assume the reason that I can't just do a spindle swap is because the spindles use ball joints that won't work in my A-arms and the A-arms won't work on my cross member... right? __________________ Josh '70 Custom Camper / 20

10-09-2009, 04:45 PM	#4
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: '70 drums -> '78 discs (8-lug) while i can never rememberr the details of this, I can say a crossmember swap is simple if you plan on already having the motor out. While the 16.5 rims will clear, they won't bolt on. The 70 and older 8 lug trucks were 1/2 inch stud, in 71 they went to 9/16ths.

10-09-2009, 06:13 PM	#5
jkeady Registered User Join Date: Apr 2004 Location: Salem, OR Posts: 127	Re: '70 drums -> '78 discs (8-lug) Cool, thanks for the feedback. This is exactly what I needed to know. I'll skip it for now and make this a Spring project. Too much other stuff to worry about now. __________________ Josh '70 Custom Camper / 20



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