Brake question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**Bernie** · 12-31-2003, 07:19 PM

I know questions about brake setups have been asked before. I did a search and seemed to get contradictory results.

Here's my question. I have a, mostly 1969, K20 with axles off a 1978 so there are discs on the front and huge drums on the rear. I need a master cylinder, booster and prop valve. Someone said that it is better to go with the 1971 3/4 ton setup because the 1978 rod would be the wrong length. I can see this, but on the other hand there were several master cylinders for use in 1978. Which one you used depended on the size of the rear brake drums. So would a 71/72 master cylinder for disc/drum work with all 78 systems ? Or are the rods really the same and I should go with a 78 master cylinder ? Sorry so long , I'm deeply confused. Thanks

gr8scott51 · 12-31-2003, 07:55 PM

I'd use the 71/72 booser/master cylinder to mate with your brake pedal linkage. The proportioning valve has to be for disc/drum. If the 78 rear drums are larger than 11", you may have to use an adjustable proportioning valve to get the right balance.

good luck, scott

**Bernie** · 01-01-2004, 12:46 PM

Thanks for the reply Scott. I know that this is a fairly common swap. I would really appreciate hearing from more people who've done it. Thanks

12-31-2003, 07:19 PM	#1
Bernie Senior Member Join Date: Jan 2001 Location: Northern Illinois Posts: 516	Brake question I know questions about brake setups have been asked before. I did a search and seemed to get contradictory results. Here's my question. I have a, mostly 1969, K20 with axles off a 1978 so there are discs on the front and huge drums on the rear. I need a master cylinder, booster and prop valve. Someone said that it is better to go with the 1971 3/4 ton setup because the 1978 rod would be the wrong length. I can see this, but on the other hand there were several master cylinders for use in 1978. Which one you used depended on the size of the rear brake drums. So would a 71/72 master cylinder for disc/drum work with all 78 systems ? Or are the rods really the same and I should go with a 78 master cylinder ? Sorry so long , I'm deeply confused. Thanks __________________ Bernie

12-31-2003, 07:55 PM	#2
gr8scott51 Registered User Join Date: Mar 2003 Location: Bremerton, WA Posts: 1,839	I'd use the 71/72 booser/master cylinder to mate with your brake pedal linkage. The proportioning valve has to be for disc/drum. If the 78 rear drums are larger than 11", you may have to use an adjustable proportioning valve to get the right balance. good luck, scott __________________ Silence is golden, duct tape is silver. - Scott

01-01-2004, 12:46 PM	#3
Bernie Senior Member Join Date: Jan 2001 Location: Northern Illinois Posts: 516	Thanks for the reply Scott. I know that this is a fairly common swap. I would really appreciate hearing from more people who've done it. Thanks __________________ Bernie



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