MC years/interchangeablility - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**JIMs70GMC** · 06-20-2015, 07:52 PM

Will a MC from a 1985 work on an 1983? I have a MC w/ hard lines to the proportioning valve from a 1985 I want to put on my 1983. I included some pics. I think my 1983 MC has an internal seal problem because after I bleed the brakes and get the pedal where it is nice and firm, a couple pushes later it gets soft again and goes to the floor. Thanks,

**JIMs70GMC** · 06-20-2015, 10:37 PM

Answered my own question, will not work. Different GVW ratings.

Keith Seymore · 06-21-2015, 10:39 AM

I'd try it and see.

Here's all the ways (that I can think of, offhand) that a master cylinder swap will not work:

bore size
quick take up vs non (affects the diameter of the housing at the rear)
flare size
ISO vs SAE flares
outlets on inboard side vs outlet on the outboard side
front outlet goes to front system vs front outlet goes to rear

Judging by the pics you posted it looks like it would drop in. I'd try it, checking for pedal travel, effort and force. Especially since it is a relatively easy swap.

K

69heavychevy · 06-21-2015, 11:56 PM

It should work...I swapped the master cylinder in my 80 C10 with 1.25" rotors and 2" rear brakes with a MC from an 83 C10 with 1" rotors and 2-3/4" rear brakes. I swapped over the booster and MC hard lines as well since my original hard lines wouldn't line up correctly to the 83 MC.

BTW my original MC looked like the one in your second pic and my replacement looked like the one in the first pic.

06-20-2015, 07:52 PM	#1
JIMs70GMC user # 2756 Join Date: Jun 2001 Location: Chesapeake, Virginia Posts: 4,612	MC years/interchangeablility Will a MC from a 1985 work on an 1983? I have a MC w/ hard lines to the proportioning valve from a 1985 I want to put on my 1983. I included some pics. I think my 1983 MC has an internal seal problem because after I bleed the brakes and get the pedal where it is nice and firm, a couple pushes later it gets soft again and goes to the floor. Thanks, Attached Images __________________ 1970 K25, 8' stepside bed 350/465/205 44 up front, 60 in the rear 4.10s rolling on 33" Dunlop MTs 1986 K5, 350/465/208 Dana 60/14 bolt from a cucv 36" Super Swampers TSL/SX 1983 K20 w/ CUCV axles, 350/700R4/208 sitting on 37" Goodyears 1986 M1031 6.2 diesel, TH400/NP205 locker in the rear and a LS in the front, all stock for now..... 1986 K30, 350/400/205 dana 60 and 14 bolt. I kept the drivetrain. Body/bad and chassis are gone. 1981 K30, 350/465/205 dana 60 and dually 14 bolt. Has a G80, and a flat bed. Going to replace the flat bed. 1985 K20, 350/400/208 10 bolt and SF 14 bolt. I wonder where I can find some 1 tons. Hmmmmm

06-20-2015, 10:37 PM	#2
JIMs70GMC user # 2756 Join Date: Jun 2001 Location: Chesapeake, Virginia Posts: 4,612	Re: MC years/interchangeablility Answered my own question, will not work. Different GVW ratings. __________________ 1970 K25, 8' stepside bed 350/465/205 44 up front, 60 in the rear 4.10s rolling on 33" Dunlop MTs 1986 K5, 350/465/208 Dana 60/14 bolt from a cucv 36" Super Swampers TSL/SX 1983 K20 w/ CUCV axles, 350/700R4/208 sitting on 37" Goodyears 1986 M1031 6.2 diesel, TH400/NP205 locker in the rear and a LS in the front, all stock for now..... 1986 K30, 350/400/205 dana 60 and 14 bolt. I kept the drivetrain. Body/bad and chassis are gone. 1981 K30, 350/465/205 dana 60 and dually 14 bolt. Has a G80, and a flat bed. Going to replace the flat bed. 1985 K20, 350/400/208 10 bolt and SF 14 bolt. I wonder where I can find some 1 tons. Hmmmmm

06-21-2015, 10:39 AM	#3
Keith Seymore Registered User Join Date: May 2009 Location: Motor City Posts: 9,166	Re: MC years/interchangeablility I'd try it and see. Here's all the ways (that I can think of, offhand) that a master cylinder swap will not work: bore size quick take up vs non (affects the diameter of the housing at the rear) flare size ISO vs SAE flares outlets on inboard side vs outlet on the outboard side front outlet goes to front system vs front outlet goes to rear Judging by the pics you posted it looks like it would drop in. I'd try it, checking for pedal travel, effort and force. Especially since it is a relatively easy swap. K __________________ Chevrolet Flint Assembly 1979-1986 GM Full Size Truck Engineering 1986 - 2019 Intro from an Old Assembly Guy: http://67-72chevytrucks.com/vboard/s...d.php?t=342926 My Pontiac story: http://forums.maxperformanceinc.com/...d.php?t=560524 Chevelle intro: http://www.superchevy.com/features/s...hevy-chevelle/ Last edited by Keith Seymore; 06-22-2015 at 07:32 AM.

06-21-2015, 11:56 PM	#4
69heavychevy Registered User Join Date: Jan 2007 Location: Garland,TX Posts: 431	Re: MC years/interchangeablility It should work...I swapped the master cylinder in my 80 C10 with 1.25" rotors and 2" rear brakes with a MC from an 83 C10 with 1" rotors and 2-3/4" rear brakes. I swapped over the booster and MC hard lines as well since my original hard lines wouldn't line up correctly to the 83 MC. BTW my original MC looked like the one in your second pic and my replacement looked like the one in the first pic. __________________ 80 C10 SWB Step Side - 350 w/ vortec heads, TH350, 12-bolt 3.73



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