Brake Question on Frame conversion truck

[Auctioneerhere]

I have a 65 GMC body on a 1975 frame.

All the 1975 brake lines are intact, so I am wondering what master cylinder will work & just "bolt up" to the firewall.

I don't need power brakes, so just looking for a Master Cyl that will work.

I tried a 1970 Impala drum/ drum, but it did not act like it was going to work.

[Captainfab]

You just need a manual master cylinder for a '75 truck.

[AcampoDave]

I don't think the piston on a 75 mc has a deep enough recess to accommodate your stock pushrod. Check out a 72. That's what I run on my 66 with a late 70's front cross member and the piston recess depth is the same as stock. Works great no booster.

[Auctioneerhere]

Thanks, I have both, so I will try them.

[AcampoDave]

Captainfab, is a manual disc mc for a 75 different than a power booster style? I once mistakenly bought a late 70's booster style m.c. thinking I could use it, but the piston only had a shallow dimple for the pushrod.

[Captainfab]

No. The '73+ manual master cylinders are not the same as the power masters. The manual masters I have seen actually have the pushrod secured to the piston in the master

Originally Posted by AcampoDave

Captainfab, is a manual disc mc for a 75 different than a power booster style? I once mistakenly bought a late 70's booster style m.c. thinking I could use it, but the piston only had a shallow dimple for the pushrod.

[AcampoDave]

Thanks I never knew that. I havent seen many squarebodies with manual brakes.

[Auctioneerhere]

Heading to CarQuest to get a 1972 disks, no power master cyl.

I asked for a 1973+ & they said book shows same part number.

We will see.

[Auctioneerhere]

Here is what I found... the rear of the master Cyl for the "newer" 73 up truck is not recessed so it will not bolt up.

I screwed up & actually bled it first before test fitting it.

I suppose I can call another parts store.

I'd like to just drill it out some but I have no idea how much metal I have to play with there.

[luvbowties]

Originally Posted by Auctioneerhere

Here is what I found... the rear of the master Cyl for the "newer" 73 up truck is not recessed so it will not bolt up.

I screwed up & actually bled it first before test fitting it.

I suppose I can call another parts store.

I'd like to just drill it out some but I have no idea how much metal I have to play with there.

Since you'll be driving the truck, why not make the truck fit the '75 mc? Shorten the brake rod, & future m/c-replacements will be stock '75 units--like the Captain 1st advised. To know exact amt. to shorten, measure depth of the the recess in the recessed piston. Or, unbolt rod, bolt up the '75 m/c, & measure how much too long your rod is to bolt back up to pedal assy.
Make the end of the rod rounded like a bullet-nose, so bevel in m/c will hold rod centered. [If a builder were a perfectionist, he might cut a section from the rod, thread the 2 ends, and install a connecting-nut* with jamb nuts to make it infinitely-adjustable.]

This way, there'll be just 2 model years(instead of 3) to remember--a '65 and a '75!
*Can never recall technical name of this approximately 1" to 1 3/4" long nut, sold by Lowes for one source. EDIT: "coupling nut"!!!
Hope this makes sense,
Sam

[Auctioneerhere]

Originally Posted by luvbowties

Since you'll be driving the truck, why not make the truck fit the '75 mc? Shorten the brake rod, & future m/c-replacements will be stock '75 units--like the Captain 1st advised. To know exact amt. to shorten, measure depth of the the recess in the recessed piston. Or, unbolt rod, bolt up the '75 m/c, & measure how much too long your rod is to bolt back up to pedal assy.
Make the end of the rod rounded like a bullet-nose, so bevel in m/c will hold rod centered. [If a builder were a perfectionist, he might cut a section from the rod, thread the 2 ends, and install a connecting-nut* with jamb nuts to make it infinitely-adjustable.]

This way, there'll be just 2 model years(instead of 3) to remember--a '65 and a '75!
*Can never recall technical name of this approximately 1" to 1 3/4" long nut, sold by Lowes for one source. EDIT: "coupling nut"!!!
Hope this makes sense,
Sam

I pretty good on fabbing things up, I just want to bolt & go. I do like the design of the older MC better for this application.

This is for a pulling truck, it won't be street driven much.

[AcampoDave]

That was my experience too. The 73 and up I got was way shallow. When the parts guy brought out the 72 the difference was clear. I believe 71 to be the same as 72. After buying a 72, I called Early Classic and asked if that is what they used in their kits and they said yes. My 72 m.c. piston recess is exactly the same as my stocker was. The push rod has to fit because if it bolts up with even a bit of pressure applied on the piston, brake bleeding becomes a bear because it wont fully retract.

[61K10]

call master power brakes---they can send you the right m/c piston