3/4 ton master cyl. in 1/2 ton truck? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Southpa · 06-10-2002, 02:42 PM

Its nice to be home again, staying this time. I want to ask about swapping my master cylinder which is leaking out the cap so much that I have to hang a can under it to catch the "drippings".
Its a 1970 1/2 ton but I've swapped front ends with a 71 so now I have front disc brakes. I installed a 3/4 ton booster and have a 1/2 ton master (leaker) with the single hold-down clip. What I want to do is replace it with a 3/4 ton master (the kind with 2 hold down clips). Any problems with that? Are the line fittings to the prop. valve the same size? Would this produce too much pressure to my front calipers and/or rear wheel cylinders? or are all calipers/wheel cylinders basically the same between 3/4 and 1/2 tons? Any suggestions? much appreciated!

Mike C · 06-10-2002, 07:07 PM

The brake system is carefully engineered for the diameter of the pistons in the rear and in the front. You can get the 1/2 ton master with 2 hold downs. If you do run the 3/4 and I would not, the size of the fittings that screw into it are reversed, just so somebody WOULDN't do that

Longhorn Man · 06-10-2002, 07:43 PM

Plus, out of the 3 trucks I have owned, which gives me 6 master cylinders to date, EVERY ONE leaked like that.
I've tried tightening the clip, but that never seems to help.

1-PU70 · 06-10-2002, 08:45 PM

To get the cover from leaking with the master still on the truck remove some fluid from the master then stuff some rags in it. Take a pice of glass or flat pice of steel and sand the lip around the master till it is smoth. Should take care of any leaks.

>X< · 06-10-2002, 10:16 PM

i'm kinda doin somethig like that,. i'm using discs from my 72 3/4ton on my 1/2 ton project, the people at early classic told me that i could ust the master cyllander if i wanted to, but if i put some rear discs on it i will have to change it anyway, if i use the discs from my 3/4 ton can i use that master cyllinder too?

06-10-2002, 02:42 PM	#1
Southpa Registered User Join Date: May 2000 Location: Victoria, BC, Canada Posts: 2,410	3/4 ton master cyl. in 1/2 ton truck? Its nice to be home again, staying this time. I want to ask about swapping my master cylinder which is leaking out the cap so much that I have to hang a can under it to catch the "drippings". Its a 1970 1/2 ton but I've swapped front ends with a 71 so now I have front disc brakes. I installed a 3/4 ton booster and have a 1/2 ton master (leaker) with the single hold-down clip. What I want to do is replace it with a 3/4 ton master (the kind with 2 hold down clips). Any problems with that? Are the line fittings to the prop. valve the same size? Would this produce too much pressure to my front calipers and/or rear wheel cylinders? or are all calipers/wheel cylinders basically the same between 3/4 and 1/2 tons? Any suggestions? much appreciated! __________________ 1970 GMC 1500 Custom Original 350/TH350 Victoria, BC, Canada You can wish in one hand and crap in the other. See which one gets filled first.

06-10-2002, 07:07 PM	#2
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,712	The brake system is carefully engineered for the diameter of the pistons in the rear and in the front. You can get the 1/2 ton master with 2 hold downs. If you do run the 3/4 and I would not, the size of the fittings that screw into it are reversed, just so somebody WOULDN't do that __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

06-10-2002, 08:45 PM	#4
1-PU70 Registered User Join Date: Apr 2000 Location: Bradenton, FL Posts: 1,036	To get the cover from leaking with the master still on the truck remove some fluid from the master then stuff some rags in it. Take a pice of glass or flat pice of steel and sand the lip around the master till it is smoth. Should take care of any leaks. __________________ 1970 CST/10 402,700R4,3:73 posi,AC,PS,PB,TLT,PW,Buckets with heaters

06-10-2002, 10:16 PM	#5
>X< registered IWATA user Join Date: Feb 2002 Location: Baton Rouge Posts: 4,483	i'm kinda doin somethig like that,. i'm using discs from my 72 3/4ton on my 1/2 ton project, the people at early classic told me that i could ust the master cyllander if i wanted to, but if i put some rear discs on it i will have to change it anyway, if i use the discs from my 3/4 ton can i use that master cyllinder too? __________________ -'63 Ford Fairlane 500 coupe, v8, auto, faded and rusty. awaiting built roller 302 and some flat black -'99 Honda Prelude. vtech/5spd. no pipe, no intake, bone stock. awaiting new top end. -01 GMC Yukon SLT 5.3 dented and scratched with a noisy tranny. Take off that Von Dutch hat before i stab you with a 000 Mack.

06-10-2002, 07:43 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Plus, out of the 3 trucks I have owned, which gives me 6 master cylinders to date, EVERY ONE leaked like that. I've tried tightening the clip, but that never seems to help.



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