Gmt800 master on gmt400 hydrobooster

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romanos93

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I can't seem to find a thread with relatable information.1999 k2500 crew cab 7.4l. bought with upgraded brakes, 4 wheel disc , from a gmt800. Recently discovered my master cylinder in leaking in the front. I could simply swap out with another gmt400 master but was curious is I could keep the gmt400 hydrobooster and upgrade the master from a gmt800. And if it would be worth it. Thank for any and all inputs!
 

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Supercharged111

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I believe the 800 master won't fit without some grinding, and the 800 hydroboost has a different bolt pattern. . . or am I thinking of the vans? Regardless, if both ends came from a GMT800, the best starting point for a master is what the general offered. Drums don't need as much fluid, so you're probably not getting enough out of the rear brakes as it sits.
 

1998_K1500_Sub

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Upgrading to an 800 MC, with their larger rear-circuit reservoir, would be a wise move. The disc brakes need more reserve fluid volume in the MC than drums do, to accommodate pad wear and the resulting "dead pool" of fluid in the pistons.
 

romanos93

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I believe the 800 master won't fit without some grinding, and the 800 hydroboost has a different bolt pattern. . . or am I thinking of the vans? Regardless, if both ends came from a GMT800, the best starting point for a master is what the general offered. Drums don't need as much fluid, so you're probably not getting enough out of the rear brakes as it sits.
What grinding would be involved? The casting?
 

arrg

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Have a link for it?
 

Schurkey

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What donor vehicle did your brakes come from? Specifically, what bore diameter was the master cylinder they're intended to be used with?

What bore diameter master cylinder do you have now? It's not a Quick Take-Up master, so you must have had JD7 or JD8 brakes originally...right?

As said...you need a larger reservoir for the rear brakes.
 
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