Gmt800 master on gmt400 hydrobooster

[Erik the Awful]

If the master cylinder has a larger bore, it will move more fluid, but you won't be able to develop the same brake system pressure. That was one of the problems people were having with throwing GMT800 master cylinders onto the GMT400 brake system. The pedal felt nice, but in an emergency stop they couldn't even get near getting their brakes to lock up because the force multiplication wasn't there.

The master cylinder size has to be in correct proportion to the size of the front calipers and the rear cylinders/calipers. If the master cylinder is too small, you'll get a higher force, but only if it can move enough fluid to get the pads in contact with the rotors. If the master cylinder is too large, you get a lower force, but you can move the pads further.

Calipers typically use more fluid than wheel cylinders, so that's why the GMT800 has a larger bore.

Fun related fact - the average person can only press hard enough on the pedal to use about 1/4 of the braking power of a Formula One car.

 

[romanos93]

If the master cylinder has a larger bore, it will move more fluid, but you won't be able to develop the same brake system pressure. That was one of the problems people were having with throwing GMT800 master cylinders onto the GMT400 brake system. The pedal felt nice, but in an emergency stop they couldn't even get near getting their brakes to lock up because the force multiplication wasn't there.

The master cylinder size has to be in correct proportion to the size of the front calipers and the rear cylinders/calipers. If the master cylinder is too small, you'll get a higher force, but only if it can move enough fluid to get the pads in contact with the rotors. If the master cylinder is too large, you get a lower force, but you can move the pads further.

Calipers typically use more fluid than wheel cylinders, so that's why the GMT800 has a larger bore.

Fun related fact - the average person can only press hard enough on the pedal to use about 1/4 of the braking power of a Formula One car.

So in my case a 800 mc should be beneficial? I wish my current master had a part number on it but it's definitely a 400 from looking at it.

 

[romanos93]

I would expect JB6 brakes to have a Quick Take-Up master cylinder, and to have a vacuum booster. Neither of those are present on your truck. One wonders if the hydroboost and non-Quick Take-Up master cylinder have been "upgraded" from a greater GVW GMT400.

JD6 might have Hydroboost, but still with the QTU master.

But GM has not been consistent in the option codes.

What I was told when I picked it up was just the calibers I do have a tag on my hydro but not the master unfortunately.

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[Erik the Awful]

So in my case a 800 mc should be beneficial? I wish my current master had a part number on it but it's definitely a 400 from looking at it.

If you have GMT800 brakes, you want the GMT800 master cylinder. If you have a mish-mash, go fully GMT400 or GMT800.

If you're feeling really froggy, research brake system math, get the specs for each part in the brake system, build a spreadsheet, and buy the parts you want that don't throw the numbers out of spec.

Master Cylinder Math - JOES Racing Products

www.joesracing.com