GU Break system questions

Hi JoseM
All the systems are the same .There is no proportioning valve the only valve is the load sensing valve.
Your problem can be solved by increasing the booster output , replacing the master with a smaller diameter one [not recommended ] You can also fit high coefficient brake pads.
If the load sensing valve is not adjusted or working properly you can either over brake or under brake the rear which will effect overall braking.
also check the vacuum output ant the booster through the whole braking range

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Originally Posted by Rip'n'Shred

Its been a long time since I did the brake module in my apprenticeship but I think????? if you change the slave cylinder size to a larger size you increase the force applied to the pads but reduce the distance the piston will move. I think???? Maybe someone can confirm this??? Struggling to remember which way around it goes.

I would try to contact a brake expert if I was you.

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Yeah, that is part of the problem, our "experts" :clownredpuff: dont know their arss from a hole in the ground.

I've been all over the net and haven't been able to find pressure ratios for neither system.

What Im trying to figure out is if it would be worth it, changing master cyl and valve (not the rear one (proportioning), they are the same part # for all applications). See, all the components are working perfectly, the thing is that they were not configured to hold a 120lbs/38.5" wheel, therefore Im trying to figure out a way to generate more power than stock. In my truck, stock no longer works for anything anymore...

Usually the master cylinder is a different bore size between the front disc system and 4 wheel disc system. The ABS system does not have any effect on braking unless you have a traction loss or a hard brake application. Check with nissan spares for the part number difference with the master cylinder. Not sure what other valve you are talking about as the master cylinder is what controls the amount of pressure that goes to the calipers by using different size pistons and bores for front and rear brakes.

I forgot about this thread.

I swaped master and booster for a Mustang's hyd booster. It does certainly have some stopping power now...

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Originally Posted by JoseM

I forgot about this thread.

I swaped master and booster for a Mustang's hyd booster. It does certainly have some stopping power now...

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was it a straight swap? have you got any pics? where can i buy one? How much was it?

You will need to change the master cylinder, as Rip'n'shred has stated, the swept volume of the original cylinder would have been designed for a specific system, you will probably find that the piston area for the rear brakes is too small. The piston may be bottoming out or reaching the limit of its travel but still not providing enough hydraulic pressure to provide effective braking. The proportioning valve will adjust pressure depending on load but if you don't have enough pressure to start with, it useless. Larger piston = larger surface area = larger pressures with less piston travel = better brakes.

As stated earlier, time to go to a brake expert.

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Originally Posted by MudRunnerTD

was it a straight swap? have you got any pics? where can i buy one? How much was it?

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http://i693.photobucket.com/albums/v...NTYzLmpwZw.jpg

Got it from a wreckers for $100 usd.

We had to cut and weld the rod for an exact fit with the pedal. And reposition the lower bolts to make it fit on the fire wall as per factory. No big deal.
http://i693.photobucket.com/albums/v...0725-00318.jpg
http://i693.photobucket.com/albums/v...0725-00317.jpg

The pwr steering pump is coping great; however, I had previously put n oil cooler due to some cavitation with the 38s
http://i693.photobucket.com/albums/v...1303090521.jpg

I figured it was easier and faster to become my own expert...