GU Break system questions

Hello all!
Not long ago I swaped my rear dif with drum breaks for one with disc breaks, but I jumped to the opportunity without doing the homework -- it was free :wink:

What is the pressure difference on the break system for a GU with 4 wheel disc breaks vs one with rear drum breaks? Is this regulated by the valve or both the valve and master? Dont have ABS...

Im asking, 'cause there is no difference on breaking power and Im thinking it could be due to lack of pressure. Any better ideas?

BTW. Got a 2000 TB45 with 38.5" tires 15" wide :icon_bonk:

Hi mate,

There is a Brake proportioning valve on the rear diff to balance the brake output front and back. It is spring loaded and will vary depending on the weight of the car on the day of braking. ie. if it is empty or full will change the proportioning tension.

When doing a lift there is a need to add an extension bracket to the proportioning value to adjust the output.

Just saw your sig line though! 38.5" tyres will severely affect your ability to Brake and stop! Flat, uphill or downhill wont make a difference with rubber that big mate. You will find you have ridiculous run-on downhill and need to ride the brakes hard.

I assume also given that you had Drums on the back that it is a Ute? running 38s you will have a decent lift too? if that is the case you likely dont even have your proportioning valve setup?? If that is the case your back brakes might not even be applying?

Hey Jose, i just saw your intro, nice car mate.

http://i693.photobucket.com/albums/v...MDE2LmpwZw.jpg

the GU wagon came out with 4 wheel disks from scratch in Australia i think?? pretty sure? I note that you have your Gearing and running gear sorted and supporting Aussie traders like superiors. Nice one.

Check your proportioning valve and bracket mate, i have no doubt at all that you have not set it up.

Good luck, it sounds like your club does good work mate.

Thanks for the input mates; however, the day I lifted the troll I did put on the 6" extensiion for the proportioning valve, and I do expect to have some run-on, due to the large rubber and rims (120lbs total :eek:), but my question was somewhat different: Does anyone know if there is a pressure difference between the front disc break sys and the 4 wheel disc break system? Is this regulated by the valve, the master, or both? Anyone...?

See, allthought there will be run-on, there should had been some improvement with the swap, so comming from the fact that the 4 disc system, came out of a zd30 with abs, and knowing that the master and slave for the abs is different to the one I have, I was wandering if anyone knew if and how much would the pressure vary. From common sense, I would think the abs system would have a better capacity to mantain sys pressure, but it doesnt necessarily mean that it would be more pressure, so before getting creative I decided to ask..

P.S.: When I say "the valve" I dont mean the proportioning valve, I refer to the one in the engine bay right after the master...
Also, the TB45 manual (my case) came with rear drum breaks, the auto did bring rear disc as well and abs, not the manual...
Another difference between the two is the r&p, the aut came with 3.9 and the manual with 4.11

No worries Jose, my understanding is that the proportioning valve at the back controls the differential. The system should have equalised pressure to all from after the master cylinder and the proportioning valve allows the user to increase the pressure applied to the back brakes. I still think your problem is at the back?? I certainly am not a brake specialist though and hope you get another response if that does not sort it. When you did the disk brake swap did you readjust the proportioning valve or leave it set as per the drum brake setting?

I would have thought you'd see a reasonable improvement going drum to disk?


Good luck mate.

My same thought exactly, but no noticeable improvement. And no, I did not adjust it, just left it as it was. May be we are getting somewhere. Let me fiddle with it, I'll let you know if it gets better or hit a tree :driving2:

Quote:

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Originally Posted by MudRunnerTD

No worries Jose, my understanding is that the proportioning valve at the back controls the differential. The system should have equalised pressure to all from after the master cylinder and the proportioning valve allows the user to increase the pressure applied to the back brakes. I still think your problem is at the back?? I certainly am not a brake specialist though and hope you get another response if that does not sort it. When you did the disk brake swap did you readjust the proportioning valve or leave it set as per the drum brake setting?

I would have thought you'd see a reasonable improvement going drum to disk?


Good luck mate.

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Proportioning valves and brake fluid pressures are definitely worth looking into, but I don't know if you'd feel much difference from swapping drum to disc...
Drums have good stopping power as they have a pretty good surface area and a self energising action, they just tend to fade much faster than discs as heat dissipation is far poorer.

I agree with bear. Drums are great at stopping power, just have problems with heat, water, mud, etc.

I would think that a disc drum setup would have a different master cylinder than a disc disc setup. More than likely.

It all comes down to piston sizes of both master and slave cylinders (or calipers) that dictates hydraulic pressure and clamping force.

My initial question exactly. I have not been able to obtain actual info to back up my thoughts. I know the master and slave are different, but dont know if the actually work at higher pressures...

Quote:

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Originally Posted by Rip'n'Shred

I agree with bear. Drums are great at stopping power, just have problems with heat, water, mud, etc.

I would think that a disc drum setup would have a different master cylinder than a disc disc setup. More than likely.

It all comes down to piston sizes of both master and slave cylinders (or calipers) that dictates hydraulic pressure and clamping force.

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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.

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

Quote:

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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...

Quote:

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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.

Quote:

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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...