GU Break system questions

[JoseM]

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

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

[MudRunnerTD]

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?

[MudRunnerTD]

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



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.

[JoseM]

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 ), 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

[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.

[JoseM]

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

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.

[BearGUST]

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.

[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.

[JoseM]

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...

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.

[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.