rear brakes working harder than front !

[southaussie]

for some reason my rear brakes are working harder than my front.

i think previous owner changed all brakes for the twin cal type.

could this be the reason why and if so is there a fix, if not any ideas!! ???

[db_notso]

right dont know how you know rear brakes are operating harder unless there locking up on you....

suggest a brake fluid flush to clear fluid at all four brakes first to make sure not a locked line etc....

if only rear brakes have been upgraded to bigger calipers and fronts are standard then the surface area of the rear brakes would be higher (on the pistons) causing rear to act like front...

or rear tyres bald and fronts new tread? cause rear to lock up earlier than fronts...

off top of my head possible both front calipers siezed.... very unlikely though....

but what your describing is wierd so how do you know rears are working harder than fronts?

[phroz]

right dont know how you know rear brakes are operating harder unless there locking up on you....

suggest a brake fluid flush to clear fluid at all four brakes first to make sure not a locked line etc....

if only rear brakes have been upgraded to bigger calipers and fronts are standard then the surface area of the rear brakes would be higher (on the pistons) causing rear to act like front...

or rear tyres bald and fronts new tread? cause rear to lock up earlier than fronts...

off top of my head possible both front calipers siezed.... very unlikely though....

but what your describing is wierd so how do you know rears are working harder than fronts?

its quite easy to know if the rears a stronger than the fronts usually when it does a uturn in the wet

yes its quite possible, fix is to get a brake guy to stick in a proportioning value in the master cyl not unlike a drum brake rear brake master either way a brake guy can fix it up for you by reducing the amount of fluid pressure to the rears

[old mate]

take pics of your brakes and show us.

i find it hard to picture someone doing that but you never know these days.

[machone]

i actually had this done one my old ht prem i changed the whole diff over because i put the crown through the casing (too many burn outs lol) but mine was a V8 diff and the diff housing i got was for a 6 i didnt realize the diff center fitted in no probs but not knowing the brake lines were smaller in diameter on the diff housing ...i bolted it up all right went for a test drive my rears locked up spinning me around it was a bit nerving to say the least.lol

[southaussie]

old mate: ok photos soon.....



db_notso: as for how do i tell ...

1. under normal driving, when i washed the car, the rear rotors were super hot, expecially in comparison to the fronts.
2. its a slightly obvious back grab and rear pull down as opposed to forward front dipping or controlled distributed even stopping.

phroz: proportioning value in the master cyl --- thanks will ask brake guy

[BlackVXGTS]

yes its quite possible, fix is to get a brake guy to stick in a proportioning value in the master cyl not unlike a drum brake rear brake master either way a brake guy can fix it up for you by reducing the amount of fluid pressure to the rears

There is already a proportioning valve in the master cylinder - perhaps this isn't working properly and needs to be checked:

"A master cylinder with a 25.4 mm (1”) diameter bore is used on all VT Series vehicles, regardless of the braking system fitted. The only difference being that the master cylinder used with ABS has a screw in blanking plug installed into the lower of the two front brake outlets in the master cylinder.

In all vehicles, a proportioning valve is located in a parallel bore in the same casting. This valve is used to maintain the front to rear hydraulic pressure balance and, should one of the two separate systems fail, a separate piston and differential switch (brake warning lamp switch) are incorporated into the design, so that the vehicle operator can be warned of a system malfunction."

[southaussie]

mine is a NON abs and i also get no warning light on dash !

really pouring with rain at the moment so cant get photos yet

might see about getting the valve checked

you guys have been a great help !! will let ya's know of the outcome

please continue to post if ya think of anything else

There is already a proportioning valve in the master cylinder - perhaps this isn't working properly and needs to be checked:

with ABS has a screw in blanking plug installed into the lower of the two front brake outlets in the master cylinder.

the vehicle operator can be warned of a system malfunction."

[Brett_jjj]

Im not too sure about the later models,but i know that the VR/VS ute master cylinders dont have this proportioning valve fitted to the M/C.The utes use a brake proportioning valve thats connected to the rear of the body,so the braking pressure thats distributed to the rear brakes depends on the load on the rear of the ute.The lighter the load,the higher the rear end is,the less braking pressure is distributed to the rear brakes,and the heavier the load,the lower the rear end, so more braking pressure is distributed to the rear brakes..What Im getting at is that maybe someone has fitted a master cylinder from a ute,thats if the later models use the same proportioning valve connected to the rear of the body.

[southaussie]

the photo asked 4

[graham7773]

southaussie, according to my GMH manual, all of the commodores from VT on had twin piston calipers as standard equipment on the front brakes.
Brett_jjj, all Holden utes and one tonners from VS back to the HQ had a brake proportioning valve fitted on the chassis and brake system to control rear wheel lockup. I only know this as I worked on the Acacia Ridge Holden plant production line for a while and I have owned several one tonners and one ute

[DLFHUB666]

southaussie, according to my GMH manual, all of the commodores from VT on had twin piston calipers as standard equipment on the front brakes.
Brett_jjj, all Holden utes and one tonners from VS back to the HQ had a brake proportioning valve fitted on the chassis and brake system to control rear wheel lockup. I only know this as I worked on the Acacia Ridge Holden plant production line for a while and I have owned several one tonners and one ute

Hey graham i think he knows the vt had twin pots on the front, what he is saying is that he has twin pots on the rear. And is asking if this will effect the way the car brakes. And i dont think it should if the proportioning vavle is working properly.

[Brett_jjj]

Brett_jjj, all Holden utes and one tonners from VS back to the HQ had a brake proportioning valve fitted on the chassis and brake system to control rear wheel lockup. I only know this as I worked on the Acacia Ridge Holden plant production line for a while and I have owned several one tonners and one ute

Ive got two HQ utes and the proportioning valve is not connected to the body on either of these,its obviously bolted to the body at the rear, but theres no arm that goes up and down with the body to regulate the pressure to the rear wheels..The commodore utes have an arm that goes from the proportioning valve to the body,this arm can move up and down with the body to regulate the rear brake pressure.The commodore workshop manuals also call this proportioning valve on the utes a load sensing valve..

[db_notso]

so he has made the surface area of the pistons on the rear bigger than standard and not upgraded front brakes to bigger size OR as some expensive methods custom brake proprtioning....

with only upgrading the rears then dropping line preasure to the rear so as like standard brakes, will not fix the problem as its an hydraulic system and as such fronts need to be made bigger for proportion to weight ratio to remain intact to maintain balance under braking.....

basically from what i have read (some funny) you need to fit standard brakes to the rear...... or get better (double opposed pot) front brakes as power brakes likely wont need a booster upgrade to improve braking with larger front and rear brake calipers ....as in my vt....

also just because there hot doesnt indicate over working foot brake can also show a poorly adjusted handbrake,
but pulling down in the rear is an indication....

[Mick1988]

I like line lockers...