Brake wear expectations? Upgrades?

[yabanja]

How many miles are people getting out of the brakes on their FG's? Most of my braking is done with the exhaust brake so I would expect a significant life. Do the drums usually need to be replaced? What shoe material are people using? Any upgraded shoes available?(I come from a history of racing cars and know the difference compounds can make). Anyone done any modifications to the vacuum system to increase brake boosting for larger sized tires?

Tons of questions but inquiring minds want to know!

Thanks in advance!

Allan

 

[pugslyyy]

I use the exhaust brake mostly. You have to pull the hubs to get the drums off so I hope they last a long time.

 

[Aussie Iron]

How many miles are people getting out of the brakes on their FG's? Most of my braking is done with the exhaust brake so I would expect a significant life. Do the drums usually need to be replaced? What shoe material are people using? Any upgraded shoes available?(I come from a history of racing cars and know the difference compounds can make). Anyone done any modifications to the vacuum system to increase brake boosting for larger sized tires?

Tons of questions but inquiring minds want to know!

Thanks in advance!

Allan

One of the recommended up grades is to increase the amount of vacuum storage. As in fitting an extra tank which is done by one of the major builders when they do a wheel upgrade. I've not yet worn out a set of pads and find what I have works well. Saying that I can't say weather they are standard or not and yes it is a job to get to them but they can be inspected through the holes in the backing plates.

Dan.

 

[pugslyyy]

I've thought about increasing the vacuum, but have not done anything yet. It would be an easy and inexpensive upgrade.

 

[Alastair D(Aus)]

I have never understood the logic of increasing the vacuum tank size when doing a wheel upgrade. Increasing the size does not change the vacuum just how many times in quick succession you can apply the brakes. Why would that help when you change the wheels? What am I missing?

 

[ploz58]

im also interested in the vacuum upgrade questions, thanks for the wisdom out there.


Kind regards

Phil.

 

[Amesz00]

I have never understood the logic of increasing the vacuum tank size when doing a wheel upgrade. Increasing the size does not change the vacuum just how many times in quick succession you can apply the brakes. Why would that help when you change the wheels? What am I missing?

It comes from making the vehicles comply with ADR for omnibus braking, which in the tests requires multiple successive stops. No it doesn't actually increase braking force.

 

[Decanter]

If its a larger vacuum booster it would help. That upgrade made a significant improvement on my old Jeep.

 

[gait]

I've puzzled over it for a long time .....

logically ........

the movement of the brake pads, thus the displacement of the slave cylinders, thus the displacement of the master cylinder, and thus the displacement of the vacuum side of the booster, for a single application of the brakes is independent of the size of the wheels ........

but then logic rarely applies to ADR (Australian Design Rules).

Adding a bit more logic .....

Since testing with larger than original wheels seems to indicate a larger vacuum tank is required then either the vehicle is being tested against requirements it wasn't originally tested against and therefore would not have passed with standard wheel size or it never complied with ADR in the first place.

Alternative logic may suggest that one has to push the pedal just that little bit further with big wheels to achieve the braking g-force required by ADR which requires a tad greater displacement of the booster and thus exhausts the vacuum with fewer pedal presses.

I believe the other recommended change is to adjust the front/rear proportioning valve.

All very bizarre to me as I used to have a Toyota Coaster (small bus) which frequently sounded its low vacuum alarm on steep descents needing a few braking cycles and occasional stops as the exhaust brake wasn't anywhere near as good as the Canter - I was surprised the first time it happened. Never heard an alarm off the Canter, either before or after big wheels. I have a bit of difficulty reconciling the performance of the Coaster and the Canter with the ADR which I've never read.

In China the big trucks don't have exhaust brakes, they have large tanks of water for spraying on brake drums and wheels. The water on the road indicates a slow moving truck around the corner .......

To answer the original question ... in the last 100,000 km I've adjusted the brakes twice, they are hardly worn as I rely heavily on the exhaust brake.

Rhetorically. Maybe if I'd adjusted the brakes before the brake test with big wheels the extra vacuum tank wouldn't have been required.

Finally ... I hate drum brakes.

 

[whatcharterboat]

Hi Julian,

How are you mate?

I've puzzled over it for a long time .....

logically ........

the movement of the brake pads, thus the displacement of the slave cylinders, thus the displacement of the master cylinder, and thus the displacement of the vacuum side of the booster, for a single application of the brakes is independent of the size of the wheels ........

but then logic rarely applies to ADR (Australian Design Rules).

Adding a bit more logic .....

Since testing with larger than original wheels seems to indicate a larger vacuum tank is required then either the vehicle is being tested against requirements it wasn't originally tested against and therefore would not have passed with standard wheel size or it never complied with ADR in the first place.

Julian, you are not considering one big point here.....the greater the rolling diameter of the wheels, the less effective the brakes are.

The extra vacuum tank was required so that the Canters fitted with bigger wheels could meet ADR 35. The "vacuum fail" test requires the system to hold enough vacuum to stop at x deceleration rate(can't remember exactly the figure) after 7 full applications of the brake pedal with the vacuum circuit disconnected from the pump of course. So the pedal is depressed 7 times at a given pedal pressure and then the brake test is carried out with the 8th application. It's an 80kph stop from memory. In standard trim I bet they must only just make the required deceleration force in that test.

Alternative logic may suggest that one has to push the pedal just that little bit further with big wheels to achieve the braking g-force required by ADR which requires a tad greater displacement of the booster and thus exhausts the vacuum with fewer pedal presses.

By the way, pedal pressure is measured during all tests and can't exceed what is stated in the ADR's so it wasn't a case of maybe pushing harder on the pedal to make it pass originally.

 

[gait]

good to see you still around John,

if the only difference between standard and big wheels is the 8th pedal press the system must indeed be marginal when standard,

 

[yabanja]

I've puzzled over it for a long time .....

logically ........

the movement of the brake pads, thus the displacement of the slave cylinders, thus the displacement of the master cylinder, and thus the displacement of the vacuum side of the booster, for a single application of the brakes is independent of the size of the wheels ........

Actually, the brake shoes have a particular amount of leverage based upon their distance from the center point of rotation. The larger diameter the tire the more leverage it takes to stop it for the same reason. This is why performance cars go to bigger diameter brakes(one of the reasons-the other being heat dissipation).

Hopefully that makes sense?

Thank you for the input on the 100k miles w 2 adjustments. (Mine only has 52k on it!)

Allan

 

[gait]

yes, the leverage between the brake pads and tyre surface is less with larger diameter wheels, but .....

the movement of the brake pads is limited by the drum. Once the pads contact the drum they can't move much further.

What occurs to provide the same braking with big wheels as little wheels is more pressure applied, but little brake shoe and thus little pedal movement.

It appears that there is insufficient vacuum in the reservoir on the 8th pedal push to provide for that little bit of extra movement required with the big wheels.

I would make a fairly sound prediction that with original wheels a 9th pedal press would surely fail the brake test.

 

[yabanja]

yes, the leverage between the brake pads and tyre surface is less with larger diameter wheels, but .....

the movement of the brake pads is limited by the drum. Once the pads contact the drum they can't move much further.

What occurs to provide the same braking with big wheels as little wheels is more pressure applied, but little brake shoe and thus little pedal movement.

It appears that there is insufficient vacuum in the reservoir on the 8th pedal push to provide for that little bit of extra movement required with the big wheels.

I would make a fairly sound prediction that with original wheels a 9th pedal press would surely fail the brake test.

Less leverage=more pressure required to make same stop-therefore more vacuum? Likely you are right on borderline performance to begin with though!!!

Allan

 

[Alastair D(Aus)]

Ok thank you for explaining why the larger tank is required. Not related to making the vehicle fit for purpose, which a simple brake test would prove. Some official has decided that if you fit SS then the vehicle should be required to meet a different standard. Posssibly related to when this was first done for mining and tourist busses?

I am currently trying to build a new house and the extent of approvals and multiple departments one has to keep happy is amazing and very frustrating. I am happy to comply with standards that improve quality but so much is just paper trails - I think we caught the EU disease in many areas.