| Author |
Message |
bally
Samba Member
Joined: April 29, 2006
Posts: 1182
Location: Melbourne, Australia
|
 Posted: Wed Jul 27, 2016 2:04 pm Post subject: Disc brake poor performance? |
 |
|
My 60 model bus has discs up front and early bay drums on the back. I'd expect it to stop pretty well but it doesn't. I've had the brakes tested at my local MOT Station and whilst they are within tolerance they are more like poor stock drums than a new system with bigger rear drums and discs up front. We also established that the servo which was meant to enhance performance is not working, probably due to a linked and collapsed vacuum hose. The discs should improve braking without the servo so I'm curious why performance should be so poor. Friends with similar set ups, both with and without servos report vastly improved braking. What could be causing my brakes to be so poor? For the record they are CSP brakes which were fitted 7 or 8 years ago but weren't used until the Resto was finished towards the end of last year.
Cheers Dave |
|
| Back to top |
|
 |
chrisflstf
Samba Member
Joined: February 10, 2004
Posts: 3439
Location: San Diego
|
| Posted: Wed Jul 27, 2016 3:29 pm Post subject: Re: Disc brake poor performance? |
|
|
I would try some new pads first and check to see if the rotor is glazed.
You could have a bad master as well |
|
| Back to top |
|
|
DerrickfromNC1
Samba Member
Joined: October 24, 2008
Posts: 1300
Location: North Carolina
|
| Posted: Wed Jul 27, 2016 5:11 pm Post subject: Re: Disc brake poor performance? |
|
|
What do you mean by poor performance?
Excessive stopping distance?
Too high pedal pressure?
Excessive pedal travel b4 engagement? (low pedal)
Having to pump brakes? |
|
| Back to top |
|
|
easy e
Samba Member
Joined: May 28, 2008
Posts: 3931
Location: 1 hr north of Santa Barbara
|
|
| Back to top |
|
|
55samba
Samba Member
Joined: June 21, 2002
Posts: 805
Location: CA Bay Area
|
| Posted: Wed Jul 27, 2016 8:40 pm Post subject: Re: Disc brake poor performance? |
|
|
The determining factor in how you disc brakes will work is the leverage you have based on caliper and master cylinder bore sizes. It is a trade off between leverage and distance. If for example you are using a bay window master cylinder designed for a booster you will have a high effort without the booster because the master cylinder piston is large.
If you go with an un-boosted system you need a small piston for the master cylinder. The trade off is more travel. In this instance I have used a 2lb residual valve to keep the pads close to the rotor.
Bottom line is going to disc brakes does not guarantee better stopping power, it has to be engineered to work as a system.
In your case it seems the system was designed to use a booster. So you need to get it working.
|
|
| Back to top |
|
|
bally
Samba Member
Joined: April 29, 2006
Posts: 1182
Location: Melbourne, Australia
|
| Posted: Thu Jul 28, 2016 12:35 am Post subject: Re: Disc brake poor performance? |
|
|
| chrisflstf wrote: |
I would try some new pads first and check to see if the rotor is glazed.
You could have a bad master as well |
Thanks Chrisflstf. I'll check the pads and rotor. What do you mean by bad master? They work, just not well enough so what might the master fault be? The vans done just over 1000 miles on this set up. |
|
| Back to top |
|
|
bally
Samba Member
Joined: April 29, 2006
Posts: 1182
Location: Melbourne, Australia
|
| Posted: Thu Jul 28, 2016 12:38 am Post subject: Re: Disc brake poor performance? |
|
|
| DerrickfromNC1 wrote: |
What do you mean by poor performance?
Excessive stopping distance?
Too high pedal pressure?
Excessive pedal travel b4 engagement? (low pedal)
Having to pump brakes? |
Thanks DerrickfromNC1
Yes, excessive stopping distance due to too much pressure required to effectively operate brakes. There does seem to be a little too much pedal travel too. |
|
| Back to top |
|
|
bally
Samba Member
Joined: April 29, 2006
Posts: 1182
Location: Melbourne, Australia
|
| Posted: Thu Jul 28, 2016 12:41 am Post subject: Re: Disc brake poor performance? |
|
|
| easy e wrote: |
Do you have a residual valve in the master cyl bore?... external screw-in one(s)?
What master cyl are you using? |
Thanks easy e I'll need to check - it's the master cylinder provided with the kit and that was delivered straight to the shop about 8 years ago. It's a dual circuit item which I believe is from a Bay - it all happened a long time ago and there are no records to look back at. |
|
| Back to top |
|
|
bally
Samba Member
Joined: April 29, 2006
Posts: 1182
Location: Melbourne, Australia
|
| Posted: Thu Jul 28, 2016 12:44 am Post subject: Re: Disc brake poor performance? |
|
|
| 55samba wrote: |
The determining factor in how you disc brakes will work is the leverage you have based on caliper and master cylinder bore sizes. It is a trade off between leverage and distance. If for example you are using a bay window master cylinder designed for a booster you will have a high effort without the booster because the master cylinder piston is large.
If you go with an un-boosted system you need a small piston for the master cylinder. The trade off is more travel. In this instance I have used a 2lb residual valve to keep the pads close to the rotor.
Bottom line is going to disc brakes does not guarantee better stopping power, it has to be engineered to work as a system.
In your case it seems the system was designed to use a booster. So you need to get it working.
|
Thanks 55samba - I think you've probably hit the nail on the head here: I seem to recall it is a bay master cylinder supplied in the kit which is why the servo was added as the bay cylinder would be mated to a servo in a bay (or in the bay it was designed to go in) I'll replace the failed hose and re-assess!!
That's a very useful graphic!
Thanks for all your input.
Dave |
|
| Back to top |
|
|
|
