[urq] bomb test variation with S4 brakes?

Tue Aug 8 07:19:05 EDT 2006

Martin et al,

I can unequivocally tell you that the 5k/2c bmc made a noticeable difference in pedal travel and feel after my G60/rear vented rotor swap.  In fact, I was guided by the same theory you are setting forth below-shouldn't be much difference in pedal travel, etc, so I had planned on keeping and using the oe bmc.  After a few months of merely adequate performance, I decided to swap out the bmc.  The larger bore bmc did, in fact, make a noticeable difference.  The oe bmc was only 2 yrs old, so I don't think it was a case of it being on the way out either...

Tis all.

-----Original Message-----
From: urq-bounces at audifans.com [mailto:urq-bounces at audifans.com] On Behalf Of Martin Pajak
Sent: Monday, August 07, 2006 9:11 PM
To: 'Buchholz, Steven'; urq at audifans.com
Subject: Re: [urq] bomb test variation with S4 brakes?

Steve,

I beg to differ with you.  
Increase in piston number is theory on paper.  In real life this is actually a bit different.  There are many things to consider including how good the callipers are (how far they retract after brake application) and how good the sliders themselves are.

Previous car was '83 with G 60s up front and the travel was minimal.
The difference would be something your foot would not even register, not to mention reduce # of pumps from 30 to 10!

BTW S4/V8 rear callipers use the same piston as Ur-q and in fact use the same pads as well!!
Oh and my '85 with SQ callipers (4 piston fixed) has the shortest pedal travel of them all.. probably because of lack of slider.

Hope this helps.

Martin Pajak

http://www.quattro.ca

1982 Audi Ur-quattro (50,000 mi) new project
1983 Audi Ur-quattro (85,000 mi) Concourse d'Elegance
1985 Audi Ur-quattro (214,000 km) Euro spec. import mit 3B :)
1987 Audi 4000s quattro (212,000 km) wintervagen mit 7A :)

-----Original Message-----
From: urq-bounces at audifans.com [mailto:urq-bounces at audifans.com] On Behalf Of Buchholz, Steven
Sent: Monday, August 07, 2006 11:46 AM
To: urq at audifans.com
Subject: Re: [urq] bomb test variation with S4 brakes?

... beg to differ here ... pedal travel will also be altered by the piston diameters of the brake calipers (altered by the ratio of the areas of the surfaces upon which the pedal force is applied) ... I suspect the dual piston G60s have more area than the G54s ... and I'm pretty sure the S4 rears have larger diameter pistons as well ... so you *should* expect more pedal travel.

If you changed the brake M/C to compensate for the larger diameters then the travel would be the same, but if you're running the same M/C I would not at all be surprised to hear that you get less overall pedal applications before losing assist.  

If the dynamic test works ... i.e. you do a panic stop and find that the brake assist is acceptable, consistent and does not increase over time, consider the problem solved.  When that situation changes then you should consider a bomb replacement ... 

Steve B
San José, CA (USA)
> 
> Number of of times you can pump the brakes will only be determined by 
> your pedal travel, not what brakes you have..
> If you have air in the system or spongy hoses, your pedal travel will 
> be longer and number of pumps less.. however I can not see how that 
> number can be reduced to 10 if you have properly functioning brakes.
_______________________________________________
Audifans urq mailing list
Send posts to: mailto:urq at audifans.com
Manage your list connection: http://www.audifans.com/mailman/listinfo/urq
Have an urq question?  Check the Audifans Knowledgebase!
http://www.audifans.com/twiki/bin/view/Audi/UrQuattro
Have an urq answer? ... Please help others by adding to the KB ... all contributions welcome!

_______________________________________________
Audifans urq mailing list
Send posts to: mailto:urq at audifans.com
Manage your list connection: http://www.audifans.com/mailman/listinfo/urq
Have an urq question?  Check the Audifans Knowledgebase!
http://www.audifans.com/twiki/bin/view/Audi/UrQuattro
Have an urq answer? ... Please help others by adding to the KB ... all contributions welcome!