Notices
964 Forum 1989-1994
Sponsored by:
Sponsored by:

Educate me on brake options!

Thread Tools
 
Search this Thread
 
Old 10-17-2018, 07:04 PM
  #1  
SRM11
Rennlist Member
Thread Starter
 
SRM11's Avatar
 
Join Date: Jun 2018
Location: Vancouver, BC, Canada
Posts: 108
Received 7 Likes on 4 Posts
Default Educate me on brake options!

I've done lots of searching and reading, and I'm still a bit confused. I seem to find a lot of conflicting information

1991 964. Have factory brakes and looking to upgrade. The car isn't tracked and even through hard pushing through the twistys, I never have any brake fade.

It has the 2 pot rear calipers, which just look so tiny. The upgrade is mostly for cosmetics.

What are my options? Can I get the larger 4 pot rears? Do I need to change the proportioning valve or no? Any other ideas?

Is there any real improvement with the 4 pot rears that would also justify doing it?

If yes - what am I exactly looking for and where's the best place to get them? I don't want to spend an arm and a leg on doing it but since I am planning on powdercoating and rebuilding the brakes this winter, I might as well upgrade if I can.

Thanks in advance
Old 10-17-2018, 07:19 PM
  #2  
Spyerx
Rennlist Member
 
Spyerx's Avatar
 
Join Date: Mar 2012
Location: SoCal
Posts: 16,688
Received 1,840 Likes on 1,121 Posts
Default

get 92+ rears + pads
put in 92+ proportion valve

Benefit? Heat management. You probably won't notice a difference on the street. Unless your wheels get too hot to touch you're not using your brakes much and very well may never notice it. And if you have smoking brakes on the street you'll probably get thrown in jail soon.

I think the 4 piston rears do look 'better'.
Old 10-17-2018, 07:21 PM
  #3  
cjoenck
Rennlist Member
 
cjoenck's Avatar
 
Join Date: Dec 2007
Location: Chicago, IL
Posts: 734
Likes: 0
Received 87 Likes on 70 Posts
Default

The technical questions have all been answered here and on the Pelicanparts forum. Look for Bill's responses and discussion.
Regarding source for the 4 pods, I went to a dismantler and had them completely rebuilt by GoldLine Brakes outside Seattle. No affiliation but they were fantastic. If you want to powder coat them anyway, that would be one way to go. GoldLine will paint them in any color you want.
Old 10-17-2018, 09:50 PM
  #4  
-nick
Three Wheelin'
 
-nick's Avatar
 
Join Date: Feb 2003
Location: Cambridge/Boston, MA
Posts: 1,781
Received 106 Likes on 81 Posts
Default

You might want to consider the negative impact of the additional weight (larger caliper & larger rotor). This is trading performance for aesthetics.
Old 10-18-2018, 12:00 AM
  #5  
Peteinjp
Rennlist Member
 
Peteinjp's Avatar
 
Join Date: Jul 2017
Posts: 1,525
Received 214 Likes on 164 Posts
Default

I’m in the same boat and I do think there is as advantage to the later caliper if you take into account that the original tire that the system was designed for was a 225 and that most have gone up to 255 which means that more rear bias is appropriate.

Pete
Old 10-18-2018, 01:05 AM
  #6  
boostedt0y
Banned
 
boostedt0y's Avatar
 
Join Date: Aug 2010
Location: Bay Area, CA
Posts: 534
Received 79 Likes on 41 Posts
Default

I just picked up a set of 4 piston rear calipers for my 90 c2. I will be installing along with stoptech slotted rotors and ferodo 2500 pads on all 4 corners. I plan to gut the proportion valve based Bill’s recommendation.

the benefit of the 4 piston rear calipers is heat management and wider selection of matching front and rear pads. Not many pad options for the 2 piston rear calipers.
Old 10-18-2018, 09:01 AM
  #7  
cjoenck
Rennlist Member
 
cjoenck's Avatar
 
Join Date: Dec 2007
Location: Chicago, IL
Posts: 734
Likes: 0
Received 87 Likes on 70 Posts
Default

Originally Posted by -nick
You might want to consider the negative impact of the additional weight (larger caliper & larger rotor). This is trading performance for aesthetics.
The weight difference for the calipers is negligible and the rotors are the same. I would be very surprised if you could feel the difference in weight. One of my old 2 pods was sticking so rather than rebuild the original I upgraded to 4 pods in the back for the reasons stated above.
Old 10-18-2018, 10:42 AM
  #8  
cobalt
Rennlist Member
 
cobalt's Avatar
 
Join Date: Oct 2003
Location: New Jersey
Posts: 22,682
Received 2,256 Likes on 1,339 Posts
Default

Originally Posted by boostedt0y
I just picked up a set of 4 piston rear calipers for my 90 c2. I will be installing along with stoptech slotted rotors and ferodo 2500 pads on all 4 corners. I plan to gut the proportion valve based Bill’s recommendation.

the benefit of the 4 piston rear calipers is heat management and wider selection of matching front and rear pads. Not many pad options for the 2 piston rear calipers.

FYI I installed Stoptech slotted rotors on my sons Audi. I Like the rotors however if you let the car sit for any period of time they rust badly and cause raised areas around the slots. It got so bad after 5 weeks of the car sitting outside I had to ditch them and buy factory. If the car sits inside or is driven regularly you should be fine. Although factory rotors aren't all the expensive and last a lot longer.
Old 10-18-2018, 12:04 PM
  #9  
boostedt0y
Banned
 
boostedt0y's Avatar
 
Join Date: Aug 2010
Location: Bay Area, CA
Posts: 534
Received 79 Likes on 41 Posts
Default

Originally Posted by cobalt
FYI I installed Stoptech slotted rotors on my sons Audi. I Like the rotors however if you let the car sit for any period of time they rust badly and cause raised areas around the slots. It got so bad after 5 weeks of the car sitting outside I had to ditch them and buy factory. If the car sits inside or is driven regularly you should be fine. Although factory rotors aren't all the expensive and last a lot longer.
thanks for the heads up! My car is garaged and is driven at least every other week so I think I’ll be fine. Crossing my fingers
Old 10-18-2018, 12:32 PM
  #10  
Spyerx
Rennlist Member
 
Spyerx's Avatar
 
Join Date: Mar 2012
Location: SoCal
Posts: 16,688
Received 1,840 Likes on 1,121 Posts
Default

"race" rotors typically don't have the coatings on them to minimize corrosion. I have brembo and the ones on my 964 are coated and don't corrode like the ones on my RS which are full race rotors. Its not bad, but I try to avoid spraying them when washing the car (ie wheels off for wash).
Old 10-18-2018, 01:12 PM
  #11  
-nick
Three Wheelin'
 
-nick's Avatar
 
Join Date: Feb 2003
Location: Cambridge/Boston, MA
Posts: 1,781
Received 106 Likes on 81 Posts
Default

Sorry, I read the original post as "brake upgrade" not just 4-pot rear caliper upgrade Big reds/etc add quite a few pounds of unsprung rotating mass. You are definitely correct, swapping the 2-pot rears to 4 has no ill effects. Carry on...!

Originally Posted by cjoenck
The weight difference for the calipers is negligible and the rotors are the same. I would be very surprised if you could feel the difference in weight. One of my old 2 pods was sticking so rather than rebuild the original I upgraded to 4 pods in the back for the reasons stated above.
Old 10-18-2018, 02:00 PM
  #12  
JasonAndreas
Technical Guru
Rennlist Member

 
JasonAndreas's Avatar
 
Join Date: May 2002
Location: USVI
Posts: 8,138
Received 112 Likes on 90 Posts
Default

Originally Posted by cobalt
FYI I installed Stoptech slotted rotors ... they rust badly and cause raised areas around the slots.
I may be dealing with this problem of slots having raised edges now too.

Originally Posted by Spyerx
"race" rotors typically don't have the coatings on them to minimize corrosion.
The Stoptech hubs are coated and fine. It is the actual slot on the disc.
Old 10-18-2018, 03:11 PM
  #13  
Lorenzoh
Pro
 
Lorenzoh's Avatar
 
Join Date: Dec 2017
Posts: 559
Likes: 0
Received 21 Likes on 16 Posts
Default

How can you visually tell the difference between the 2 pot and 4 pot calipers when looked at them on a car?
Old 10-18-2018, 03:35 PM
  #14  
SRM11
Rennlist Member
Thread Starter
 
SRM11's Avatar
 
Join Date: Jun 2018
Location: Vancouver, BC, Canada
Posts: 108
Received 7 Likes on 4 Posts
Default

This is perfect, thanks guys. I was really looking for the 'coles notes' version.

I do run a 265 tire in the rear (and the brand fits wider than most, so it's closer to 275) so I'm sure there will be some benefit as well.

boostedt0y - where did you get the 4 pot calipers from? Or anyone else have recommendations? Or what I should look to pay approx?

I found some 964 turbo rear calipers for sale - could those work?
Old 10-18-2018, 06:12 PM
  #15  
Bill Verburg
Addict
Rennlist Member

 
Bill Verburg's Avatar
 
Join Date: May 2001
Posts: 12,389
Received 579 Likes on 398 Posts
Default

ideally you would want bias to be < 1.5 and > 1.425, and then not use a p/v or at least use the least intrusive one that you can get away w/. This will depend on how the car is setup,
to use more rear the car needs to be
stiffer
have an effective lsd
good tire bias

All stock 964 are fairly heavily front biased, factory removed the p/v for racing use in the Cups
The following is @70bar line pressure, a fairly hard stop, but line pressures to ~ 100bar can be seen, All on stock rotors, only the Cups use bigger rotors and then only in front
964 Cup bias is 1.713 w/ 2381NM front & 1390NM rear no p/v
964 4/4 bias is 1.889w/ 2203NM front &1167NM rear (no p/v) This goes to 3.498 w/ 2203NM front and 630NM rear when the stock 55bar p/v is in place
964 4/2 bias is 1.643 w/ 2203NM front &1341NM rear (no p/v) This goes to 3.042 w/ 2203NM front and 724NM rear when the stock 40bar p/v is in place

As you can see bias is worse w/ 4/4 than w/ 4/2 and all are are too much front,

reasons to go to 4/4: looks, uses same pad f/r, longer rear pad life

use stock front and a stock normal 993 rear
964 4/993 4 bias is 1.547w/ 2203NM front &1424NM rear (no p/v) This goes to 2.865 w/ 2203NM front and 769NM rear when the stock 55bar p/v is in place


Quick Reply: Educate me on brake options!



All times are GMT -3. The time now is 04:54 AM.