Home  |  Forums  |  914 Info  |  Blogs
Tuesday, 24 December 2024
 
 
914World.com - The fastest growing online 914 community!
 
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG. This site is not affiliated with Porsche in any way.
Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners.
 

Welcome Guest ( Log In | Register )

> Brakes don't Bite
bkrantz
post Sep 1 2022, 08:16 PM
Post #1


914 Guru
*****

Group: Members
Posts: 8,173
Joined: 3-August 19
From: SW Colorado
Member No.: 23,343
Region Association: Rocky Mountains



As part of my rebuild I completely replaced the brake system:
calipers and rear pressure valve rebuilt by PMB
new ATE 19mm master cylinder
new hard and flex lines
new disks and Porterfield R4-S pads

I went through many (many!) episodes of bleeding, with different methods. The pedal feels very firm from the first push, and does not pump up. Rear clearance is set at .004". I went through the PMB bedding process, and have driven around a bit.

But the braking force seems weak. When I get on the brake pedal, I do not feel any "bite". Another 914 friend drove the car and also agrees.

Any suggestions?
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
 
Reply to this topicStart new topic
Replies
gereed75
post Sep 3 2022, 09:51 AM
Post #2


Senior Member
***

Group: Members
Posts: 1,315
Joined: 19-March 13
From: Pittsburgh PA
Member No.: 15,674
Region Association: North East States



Different car but maybe a useful data point - I had some unknown old and what appeared to be metallic very hard pads on my race car with Willword calipers. I called Willwood to get their recommendation for a pad. I gave them car weight, HP, typical track cycles (speeds braking from down to corner speeds how many times per lap and how much time between applications).

I was surprised when they recommended an aggressive street compound. They said my loading was just not enough to get sufficient heat into a race pad to generate good friction. My point is Race oriented compounds need a lot of heat to get into efficient friction ranges. The new ceramic street compounds are very good at generating initial bite with minimal loading while providing good wear characteristics.

Not sure what type of compound the R4S is, but you might be asking it to do something it is not designed for
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
Superhawk996
post Sep 3 2022, 10:07 AM
Post #3


914 Guru
*****

Group: Members
Posts: 6,597
Joined: 25-August 18
From: Woods of N. Idaho
Member No.: 22,428
Region Association: Galt's Gulch



QUOTE(gereed75 @ Sep 3 2022, 11:51 AM) *


Not sure what type of compound the R4S is, but you might be asking it to do something it is not designed for

R4S is a street / performance compound so not outright race pads. R4S also have a good history for most but certainly may not be for everyone.

having said that I don’t disagree a bit with prior comments of re-bedding and or consideration of a pad change as a possible improvement - it all depends on driving style.

Each pad has its own friction curve. Some (race pads) have low friction until the get hot. Others have high friction when cold but fall off drastically when hot (prior to actual fade).

One thing that has frustrated me for years in the aftermarket is the unavailability of the curves. They are easily obtained on a brake dyno. The problem is the data is so specific to a particular pad, rotor, caliper combination so the data doesn’t necessarily apply the same between a Nissan and a 914 for example.

For example the Porterfield is listed by PMB as 0.41 mu (friction coefficient) but doesn’t tell you what temperature that is at. No pad has a singular average mu at all temps. This doesn’t reflect on PMB - like I said the pad suppliers just don’t provide good data.

That leaves us with trial and error.

I really used to like Ferodo back in the day but Only God knows what they are like today with all the EPA regulatory restrictions limiting raw materials.

FYI - get ready for things to get worse. Copper is being regulated out of pad formulas for OEMs. It has caused a lot of chaos trying to find new friction compounds that work as well as those that had copper in them. This will eventually trickle down to the aftermarket. If you have a particular pad that you love - stock up now.
User is online!Profile CardPM
Go to the top of the page
+Quote Post
bbrock
post Sep 3 2022, 11:12 AM
Post #4


914 Guru
*****

Group: Members
Posts: 5,269
Joined: 17-February 17
From: Montana
Member No.: 20,845
Region Association: Rocky Mountains



QUOTE(Superhawk996 @ Sep 3 2022, 10:07 AM) *

FYI - get ready for things to get worse. Copper is being regulated out of pad formulas for OEMs. It has caused a lot of chaos trying to find new friction compounds that work as well as those that had copper in them. This will eventually trickle down to the aftermarket. If you have a particular pad that you love - stock up now.


I can't let this pass without comment. This isn't coming as some random restriction to stick it to auto parts manufacturers. Copper is toxic as hell to aquatic life which is why it is great for household plumbing because not much can live in it. Copper content in storm water in some metro areas exceeds safe limits for marine and freshwater life and a major source of that copper has been found to be brake dust running off of streets. AFAIK, the regs will reduce the amount of copper in brake pads but not eliminate it completely. Yeah, it's a PITA to have to reformulate brake pads again, but living with degraded natural systems we depend on for food and oxygen is no picnic either. Just saying...
User is offlineProfile CardPM
Go to the top of the page
+Quote Post

Posts in this topic
bkrantz   Brakes don't Bite   Sep 1 2022, 08:16 PM
Superhawk996   Brake feel is highly subjective. The obvious thi...   Sep 1 2022, 08:51 PM
mgphoto   19mm master cylinder, push the pedal harder, they ...   Sep 1 2022, 09:54 PM
barnfind9141972   I did the same thing and also couldn’t get much ...   Sep 1 2022, 10:27 PM
Mikey914   The system is notorious for holding bubbles. You w...   Sep 1 2022, 11:07 PM
ChrisFoley   As part of my rebuild I completely replaced the b...   Sep 2 2022, 07:55 AM
Superhawk996   Adjust the rear brake regulator to begin regulat...   Sep 2 2022, 09:24 AM
ChrisFoley   [quote name='ChrisFoley' post='3026647' date='Sep...   Sep 2 2022, 10:58 AM
Superhawk996   [quote name='Superhawk996' post='3026665' date='S...   Sep 2 2022, 11:17 AM
Superhawk996   Add a master cylinder brace to prevent floorboar...   Sep 2 2022, 09:28 AM
JamesM   As part of my rebuild I completely replaced the b...   Sep 2 2022, 09:27 AM
Superhawk996   Can you lock the brakes up if you stand on them? ...   Sep 2 2022, 09:31 AM
jim_hoyland   What MPH would the front lock-up test best be done...   Sep 2 2022, 09:57 AM
Superhawk996   What MPH would the front lock-up test best be don...   Sep 2 2022, 10:06 AM
emerygt350   I just went and tried Locking them up tonight (hav...   Sep 2 2022, 06:32 PM
bkrantz   Thanks for all the replies. Yes, I can lock up th...   Sep 2 2022, 07:38 PM
Superhawk996   But I still think I should feel more bite and urg...   Sep 2 2022, 08:41 PM
JamesM   Thanks for all the replies. Yes, I can lock up t...   Sep 3 2022, 12:44 AM
Van B   I love the motive pressure bleeder. I don’t kno...   Sep 2 2022, 08:23 PM
bbrock   I have essentially the same setup as you and get r...   Sep 2 2022, 08:26 PM
iankarr   It takes several bleeds to get air out of a totall...   Sep 2 2022, 10:34 PM
Geezer914   Pressure bleeding is the best way to bleed the Bra...   Sep 3 2022, 05:20 AM
jim_hoyland   Pressure bleeding is the best way to bleed the Br...   Sep 3 2022, 06:23 AM
gereed75   Different car but maybe a useful data point - I ha...   Sep 3 2022, 09:51 AM
Superhawk996   Not sure what type of compound the R4S is, but ...   Sep 3 2022, 10:07 AM
bbrock   FYI - get ready for things to get worse. Copper...   Sep 3 2022, 11:12 AM
930cabman   FYI - get ready for things to get worse. Coppe...   Sep 9 2022, 01:16 PM
bbrock   Sounds as though the consensus is having the abil...   Sep 9 2022, 03:16 PM
Superhawk996   It was the early version of ABS @Superhawk995 :...   Sep 9 2022, 04:47 PM
PatMc   [quote name='bbrock' post='3026923' date='Sep 3 2...   Sep 15 2022, 10:06 PM
jim_hoyland   What's a recommended for light daily driving ?...   Sep 3 2022, 12:25 PM
JamesM   What's a recommended for light daily driving ...   Sep 3 2022, 12:49 PM
bkrantz   Thanks, again. I will try bedding again with some...   Sep 3 2022, 08:09 PM
michael7810   Thanks, again. I will try bedding again with som...   Sep 4 2022, 06:36 AM
ChrisFoley   I used to sell KFP pads because I liked their perf...   Sep 4 2022, 05:02 AM
bkrantz   I ordered a set of Textar OEM style pads for F and...   Sep 5 2022, 07:57 PM
jim_hoyland   I just ordered the Pagids from PMB, Here’s the i...   Sep 5 2022, 08:46 PM
Montreal914   Mentioned before but the stock system was designed...   Sep 5 2022, 09:12 PM
robkammer   This is a thread I thought I would need to start. ...   Sep 8 2022, 01:25 PM
ChrisFoley   venting clearance of 3mm. Hmm, what?   Sep 8 2022, 03:17 PM
Superhawk996   On my last spirited drive with lots of hard braki...   Sep 8 2022, 03:50 PM
robkammer   Guys: Oops, not 3mm, .003". Clearance between...   Sep 9 2022, 07:39 AM
bbrock   Hmm. I have PMB plated calipers that I rebuild my...   Sep 9 2022, 08:12 AM
robkammer   Thanks All: Good comments all around. Still not su...   Sep 9 2022, 01:14 PM
bkrantz   I replaced the pads with "stock" Textars...   Sep 15 2022, 07:48 PM
robkammer   All: This is all great info. So, an update, last S...   Sep 16 2022, 04:11 PM
bbrock   All: This is all great info. So, an update, last ...   Sep 16 2022, 06:41 PM
Superhawk996   Going on two years and getting tired of screwing ...   Sep 17 2022, 11:05 AM
michael7810   For $35 you can try a set of Textar pads for ...   Sep 16 2022, 04:25 PM
ChrisFoley   New caliper seals cause a long pedal which will pu...   Sep 17 2022, 07:02 AM
PatMc   I would try a conventional bleeding method…one p...   Sep 17 2022, 07:47 AM
robkammer   Thanks All! Have not checked the pedal box, bu...   Sep 17 2022, 01:32 PM
Literati914   Man this is frustrating, hate that you’ve not go...   Sep 19 2022, 09:20 AM
Superhawk996   Man this is frustrating, hate that you’ve not g...   Sep 19 2022, 09:48 AM
rfinegan   Last week I rebuild all 4 calipers, Potterfield pa...   Sep 19 2022, 10:08 AM
scott_in_nh   I very recently got around to installing the KFP 1...   Sep 21 2022, 12:48 PM
bbrock   I do notice they are getting better, but my quest...   Sep 21 2022, 01:44 PM
NARP74   The numbers are on the round barrel, mostly on the...   Sep 21 2022, 01:59 PM
NARP74   For the pedal box flex, I had someone press the pe...   Sep 21 2022, 02:04 PM


Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 

- Lo-Fi Version Time is now: 24th December 2024 - 04:03 PM