[Anchorman]

After my DE event this weekend, a look at the wheels I had cleaned immediately before the event made it evident that the front brakes are doing the preponderance of braking. Based on the amount of brake dust (with MetalMasters), it looks like there's at least a 4:1 front:rear effort. My car is used for just a few DE events a year, and lots of all-around street miles. What's the recommendation?

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[BruceWard]

That is normal. Although there is a 928 brake bias valve that will shift more of the braking to the rear. Jim Child uses the 928 valve and likes it. The part number is 928 355 305 02 .



Here are a couple of links to relevant threads including part numbers of valves that shift even more braking to the rear.



http://65.61.16.109/forum/topic.asp?TOPIC_ID=8859

http://65.61.16.109/forum/topic.asp?TOPIC_ID=252



I will probably swap in the 928 brake bias valve when my 968 becomes non stock.

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[flash]

these cars, like most, are front biased to keep the average driver out of trouble - the weight transfer to the front wheels brings the car to a more controlled and predictable stop - however, as you get more skilled, you find that you want to slow the car down, more than you want to stop it, and usually not in a straight line - that means a desire to change the bias to something a bit more even - i plan to do this too, after i get the weight set on my car



the down side is that the rear could have a bit more tendency to break loose on wet ground



i have no idea how this will affect the anti-lock system

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[Anchorman]

Thanks for pointing to those threads, Bruce, and for the part number. When I do my next fluid flush, I think that bias valve will be going in. Flash, I understand your observations. Re wet ground, I'll turn it around - the up side is that the front could have less tendency to break loose. I can't imagine any effect on anti-lock. The system still should ease the fluid pressure to the locking wheel.

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[Jason Judd]

Anchor,



Although I didn't drive your car, it felt fine while we were together... no surprises.



You might want to consider some track pads for your next event, though. But, be ready for even more dust accumulation!



I think your car behaved well; for which you can take at least partial credit!



Jason

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[Anchorman]

Thanks for the kind words, Jason.



I also think the car feels and performs well. I was simply observing, though, that there was obvious physical (not handling) evidence that the bulk of the braking was being done up front, and it seems to me that more could be transferred to the rear without otherwise adverse effects.



Next time, though, I'll give you a shot at the wheel. However, the relative lack of power, compared to your machine, will probably not provide you with as much fun as you normally have.

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[Dave]

The 928 valve does help. You have to be patient to wrench it in, but it's quite doable. The inside passenger wheel well liner comes right out and you'll see the valve and lines.



It helps to cycle the ABS in between bleeds when the ABS hydraulic unit is messed with (as in this swap). I found the easiest way to do so was to wait for a light-rain day/evening. Found safe place and stomped the SNOT outta the brake pedal to get the ABS lighting up like a Christmas tree.

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[flash]

how bad was the bleeding process itself?



are you saying that you bleed it, drive it, stomp it, bleed it? that kind of thing?



i have been putting this off, as i said, until i get the weght balance thing finished, but i do plan to do it if i still need it

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[pzwerner]

Have you ever tried different compounds on the rears?? Over the years Porsche used this method for better balance and wear. We have used it on our FP BMW before. Just a thought that might be easier than changing the bias. There are several good racing shops that probably help you.. Hope this helps.....



PFZ

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[Anchorman]

I had not thought about different front and rear pads. Don't quite know how to make the right choice to achieve more rear bias, but I'll look for - and welcome - further guidance and thoughts.

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[Dave]

Flash - Just the usual bleeding process, but with a "take the car out in the rain, engage ABS like crazy" session inserted between bleeds.



I bled the whole system as part of the M030 caliper/stainless line/928 valve install. Then, about a week later and after the ABS exercise, just re-bled all four corners again.



It wasn't clear to me, but appears there is some hydraulic fluid storage in the ABS unit itself, thus the above process.



In all of the above (valve, pad compounds, etc.), do be careful to keep the ABS fully operational. Last car I saw with bad rear bias and ABS out bounced all four corners off of walls at the track. Rear lock is bad, bad, bad...

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[Cloud9...68]

Many, many moons ago I took a 3-day Bondurant high performance driving course (though sadly I haven't done so much as a DE in the 26 years since; planning to change that soon), and one of the things that sticks in my mind is the instructors' statement that the front tires accomplish about 80% of the braking, so your observation of 25% the brake dust on the rear wheels relative to the fronts seems pretty normal to me. Though I know that all race cars have brake proportioning valves, so "normal" is probably not necessarily synonomous with "desirable." Good luck with the mod.

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[Anchorman]

Thanks, Cloud. I will be moving forward with the proportioning valve change.



I can't tell you how much I recommend doing a DE event. Exciting and educational - you learn about the car, you learn about you, you learn...period. I've now done three, and intend to do more.

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[Dave]

Another one catches the bug, hee hee <img src="/forum/images/smilies/968/laugh.gif" class="smilie" alt="" />

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[Anchorman]

In a way, I guess that's right. However, I have no plans to modify the car any more than I have, I just plan to keep driving it daily and once in a while in a DE event.

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[Dave]

Yup, that's how it happens. I spent 4 years daily-driving and DE'ing my 944 in bone-stock format and LOVED it. All time off is planned around DE events, there's the longing for the "smell of brake dust in the morning", tell-tale cans of ATE Blue in the garage...



Absolutely the most fun you can have with your clothes on. All of this comes to you for the low-low price of a few entry fees, consumable parts (pads, fluids, tires), and a couple of hotel stays for multi-day events.



Really one of the best bargains going and a great way to get a two-for-one deal on a car (both transport and track appliance). If you haul furniture in it or take it camping once in a while, you'll realize it is the most flexible thing on four wheels you've ever owned. Gotta love Porsche for packaging it all up for us!



Now, when/if the Mod/Racing bug starts to bite... look long and hard down over the edge of that slippery slope. It's steep, fast, and slick. Once started, it's runaway train time.



I wouldn't go back, but one does have to sporadically question the rationality of it all <img src="/forum/images/smilies/968/wink.gif" class="smilie" alt="" />

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[Jason Judd]

Now, when/if the Mod/Racing bug starts to bite... look long and hard down over the edge of that slippery slope. It's steep, fast, and slick. Once started, it's runaway train time.



____________________________



Hi, everybody...My name is Jason; and I'm powerless over my emotions.



Jason

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[Anchorman]

Based on a newly-gained understanding of how brake proportioning valve works, it would seem that changing it is likely to have an effect only on the track. I could be wrong, but I'm guessing that the hydraulic pressure needed to trigger the valve is only reached in pretty extreme braking situations, ones that are rarely reached in normal street driving. Therefore, this may not be a mod I need to do.

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[Lemming]

[quote name='Jason Judd' date='Nov 6 2005, 10:51 AM']Now, when/if the Mod/Racing bug starts to bite... look long and hard down over the edge of that slippery slope. It's steep, fast, and slick. Once started, it's runaway train time.[/quote]



I used to have disposable income, until I bought a track car <img src="/forum/images/smilies/968/blink.gif" class="smilie" alt="" /> Good thing that I have no alimony, no children, and no sense <img src="/forum/images/smilies/968/unsure.gif" class="smilie" alt="" />

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[mattipuh]

<!--quoteo(post=12090:date=Nov 4 2005, 07:42 AM:name=Dave)-->QUOTE (Dave @ Nov 4 2005, 07:42 AM) <{POST_SNAPBACK}><!--quotec-->In all of the above (valve, pad compounds, etc.), do be careful to keep the ABS fully operational. Last car I saw with bad rear bias and ABS out bounced all four corners off of walls at the track. Rear lock is bad, bad, bad...<!--QuoteEnd--><!--QuoteEEnd-->

Did 5/33 update last tuesday - bled with motive bleeder once, without abs wakeup - friday some track driving: for 3-4laps brakes felt superb, but after that they started to lock (abs not working) - also rear wheels started to do little whine in braking (think they were close to lock, but not locked, because car stayed well in line still).

maybe there's need for 2nd bleeding. I tested the abs this morning again on wet tarmaq and they worked fine. but on track, in heavier conditions, they didn't work. couldn't see that abs wouldn't handle 5/33 valve... well, let's see after 2nd bleed - hope system would be operative with this valve aswell, because I just love the brakes with 5/33 and bigger fronts - brakes are really good now. [img]style_emoticons/<#EMO_DIR#>/smile.gif[/img]

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