vibration under braking

[2013kAB]

thanks. ^^

i might be reading the referenced thread wrong? sounded like replacing the bushing was done via burning it out, but on the other hand one could have replaced it with a whole other case/bushing (which would have been easier). but the later was not acceptable for a racing club?

this weekend i was able to get out on country roads and get up to ~75mph and did 3 "hard" stops - progressive firm squeeze of the pedal. before that, i did a few 60-40mph firm slow downs, maybe 3 with about 1/2mile or mile between them. then drove about 1 mile, then stopped again etc. then after driving about 5-8 miles with 1 easy stop from 60, i did another 2 ~75mph stops.

All stops were nice and smooth. not a hint of vibration. There were some noises, like a groaning noise that was very brief after the initial firm squeeze, but then disappeared mid-way through the braking and remained smooth all the while.

The next day i was on those same roads and did some brief warm up stops from 55-40 or 35. probably 3 or 4, with 1/2 to 1mile inbetween. then did two firm 75mph stops again, but this time i think i felt some vibration. it was not specifically in the steering wheel, but a little in the pedal, or just in the floor board - it might have been butt-dyno. very faint.

The trips were 30 miles of country roads, all 55mph, a stop sign every now and then. followed by a few miles of 25mph driving in the destination city. nice and easy.

it occurs to me that my new carbotech pads (who's break-in says stops from 60-65mph) could over heat with a few 2-4 75-80mph stops?

so in the course of someone really pushing and whipping around it'd be really easy to overheat "street" pads no?

another thing, with regard to bedding-in the carbo XP10's, XP 8's, (which i have not put in yet) couldn't you just go out on the country roads, get some heat in them with 4 or 5 60-5mph stops, then do some 80-90mph to 5mph stops? as opposed to bedding in on the track?

i can usually end up with a good 10-20mile drive at 60mph with little or no braking to allow for cool-off before some city driving (35mph and below) before i get home to park.

finally, if for some reason i did overheat the carbo 1521 street pads, despite being careful, which lead to the hint vibration on day 2 of my weekend, i'm wondering if i should switch to the track pads and drive around town for a week?

i ordered some cooling ducts today too.

 

[2013kAB]

so far so good, few more tests on the country roads from ~75-80.

i have a question about hubs. i see frpp has replacement hubs with 3" arp preseated studs.

what does the extra length get you - nevermind found the answer.

also, im guessing these hubs are more tolerant to heat and stresses, but if you strenghten this link in the chain what could be the next link down the line that would break?

thanks

Sent from my Nexus 7 using Tapatalk

 

[Pentalab]

I have run into this problem and I am not sure if the solution should be so radical. 1st I imagine that your traction and stability control were off. I had huge repeated brake shudder going into turn three at willow. That is the fastest turn and makes you get on the brakes hard from above 100 mph. Had no problems before and have had no problem since. I kept my rotors and pads but I changed my front camber which was previously at 2.5 to 1.5. Voila, the break shudder disappeared on the next track day and have not had it since. I theorized that the combination of radical camber change and grippier race pads confused the anti-lock system and caused the heavy vibration that could be felt throughout the entire car and especially in the steering wheel. Which may all be true, however, I can say that I no longer have brake shudder.

You might have eliminated the issue, by dropping down to -2.4 to -1.6 degs. Some where between those 2 extremes the issue will diminish.
On a similar note, I read on one of the ricer forums where several of them mentioned the inline braking effectiveness dropped off when they used -2.7 degs of camber. That was on fwd cars, and may well not be applicable on a mustang.

 

[Whiskey11]

You might have eliminated the issue, by dropping down to -2.4 to -1.6 degs. Some where between those 2 extremes the issue will diminish.
On a similar note, I read on one of the ricer forums where several of them mentioned the inline braking effectiveness dropped off when they used -2.7 degs of camber. That was on fwd cars, and may well not be applicable on a mustang.

On strut cars specifically, the camber change under dive is going to have a profound impact on braking distances depending on where you are at in the camber curve. At ride heights closer to stock you are going to be gaining some negative camber on application of the brakes which is going to change the contact patch some. The more negative camber you have the less contact patch. Their is a tradeoff and this is partially why Short-Long Arm/Double Wishbone suspensions have a huge advantage over a strut... that and just about every other reason struts suck, SLA's don't have that issue.

Drag racers will experience a part of this issue with the 2015 Mustangs and their rear suspension and that will definitely be interesting to watch. I suspect it wont take them long to figure it out.

 

[2013kAB]

so far so good, few more tests on the country roads from ~75-80.

i have a question about hubs. i see frpp has replacement hubs with 3" arp preseated studs.

what does the extra length get you - nevermind found the Answer.

also, im guessing these hubs are more tolerant to heat and stresses, but if you strenghten this link in the chain what could be the next link down the line that would break?

thanks

Sent from my Nexus 7 using Tapatalk

Sent from my Nexus 7 using Tapatalk

 

[dontlifttoshift]

Extra length in the studs, as far as I know that is it.

 

[Sky Render]

Extra length in the studs, as far as I know that is it.

I believe the ARP studs are also rounded on the end.

 

[Norm Peterson]

another thing, with regard to bedding-in the carbo XP10's, XP 8's, (which i have not put in yet) couldn't you just go out on the country roads, get some heat in them with 4 or 5 60-5mph stops, then do some 80-90mph to 5mph stops? as opposed to bedding in on the track?

i can usually end up with a good 10-20mile drive at 60mph with little or no braking to allow for cool-off before some city driving (35mph and below) before i get home to park.

Maybe.

I (mostly) bedded-in a set of XP8's in similar fashion to what you're describing, but still got into a green fade situation toward the end of the first track day on them. In fairness, the track went from wet (without it actually raining once the sessions started running) to almost fully dry, so braking during the first couple of sessions wasn't as hard as was possible later.


Norm

 

[2013kAB]

well there's no reason not to bed them in at the track so i'll do that. well, maybe a waste of a couple of laps. but that's not a big deal to me. rather do it right this time around!

 

[2013kAB]

i never inspected the pads that came off the car after the vibration. it was a dealer install of new rotors and pads, just left the stuff in the box and shelved it. so i looked at the front pads, three seemed fairly normal the fourth had about 1/4-1/3rd of it crumbled away (the shorter radius side). yikes. so that should explain. unless the dealer did something funny when taking it out but doubt that.

 

[Norm Peterson]

Pad material crumbling away sounds like they were badly overheated.

Scroll almost to the bottom of this link.


Norm

 

[2013kAB]

actually here's the pad then. sorry for the poor qual pic (cell phone).

edit: norm, funny i had another thread on overlapping pads. i had that too. we removed a thin-washer-spacer on the calipers and still have clearance with the rotor plus no more overhang!

after reading a bit more this weekend, it sounds like installing the track pads for a couple-few days of driving (10-20miles low speed commute /day) might not be a bad idea.

it removes the transfer layer of the street pads i've had on for the last month+. the reason is the abrasive nature of the track pads at lower street pad temps. there was also a comment that you'll know when the street pad transfer layer is worn off when the track pads start to squeal.

then i'd bed in the track pads with a couple of warm up laps. i could get heat in them for the first 2 laps (warm up), then a lap or 2 at higher speeds, then park the car to let it all cool down (hopefully enough time in between sessions). then normal (for me ha!) higher speeds.

sounds like swapping back to street pads i could drive a coupe-few days then re-bed the street pads.

as a reminder these are carbotech 1521's for street and xp10's front/xp8's rear.

thanks