The reason for the poor m.p.g. on my PT

As far as your parentheses go, the same applies for Chrysler products. I've
changed the heater core in my '86 Dodge Lancer... What a bitch! Same
procedure, sans airbag removal...

I also changed a heater core on an '86 Ford Escort that I owned... So
simple it wasn't funny... Remove glove box, remove three screws on core
cover inside car, disconnect core hoses under hood. Give the tubes under
the hood a push, then pull the core out from inside the car... Had it
replaced and put back together in under 45 minutes... *That's how it should
be!*

 

Untill you get into a vehicle such as the Caravans or Town and Country
vehicles with ABS Brakes. Crack a line and get air into the Hydraulic unit
and now you need a scan tool to perform a bleed test of the Hydraulic unit

Me personnally the Japanese Metal is junk.

Keep in mind that the piston does not slide in the bore of the caliper, it
actually slides on the seal ring inside the caliper. rust pitts wont hurt
the caliper unless it is at the seal.
Also you have to be careful pumping the brake pedal past its normal travel
when trying to bleed the brakes, thats a good way to tear or damage the
seals inside the master cylinder. If the piston extends past the normal
travel in the bore the corosion/buildup will damage it

 

See below re: United Brake Parts rotors.

Nope - Hate to break it to you, but United Brake Parts is NAPA's
in-house brand - they are private-labeled for NAPA by - wait for it -
RAYBESTOS (parent company: Dana) - made in Canada IIRC. You did find
those in a NAPA store, right? 'Cause that's the only place they are
sold in a United Brake Parts box.

Mmmm - cheaper I would agree with. Way cheaper? That's arguable. It's
common to pay $60 per axle ($30/wheel) for an upper-mid grade of pads.

Rock Auto Parts (www.rockauto.com). Drilled down for calipers for my
'99 Concorde. If I counted right, 28 permutations (left/right,
front/rear, various manufacturers, different grades, some with pads
included) of part numbers.

Examples in their list (all prices are netted out after core returned
and core price refunded):
Raybestos right front - $32
Raybestos right front "Professional Grade" *loaded* *with* *pads* - $52
Raybestos right front "Professional Grade" *loaded* *with* "Super
Premium" ceramic pads - $62

Similar results on www.napaonline.com

BTW - I just checked calipers for your Corsica at napaonline.com and
Rock Auto:
Prices ranged from $17 to $37 w/o pads on both sites.
Rock Auto - Raybestos Prfessional Grade *with* *pads*: $38!

Next question!

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

don't need a scantool if you follow the procedure for brake bleeding in the
factory service manual for abs systems

 

True, however if you maintain your brakes, change the fluid, don't let them
get ground down to the steel, why then would this happen? Actually
both my T&C's are ABS vehicles and it is true about that, but if you
don't do something stupid and the bottom of the vehicle isn't all
corroded out due to salt on the road or some such, then you won't get
air into the lines.

And, even if you do - well then, do all the parts replacements, fluid
flushing and such, and take it to a dealer to get it bled. You still will
save a bundle.

Well, once again we are talking maintainence here. If you change the
brake fluid every once in a while, water isn't going to corrode up the
inside of the MC. And if the MC is corroded to the point that it will
only hold a seal during a very small amount of travel, well what
happens during that panic stop when you jam down on the brakes,
and push the cylinder into the corroded zone?

If the MC cannot survive a regular bleed cycle, it's dangerous to
have on the vehicle IMHO. Better to find that out when the car is
in the garage, I think.

One other thing too I'll say about bleeding, if you instruct your assistant
to push gently on the pedal, you can control how far down the pedal
travels by how much you open the bleed screw, and it doesen't take
much pressure at all to bleed them. I've personally tried a number of
the brake bleeding tools, like the one way valves, the vacuum bell jars
and such, and nothing works as fast or as well as an assistant on the
brake pedal. That's where it helps to have kids - wives are rather
unpredictable doing this job, they tend to get impatient and take it
out on the brake pedal.

Ted

 

You mean the one where you stomp on the pedal 50 times in a row or
some such? I think that only worked on the Bendix 10 systems that
were pieces of crap. The bendix 4 systems you have to use a scantool,
and the later teeves ones, I don't remember.

Ted

 

The factory Service manual does state that the DRB has to be used to bleed
the brakes with that set up. You are right as far as the Bendix 10 system,
since there is no program to bleed them with a scan tool use a scan tool to
actuate the hydraulic valves as you are pushing on the pedal and it makes it
alot easier

Glenn

 

Actually I put that in there to yank your chain, Bill. I guessed you might
read that.

What was that you were saying last year about supercooling in liquid
nitrogen?

Most of the auto rotors I've seen are machined castings.. I very much doubt
that the machining on the casting is any worse than the wear the rotor is
going to get in actual operation so I'd dismiss that. It's more likely you
could have casting
problems, such as voids in the material, molding problems, or the metal
may not be of the same composition throughout the casting itself or might
not have been cooled evenly. But, the question really is how much
accuracy is really needed here? As soon as you use the rotor your
going to be fatieguing it.

That is a good point.

Ah, Bill, but your missing some things. When braking a
vehicle not all of the energy is being absorbed by the friction components.
Some of it is going into the frame of the vehicle and stresses on the
suspension and tires.

A panic stop is going to put a very high amount of kinetic energy into
the suspension and frame and tires. The frame, in fact, will compress
much like a spring, as the energy is dumped into it, as will the suspension.

You can see this very easily by doing a very hard stop at a stoplight,
you will feel the car bounce back after it stops, as the springiness
discharges the stored kinetic energy to move the car backwards.
An oscillation will occur here, which the frame and suspension is
designed to very quickly damp out, of course. But, the point is that
this energy will not be discharged into the friction components.

By contrast, a long slow stop won't slam the car frame back and forth,
because much more of the kinetic energy is being discharged into
the friction components. So the brakes will get hotter.

Now, think about the difference between a hard and a soft pad.
A hard pad when pressed against the rotor is not going to deform
on a microscopic level as much as a soft pad, with the same amount of
braking force. So there will be less friction between the hard pad
and the soft pad for a given braking force. Less friction means that
the rotor is going to spin more during the braking decelleration
process, and the frame and suspension will not be called on to
absorb as much braking energy. Thus the longer spinning means
that the pad is going to get hotter, since it's absorbing more braking
force.

But there is the rub, braking isn't just the pads and rotors. You can get
the same decelleration with 2 vehicles at a different rate. One drive
may brake harder, earlier, then let off later on. Another may brake
lightly, but constantly. The decelleration, measured over the same
stopping distance, is the same, but the brakes are taking up more
kinetic energy with the second driver, the frame is taking up more
kineic energy with the first driver.

And, even there I also suspect your assumption about given braking
force is wrong too. I think people tend to only want to press on the
brakes at a certain foot pressure, and they learn with bigger vehicles
to start the braking earlier, and with lighter vehicles to brake later on.

Did you ever see the Lucille Ball/Desi Arnaz movie "The long long
trailer" If you never have, watch it sometime it is a scream. There's
a scene in it when they just got the trailer that Desi brakes at a traffic
light - and ends up in the middle of the intersection with the trailer
perfectly at the stop line, and everyone looking at him like what
an idiot.

It doesen't have to be a big difference between the soft pad and
the hard pad. I think we all can agree that material of both the rotor
and pad will wear off faster, the hotter the materials are, since the
molecular bonds are weaker the hotter the material gets.

That's why if I descend a long hill here in my 68 Torino, if I
let it coast then press hard on the brakes to slow it down,
periodically on the way down, rather than just gently riding the brakes
all the way down like the rest of the idiots on the road do, that
at the bottom of the hill my brakes haven't faded yet. Before I
learned to drive I did ride the brakes all the way down once or
twice and with a 4 wheel drum system, when it fades, it's just
like trying to brake on solid ice, and it definitely faded!

If the hard pads only get 10 degrees hotter then the soft pads, I
think that's enough of a difference to affect wear rates.

If a DIY'ers time is that valuable, it would be cheaper for them to
take the vehicle to the garage and pay whatever they ask to fix it.
Otherwise I think the DIYer is putting on airs.

Ted

 

I suspected as much. Good thing I didn't over-react. (you bastard!)

It changes the molecular structure - has to do with grain structure,
precipitation of carbide particles. At the end of the process, the
metal structure is extrremely stable - no distortion due to heat because
of the extreme consistency throughout the part. The process is not just
a mere brief temperature change - it involves soaking at the
super-cooled temperatures for many, many hours - the change in the grain
structure doesn't happen immediately. It's grain growth - but in
reverse. Take a course in materials science, specifically metals and
alloys, at your local university.

That's not an accurate use of the word "fatique" when talking about
materials. The point is that the best, most stable and warp-resistant
rotor will be the one with the most uniform and stable composition and
structure throughout, all stresses relieved. You allude to much of that
in that previous paragraph, yet you seem not to grasp their importance.
How much accuracy is really needed here you ask? How much runout is
needed to cause pulsation - maybe 8 or 10 thousandths. Whatever that
number is, the amount of thickness variation that it takes for the same
affect is about 1/5 or less of that number - so we're down to 2
thousandths of an inch or less of thickness variation.

It almost sounds like you're now trying to say that warped rotors don't
cause brake puslation.

But, for a given deceleration curve of a given vehilce, those factors
are equal. That allows the discussion to focus on what happens at the
friction components themselves, which is what you started out doing.

True. But you're just muddying the waters with that. Let's keep those
equal and say that the driver is going to apply whatever pressure it
takes for a given deceleration "schedule" if you will - I think that is
a valid assumption once a driver adjusts to a new feel. For example -
after the initial adjustment, the guy's wife is going to perceive the
same driving cahracteristics of her husband after the more aggressive
brake pad is installed - if she thought he was a smooth, slow driver
before, she will continue to think that - if she thought he was rough,
she will continue to perceive it exactly the same way - he will change
how he uses the pedal to give the same effect. It's not like he's going
to be throwing her thru the windshield and telling her that he can't
help it - these new brakes are more powerful. No. He's going to adjust
his pedal modulation to give the same effect as with the old crappy brakes.

Moot point for the experiment as I would set it up as explained above.
And I think my assumptions are valid.

Unrelated to the discussion.

Back to my premise that under a given driving condition/slowing/stopping
situation with the same driver, same car, the driver will have adjusted
his use of the brakes to give the same effect. So - given that - the
rotor will not spin any more.

We were previously talking about changing the pad characteristics - not
changing the agressiveness of the driver in how quickly he stops the
same car in a given situation.

Except we're not talking about variations due to the driver - we're
talking about given pad/rotor combinations.

You're screwing with me I know.

yadda yadda yadda

We're talking about the same vehicle - pick one and stick with it for
the discussion of comparing pads and rotors.

Yes - we're both old.

OK - no problem with that. *BUT* I disagree that there is more total
heat generated in the brake components under the same deceleration
schedule on the same vehicle with different pads - the law of
conservation of energy says I'm right. I'm willing to give you that,
though the total heat generated in the pad/rotor combination is the same
(for a given amount of vehicle energy burned off at the same rate), the
splitting of that quantity of heat between pad and rotor will be
different. You've helped me see that as a possibility.

You're right about that. I understand that they now teach students to
ride the brakes on a descent rather than pump them. I guess it's the
results of having to teach them to hold the pedal down in a panic stop
with ABS brakes, so they misapply and extend that to speed control on a
descent.

I don't understand your conclusion that the harder pads will get hotter
under the same slowing or stopping conditions. On the heat split
between pad and rotor that I mentioned above, for the same total heat in
the pad/rotor combination (according to the law of the conservation of
energy), I would think the rotor would get hotter and the pad cooler
with the harder pad, but that's a little bit of guessing on my part.
But the total heat shared between pad and rotor is, by definition, the same.

Well - you know yourself that people have different availability of time
and money at differetn times in their lives, or even from one week to
the next. Yeah - if money is really realy tight, and I have free time
on my hands, I would do the rebuild - been many years since that was the
situation. But if I have even a little money to throw at it, and a new
caliper costs $35, and I'm moderatly but not extremely busy, then I
replace the caliper. If I have money but absolutely no spare time -
yeah - then it goes to the shop - except not if the caliper is $250!

So there's no right answer. The variables that go into the decision are
availability of time, availability of money, price of parts, paranoia
about shops working on one's vehicle, desire to DIY for relaxation even
if it costs more (then you call it a hobby and your wife has to accept it).

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Well, there are 2 problems with that argument:
1. The difference in amount of energy stored in the frame is insignificant
when braking from a reasonable speed. How much energy is absorbed by
the frame? If one releases the brakes at the optimum time, on some
cars, one can get the car to reverse after stopping. But how fast?
Maybe 5mph. Some energy is absorbed by the shock absorbers, but
again, I think this is minimal.

We should remember that kinetic energy is calculated as 1/2 M V^2. In
other words the total energy to be absorbed during braking is highly
dependent upon the starting speed. So, when braking from 10mph, the amount
stored in the frame may be significant, but when braking from 60 mph it
will be insignificant. I believe the amount of energy absorbed by the
frame is limited, irrespective of the starting speed (unless the starting
speed is very low).

2. When braking at a higher rate, the amount of time to come to a halt is
less. This means that the amount of time for the rotors, pads, etc. to
transfer the heat generated when braking into the atmosphere is less.
Hence the rotors will get hotter.

 

And item 3:

When stopping gradually, normal drag (tires, engine, wind, etc.) all help
to reduce kinetic energy (and help to reduce heating of the rotors and
pads).

 

my wife is the best brake bleeder on the street

 

not to get in a pissing match here but you don't need a scantool to bled the
brakes

 

All true, except, again, they all get negated when the driver, after a
short adjustment period, modifies his use of pedal pressure to give
essentially the same deceleration curve in a given situation to
compensate for differences in pad characteristics. By "negate", I do
not mean the effects of the things mentioned are not there - I mean they
are essentially identical for the different pad scenarios and can be
ignored for comparison of heat, wear, whatever effects on the pads and
rotors.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Bill,

I don't think we are in disagreement here. To brake from any speed to
another speed requires the same amount of kinetic energy to be converted
into other forms of energy. If the decelleration profile is the same, then
the amount of energy that is converted into heat must be the same,
irrespective of the pad/rotor combination.

I also agree with you that dirvers will change the amount of pressure
applied to the pedal to get a similar decelleration profile if pads/rotors
are changed. In fact, I just put on new Akebono pads and Brembo rotors and
found a much reduced pedal pressure is required -- does this mean that I
should expect to replace the pads sooner?

 

If you get air into the Hydraulic assembly you do need to use a scan tool to
perform the ABS brake bleed. Im not talking about cracking a bleeding on a
caliper.

 

I'm not sure if higher coefficient of friction inherently means faster
pad wear.

Are these the Akebono ProACT's? Several people tried them and liked
them on the 300M Club, but mine developed serious pulsation - I suspect
a filming issue rather than rotor warp, but never did investigate that.
I'd be interested to see how yours do over the long haul.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

They are the ProACTs. Filming has been an issue with just about every set
of pads on this vehicle, although I did not notice it much with the last
set. The original, factory-fitted pads had an uneven filming problem after
about 25-30k miles. I have rented a similar model and it also had the same
problem. It's a '97 Grand Voyager. I assume that it is a filming problem
because the problem comes and goes -- and I doubt that rotors would
un-warp themselves.

Well, there is one advantage these pads have over others: since the pad
material is bonded, not riveted, there is slightly more material to use.

Would the factory pads have been ceramic?

 

Exactly. Finally someone gets it! (although it may be that some rotors
could warp when hot and unwarp when they cool down due to uneven
stresses - not sure if that's possible or likely, but it's the only way
it could go thru cycles of warp and unwarp)

I think that's pretty much true on most vehicles these days - at least
the ones I've seen in my DIY'ing.

Not sure - I don't own a Cruiser.

If you have filming problems, see if Performance Friction "Z-Rated" pads
are available for the Voyager - regional chains like Advance carry PF
brand, but generally not the "Z-Rate" - try
http://www.frozenrotors.com/products/pfc/. I have been using those for
over a year now on my Concorde, and the brakes are as smooth with those
for longer than they have been with any other pads I tried. I also got
good service out of Hawk HPS pads - they would be my next choice if the
Perf. Frictions weren't available.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')

 

Bill Putney wrote:

Oops - meant Voyager (got thrown by original topic). But it's true - I
don't own a Cruiser either.

Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')