Rear from a explorer in a model a

Too much brake capacity, especially on the rear, is what is being referred to here. Locking rear brakes, at all, much less before the fronts reach lockup, is what puts you into the weeds, if you are lucky, and into the opposing traffic lane, if you are not.

The typical vehicle has a forward weight bias as built. When stopping, the weight bias gets a bit worse.
So, that is the reason front brakes almost always have greater capacity than rear brakes. Building a 2200
pound vehicle with rear brakes from a 3500 plus lb vehicle, especially coupled with skinny tires, is likely
to result in a disappointing outcome.

Ray

 

You must not work on COP CARS for a living! I beg to differ on that one! That would be hands on experience..... maybe a Grand Marquis that grandma owned , But COP STUFF? Fogettabouttittt!

 

it's not the axle that take's a shit........(snaps). Well,sometimes,1 in 20 years.,and that's from/where the bearing rides, but never a "snap" issue....Usually soaked brakes,and the tell tale of oil on the backing plate.......=Bearing/axle love there... I see the worst beating everyday on these....Guy's who have NO idea of how to even check oil! ,and beating the HELL out of stuff.....One of my daily routines.......
Like I say- Stay away from anything PD related..........if that's the case.......
And- to my dismay,(well,appreiciation) 4 2005 CVPI'S are going out this year....... And they are active patrol...........Thank God!

 

X2, I'm a police fleet mechanic and get a real chuckle when ever I read how great the ford 8.8 rear end is.

 

I have installed them for a couple dozen off-road guys. They like them, and they are way more abusive than cops.

My DD has one, works great.

 

I can't see the problem, because so far, nobody has given any explanation as to WHY this is dangerous. I'm all for being safe. So, tell me why rear disks, and front drums don't work if properly proportioned. It's part of being a mechanical engineer... I need an explanation.

 

It isn't specifically the rear disc/front drum that is the issue. A small disc rear and larger drum front might be just the ticket.......

Based on your last post, I have to assume you either did not read (my) post #31, or if you did, the point was missed.

The object in setting up brakes is to have the correct balance between front and rear braking 'force' or'capacity'. On drum brake vehicles, the front brakes are typically larger diameter and/or wider shoes than the rear brakes. Same for disc brake equipped passenger vehicles. Disc front/drum rear have the more powerful braking capacity at the front.

The dynamic stability of the vehicle, when braking, and especially when braking hard in an emergency, is far better and more predictable when the front brakes do most of the work. As I said in post #31, locking rear brakes first almost always puts a vehicle in a sideways skid. The rear end will come around, left or right, depending on variables, and it is much more difficult to control what happens next. THAT is the unsafe outcome you are being warned about.

The point being, the size and capacity of the disc brakes on the Crown Vic rear axle are presumed to be more powerful than whatever unspecified drum brakes you have in mind for the front end. If that is a correct presumption, there is absolutely no proof you can "dial out" that imbalance with a "proportioning valve". Like everything else in life, they have their limitations........

The better choice is to select brakes that from the outset are sized for their respective position and minimize the need for 'corrections'.



Ray

 

To over simplify, disc brakes sweep two large stopping surfaces that have a better chance at cooling very quickly. Drums, well, they're drums with the inherent heat retention and less stopping area (even though it looks like visually more on some). A little heat makes a disc brake stop better with some pad content combinations, so even if the bias "feels" right the rear brakes can lock up before the fronts and you can't steer the rears out of trouble. To feel that a light car doesn't need much help beyond bias control, well they'd be the 1st to lose control if the rears lock up in a panic situation. Pressure is but 1 element in braking and it's not the end-all do-all. Everything matters. 4 wheel disc brakes are superior in every way we can imagine.

And back to what started this, the offset in the rear axle goes all the way to the vibration dampener on the front of the engine in most cases. Some time in the 60s engineers moved everything to the right just a bit for the extra real estate needed for steering, brake boosters, pedals, etc. Mid to late 60s GM cars were 1/2" to the right (1" offset), some were as much as 3/4 (1 1/2" to the right). Tub a shit load of cars and this factor will never leave your mental references. If you're lucky you can pull the axle from the long side, narrow the housing to center it all and merely cut the splined portion down with a chop saw followed by a light bevel with a fresh 50 grit grinding disc while spinning the axle to keep it true. Viola, centered pinion.

Yes, I know it's "voila", but it's my story so I ended it my way

 

As a mechanical engineer,
I'd think you should know where to find this information published several hundred times over. A big part of a formal education is knowing where to find things, the info, the calculations the scholarly articles that you seek.

I might be wrong, but I would not think I'd ever see an engineer on a public forum say such a thing as "nobody has given me an explanation" . You haven't read the countless books written, why read a post?

 

Ray,

Sorry, I DID miss your post. My bad.... Too early in the morning.

To you, and Highlander, thank you for taking the time. I understand brake bias, and the weight transfer that necessitates it. Growing up as a teenager with a car that had a hand EBrake, and avid motorcycle rider, I'm also very aware of why locking the rears, especially before the fronts is a very bad idea.

My train of thought was simply that the front drum brakes were more than adequate for this vehicle, and the adjustable proportioning valve would be able to "Dial Back" the rears to a good balance. Obviously, some think that this combination cannot be made to work properly.

I honestly don't know if it will, or wont, but for the time it takes to swap out an axle that I already have, I think it's worth trying. If it doesn't work, It'll be obvious when driven, and I'm only out a couple hours of my time.

I'm still open to constructive input on the subject.

Thanks!
Jade

 

Don't be a dick. The world has plenty already.

 

I really would be happy with more dicks and wayyyyyy less dumb asses.

Tell me where my statement was incorrect - and why the truth and saying the obvious makes it a dick move.

Or does someone need to spoon feed that to you too.

Hey, it's ok to not know something.
But if you say "as a mechanical engineer" then you should be able to find it. Now that's only one of two things, you're a liar or a dumbass.
Now that's being a dick, just so you know the difference.

 

OK, now I get it. Because I'm an engineer, I'm not allowed to participate here. Only non engineers are allowed to ask for an explaination of why, when someone says "That won't work". I instead should do calculations on pedal ratio, line pressure, clamping force, coefficients of kinetic and static friction, and of course braking torque vs tire load. Got it.
I was under the misguided assumption that this forum was for the enjoyable sharing of information. I was hoping to get some empirical evidence from someone who might be able to say something like... "Hey man, I tried that, and I never could get the rear brakes to settle down, no matter how much I fiddled with the adjuster.", Or " The Piston on the calipers are SOOO much bigger than the ones on the drums, that it'll be too far out of balance to ever be adjusted right.

From now on, I'll just look it up my damn self.
Thanks for setting me straight. I appreciate it.

It's a shame though, cause I really enjoy the conversation here most of the time.

Jade

 

And this is how a thread gets killed.