DjGreggieP
DjGreggieP HalfDork
1/8/21 11:58 a.m.

Do to the number of articles pertaining to brakes recently, I figured I'd ask the community as a whole instead of clogging up the comments on other topics. 

So, I made an odd observation on my car and I don't know if its going to be 'fixable' or if its just a case of 'it is what it is'.

Car is a 1999 Chrysler/Dodge Intrepid. Non ABS Car.

I was recently changing out my brake fluid in advance of painting calipers (Red is worth 20kw) and swapping in fresh rotors and pads since a previous inspection I saw the front pads were very worn down (daily driven). Car was wearing Hawk HPS Pads all around, PowerSlot Slotted front Rotors, and Napa Ultra Premium rear rotors ('U' shaped groove).

So I changed fluid, painted the calipers and went about changing everything over to new parts. Front pads were well worn and needed replacement. But the rear had lots of pad left. Like looked like they had recently been changed amounts of pad. I changed everything regardless since I had everything to do so (Hawk HPS Pads, PowerSlot Slotted Rotors all 4 corners this time) and I do know they pads had years of usage.

Everything seemed normal on the rear for functionality. Sliders slide, the fluid gravity bled out without issue, they seemed to 'brake' when the pedal was pushed and held the wheel from turning by hand, and the wheel spun easily after the brake pedal was released.

It is a nose heavy car. And I know it is front brake biased, tho unsure the exact percentage. Is this just a nature of the beast kind of issue? Car has always seemed great slowing down, better than a lot of vehicles I have driven, but strangely never driven any other Intrepid's to see if it stopped any differently at all. 

MadScientistMatt
MadScientistMatt UltimaDork
1/8/21 12:25 p.m.

I suspect it uses a proportioning valve or similar means to reduce pressure on the rear brakes, so the rear brakes don't apply too hard and lose traction.

Jesse Ransom (FFS)
Jesse Ransom (FFS) GRM+ Memberand UltimaDork
1/8/21 12:29 p.m.

I wouldn't find that shocking. The rears on even a car with even fore/aft weight distribution are doing MUCH less work than the fronts, and if it starts front-biased it only gets more extreme. Stock brake bias will always tend toward locking the fronts first, so the rears aren't even doing as much braking relative to the weight on the tires during a braking event as the fronts.

Er, to clarify, even if the car's got 80% of the weight on the front tires under braking, the front will still be doing significantly more than 80% of the braking so the rears don't come close to locking up and going sideways.

Okay, I'm going to shut up before I go too far down a rabbit hole, but I have it in my head that the ABS era has changed mechanical bias tendencies because of the lack of lockup, but I don't know whether that's true, how much, or even what direction.

rslifkin
rslifkin UberDork
1/8/21 12:37 p.m.

How little use the rear brakes get varies depending on the proportioning scheme.  Some start out heavily front biased even under light braking, which means very little wear to the rear brakes, especially with a front heavy weight bias.  Others start out much more balanced and then bias further forward as brake pressure increases, which means under gentle braking on the street, the rear brakes see more use. 

DjGreggieP
DjGreggieP HalfDork
1/8/21 1:21 p.m.

So it's going to fall under the classification of 'normal', and any attempt to 'fix' it will likely result in issues with the braking feel overall. It does explain why the rear doesn't seem to want to rotate on the track (go kart track, rather tight for a large car) under braking. 

Thanks guys! I'll hopefully get this car out in the spring and get it back onto a track. 

Yep, what they said.

Curtis73 (Forum Supporter)
Curtis73 (Forum Supporter) GRM+ Memberand MegaDork
1/8/21 9:01 p.m.

You might do some digging.  GM and Chrysler (and a few Fords) were notorious for parts-bin swapping.  Often times, the year that "This model now has 4-wheel discs" means "we slapped some discs on the back and didn't do anything else."

Stealth, Caravan, Impala/Caprice/Roadmaster, the first few years of GM 1500s with rear discs, Mustang, among others were guilty of this.

My Impala SS had rear discs, but the master, prop valve, and other goodies were straight from a drum-rear Caprice.  Since drums take considerably less pressure to operate than discs, the overall brake torque proportions were off.  Not dangerous, but notable.  If it's braking fine, I would leave it alone.  If you notice after some spirited driving that the fronts are smoking hot and the backs are just warm, maybe dig a little deeper.

For instance, if your vehicle would work well with 70/30 braking, your prop valve may have to be set up for 90/10 pressure if you have disc/drum.  If you have disc/disc, that pressure bias may need to be 75/25 to achieve the same 70/30 brake torque.  If they didn't do that from the factory, you may have some sleuthing to do.

My first stop would be something like Rock Auto.  Look up the prop valve for your car, then click the info button and see what it fits.  If it fits Intrepid, Premiere, and Caravan from 1987-2003, you can be pretty certain they just slapped in the old disc/drum prop valve.

rslifkin
rslifkin UberDork
1/9/21 9:12 a.m.

In reply to Curtis73 (Forum Supporter) :

I know Chrysler gave at least some thought on disc vs drum.  In the Jeep world, when they swapped the 1st gen Grand Cherokee from rear drum to disc they did change the prop valve. 

Donebrokeit
Donebrokeit UltraDork
1/9/21 9:18 a.m.

I have worked on many LH cars and I would say this sound normal, if i recall the LH cars were 3:1 brakes systems.

 

wvumtnbkr
wvumtnbkr GRM+ Memberand PowerDork
1/9/21 9:21 a.m.

Our racecar gets 1 weekend out of front pads and 3 weekends or more put of rear pads.

 

This is even with running a less aggressive pad on the rear.

 

This car is also a 50 /50 front to rear weight biased car.

 

I would think a front heavy car would exaggerate this situation even more.

 

In other words, totally normal in my opinion.

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