Rear Disk Brakes...Is there really a need? Talk it over.

Troy, I accepted the conventional wisdom and advice from Carey and did not originally build Natalie with rear disc brakes.  I locked them up a lot.   Then, I had the opportunity to drive Jack's car in Arkansas in the mountains.  What a difference.

The summer of 2012 I had a couple of near misses.  My car accelerates faster than people are expecting and is closer than it appears due to the size....and my driving style has created a few situations.

Last winter, Carey installed rear disc brakes and a bigger master cylinder on Natalie.  She stops quicker, straighter, with far less locking up.

It's one of the things I scrimped on in the beginning, but seat time changed my mind.

When the beetle platform was first put together, highway speeds were lower and no one envisioned what we'd be doing with them now. A drum brake beetle will lose it's brakes at somewhere between 30-40 mph when panic stopped from 75mph, and it's a very scary experience. VW recognized the need for better brakes as speeds got higher and put front discs on the Ghia, 411/412 and the later model buses. I have found that unless you're pushing the car really hard, a front disc upgrade is more than adequate. Type 3 rear drums are a fantastic upgrade to these cars and with I don't think you could ever tax rear discs beyond their capabilities (on the street). It's their ability to shed heat way beyond what a drum is capable of.  

Typically, it's a bit tougher to "lock up" disk Brakes, but that, alone, isn't enough reason to go that route.

You always hear the argument that 80% of your braking power is in the front wheels, and that is very true.  In all the years I drove beetle sedans I changed front shoes every other year or so and never changed rear shoes even once.  Same thing on all of my cars - almost never touched the rears.

That said, the only advantage I can think of for rear disks on speedsters is what Jack Crosby keeps telling us - the car will stop in a straight line with no pulling to one side or the other if you have disks all around.  Very true.  

Ford must be convinced of greater stopping power with rear disks, because my last pickup (F150) went from rear drums to rear disks when you ordered the "trailering package", so those crafty designers had to know something I don't.

One thing I found that increased drum stopping power is an 11 pound residual valve between the master cylinder and the rear brakes.  It holds the shoes a bit closer to the drum when off-pedal and gets the shoes to engage sooner with a bit more pedal-power (it seems to me, anyway).  A residual valve is not needed on rear disks.

This help?  Gn

Here's the thing- a replica speedster is very light in the front. Everybody agrees that front discs are "de rigueur", because front brakes generally provide the bulk of stopping power on a car. However, because of the significant rear bias in most of our cars (SAS and spyders excepted), the rear brakes actually do quite a bit more of the work than we're used to.

Properly adjusted drum-brakes probably work adequately. However, they require more care and feeding than disc-brakes (which are self-adjusting). When running 4 wheel discs, a different (bigger bore) master cylinder is something that is really needed-- just putting a brake kit on, without changing the master cylinder is a recipe for middling brake performance. Some guys a lot smarter than me have figured out that the rear cylinders on most readily available brake kits are actually smaller than ideal. A biasing valve installed on the front circuit (rather than the rear) might be needed.

The take-away is that more (not less) braking power ought to be applied to the rear as our cars have a significant rear weight bias.

A good test is to lock up the brakes on a dry surface. Ideally, all 4 wheels lock up at pretty much the same time (with a slight bias to the front brakes). If you can do that with drums, then by all means-- rock on. I like discs for the ease of set-up, better "feel", and ultimately for potentially better braking performance.

Brakes are really, really cheap in the big scheme of things, especially in comparison to a stay in the ICU. A guy can do as he pleases, but I'd economize elsewhere.

I'm not a mechanic, brake expert, etc.

That being said, for the slightly additional extra cost, I'd feel better about having disc brakes on all 4 for any car (356 rep or other) that I'd buy. In fact, if it didn't add too much cost, I'd even consider upgrading to ABS if it were ever an option.

How's that current widebody project coming along Troy, lol?

i HAD TWO SPEEDSTERS AT THE SAME TIME, ONE WITH FRONT DISC ONE WITH FOUR DISK. i NOTICED A BIG DIFFERENCE BETWEEN THE TWO. Oops cap lock.

Very few of us will ever be close to flipping one of our replcas.  However, almost all of us will have the occassional panic stop.  Many times we unintentionally cause them just be being where we are in our cars.  Remember that time when that other driver's jaw dropped as he looked at your car, and he completely forgot that he was driving through an intersection with other traffic around?

Your circumstances will vary, but our cars do have the ability to render other drivers dumb, both literally and figuratively.  In those cases, I want the best brakes I can get.  For my $$, that's 4 x discs. 

2 speedster...2 set ups.m one with disc on all 4 and one with just the fronts.  I did notice a difference in having all 4...better stopping power all around.  Just make sure you put on the bigger master cylinder.  When I built my 2nd vintage I had them do all 4 but they put the master cylinder for 2 and the brakes were not right until we switched out to bigger master cylinder.

Troy:

Disc brakes up front with rear drums in the rear are adequate for the reason you mentioned, locked up brakes are locked up brakes, and I've locked up on at least one emergency braking situation (VW disc brakes front and 315-type rear shoes/drums.

I would qualify that rear drums are adequate if: (1) you have the wider 315-type 40mm shoes (rather than the earlier 270-type 30mm wide shoes); (2) the rear shoes properly adjusted (probably one reason for advocating disc brakes at the rear would be eliminating this aspect and eliminating a maintenance issue); and (3) you have braided SS steel brake lines (or great like-new condition rubber lines).  If you have old rubber lines you'll be amazed at how replacing with a set of braided SS lines will stiffen up an otherwise soft pedal feel.

But for the low cost of adding rear discs, and if you are looking for a project that will reduce at least the need to adjust rear shoes, then why not.  Just not a great performance gain. 

Grant

It would be an excellent thing to see some 60-0 stopping distance figures on these cars, differently configured. 

It's not about locked up brakes.  It's about maximum performance before they lock up.  It's the difference between a zig-zag panic stop with the possibility of loosing control vs. a straight ahead, controlled stop in minimum distance.

Been there, done that and hated the drum brake emergency stop on I-40 outside of Nashville.

Good enough may be ok for some but not when it costs you your life.

I doubt there would be a difference...but I don't know...I think I have made one panic stop in nearly a million miles of driving...to miss a deer..

My cars all have disc brakes including my yet to arrive JPS...but if they didn't I wouldn't worry about it. 

If you drive with adequate sight and stopping distance drum brakes should be fine.  

I am no expert but I am a old motorcycle rider and know the necessity of driving defensively and keeping your vehicle in tip top shape.   

I upgraded to rear discs 2 seasons ago and immediately noticed the improvement.

I find it difficult to understand that others won't admit to the enhanced stopping power.

I can only speak for myself...I don't think it is a refusal to admit to it... If I saw some empirical data that proved that rear disc provided a shorter straighter stopping distance I would be the first to admit to the fact.. till I do, I am simply skeptical.   

I'm not advocating for one way or the other, but how can you argue with a locked up wheel scenario?  These cars don't have ABS and in a panic stop you are going to lock up all 4 wheels and once they are locked up it couldn't matter less if there is a drum or a disk behind that wheel.

Most of the comments seem to be about what makes us "feel" safer, but are we really?

Like Bart said, I'd like to see some real data.  I'm sure that disks aren't going to be worse than drums, so until the data comes along, I guess there is no harm in erroring on the safe side and putting disks on the rear.

Sounds like a job for Myth Busters.

As I understand it disks provide much better fade resistance, but I have never heard that a disk is notable better at stopping the first time.  That said, I do like the idea of a much straighter stop due to the lack of needing periodic manual adjustment.

Great topic Troy.  A lot of good input from fellow members.   Here's my $0.02:

First of all, we can all agree that front discs are far superior to front drums, that's a given.

Braking tranfers weight to the front tires, the harder you stop, the greater the weight transfer.  Rear engine cars have an inherent braking advantage since the heavy lump of metal is not already loading the front end, but make no mistake, significant weight is transfering forward even with a rear engine.  The rear brakes have an interesting job.  At slight braking 60%+ of the weight of the car is on the rear axle.  In a hard emergency stop, weight transfer may only leave 30% of the weight of the car on the rear axle.  The worst case is having the rear brakes lock up prematurely in an emergency stop due to lighter loading causing a potentially disastrous spin. (Ever been on ice and have the back of the car suddenly pass the front of the car, giving you a great view of the road behind you through the windshield?  Congratulations if you survived that experience).  To prevent his scenario, engineers use smaller less powerful brakes on the rear axle, smaller diameter rotors, or drums, proportioning valves, anti-lock, etc..  Look at a modern car, you may have 13" rotors in front with 4 piston calipers, and 11" rotors in back with single piston calipers.

A locked wheel, whether with or discs, has the same stopping power.  The difference is the additional sensitivity and consistency of a disc brake vs. a drum brake that may be more prone to premature lock.  My experience has shown me that at the limit, I can better trust discs, where drums have often surprised me, when driving at 10/10ths.  We all know that maximum braking happens just on the verge of lock up, skidding to a stop greatly increases braking distance, not to mention the risk of loss of control if rear brakes lock up before the fronts.

So if you slam on the brakes and slide to a longish stop, it does not matter if you have rear drums or discs, at that point you are just along for the ride.  If your rear drums are adjusted perfectly to lock up a millisecond after the front discs and you can consistently apply the perfect brake pressure to stay right the the edge of lock up until the cars stops, then again no difference, stopping distance will be determined by the available traction between the tires and the road surface.

But in reality, no one can consistently and continually adjust rear drums so finely, and unless one of us in currently a factory formula 1 driver, our braking foot is also not so finely calibrated and skilled.  Without modern electronic wizardry, rear discs offer much greater sensitivity and consistency when driving at the limit.  Now for street use, if anyone is driving that hard on public roads, I pray you are not anywhere near my family risking the lives of my loved ones.  I don't drive hard enough on the street to notice a difference, I save that for the track.

stop shouting 

And the normally shouting pot calls the shouting kettle, black........sigh...

Anyway, if I had the choice of 4-wheel disks OR front disks and rear drums BUT with vacuum assist on all four, I would do the vacuum booster in a heartbeat.  Even with having to periodically balance the rear drums manually, that brake booster would be SO nice, but the only guy (other than all of the SAS cars, plus, the SAS cars have ABS, too)  that has one is Simon Hambly over in the UK.

This isn't necessarily true, Troy, and gets to the meat of the argument.

In the real world (where guys struggle to find a plugged idle jet and clean it), drum brakes are almost never adjusted correctly. Improperly adjusted drum brakes mean all 4 wheels are not going to lock up at the same time. More likely, in a panic-stop, one will lock up, and one will not. I've driven some cars that were pretty bad.

Even if the fade-resistance and "feel" were the same (they are not), disc brakes are a better solution because they don't require adjustment. As I said, a guy can do what he likes, but I'll bet there's not one guy in 100 on this site who regularly checks their drum brake adjustment.

There's an important aside that I hit on in my post above, and I feel needs to be gone over again: the imperfect design of some VW disc brake packages. The standard aftermarket 2 circuit master cylinder works pretty well with front discs and rear drums, and not very well at all with 4-wheel discs. When you add the rear discs, YOU REALLY NEED TO CHANGE THE MASTER CYLINDER to a big-bore model. After you get it all together, you really need to try your brakes on a wet surface to ensure that the fronts lock just before the backs (but that the backs do indeed lock). There are a lot of different brake kits, with parts mixed and matched as needed. It's up to you to make sure they are playing well together.

"Stop" is never as sexy as "go", but it's many, many times more important.

Ever stop to wonder why all modern cars don't have drum brakes on the rear of they are "ok"? 

Because I have drum brakes on the rear I cannot stop to wonder... it's dangerous man.

Great point Jack!

Do rear discs move the wheels out.

If so, I can stop considering them.

I love mine! I just couldn't get the drums adjusted evenly. I did the fronts first and loved them so much I did the rears. Set 'em and forget 'em! Blackie stops damn good too!

~WB

Jack.

"Modern cars" have ABS and I'm pretty sure there are still some "modern cars" that come with disc brakes so I'm not sure it's a valid point.

Again, I'm not arguing one way or the other, I'm just trying to understand why discs would be better, if they really are better.

The anecdotal information in most of these posts is interesting, but not really scientific.  On the other hand, there have been some very good points made by Pdrvr and Stan.

Troy--I believe that all modern cars come with disc brakes--not just "some"..  I'm not aware of any still using drums but maybe you know different.  Any car makers still using drums come to mind?

Jack-

There are some inexpensive cars (some Kias, et al) that can still be had with rear drums. All new cars have front discs and ABS.

I think the Ford Focus has rear drums.  They're not cars but I know that Toyota Tacomas have rear drums. 

http://www.tacomaworld.com/for...um-brakes-why-3.html

The first sentence of my last message should have said come with drum brakes, not disc brakes.

I don't think there's really denying the advantages of the superior technology discs afford, but for those who want to improve the performance of their rear drum brakes-  http://www.thesamba.com/vw/cla...detail.php?id=846684 

These semi-metallic shoes still won't equal discs, but are supposed to be a big step in the right direction.

What about discs in back and drums in front?? 

Jim.....   Thats called "A swift kick in the head".....   

I have to weigh in here....

I have CSP solid discs in front and type1 drums in the back. I do have the wider type3 shoes in there, drums were machined to take the shoes. This year I experienced brake fade for the first time.

We were at Cowan's Gap and I hotfooted my way out of there with Mr. Frazer. Before anybody gets their panties wadded up it's a state park and there are no houses or intersections. Plus, I only drove quickly where I could see, using good sightlines. Anyway, it is two miles of curved bliss. Many times I crossed the center line, which is grooved and bumpy as heck, I was driving pretty fast. I would say it was 9/10ths or more. 

My point is I made my brakes fade in TWO MILES. I wonder if they would with four wheel discs and vented in the front? Remember, my Spyder only weighs 1450 pounds. But I definitely think that will be a mod for the future, vented front rotors and solid disks in the back, along with a different MC.

Troy--excuse my post.  I should have known what you meant--my bad.

Danny

I tracked two Miatas (one with V8 power) and spent a fair amount of time trying to improve their braking performance.

The biggest improvement (decrease in brake fade) came from choosing the right pads. Regular, generic pads work great for everyday driving, but for spirited drives or drives on the track performance brake pads are the way to go.

Over the years I've switched to ss brake lines (waste of money), switched to high temperature brake fluid (on the track regular brake fluid can boil after a hard 20 minute session), switched to larger calipers, larger rotors, and performance brake pads.  Performance brake pads gave me the most improvement.

During one track session I heated my V8 Miata's front brakes up so much the heat from the rotors melted the front bearing grease, but the brakes didn't fade.

While driving my 2006 Mini Cooper S (stock brake pads) on the same track my brakes faded at the end of the long straight-a-way and I ended up going off the track. 

Very embarrassing.

Hell, No need for any rear brakes if you have our all new Massive CoolStop 12.5 front disc brake kit.......

Just sayin!!!

Kevin- Will a 15" Fuchs alloy fit around the 12.5" disc and caliper? 11" vented disc and larger (than Ghia or type 3) caliper? Or is the move up to 16" alloys necessary? Al

When Chris and I spot at Daytona for the Rolex, we're directly opposite the "Bus Stop" chicane on the far side of the track.  Even from that distance, you can clearly see the front rotors of most cars get red hot as they approach the chicane.

All of the TRG-prepped Porsches run some sort of ceramic brake pads, along with cross-drilled and vented rotors, just to prevent brake fade in competition.