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Sometime back, someone here suggested that there was really no advantage to having rear disk brakes over drum brakes, unless they are anti-lock, which I don't think any of us have.  His point was that it makes no difference which type you have if the rear wheels are locked-up, you're going to stop in the same distance either way.

Seemed to make sense to me, but I still see lots of discussion about adding rear disks so I'm wondering if there is more to it than there seems to be.

Even now, as I write this, it makes me wonder if not having anti-lock brakes means it really makes no difference on the front wheels as well?  A locked-up wheel is a locked-up wheel...right???

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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.

Last edited by Stan Galat

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?

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.



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. 



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.

Originally Posted by edsnova - Baltimore - BCW 52 MG TD:

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

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 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.   

Last edited by bart

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.

Last edited by Troy Sloan

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.



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.

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