924Board.org

[ramiroelliot]

Hello, I plan to improving the engine performance of the 924, and, being responsible, the brakes should be improved to.

Is it complicated to swap the drum brakes for disc brakes on the back? Any compatible affordable options?

How about the front disc brakes? They don't look like they can dissipate any heat and that doesn't sound good for hard driving.

[Cedric]

What will you use the car for? And how much engine will be there?

Std brakes can do alot with proper pads and fluid, even though the brake feel isnt the best with the drums.
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1980 924 Turbo
www.instagram.com/garagecedric/

[MikeJinCO]

The long pedal travel is very disconcerting. When I did HPDE driver school at Pikes Peak IR in Colorado we had go from high speed around the oval in my case probably 85 to a 25mph hair pin, I had changed from stock rear pads, probably Chinese garbage from a Super Beetle to Porterfield RS-4 it always stopped even tho a bit spooky. It is an inexpensive upgrade, changing to better SS brake lines probably helped also.
The premium way is to get the entire 5 lug system off a pre 86.5 944 using the stock MC But that gets rather expensive due to the 5 lug wheels and new tires also. That brake system came off an early 911. If you search this site you will find several threads on adapting other rear discs, doable but not easy.
As Cedric said make the best of what you have.
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Mike


'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

[Beartooth]

There are basically three options: first, keep the stock brakes setup and upgrade pads and shoes and such (like MikeJ laid out); second, find the parts you need to upgrade to the later brake setup; third, DIY brake upgrade using bits and pieces from other cars (the low-buck approach) or brand new aftermarket pieces (the expensive approach).

The first option is fine if you aren't planning on doing track driving or a lot of very aggressive twisty road driving. I've put a few thousand miles on my 931 with the older setup, and haven't had any significant complaints about braking. But then, most of the aggressive driving I'm doing is on gravel. I can't say I've done anything to push the limits of braking.

The second option could be fairly cheap and easy if you come across a parts car, or very expensive if you have to piece everything you need together off ebay or whatever. If you're considering that route, there's plenty of reading on the forums here (I think ideola has a thread that encapsulates all the items needed and pitfalls), and I think some good info on the 924.org technical section. You can use some parts off a 944, but a 924 or 924S parts car would be far preferable because if you swap everything from a 944, you'll have the wheels sticking out too far. I think the offset is built into the rims, but I might be misremembering there. Finally, using parts from a 944 or 924S could mean having to change brake lines, because earlier cars have a diagonal brake hydraulic circuit, where later cars have a straight front-rear.

The third option is probably out for a lot of us. I'm contemplating it, partly because I don't want to invest in another set of rims and tires, but it's the kind of thing I've never done before, so it would be a bit of on-the-job learning, I suppose. The advantages, assuming one is prepared to undertake the fabrication and machine work to get it done, are that you can use the rims you've got (and a lot of other rims, since the 4x108 bolt pattern is pretty common), the sky is the limit as to how much brakes you can get (although I hear the front spindles aren't up to really severe track duty), and it could be the cheapest major upgrade and way to get a full disk setup. I would say that this route is only practical and economically viable for someone really dedicated; it may be the kind of thing you only do as a learning experience. The later (five-lug) brake setup is reputed to be very capable with good brake pads and maybe some better ducting. Again, there are some good threads to be found exploring the four-lug upgrade path - look for one by user "safe" for one that's pretty far along and appears to be approaching completion.
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1980 931 diamond in the rough

[Karlio]

Proper brake lines, braided stainless and banjos from master cylinder to wheels is a recommendation. Good quality racing fluid. Good quality pads, Hawk, porterfield,mintex carbonne Lorraine.. Good quality front discs, brembo if you can find them. Mintex racing rear shoes.
Two very important things are the correct bedding in procedure for the pads your using and the discs and secondly keeping the rear shoes adjusted as you use them.

Done 1hour races at Spa and regular 40 min races on the above set up with solid discs, not even a hint of brake fade etc, if the pedal gets a little long nip the rears up,simples.

[Raize]

Air ducts for the front brakes are a possible solution. I think with the disc also being the hub containing the bearings it's a bit risky to just rely on super high temperature pads.

https://www.bmw2002faq.com/forums/topic/150659-brake-cooling-again-solid-rotors/

I believe the rear drums do virtually nothing, based on the temperature of the rear wheels vs the front after some hard driving. The rear wheel cylinder is only 19mm compared to the 48mm front, so it makes sense.

[Beartooth]

That ducting idea might make a big difference; I'd think of it as a must-do on a track car with 4-lug brakes. For severe duty, the 4-lug setup is doubly-compromised because of the non-vented disks and the drums. I've read something like 30% of braking is done by the rear wheels - that's probably on a more nose-heavy car, but I think the possibility of the rears fading significantly but going unnoticed is still strong. I've driven an all-drum-brake car, and one hard stop from high speed was enough to fade the brakes. The car was generally more under-braked than a 924, but the rear drums were sized similarly in proportion to the weight to the 924. Overheating the wheel bearings is another concern, to be sure.

That said, this is more academic for most 924s (especially at NA power levels). One panic stop isn't going to cause any significant brake fade, nor is mildly aggressive driving. Driving hard down a twisty mountain pass is another story, however. I side more with Raize. I just can't imagine the 924's drum doing much in track use. That said, I suspect something's wrong if you're not getting much heat in the drums from aggressive driving. The rear drums on my truck got pretty jacked up over time (oil leaking from the axle, for one thing), and I was surprised at the difference after I got them fixed. One thing to note on the size difference of the wheel cylinder versus caliper piston is that you get more braking action relative to the pressure applied from drums. So in a disk-drum setup, if you sized the cylinder area on, say, a straight 65/35 proportion, the brakes would be heavily rear-biased.
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1980 931 diamond in the rough

[Cedric]

You guys are overcomplicating the question, these brakes have been used in 24h racing with just pads and fluid, and other shorter racing series for decades(see Karls answer aswell). Cooling ducts will help to reduce the rate of wear, but they will absolutely be fine with good pads+fluid. And of course rebuilt calipers are a good and cheap idea, or else there is a risk of dragging pistons which will melt pads.

The drums do work under track use, as its the rear its only a smaller portion, like the 30% number thrown around here.

Back in the day when i tracked an n/a i tried both racing and "good brand" rear shoes, and both worked fine. The important/and slightly annoying thing is to keep up the adjustment as Karl pointed out, which will need a fairly frequent look at.
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1980 924 Turbo
www.instagram.com/garagecedric/

[Beartooth]

I'm not disagreeing or suggesting brake upgrades should be an automatic for every car that's driven aggressively, it's just that I can't imagine brake fade isn't significant if the car is pushed hard enough. Not a big deal for most drivers - I've never experienced significant brake fade on mine - but it is something that could cost lap times on the track, or require you to back off in the downhill mountain pass scenario. There's also the question of pad life: I remember seeing reports that it was pretty bad with track use. I do have to wonder what the calculus was behind every 944, plus the "budget Porsche" 924S coming with something like twice the braking capacity. It probably had as much to do with buyer expectations and simplifying production lines as anything, but I have to wonder how adequate Porsche engineers felt the basic 924 brake setup was.

Anyway, maybe the disks hold up better than I'd expect, even being unvented, but the drums ideally should go for serious performance use. Maybe the most frustrating thing about the stock setup for me is that the shoes don't have self-adjusting mechanisms. Some people poke fun at "primitive" American cars, especially of the 924 era, but manually adjusted shoes all disappeared in the mid-60s on American cars. Next, pedal feel isn't great even when they're in adjustment. An upgrade would be nice just for the sake of fixing those gripes, although it's a silly amount of time and money if that's the only reason - given the generally available options.

Ultimately, I guess I'm a little obsessed with the idea of piecing together a setup that gives me vested disks in the front and disks in the rear; at some point, I plan to raid some junk yards and bring home some boxes of rotors and calipers and such and see if I can make headway - along the lines of what safe's been doing. First, I should probably rustle up some junk rotors and drums to have machined into hubs though; that alone could take a while...
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1980 931 diamond in the rough

[Raize]

I used to have brake fade very quickly on stock pads if I would drive it hard on B-roads.

Now I put high performance pads (EBC yellow) and the cold performance isn't good enough to lock up the wheels when cold, although they work well once warmed up a bit and don't fade.

May be better with the sintered metal Carbon Lorraine type pads, I've not tried those. Perhaps that can give you the best of both worlds.




I'm doing my own 4 bolt 4 wheel disc brakes and I might just open source the design for people to copy if it works, I don't think the "IP" has much real value at this point.

[Beartooth]

It seems the pads used are critical with the stock brakes. I'd remembered (and just found again) a post with a pic of around ten sets of used-up brake pads from an endurance race - by Cedric actually. They were basic pads they had to run because the performance pads they had on order didn't get there in time. But apparently good pads (Hawk HP+ are what Cedric mentioned) would last over five times longer! Of course, for a street car, you don't want to get crazy - too easy to get in an accident you could have avoided because you couldn't stop with cold brakes. I've never used EBC yellow pads (I have reds on my Mercedes), but I thought they'd be better cold. One might have to try several pads, probably starting from the most street-biased end (unless it's a pure track car) to find the right compromise.

I'm kind of in between, but if I stick with the stock brakes much longer, I'll definitely invest in better pads and shoes. Unfortunately, while there seems to be a variety of options for pads, I'm not seeing much for performance brake shoes. The one source I did find was https://porterfield-brakes.com/; they have a street compound and two racing compounds available. Not cheap at $90-170 though... Still, for a lot of people, spending about $750 on new disks, drums, pads, shoes, and other incidentals and being done with it in a weekend (not counting ongoing adjustments) is the right answer. You might get the parts for the 477 brake conversion for that - but then have to spend a bunch more... Also, it's more like $350 if your disks and drums are good, or have enough material to be turned.
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1980 931 diamond in the rough

[Cedric]

If i remember correctly I got 2 seasons or so of trackdays on the front pads on my n/a, so they last a long time even though I hammered it. My friend have had similar experience in his na. I have used the HP+ on my 931 aswell, its not considered a full race pad, but it works well on both road and track. They improve after a braking or two when they get some heat in them, but ive never had any issues on the road apart from the dust. Ive never over heated them, not on the na or turbo, but ive stepped up now a bit when ive added an additional 50hp or so On my GT86 i use ferrodo DS2500 as dual purpose pads, works well for both Swedish winter and track days, also a bit dusty similar to the hawks. Ive kept myself away from the EBC "coloured" pads, have mostly heard bad stuff about them over the years, at least for track cars, except for the newest RP compounds.

Yeah the endurance car only lasted about 45min on std pads, some pads longer and some shorter, with the correct hawk pads on they could go for several long races without changing them.

With 125hp, sticky tyres and not alot of weight(US cars are heavier though) it just doesnt push alot of heat into the brakes.
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1980 924 Turbo
www.instagram.com/garagecedric/