Brake rotors: Ventilated or solid?

Luis A.

Luis A.

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Hey guys,

My '76 Si has solid rotors on all corners. The factory blue binders indicate all cars after the 2800 should have the thicker, vented rotors. Does anyone else have an Si or can say what they really should have?
 
But isn't that strange? That later, heavier cars would have inferior rotors? I'm not with my E3 binders and won't be all week (anxiety sets in...:roll:), but those books indicate anything after the 2800's have the thicker rotors. What do the CS manuals indicate?
 
Don't know what to say, the part numbers tell the story, only the 3.0CS got the vented rotors. Perhaps the thinking was the sportier coupe made sense while sedans are not driven as hard? (U.S. e3 reference above)

Chris
 
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I've had two of the U.S. 1975 models. Sadly, they have solid rotors at all four corners. I was shocked and amazed, too. I suppose the BMW bean counters figured that since the speed limit was 55 mph, there was no reason to have better braking.

However, since the Euro model has vented rotors, as Simufly indicates, you should be able to do the swap. How easily is another question. I'd go to RealOEM and do a parts comparison between the U.S. and Euro brake systems, see which other cars share the Euro parts, then acquire the appropriate parts.
 
Who can figure BMW's thinking on brakes?The sporty 2800 coupes came with rear drum brakes while the more sedate Bavarias came with discs all 'round.
 
I think Chris hit it on the head. It is a US/Europe thing with speed limits and driving styles. In fact, the spark plugs called for (heat ranges) in the manual for US and Euro models are different based on maximum speeds.
 
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Brake rotors, etc.

Many of you may not remember but starting in late 1974 we here in the colonies were burdened with a 55 MPH speed limit that lasted for way too many years.
The E-3 that I had and others that i have driven are perfectly adequate in the braking department--unless you plan to track the car the solid rotor set-up does a very good job in normal or even spirited driving.

PS--the E-3 is not really a heavy car--about 3300-3400#--actually much light than todays BMW's.

The reason for the solid front rotor, drum rear braking system on the 2800 CS--the rear end was a carry over from the 2000 CS. I drove the BLUMAX with that stock brake setup for around 300,000 miles--included in those many years were thousands of miles driven on the freeways of California--and in the mountains of Western US and Canada without incident before converting to the 4 wheel vented disc and s/s brake lines setup in 1995 that it now has.
 
If you want to convert the rears to vented rotors. Beware that the rear stub axles for the vented discs are different and there is no solution OTHER THAN replacing the rear stub axles. Well there is, read below.

Solution, you will need the stub axles from a 3.0CS or better yet, find a complete E9 rear trailing arm assembly. That's the easiest answer.

1). They are NOT the kind of part that you want to remove at the local pik-a-part yard

2). If available, a pair of used 3.0CS stub axles will cost some coin unless you stumbled across a gentle soul building karma or someone who is unaware of the value of E9 parts. Better solution is to find the whole E9 rear trailing arm assembly and that may cost you a lot more coins.

Expense is the primary reason I recommended making the vented front E3 brakes as stout as possible and making sure that the E3 solid rears are operating as designed.

G-Man
 
My 2800 Bavaria (now an Alpina equipped vehicle) has E9 coupe vented disc brakes at all 4 ends! The vented discs fit over the E3 hubs and the only thing needed to make the conversion fit is the spacers for the calipers which space the outside half of the calipers the same distance out as the increased thickness of the vented rotor(s). Also the longer caliper bolts holding things together. The little o-rings to seal the brake fluid pathways between the caliper halves are not available through BMW, but any Porsche dealer can get them and usually has them in stock! These kits are/were available from Alpina.

Gary
 
Gary,

The tip on getting the in-between calipers sealing rings at a P-car dealership is a good one. Didn't know that. Which model uses it? I sourced the rings from W&N as I split the calipers to have them plated in the original yellow cad (now zinc) finish. I opted to remain stock and bought stock solid rotors front and back.

So you did the Alpina upgrades or it came that way? Sounds like a nice car either way! Pics?
 
My E3 Alpina was originally modified by Dietel Enterprises in the early 1970's. Mike was the only authorized Alpina distributor/modifier in the US at that time. The car first got some Alpina suspension work and a close ratio 5-speed. It then got a 3210 cc 7-Series engine with 530i fuel injection.

It now has a full heavy duty suspension, a 3.9 liter engine with an Alpina head and 300 degree cam, engine oil cooler, later euro L-Jetronic fuel injection, headders, a heavy duty close ratio 5-speed, and a 3.45 limited slip with the Euro 635csi differential oil cooler. The trans and lsd were rebuilt by Peter de Latt - probably the best in the Western Hemisphere until his passing.

Can't wait to get it back on the road, but doing each little project 100% before I start it up. The power to weight ratio will be better than my E34 M5, but I doubt that it will out handle the M5! 20 years of suspension development can do wonders.

Gary
 
G-Man said:
If you want to convert the rears to vented rotors. Beware that the rear stub axles for the vented discs are different and there is no solution OTHER THAN replacing the rear stub axles. Well there is, read below.

Solution, you will need the stub axles from a 3.0CS or better yet, find a complete E9 rear trailing arm assembly. That's the easiest answer.

1). They are NOT the kind of part that you want to remove at the local pik-a-part yard

2). If available, a pair of used 3.0CS stub axles will cost some coin unless you stumbled across a gentle soul building karma or someone who is unaware of the value of E9 parts. Better solution is to find the whole E9 rear trailing arm assembly and that may cost you a lot more coins.

Expense is the primary reason I recommended making the vented front E3 brakes as stout as possible and making sure that the E3 solid rears are operating as designed.

G-Man
Click to expand...

G-Man,
What is the difference in the axle stub which requires the later version for vented rotors? Does this only apply to US spec cars?
Thanks,
Jim
 
My 72 Bavaria is non-vented all around and in some ways I am happy about this......since just paid $280 for rear vented rotors for my 3.0 CS after spending days hunting them down (Mesa has no more, IE found a pair for me).

The other thing about Bavarias, rear sway bar was an option so that also lets you know where BMW's head was at back then. $150 got me a whole lot better handling.
 
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