Unique Rear Brakes - 6.3

[Styria]

I guess I could stand to be corrected, but I have reason to believe that only the 1969 300SEL 6.3s are fitted with ventilated disc rotors, and higher capacity brake calipers. I find this quite remarkable in view of the fact that good authorities contend that the braking capacity or capabilities, especially on the large engined M100 V8s is on the marginal side - in fact I read on the M100 site that one of the contributor's Alfas has the same swept brake volume as the 116s and 107s.

After 1969, 6.3s were fitted with solid rear rotors that were the same as the 116 models that followed the 109s, and I have reason to believe that all 126s, including the 560 Coupe and Sedan versions, had the same rear discs and calipers.

The piston size on the 116 and 109 calipers is 35mm, whereas the 1969 6.3 has calipers with a piston size of 42mm. Whilst I think that the 'normal' 116 and 109calipers could well be interchangeable, the internal designs of the two units are different. All calipers utilize the same size rear disc brake pads, and I suspect that this could well apply to the Ch. 126 models as well. I am still trying to ascertain if, in fact, the "odd" 1969 6.3 braking system could be adapted to the rears of the other models.

I have said this before (somewhere) and I'll say it again - I really think that the method of securing the rear calipers on the 6.3s is really quite marginal and probably somewhat 'dumb' - whenever one has to remove the rear calipers, invariably you finish uip with a broken thread section on the backing plate - three out of four - no kidding. Regards Styria

 

[SEL_69L]

I have seen photographs of a 300 SL gullwing with ABS. The prop shaft was marked near the diff. with black and white striping axially, about 8-10 mm wide. These stripes, as the prop shaft revolved, were detectecd with a laser beam, in much the same way as crankshaft angle detector, where info. is fed into the engine management chip, but in this case, the info. was fed into a modified ABS unit, which gave modulation commands to the brakes. The photographs did not show enough information to reveal if the car had disc or drum brakes, but I suspect that the drum brakes would be retained, so that the car could be easily changed back to original specification. It seems to be fairly common for modern lightweight hatchbacks, etc. to have ABS and rear drum brakes.

 

[TJ 450]

The topic of brakes is quite an interesting one.

I also find it very interesting that the rear brakes remained the same for such a great length of time, but also the basic chassis design was not vastly different on the W126 either, but just an evolutionary progression.

Remember also, that the calipers have two opposing pistons that are far more responsive and durable than "Fist-Type" calipers such as the Girling variety.

Change for the sake of change was not on the cards back then and they did the best that they could do at any given time. However, it is very well known that the 6.3 was an afterthought and that may account for the oddities here.

Tim

 

[Styria]

Hi Tim, just not quite sure what you mean by 'fist type' calipers, and you also bring in Girling units that I scanned for the 'Adenauer' 300s. The way I see it, both systems (as on Girling and the ATE rear) have opposing pistons calipers. Which car, or system, has the 'fist type' - are you talking about late model cars ?

Yes, I have found with 6.3s that each year was one of evolvement, especially under the bonnet. Different brackets here, different brackets there, and quite a lot of the electrical relays and part of the electrical system were constantly changed or modified. Another change were the steel rims. The earlier models had plain steel disc wheels, 6" wide (from memory), whilst the later models had steels with all the round holes and the turbo blades - in addition, they were 6.5" wide. Regards Styria

 

[AAB]

Styria,

I understand that the 300SEL 6.3 was a genuine 250 kph cruise all day car, to cruise down the autobahns, & good brakes was an advantage.

Regards,

Alex

 

[TJ 450]

Hi Styria,

Yes, the "Fist Type" calipers are on some of the W126 Coupes among others (front only), so are probably not totally relevant to this discussion. IMHO, they are an unnecessary compromise and are found on many modern cars. They have a retaining bracket on which the caliper slides and may be slightly better able to deal with some runout of the rotors due to the floating assembly.

Tim

 

[BAR]

W116 Brakes from DBA (Disc Brakes Australia Pty Ltd, replacement units) are all vented, and there is an optional slotted, vented unit.

DBA 255 Street Series Standard - vented (same for each side)
DBA 255SL/R Street Series Slotted Left-Hand or right hand (unique to each side because of slots)

I can't recall what was on the car as standard as I replaced my rotors with DBA's 10 years ago and they are still in great shape after 60,000 KMs.

 

[Styria]

Hi Brian, where ventilated discs are a standard fitting, DBA invariably have the equivalent replacement part. Of course, they can be slotted as well, but at considerable extra cost.

However, DBA would not have ventilated rear rotors, unless that is the standard type of fitting. Thus, if you'd want to fit a ventilated unit to the rears of a 116, or 126 for that matter, you'd be out of luck. Furthermore, your standard calipers would need to be modified by means of spacers to fit over the wider ventilated rotor.

My point was that the 1969 6.3 rotor is quite unique to just that particular year and model of the 109 range. I have since established that one would need different backing plates, and it is also necessary to carefully shim the position of the caliper in relation to the disc to attain the optimum centralized position. Regards Styria