Rear drums to disc brake conversion

[franjo_66]

Hi folks

I got a shock at the prices for replacement finned drums & accessories for my 1966 230SL. I could actually buy the rear 250/280SL calipers, disc rotors, brake pipes, rear brake cyclinder, rear handbrake fittings, etc for far less.

To me it looks like a pretty straight forward swap. Before I get too over-confident, has anyone else taken this step, or are there any hidden gremlins that I haven't considered ?

Thanks in advance,
Frank
1966 Black 230SL/RHD/Auto

[ja17]

Hello Frank,

Many Finback mercedes sedans of the era use the same brake drums. Normally a large supply of good used drums have been available from these donors. The finned aluminum drums were also used on the front of 190SLs so these should be available from a lot of suppliers used.

Most people who convert change the entire differential from a later Pagoda. These can be had good used for $500.00 or less.

Joe Alexander
Blacklick, Ohio

[franjo_66]

Hi Joe

Thanks for the reply. I guess I was really looking for an excuse to upgrade the braking to a more modern & efficient setup !

Would there be many benefits in changing across to the later style differentials ?

Thanks
Frank

[ja17]

Hello Frank,

The 230Sl ratio is a little unique a 3.75. The rest of the differential is the same except for the drum brakes in the early W113s and sedans of the era.  So you can find a 4.08, 3.92, 3.69 or your 3.75 in the W113 cars.  Many owners are now changing the ratio to a 3.25 found in some V8 Mercedes sedans 1972 and 1973. The advantage of the 3.25 is the nice low rpm cuising gear.  

Many of the W108 sedans of the era (250S, SE, 280S, SEL 6yl engines)  had the exact same disc brake differential assemblies. They had some of the same  ratios as the disc brake (rears) W113 cars. Your 3.75 ratio would go away and you would have to choose one of the others if you changed the whole unit with a used. The 3.69 is very close  to your original ratio of 3.75. The only other item which would have to be switched are the emergency brake cables which are a different length on the W113 diff.

Joe Alexander
Blacklick, Ohio

[rwmastel]

quote:Originally posted by franjo_66

Before I get too over-confident, has anyone else taken this step?

As it so happens, yes someone has!  That is, they did a whole rear axle replacement.  It's actually a very nice upgrade from what people say.  Here are some helpful search results:

http://index.php?topic=7254
http://index.php?topic=6804
http://index.php?topic=5958 (awesome thread!)
http://index.php?topic=1195

Rodd
1966 230SL: arabian gray, natural leather, euro, auto, both tops
2006 C230: alabaster white, ash interior.  Without: automatic transmission, sunroof, heated seats, full leather interior, full power memory seats, CD changer, Logic 7, Command, rain-sensing windshield wipers, rear window sun shade, headlight washers, electrically adjusted steering wheel, ....

[franjo_66]

Thanks for that Rodd !

Rgds
Frank

[franjo_66]

Hi Joe

Thanks very much for the insight & details.

If I wanted to keep the diff ratio as is, is it possible to just fit the later 250/280SL axles, being that my main objective is to install rear disc brakes ? Then I would simply bolt on the calipers, etc. I'm hoping that it is as straightforward as that !

Rgds
Frank

[rwmastel]

The experts who have done this kind of work can elaborate on if that is a good or bad idea.  From reading the vast majority of the threads on this forum, I will tell you that people seem to always replace the whole unit.  I can't recall anyone doing a partial upgrade.  Besides, first gear is really short (or low) on these cars, so moving to the 3.27:1 is not a problem, but a benefit.

Rodd
Pagoda Technical Manual - please contibute: http://www.sl113.org/wiki/pmwiki.php
1966 230SL: arabian gray, natural leather, euro, auto, both tops
2006 C230: alabaster white, ash interior.  Without: automatic transmission, sunroof, heated seats, full leather interior, full power memory seats, CD changer, Logic 7, Command, rain-sensing windshield wipers, rear window sun shade, headlight washers, electrically adjusted steering wheel, ....

[ja17]

Hello Frank,

This is not possible. The bolt up point on the axle for the calipers is actually cast into the right and left axle housing. You would have no way to attach the calipers.

The only possibility of keeping your ratio would be to install your original 3.27 ring and pinion gear in a later diff. housing. A very difficult procedure. The gear placement would have to be measured, set up,  installed, coated with marking die, turned under load, dis-assembled and checked adjusted repeat as many times as needed.

Joe Alexander
Blacklick, Ohio

[franjo_66]

I see what you're saying Joe. I was hoping that the bolt up points were not cast into the housings.

Seeing that here in australia we have nowhere near the number of W113/W108/etc cars, it's pretty hard to find a donor vehicle for the rear end set up.

I'll just have to sit back & wait !

Thanks again
Frank

[hands_aus]

quote:Originally posted by franjo_66

I see what you're saying Joe. I was hoping that the bolt up points were not cast into the housings.

Seeing that here in australia we have nowhere near the number of W113/W108/etc cars, it's pretty hard to find a donor vehicle for the rear end set up.

I'll just have to sit back & wait !

Thanks again
Frank

Frank ,
Have you heard of Chris Stewart in Melbourne?
He has a shed full of old mercs from which he sells parts.

I could try to find his number if you are interested.

At the time I was rebuilding my early style electric fuel pump, I bought a back up unit from him at a very fair price.


Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[waqas]

Frank,
If you do find a suitable replacement and decide to go ahead, I would recommend keeping around the original. These 3.75 ratio 230sl differentials are pretty hard to find these days-- I believe only the 230sl and the 111 fintail coupe/convertible had this exact ratio. You can always revert back if you decide to retain originality.

Waqas in Austin, Texas

[franjo_66]

Hi Bob

I haven't heard of Chris Stewart, so if you're able to email me his contact details, that would be much appreciated.

Thanks
Frank

[franjo_66]

I'll definitely keep the original setup. Especially since I've bought a whole swag of new rubber buffers, overhaul kits, etc for the rear suspension !

Rgds
Frank

[Garry]

Hi Bob,

Can you also let me know the contact for Chris Stewart.  I am in Melboourne a lot of the time and can help out for Frank if needs be.

Garry

Garry Marks
Australia
69 280SL Manual
02 320ML
05 A200

[hands_aus]

Private messages sent to Frank and Gary

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[graphic66]

Don't forget the brake proportioning valve that is required for 4 wheel disc on the SL. You also will probably need the master cylinder as well, I'm not positive on that though. The big drums, from tests I have read perform almost as well as 4 wheel discs. The main reason for the change was that buyers were wanting the 4 wheel disc setup on their sports cars. There are places now that will take your finned aluminum drum and reline them with new steel liners. The sedans that have the same size drums are big cast iron drums, not the fancy aluminum ones used on the SL. Probabl;y the best and least expensive option is to keep your drums. If you had a donor car it may be easier. If you have an auto transmission be careful going to high in your ratio as the automatic starts out in second. I still contend that these cars were designed by very intelligent people and when they put a certain ratio rear end in our cars they were very well thought out. Americans wanted big slow reving lumbering V-8's. The power band on your 230SL is way higher than most cars and putting a higher ratio rear end in will drop the revs into a lower rpm than is efficient for these well thought out cars. These engines were made to rev and the music they make at 70MPH is oh so sweet.

[franjo_66]

I did actually get my drums relined with new steel liners, so maybe the best option is to leave things be for the moment. I was talking to someone else who reckons that if you can get the rear assembly castings from a 250/280SL, then this is the easiest way to keep your original running gear, but be able to convert over to rear discs.

So many options ! But I think I'll leave things as is for the time being

Thanks
Frank

[ja17]

Yes,

Good advice from graphic66, The rear aluminum finned drum rear brakes were especially good. More complex and more difficult to re-brake or repair, but very good. Your front brakes discs do most of the braking anyway. You can convert the fronts to the later calipers or even vented front discs with just bolt up items if you want. However, a set of fresh brake hoses and brake linings will normally make these cars stop very well.

Joe Alexander
Blacklick, Ohio

[franjo_66]

Appreciate all the advice & feedback guys.

I've converted my Girling calipers on the front to a new set of the later ATE units, along with new lines, pads, rotors, etc. New steel liners on the rear drums (plus new shoe pads), so I'll leave things be for the moment.

Can't wait to get her on the road ! But that looks like being another few months away..........

Rgds
Frank

[JimVillers]

Frank .... I am late to this thread but I didn't read your "objective" of rear disk brakes.  If the objective is to improve your stopping power and brake fade, try a set of carbon-Kevlar pads and shoes.  This is the lining material that vintage racers use; you will need to find a specially supplier to reline your cores.  This lining material will increase the brake friction by about 25% while being rotor and drum friendly.  The cost will be much less that a hardware swap.

Jim Villers
190SL, 230SL 5-Speed, MGB 5-Speed

[franjo_66]

Hi Jim,

Yes I did forget to mention that the primary objective is to improve braking performance.

Thanks for the tip on carbon-Kevlar ! I'll search around to see whether anyone in Australia is able to provide this lining.

Thanks & Rgds
Frank
1966 230SL Black/Auto/RHD