4,08 to 3,46 Axle Change: what's required to convert a disc axle to drum brakes?

[jameshoward]

....And why would you want to, some might ask?

Well, I am in a state of confusion about how to proceed. This post  http://www.sl113.org/forums/index.php?topic=10886.0 hasn't provided any of the answers I hoped it would - although there are plenty of great issues and questions that have cropped up - and I want to learn more about the possibilities here. I have a 4,08 rear end at present, complete with new brakes as overhauled about 18 months ago; it's a late 230 and has drums. I don't have a problem with drum brakes; mine are perfectly set up and the braking is excellent. Afterall, drum brakes are still used on new vehicles and trucks today.

The 3,46 axle I have would need new discs and calipers; in short it needs everything. I think that another member here has recently done the same job and replaced an axle that had discs and replaced them with drums.

I'd like to know whether the hardware on the disc axle is basically the same as the older drum axle. In order to change the disc set up and use my existing drums, what would I need to do?

Bottom line is that I really don't want to splash out on a whole basket full of new parts to rebuild the discs if I can just reuse all the drum parts on the 4,08 rear end I'll be taking off the car.

I'd be very grateful for any advice on the differences in construction between the older drum axle and it's various fittings, and those of the later axles that utilised discs.

Thanks,

James

[jharkin]

james,
i recently had a 3.27 installed on my 230.
the 230 has drum brakes; the 3.27 had axles for discs, same as your situation.
as i recall right now, my mechanic just had to remove the caliper mounting posts from the 3.27 axles, and drill holes thru the backing plate to allow access for the brake fluid feed. i asked about converting my drums to discs and he advised it would be costly and more complicated. and like you he also mentioned that the drum brakes were adequate. i'll check with him tomorrow and see if there was anything more specific.
john

[Benz Dr.]

Huh? How do you simply convert a disc brake axel to a drum brake system? And further to that question, why would you even want to?

The 34.27 disc brake system will bolt right in with only the E brake cables and a small mod the the cooling lined needed. You need a brake force regular but that's about it. That HAS to be easier than all that other stuff changing braking systems.

[66andBlue]

Dear Dr. Benz,
that is precisely the question that James has been asking for awhile without getting a good answer.  
Why don't you explain in a bit more detail how you would go about adapting the 230SL emergency (hand) brake cable and whatever else is needed to fit the disc brakes on the new axle so that he can do it ?? Writing ".... but that's about it. That HAS to be easier than all that other stuff changing braking systems...." just doesn't cut the mustard in my book. I guess you know what I mean.  
After learning the details and understanding what is required, perhaps I'll send you my car and axle to do it!  

[waqas]

that is precisely the question that James has been asking for awhile without getting a good answer. 

Well, not exactly. I think Dan has summed up the conversion pretty succinctly. There's nothing more to hooking up the disc brake axle.

My understanding is that James wants to use the new 3.46 axle which happens to have disc brakes. Pagodas with all 4 disc brakes came with the brake force regulator. I presume James does not have a regulator on hand. To paraphrase his question in the other thread, he asked "can I use the disc brake axle without the brake force regulator if I change the calipers accordingly?". So far, that question remains open.

However, my understanding is that James' question in the current thread seems to be motivated not by an inability to adapt the cables, but more out of a concern for not having to use a brake force regulator at all, as well as being able to use his refurbished drum brakes instead of having to refurbish the disc brakes all over again.

James, I have no answers regarding adapting the drum brakes to the disc 3.46 axle. However, it does seem to be a lot more work (in addition to being riskier, as it was never meant to be that way). Simply adding a regulator and refurbishing the disc brakes does seem to be the easier route. Would it help if you had a brake force regulator on hand? I recall Jeffc280sl using a non-MB regulator (see this thread: http://www.sl113.org/forums/index.php?topic=3536.0 and this link: http://www.tiltonracing.com/content.php?page=list2&id=37&m=b). Also, new pads and caliper rebuild kits are relatively inexpensive (e.g. look them up at http://www.autohausaz.com). Just a thought.

[jameshoward]

Thanks for the replies everyone.

To clarify a few points: Dan, as I said in my post, I want to get the rear axle changed but don't have a fortune to spend. As I said, if I can use my perfectly good and new-ish drum set up, then why not. That's why I posted the question, which stands as no one has given me an answer as to wether it's possible without wholesale butchery of the disc axle to fit drums. Is the design of the axles significantly different, is the question.

John, I'd be very interested to hear what you're mechanic actually did to achieve your set up.

Waqas, you're right. I don't have a regulator, and my question is borne out of the desire to understand whether I need one, or whether I can just use my existing set up on the different axle. As I said, all of the brake components on the replacement  axle needs to be replaced. Not even the discs are any good. That all adds up.

I'll have a look at Jeff's post; thanks for that. If I end up going down the regulator route I'll try to find one from a sedan of the era as well as look at new non-MB options. That's good advice.

Finally, I didn't think that one could change the crown wheels easily. I'd really like to avoid a complete strip of the diff and all the hassle that goes with setting it up properly thereafter. It's well outside of my comfort zone.

Thanks again for your posts, but if anyone can answer the basic question about the design differences in the axles, I'd be grateful.

James

[jharkin]

james,
my mechanic (Gunter Mercedes of Rock Hill SC) has been a mercedes specialist for 30 years with a reputation among his local peers for expertise. his own 280sl has won awards so i trust his judgement and ability. my new axle is performing as hoped and the drum brakes are working just as well as they did before the conversion.
i asked Gunter what he did and again he reiterated that he cut off the tabs for the disc brakes, and removed what he called the ears for mounting the disc calipers because they obstructed the operation of the emergency brake cables. by the way, he was able to reattach the emergency brake cables from the original 3.75 to the new 3.27, and they work just as before.
lastly, he did not cut a hole thru the backing plate. i was wrong about that. but he did have to make a modification so he could attach the stabilizer that runs thru the bottom of the backing plate. since this is all coming thru me instead of directly from him, he's offered to let me have it up on a hoist to take pictures of the new set-up so let me know if that would be helpful.
john

[Benz Dr.]

Without any pictures I can understand what your guy did for you. What I don't understand is why?

[jharkin]

because of some damage to the parts of the 3.27 axle where the disc brakes would go (which seems to have happened in transit on the pallet) , and because there were no discs or calipers, he advised that it would be a lot less expensive and just as reliable if he did that adaption. he hasn't steered me wrong yet, so i trusted his advice, and am happy with the result.

[waqas]

since this is all coming thru me instead of directly from him, he's offered to let me have it up on a hoist to take pictures of the new set-up so let me know if that would be helpful.

Hey John, it would be great to have detailed pictures from your conversion for the sake of our collective knowledge., thanks very much. Please be sure to take some shots without the drum in place, as well as behind the backing plate.

Although many of us may not take this route, some may be interested out of curiousity. (and it would directly answer James' question in this thread).

[jharkin]

waqas,
i'll try to get whatever pics i can, but the conversion is already completed.
john