Axle swap 4.08 to 3,46 - drums to discs

[jameshoward]

Evening,

After years, I have finally managed to cobble together (largely thanks to another forum member in the UK) the parts I think I need to change my original 4,08 for a 3,46 from a donor car. My car is a late 230. I want to reduce the stress on the engine and be able to cruise a little more comfortably on those jaunts between Holland, or Belgium and wherever the next biennial event will be.

I have drums on my current axle, and I really like them. They're set up perfectly and the braking force created measures really well when the car was TUV'd recently (I live in Germany at the moment). I have no desire to change to discs, but do want to get the better ratio.

Having finally plucked up courage to start work, I prepped the car on Tue and dropped the axle yesterday.

(Cue: gratuitous photos of car with a rear axle, and then without).

There's more work than normal involved with this switch because of the conversion to discs, if that's what I decide to do. However, I was wondering whether I stick with the drums, thus avoiding lots of work, and keeping the car slightly less unoriginal. The only differences appear to be on the 3,46 disc axle, the addition of a welded bracket for the calipers, and the omission of the hole drilled through near where the shock mounts which anchors part of the brake shoe assembly on the 4,08 axle (shown in the photos).

I wondered what the learned counsel might offer by what of thoughts and advice. So please let me hear what you think.

Separately, whilst I have the Haynes Manual my BBB doesn't have the detail on rebuilding the diff carrier/upright. The Haynes manual glosses over the detail of fitting that wretched bush. I think I know from the book which order the various washers, bushes and O rings go, but if there's a BBB section that details it all, I'd be grateful.

Intermediate steps are next to drill a new hole in the flat spot on the 3,46 axle and re-locate the axle breather from the 4,08. That's tomorrow's fun and games.

Finally, a huge thank you to Waqas for the design of his spring compressor. That damn spring has been my nemesis for years and I've never managed to budge it. Having used Waqas' contraption successfully and seen the length of the thing when uncompressed, I now understand why I couldn't move it.




 

[Neil Thompson]

James you've got big balls! Keep us updated

Neil

[jameshoward]

I looked today about making up the by now well-documented alignment tool using copper pipes. I may go down this route to properly centralise the axle, or may use a plumb line. However, I was surprised to find that self-soldering copper joints don't seem to have made their way to Germany. We use them a lot in the UK. Can't find them here at all. The prospect of making the tool by soldering my own pipes is less attractive than using the plumb method. I wonder how others have fared without the copper pipe rig?

[Benz Dr.]

I use a capernters square to set up the rear axle. Place the axle on the floor and get the tubes level on each side. Adjust the center pin so that it's at a 90 degree angle to the axles. I would do all of this before I place the axle in the car.
 Adjustment of the scross strut will square the axle to the car but I really believe that the axle needs to be squared up first before you move to the next step. This is not something you can do after the axle is installed. The axle will move around alot while driving and I generally adjust the cross shaft to its original position which is fully screwed down. Not seeing any unusual tire wear, I have to believe that this must be pretty close to where it should be.

[ja17]

I've used your method Dan,  seems to work fine.

[jameshoward]

Thanks, Dan,

I've read and printed every post I can find on this site that addresses the rear axle and have seen your comment many times. I fully intend to follow your advice, but can I just confirm what you mean by the cross strut? Do you mean the rod that goes through the subframe with the 2 bushes, one in the frame and one on the outside? My last effort fiddling with the rear axle resulted in my car having a grossly misaligned axle. I discovered today that the bushes (axle end) one of the trailing arms had bulged out and this the arm was massively off centre. I must have screwed this up a few years ago but didn't notice. My compensating spring has been rubbing against the fuel tank for a while, and this may have been the cause, or at least cause in part.

Interestingly, and separately, I spent a good part of yesterday with a German chap who works extensively on rally cars. Quite grown up stuff, not hobby. It's his families' living. (I left him my diff to drill for the breather from  the original axle as I don't have a tap set, etc). Anyway, he has a friend who rallys a MB Cosworth 190 (mental car; I think he said about 350 bhp) but this guy also owns a 190SL parts site on the internet apparently. The SL guy saw my diff and asked about it and why I wanted to change it. It was explained to him that I wanted to lower the RPM and improve the cruising, protect the engine a little, etc. His view, interestingly, was that the axle change was a bad idea. He felt that the change from the 4,08 to the 3,46 was more likely to damage the engine and clutch given the stresses on the engine, etc.

Too late now, but I wondered if that had been discussed at some point.

James

[Larry & Norma]

It has been mentioned many times James that these engines thrive on high revs and
are designed to do these revs all day. I guess if you load an engine up with high gearing
you are going put some strain on it i.e. like using too high a gear in the gearbox.
You have more control as you have a manual car and can hold the gears as long as you want.

[66andBlue]

...
You have more control as you have a manual car and can hold the gears as long as you want.

That is also possible with an automatic - it does have a shift lever!    

[georgem]

Larry HALL,

I`m with you. Why oh why do we keep tinkering with something that was designed by experts to run at certain revs - I think its a no brainer that by reducing the revs the engine and drive train is being loaded up - just like holding on to a gear too long up a hill before a change. I just wish that the concept would get through that this is a 50 year old car that was designed in a different era and should be appreciated and celebrated because of this difference.


oh dear, another wind mill to tilt at..............

[jameshoward]

George (and Larry, I think, if I understand what you're saying),

I'm not not with you. But, George, the cars were designed and built 50 years ago when parts were cheap and plentiful. As none of us need reminding, that is no longer the case. A mere 20 years ago as a young soldier, I felt that my body was designed to do all sorts of death-defying things. With gay (not that kind) abandon I readily threw myself out of airplanes, ran every day with weight, did all sorts of Rambo courses, etc. When I got bashed up - which was regularly - I fixed pretty quickly and recovered completely. These days, it's a little different. My kness and back are shot after all sorts of breaks and bangs. I can't fix these problems, so I am far more careful about what I do. For that (long winded) reason, I think it makes sense to view these cars through a different lens today, unless one is fortunate enough to have very deep pockets indeed. Pagodas can, of course, be fixed at a price (unlike us) but my efforts, if perhaps misguided in the eyes of some, are aimed at reducing engine wear hence my quest for LOWER revs noting that the car was designed to run at high revs. Higher revs still equals more wear and more strain, no matter how you cut it. So surely lower - better?

How are those windmills looking?

James

[stickandrudderman]

Never mind the windmills, where's Truly?

[66andBlue]

... 50 year old car that was designed in a different era and should be appreciated and celebrated because of this difference.
oh dear, another wind mill to tilt at..............

Hello George aka "Don Quixote"  
I do celebrate my old cars and appreciate them very much but I do not need to hear their loud responses to my cheerful celebrations all the time.
So, a 3.27 axle in the 280SL suits me just fine.

Over the years many members here have done the switch and I bet if all these doomsday predictions were more than just predictions we would have heard about it here.
So, who out there has had engine problems caused by the different axle?

[Larry & Norma]

Rightly or wrongly this is how I picture it: All things being as designed an engine will never wear as there is never
metal to metal contact only oil to metal. In the real world, as we know there is wear. This occurs when the engine is under load
such that the oil is forced out of the interface. The more load the worse the effect. So an engine spinning fast but under light
load is less likely to wear as an engine spinning slowly but under heavy load. Hope this makes sense.

[georgem]

It does to me Larry

[jameshoward]

You guys...

Actually, I'm not sure you are right, Larry. As in, I don't know. Wouldn't the wear on the engine be the same? Pistons going up and down, etc. they do what they do. Wouldn't the strain be flt more on the clutch or box?

Genuinely interested, but no clue what's really correct, which is probably why I'm so happy to proceed in blissful ignorance. That said, I can't go back now.

Your sacrificial but faithful guinea pig,

James.

[Larry & Norma]

I think my reasoning is sound, it's all about the oil.
The real question is re the back axle mods is the engine under appreciable extra load that
will make a perceptible difference to engine wear. I think we have enough horses under
the bonnet not worry about it too much. Just don't labour the engine in any gear

[pagoden]

Interesting topic and debate.  I'm enjoying the well-presented arguments in this thread.  I believe our 113s were supplied with a handful of final drive ratios, ranging from 3.69:1 to 4.08:1.  I swapped mine from the 4.08 to 3.46 because first gear seemed unusable after the first few meters of travel.  My original ratio was essentially the same as the go-to final drive (4.11) for quarter-mile drag racers Back in The Day (you remember, when winters were colder and we all had to walk uphill both ways to school and back - - and if you missed all that, maybe you've seen footage of the drag races; that was my original rear axle ratio); it was pretty much good only for maximum acceleration over a relatively short distance, and most certainly not for gas mileage.  I've read that the original M-B intent might have been for Alpine driving; I can see where it would be useful in San Francisco or Santorini but seemed too rip-roarin' radical to me.  On the other hand, I did spend most of my driving life with smaller, higher-revving engines than the typical US biggies, especially the laarge V-8s they went to in the sixties and after, so cruising in the company of a busy lot of machinery is just good company for me.   It's my pet theory that those of us who prefer the lowest-revving ratios for their Pagodas tend to be folks who, down through their driving years, became used to the more peaceful and quiet experience of lower-revving big-block engines; different strokes for folks from different life experiences (pun not intentional but enjoyed).  My swap moved the revs down 15% for any given vehicle speed in any gear.  I seldom use fourth until we get up on the big slab.  And then it's the same top gearing you get with the factory Z-F 5-speed setup ... within the parameters that M-B engineers originally decided suited their components.      

[I believe I have Mr. Brough to thank for bringing that fine ratio to my attention: a pint, sir, should we live long and venture far enough.]
  
But is 3.27 a bridge too far?  Only good reports so far.  And it's been how many years since the first 3.27 swap?  Before my time, possibly (Pagoda purchase & join date ~ 5.5 years back).  No engine troubles to report?  

I appreciate the debate, especially as it's been conducted in this thread.  The range of change seems not unreasonable, being 20% at the maximum (3.27) and with the 113's original (or was it just the common european?) final drive ratio of 3.69:1 falling smack in the middle between 3.27 and 4.08.  Perhaps if we heard from seriously well-informed experts as to the behaviors of lubricative barriers at various speeds and pressures.  Meantime, the honorable and erstwhile gnuface employs the terms "appreciable" and "perceptible" in his recent post, which is where I think the crux of this matter is at, as 'twere, for the rest of us.  "Just don't labour the engine in any gear": amen.      

[jameshoward]

Just back from an interesting day at Essen having met up with Naj, Achim, Oz, Tom and Kay. Great fun. Many, many 113s.

I learnt that as I make change the axle I also need to change the brake master cylinder. Should have known this, I guess, but didn't. Every day's a school day, as they say...

In order to avoid changing the reservoir I need the early 250 cylinder. One fellow mentioned that he'd recently got a brand new one for around $120 or so. Having looked at SLS and Niemoller the prices seem pretty mega at over €200. A quick 'man look' on the Internet shows some cylinders in the US for around $50 odd. Whilst clearly not original, it does seem to offer a more economical alternative. I think one brand was called Cargone or something.  So, I wondered I others had experience of these after market cylinders, or are they a false economy? He's one link http://www.jcwhitney.com/master-cylinders/mercedes-benz-250sl/c15929d21638j1s21.jcwx

I will call MB on Monday to see what they charge. For the sake of reference should anyone else find themselves in this position, the MB for the 250 cylinder is: 001 430 8901. I think the following parts are also required: 0004 72 028 000 & 004 997 3245 (sels), and 000 586 0143 (repair kit).

Grateful for any pointers on the master cylinder options.

JH

[66andBlue]

James,
you might be better off sticking with an ATE cylinder. What model brake booster do you have?
I believe the corresponding ATE p/n is 53733004237 - but I am not sure.
Least expensive one here is this one:
http://www.autohausaz.com/search/product.aspx?partnumber=0014308901

Here is aftermarket one (but better check to make sure it fits):
http://www.ebay.de/itm/150528632031

Good luck!

[Benz Dr.]

Maybe I'm not too bright but I never bothered changing my master cylinder when I changed to the LSD axle last year. I did mount a brake force regulator though. I saw no difference in braking performance aside from the expected response from having rear discs.


 R&T used to have section about new cars and somewhere in all of that was their wear index they came up with. It stands to reason that lowered RPM's will also lower engine wear. 3.46 is very close to the same speed as a 3.92 with a 5 speed so once in high gear you aren't hurting anything. However, that ratio is obtained through the trans while any axle gearing change affects all gears equally. 3.27 with an auto isn't a great choice in hilly country.

 The cross strut I'm talking about goes through the frame as you state. Adjust it so that the threads are all taken up and it should be OK.

[jameshoward]

Thanks, Alfred. I bit the bullet today and ordered the MB part (for an early 250). Will find out tomorrow what I have to pay for it .

Separately, today I've ordered another ton of bits. In the event that this is ever useful for anyone else, I'll post the PNs here as I go and to remind me when I lose the five thousand post-it notes that are scattered around my office with part numbers written on them.

First up, and most interesting was ordering the bearing for the right hand side (the conventional ball bearing). MB have a variety of numbers: 008 981 4225 seems to be the newest (others incl 001 981 1525 (now not recognised) and 002 981 2301). Naj gave me the FAG bearing number also, which is 6202/C3. MB want something like 20 euros for the part. A local shop wanted 46 euros. I found the bearing in the UK using the FAG manufacturers number for £2.70!!! In the end I found it here in Germany for 8 euros by NOT using the MB number. My advice is to use the FAG number. (Amazon.com has them for $10).

The master cylinder number is 001 430 8901. This is for an early 250 cylinder that, I am told, will enable me to use my existing reservoir. Also required are two seals: 000 472 028 000 and 004 997 3245, as well as the "repair kit" 000 586 0143 (no idea what's in there yet, but I'm told I need it...).

ATE discs, pads and handbrake shoes. This was made unduly painful by the muppet at MB giving me the front pads PN rather than the rear. I only just picked up on this having ordered the wrong pads. I found this to be a really helpful tool - the ATE online catalog: http://www.ate-na.com/generator/www/us/en/ate/ate/themes/60_online_catalogs/10_european_online_catalog_tecdoc_us.html

ATE rear discs PN is 24.0110-0185.1
ATE rear pads: 13.0460-4036.2
ATE handbrake shoes: 03.0137-0171.2

All of that info is available on the v good ATE website, but it took a bit of cross referencing to get there having picked up the first error courtesy of my local dealer.

Finally, and out of interest, I checked the lateral support that can at times get bent (Waqas' was, having read his post). It has 2 large rubber bushes on it, both identical (A 111 351 04 44). The exterior mount looked actually fine, but I had to remove the interior one to check the state of the rod. Glad I did. It was buggered. Given the difference between the two, I suspect that at some point some idle soul changed the exterior one but didn't do the interior one. (I've posted a photo below: they're the same part; the new one compared to the exterior mount, and then the interior one (the shortest)). I have also changed the rubber boot/grommet thing that the rod goes through, as this was also shot and could let water into the subframe. Whilst in there I've sprayed the interior of that part of the subframe with waxoyl for good measure. I'll put silicone around the boot, also.

[Naj ✝︎]

First up, and most interesting was ordering the bearing for the left hand side (the conventional ball bearing). MB have a variety of numbers: 008 981 4225 seems to be the newest (others incl 001 981 1525 (now not recognised) and 002 981 2301). Naj gave me the FAG bearing number also, which is 6202/C3. MB want something like 20 euros for the part. A local shop wanted 46 euros. I found the bearing in the UK using the FAG manufacturers number for £2.70!!! In the end I found it here in Germany for 8 euros by NOT using the MB number. My advice is to use the FAG number. (Amazon.com has them for $10).

Sorry. the correct FAG # for the left bearing is:

6208N/C3

6202 is a much smaller bearing, probably for alternator front etc.

Naj

[jameshoward]

Yesterday doing this was terrrible. And expensive. I picked up the ATE brake parts, the new master cylinder, and a host of other bits and bobs that I didn't know I needed until now.

Today was better. A few pointers for anyone who tries to do this based on my experience.

First, changing the master cylinder was necessary, but a breeze. Most of the brake fluid has leaked out into my drip trays, so I just had to empty the reservoir, unscrew, pull it off and then remove the old MC. The rubber O rings and the rubber grommet were shot. Looking at the two MCs it's impossible to see a difference, but because I'm switching to discs from drums, I need to change to the early 250 MC. The switch over was very easy. You may need to cut a sliver off the grommet that goes in the rear-most fitting in order to get it in.

Next, I spent must of the day sanding down the areas that I forgot to cover up when the powder coating was done. Top tip: cover up all the surfaces that you don't want coated. For me, this meant the sides of the yoke and where the axle arms meet where the pivot pin goes. A dremel made it easier, but that stuff was on thick. I also cleaned up the bronze bushes in the yoke, and checked that the grease nipples still fed grease through (having been powder coated... ) They were fine after a quick bit of HP air-powered grease cleaned them out.

I also managed finally to disassemble the support strut thing (with the aluminium part on the end). Took some serious pressure on it, but it's done now, thankfully.

I also had to replace the bushes on one of the trailing arms, as they'd shifted off centre since I did the job a few years ago. This was probably caused by my failure to align the axle properly at the time; the cause of many woes. I used my trusty vice method, shown here. With two pairs of hands and bit of ATF as lubricant it takes about 2 mins a side to do.

Somewhat greedily, I've put a separate post up about the order of parts for assembling the pivot pin as I cannot find this info anywhere on the site, and I've spent hours looking. If anyone should know the correct order, I think it would be useful to capture it. I've photographed what I think it looks like, but it would be great to confirm it.

Still need to figure out exactly (or roughly) where to put the new brake compensating valve that I need to drill into the car. Probably tomorrow's work, together with putting the axle back together).

JH

[jameshoward]

Thanks, Naj,

That's really helpful. I've got to go to the bearing place tomorrow anyway, so I'll get a price for it in case anyone wants to go down the (hopefully cheaper) non-MB route.

James

[jameshoward]

So just called the bearing people. It seems that there are 2 different bearings. There's 6208N/c3, which is about £29, and 6208/C3, which is £9. (Who'd have thought...)

The difference between the two bearings is that the 'N' denotes that the bearing is manufactured for a circlip on the outer race. I'll take a look at the bearings that I took out of the old axle, but I don't recall there being a groove on the outer race. The 6208/C3 bearing does not have the groove and hence is cheaper to manufacture.

I now also now that the 'C3' means that the bearing is designed for high loads and relates to the additional clearances within the bearing to allow for expansion of the bearings themselves!

(I spoke to Jan at simplybearings.co.uk, who was very knowledgeable and helpful).

EDIT - the 6208/C3 is fine and a snip at £9. At that price we could change them monthly. What fun, etc... .

James