Esoteric rear axle question.

[Shvegel]

Well, After completely rebuilding and refinishing my rear axle to show standards I am contemplating buying a 3.27 ring and pinion set,  taking the whole dang thing apart and putting the new gears in.  What is stopping me is the difficulty in setting the pinion height as I am lacking the proper proprietary tools that Mercedes supplied to the dealers.  Here is what I am thinking.  Assuming that the pinion that is currently installed is installed at the correct height I figure I can drill a small hole in the opposite side of the case,  make an adapter on my lathe to mount the dial indicator in the hole so there is no measurement error, install a dial indicator,  measure the installed height of the current pinion gear and set the new pinion using that measurement as a "Zero Point" compensating for the difference in offsets marked on the pinion face of course.

Will this work or am I missing something?

[stickandrudderman]

You are missing something. diff assembly is not done by linear measurements alone. It has to be assembled with the correct pre-load on the pinion bearing and then correct mesh observed using engineers blue.
One of the tools required is a spreader which if mishandles will break the casing.
Take it to a diff specialist, that's what I do.

[Rick]

Strongly agree--   We like to do things ourselves, but there are some specialty items which are better to involve a person with the correct knowledge and tools.   An improper set up of a differental will cause rear axle / noise and howling and can destroy gears and bearings. Just not worth it.

[tom.hanson]

right now the 3.27:1 ring & pinion set is on backorder everywhere.

[Shvegel]

Well,  as luck would have it I actually do have a fair amount of rear axle setup experience.  I used to be a foreman in a Saab dealership service department back when Saabs destroyed pinion bearings the way college students destroy a case of beer so I am well versed in the ways of machinists blue and marking grease(Still have some of both).  I have or have made in some cases all the tools to disassemble and reassemble the axle so that isn't an issue. 

The pinion depth measurement is the distance between the side bearing journal front face and the face of the pinion gear. On any conventional axle you just drop a tool into the bearing journals and measure. On our cars since the rear housing is split you can only work off one journal which means you need the proper Mercedes tools or it is almost impossible to get that measurement.  Even if I were to take it in to an axle shop They would be fitting it by trial and error which takes a whole bunch of time. You would have to take a rough guess as to where the pinion needed to be, shim the pinion, set the preload,  assemble the rest of the axle center,  set the preload on the side bearings and check the backlash(another massive Mercedes toolset) and check the pattern.  If you didn't get it right it all comes apart again and again until you do.  You could easily have 2 days into setting it up.  I am just trying to save some time.

Since my first post I have realized I will also have to factor in the relative height of the new and old pinions with the rear pinion bearing installed.

Tom,  Thanks for the heads up! I have about a year before my car is done so I will keep checking.  I am not sure who sourced the replacement crush sleeves but they are much thicker and have a much smaller "Camel Hump" than the originals.  I had to put my axle on the floor and stand on an 18" breaker bar to set the pinion preload. 

[Shvegel]

Finally found the factory procedure again.  It forgot to bookmark it and it only took me 2 hours to find it again. If only they had put a rear cover on it all this wouldn't be needed.
http://automotiverepairguides.blogspot.com/2013/07/mercedes-benz-1968-72-split-housing.html

[450sl]

 Compliments Shvegel,  never give up on a job and thanks :my rear axle is next on my list , this will sure make it easier.

[stickandrudderman]

Maybe I should book myself a trip to the USA and come learn how to do it!

[Shvegel]

Stick,
Thanks for the compliment! It is pretty much nuts and bolts if you don't change the gears or carrier.  I really wanted to retain my original case since it was already painted and it was the original case listed on the data card.  However I found a 3.27 rear on eBay that was cheap enough to take a risk on it.  So I am going to rebuild that one instead.  I though as I was finishing my original axle that I should have documented the repair and kept track of the part numbers etc but I guess now I have a chance to do it when I do the next one.

Having done a bunch of Saabs I find bearings are pretty standard and if you just replace all the shims where they were before you will most likely be fine.  Probably the biggest thing is to make absolutely sure the pinion bearing races are absolutely seated in the journals.  If you don't the pinion bearings will get loose and cause lots of whining. Below is the picture of the rig I use to do mine.

[stickandrudderman]

Looks impressive, well done.

[Zum 230SL]

Having done some drafting early in my career, I think I spot an erasing shield in the lower left corner.

[Shvegel]

Zum,
Good spotting.  I had just unloaded a veritable time capsule of years past.  A good friend's father was a very high level machinist for a supplier of the Lunar Module Project during the days of the Apollo Space Missions and I was given his lathe and an entire station wagon full of tooling that had sat since 1979. 

[PIP1947]

Hi Tom
When you say the 3.27:1 ring and pinion gear is "on back order everywhere", does that mean these parts will become available to anyone who wants a set? I would like to purchase the bits and pieces for a 3:27 rear axle ratio, on the assumption that I can find a diff specialist or MB dealer with the expertise to split my diff and install the bits. How would I go about ordering the parts and what is the approximate cost?
Regards
Pip1947
'69 280SL Auto
Sydney
Australia

[rgafitanu@gmail.com]

You may get there faster by finding a 3.27 rear axle from a V8 W108 or W109.

[Shvegel]

Pip,
I would strongly suggest looking for someone to do your diff before buying the ring and pinion.  If you are lucky you will find a dealer with the proper tools but if you don't and have to rely on a diff specialist I would make sure he has done an MB swing axle ring and pinion swap before.  Rebuilding an MB swing axle isn't difficult but doing a proper job on a ring and pinion swap without tools could be a nightmare. 

[TheEngineer]

And some words about the "accordion effect" of these swing axles: As the wheels are bounced up and down by driving, the rubber bellows works just like an accordion, it pumps air. When the rear axle gets hot after a longer drive, there is a mist of hot oil that gets pushed out via the breather tube on those axles that have the breather tube on top. The axles with a breather tube on the left side of the differential housing do not have that problem because the volume of air inside of the left axle tube acts as an absorbing cushion. This is why the 3.27 ratio axle comes with the 18mm breather pipe. It connects the differential housing with the air cushion in the left axle tube.

[BRYANH815]

1i want to thank all the members who have volunteered and placed into the archives their experience, helpful hints , links and pictures. it is a real pleasure to read thru and learn thru others. Thank you Bryan Hepper Barrington Hills IL

[doitwright]

I have read about oil leaks through the top breather on 3.27 axle swaps on this forum. The 3.27 sedan axles have the breather on top of the differential housing. Some people have experienced the axle oil leak problem and others have not. I believe Benz Dr. commented that the axle tube from the original w113 axle with the breather vent on the tube could be swapped to the 3.27 sedan axle alleviating the oil leak through top breather tube explained by theEngineer. Has anyone tried this? Any special precautions to be considered? Of course the 3.27 diff breather hole would need to be plugged if the axle tube swap was done.

[Shvegel]

I would caution you against swapping the left axle tube from one axle to the other.  The left tube is also the seat for the left differential side bearing.  Differences in machining tolerances may affect both the side bearing preload and crown wheel backlash.  Much better to remove the tube and drill and tap for the breather on the boss provided for it then reassemble.

[doitwright]

I would caution you against swapping the left axle tube from one axle to the other.  The left tube is also the seat for the left differential side bearing.  Differences in machining tolerances may affect both the side bearing preload and crown wheel backlash.  Much better to remove the tube and drill and tap for the breather on the boss provided for it then reassemble.

I thought there might be internal tolerances that would be affected with a swap. I do not recall if anyone on this forum have added an additional breather hole on the axle tube when converting to a 3.27. Plugging the 2 holes after removing the tube is commonly done. I assume the tube can be unbolted from the differential housing, tapped for the vent hole and replaced just as removed. Would there be any effect on the differential by doing this? Is there a gasket or sealant that would be used on reassembly?

[Howard Long]

I have a 3.27 axle from a sedan that I plan to install when my car goes back together.  That axle has the metal U-shaped breather tube.  I assumed that the 4.08 axle that I took out of my 280SL did not have the same breather because of clearance problems with the W113 body.  Is it possible to leave the metal U-shaped breather tube on the 3.27 axle and install it in my 280SL or will I have clearance issues? 

I have also seen a photo where the metal U-shaped Breather Tube was replaced with a rubber hose, routed close to the differential body, I assumed to solve any clearance problems and at the same time leaving the breather function effectively unchanged.  Has anyone any experience with a flexible tube to provide the same effect as the U-shaped breather tube and also provide clearance with the W113 body?

Howard
71 280SL 4-speed

[ja17]

Hello Howard,

Yes the metal tube will not fit on the W113 chassis.  One solution is to remove the tube and screw plugs in the openings. However, some owners experience a leak after this fix. Not everyone experiences this issue. I suspect that the type of fluid makes a difference and the leak is through the vent. I would guess that the tube is actually to channel fluid or may be some kind of cooling loop. Dan C. suggest moving the vent back to its original position on the axle housing, instead of on top the diff. as in the 3.27, in order to cure the leak problem.  Some have also installed a flexible rubber tube in place of the metal one. This may or may not function as the original metal tube, depending on exactly what the purpose of the metal tube serves ? But it does seem to solve any leakage problem.

[clunker]

The point from Pete about the 'accordion effect" is very interesting. I have a 3.27 rear-axle en route for a swap, and plan to try the approach of a flexible hose to the replace the rigid cooling tube - not so much for cooling it seems, but to balance out this accordion effect.

Dan C. is probably right the best thing would be to tap in a new vent in the 113 location, but I am wary of attempting even that amount of machining :|

I had thought there had been some concern as to how rubber tube would hold up... I assume then that has not been an issue, and it is a reliable approach. My plan is to cut off the center U of the cooling tube, and push on good quality high temp transmission hose+clamps in its place... is that too simplistic?

[Shvegel]

I tend to disagree about the reason for the tube. Given the oil level in the rear axle the low end of the tube would be under the oil's surface and would render any effect as an air channel at the small pressures involved minimal at best.  Granted there is some "Bellows Effect" but moving the bellows even one half inch would be a huge bump effecting only one wheel.  Given the relatively large internal volume of the axle I don't think the pressures generated would be much of a factor.   I believe the tube is simply a cooling tube added to higher horsepower cars to cool the oil and increase rear axle life.  Circulation is achieved by utilizing the rotating ring gear which when driving forward would be picking up oil from the sump and throwing it in to the top of the tube where it could be cooled by the air going past. 

As for why they leak you must only look to the nearest Carnival midway.  If you have ever see the attraction where you point a water pistol at a clown's head and and if you get water in his mouth the balloon on top of his head blows up?   Well, with the axle tube in place the oil being slung forward is like hitting the clown's mouth with the water stream and there is no mess but imagine taking away the clown's mouth and replacing it with a flat face of say a metal plug then water would go everywhere.  The oil being slung up by the ring gear is simply splashing all over and some is being forced up and out the breather. 

[Benz Dr.]

I believe the vent does just that; it vents pressure out as the axle heats up. If you hit a bump in the road, any movement inside the axle would be so fast that there's almost no time for any air to enter or be pushed out. Since the internal volume of the axle probably doesn't change due to movement I bet next to nothing enters or leaves when the axle is raised up or down. An easy way to test this would be to raise the right side up while attaching a balloon over the vent. If the balloon expands then air is being compressed inside the axle and air is constantly entering and leaving. Somehow I doubt this.