rear end swap 4.08 to 3.27

[Cees Klumper]

John - my exhaust is not yet completely installed. I need to finish that and start my freshly rebuilt engine to find out about any sound difference. Mind you, my old exhaust system was never tight at the manifold-to-downpipes connection which I put up with for almost 4 years, so having a tight new system will almost have to be an improvement for me. I did ask Van Dijk whether the sound would be far off the original, and they said no. Others have complained about a more harsh/louder noise from their stainless system, but that will depend on the make. From the look and feel of it, I got a very good quality one.
I'm very interested in your Pagoda hunting in the Netherlands story - hope you can post the photo when you find it.


Cees Klumper in Amsterdam
'69 white 280 SL automatic

[n/a]

I now have the driveshaft bolts out and the driveshaft disconnected. I think there are only two issues left before lowering the axle by loosening the suspension carrier nut (keeping the axle supported by my hydraulic jack).

1. disconnecting the emergency brake cables. I can simply leave them connected to the drums and disconnect them from the underside of the car. However, the cables that came with the "new" axle have been cut, so I'd just as soon disconnect these and reuse them for the time being, particularly as new ones are about $50 a pop. Any tips on getting the shoe hold-down springs (the big ones) released so I can get the shoes off and get at the hand brake cable connection?
2. the locating strut still needs to be released. I find Haynes, page 138, a bit scanty on info. Do I just unscrew nut #1, fig. 8.15, and let the locating strut bolt pull through the "frame" as I lower the entire rear end?

So close!

John

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[jeffc280sl]

Hi John,

Sounds like your making progress.  The BBB says to unscrew hexhead bolts 7 and 9 and then remove 8 which they call the front link.  Then lossen the rear link 6 and press the cross strut towards the rear.  The BBB has a whole sequence of steps to follow in job 35-1.  Good luck.

Jeff C.
1970 280SL 4-speed

[n/a]

It's out! Two weeks to drop the thing. Any bets on how many it'll take to get the other one in?

I tried loosening cross strut nut #1 (after removing the lock nut), but it just kept rotating the mount. It turned out my cross strut was the earlier one on 35-2/1 in the BBB, not the 35-2/2 I thought it was. I just pulled hex bolt #9 and the axle swung free. I then ran the jack up underneath, loosened the hex bolt on the rear-axle suspension mount and down she came.

I still need to remove and transfer the hand brake lines and the radius arms from the old axle to the new. After that, it's going to take a bit of time to make sure I have fresh mounts and bushings everywhere I need them.

I still have to deal with the cooling tube situation folks have already mentioned, too.

Any recommendations on which brand 90W fluid to put in there? I'm a bit partial to Red Line synthetics.

Thanks to all for your continuing, much-needed support.

John

quote:Originally posted by Lax882@aol.com

Hi John,

Sounds like your making progress.  The BBB says to unscrew hexhead bolts 7 and 9 and then remove 8 which they call the front link.  Then lossen the rear link 6 and press the cross strut towards the rear.  The BBB has a whole sequence of steps to follow in job 35-1.  Good luck.

Jeff C.
1970 280SL 4-speed

Download Attachment: rear_out2.jpg
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John Livingston
Newport News, VA
1968 280SL 4 speed manual

[n/a]

Just a quick update.

I've just finished getting the radius arms off the old axle. I had a problem with one of the 36mm bolts. There wasn't enough clearance to get my socket in, so I used a large adjustable wrench. It started to round off the head until I applied some heat. Both arms are now off. I've also removed the emergency brake shoes and the cables are ready to transfer to the new axle.

Attached is a picture of the two axles side-by-side. I've been told there's a cooling tube on the 108 axle that needs to be cut off and capped somehow. I've drawn an arrow to what I suspect is this tube. Would someone please verify that that is the case? Any suggestions on where I cut it and how I cap it off?

Thanks.

John

Download Attachment: rears_compared.jpg
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John Livingston
Newport News, VA
1968 280SL 4 speed manual

[jeffc280sl]

Hi John,

I had the same trouble as you.  Ended up using a pipe wrench on the outside of the socket because ratchet would not fit.  I suppose the tube in your picture is the cooling device.  I wonder if you can replace it with a flexible hose of some type and preserve the cooling effect?  I'm sure they had a reason for putting it in.  I'll climb under my car and see how much space is available to work with.

Jeff C.
1970 280SL 4-speed

[jeffc280sl]

John,  Can't say for sure that you have the room but if the pipe can be bent a little at the point of your arrow so that it hugs the side of the differential a little closer I think it will work.  Maybe someone else has tried this and knows for sure.

Jeff C.
1970 280SL 4-speed

[Benz Dr.]

Anyone know who to get the pin that goes up into the trunk 90 degrees to the centre line of the axles? There's a fairly easy way to do it. Not 100% acurate but a lot closer than by eye or just putting it back in and hoping it's close.

Dan c

Daniel G Caron

[jeffc280sl]

Dan,

How about making a fixture out of copper pipe using a 90 degree elbow and 2 equal length sections of pipe.  Line up the ends of the pipe with the center lines of the carrier and fixed axle tube and your finished.  How would you do it?

Jeff C.
1970 280SL 4-speed

[Benz Dr.]

I use a level.

Dan c

[hughet]

I did the rear end swap a couple of years ago and it was one of best things I have done to the car. Mine is a 65 with lots of miles so the rear end was pretty loose. The disk brakes are a significant improvement! If you are swapping out drum brakes pay attention to the fact that the sedans had 35 MM pistons on the rear and that 280SLs had 42 MM pistons along with a compensator. The junk yard sent me an axle with a 35 on the right and a 42 on the left. Yikes! Fortunately, I noticed it before I did the installation and they sent me another caliper

There are a couple of ways to deal with the differential bypass pipe. Guys I talked to before doing the job said that they just bent it but that pipe is pretty stiff and I couldn't figure out a way to do it without having it hit the frame. I suspect that they have some pretty funny clunks when they get on a rough road.
 
David Latham at Bud's says that they take the pipe off entirely and replace it with a couple of those large oil drain plugs from a 230SL He says that the plugs have the same threads and are a perfect fit.
I didn't do that because I had not talked to Dave before I did the job and I figured that the pipe served some kind of purpose. I cut the pipe at the top with a pipe cutter and unscrewed the fitting on the bottom. I got out my plumbing torch and made a pipe out of a couple of 3/4 inch 45degree copper elbows and a short piece of 3/4 inch pipe. The outside diameter of the elbow is almost exactly the same size as the inside diameter of the plug so I put some oil proof silicone seal and stuck it in so that the copper pipe goes out of the bottom hole and snakes along the side of the differential up to a point where I was able to attach a U shaped hose to go from the pipe to the nipple on top of the differential. There is no interference with the frame and it hasnt leaked so far. I check it occasionally to be sure that the rubber hasn't gotten spongy. If it does, I'll probably take it out and replace it with a couple of plugs.
If I had it to do over again, I would just put in the plugs.
The bypass pipe is probably something that they put in because the V-8s were expected to put a little more strain on the axle than the sixes.

[n/a]

Mine is a 68 with rear discs, so those'll be the same.

Thanks a bunch for the tip about the 230 drain plugs. I hadn't heard that one, and it sure seems the simplest solution. I'll give that a try and will let you know.

John

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[n/a]

I checked at the 26mm drain plugs fit perfectly in the tube openings. I've ordered two.

I may have to reconsider the recommendation of my axle supplier. Both rotor backing plates are bent, one pretty badly. Makes you wonder how carefully the axle was handled. Odd, as it sure was boxed and supported well during shipment. Anyhow, is there some trick to getting these backing plates or whatever they are off? I've removed several 13mm nuts through the large hole in the axle end, but the shield doesn't seem to be budging. I was hoping to swap my original ones to the new axle.

John

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[hughet]

John,

One other thing about the axle job that I ran into. On the new axle i got, I had too much end float on the right hand side. I was aware of end float because one of the reasons I was changing out the old axle was because I couldn't allign it. On the 3.27 axles, each axle has a grooved bearing on the end that defines end float and when the bearing wears you get a loose feeling in the rear end and your disk brakes won't work as well as they should. It's not too bad to change the bearing with the axle out of the car if you have to do it because the axle and bearing can be pulled out using the axle puller that you can borrow from Auto Zone for free. Once the axle shaft (and bearing) is out, the bearing has to be pulled off the axle with an odd looking puller with very long arms. For that I took the it to an independent Mercedes repair guy who is a good friend from the St Louis Mercedes club. Reinstalling the shaft and bearing is not too tough with the axle in the car on the left side but on the right side there is a snap ring on the spline which holds the axle in the collar on the U joint. to do the job right, you have to lift the axle all the way up until you hear the ring snap and that can only be done in the car with the road springs, shocks and compensator spring out. Needless to say, it is easier to do the whole job with the axle out of the car. So check your end float for bearing wear before you put the calipers on. Hopefully you will be lucky enough not to have to worry about it.
 
Tom Hughes
St. Louis
65 230SL 4 speed manual

[n/a]

Tom,

End float. I'm beginning to wonder if I'll ever get this done! I went out to the garage and gave the axle ends a very unscientific pull, wondering if this would give me some idea of the "end float" situation. My 60,000 mile original axles didn't budge. The 120K (maybe) 108 left-hand axle moved in and out slightly, while the right-hand one seemed as tight as the originals. You think I should try for a more scientific method, or is any movement indication that it's new bearing time?

Despite any whining on my part, I greatly appreciate this input.

John

quote:Originally posted by hughet

John,

One other thing about the axle job that I ran into. On the new axle i got, I had too much end float on the right hand side. I was aware of end float because one of the reasons I was changing out the old axle was because I couldn't allign it. On the 3.27 axles, each axle has a grooved bearing on the end that defines end float and when the bearing wears you get a loose feeling in the rear end and your disk brakes won't work as well as they should. It's not too bad to change the bearing with the axle out of the car if you have to do it because the axle and bearing can be pulled out using the axle puller that you can borrow from Auto Zone for free. Once the axle shaft (and bearing) is out, the bearing has to be pulled off the axle with an odd looking puller with very long arms. For that I took the it to an independent Mercedes repair guy who is a good friend from the St Louis Mercedes club. Reinstalling the shaft and bearing is not too tough with the axle in the car on the left side but on the right side there is a snap ring on the spline which holds the axle in the collar on the U joint. to do the job right, you have to lift the axle all the way up until you hear the ring snap and that can only be done in the car with the road springs, shocks and compensator spring out. Needless to say, it is easier to do the whole job with the axle out of the car. So check your end float for bearing wear before you put the calipers on. Hopefully you will be lucky enough not to have to worry about it.
 
Tom Hughes
St. Louis
65 230SL 4 speed manual

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[n/a]

I finally got my dial plunge gauge or whatever it is out of the bubble wrap and, using considerable pressure on the axle end, the max movement I got was .008 to .009 inches. I convert this to about 0.2mm. My manual says the 280 SE 4.5 axle has a max end play of 0.7mm (p. 35-0/5). So maybe I'm okay?

John the Optimist

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[hughet]

John,
It sounds like you have a good rear axle assembly for your car. You will like the way it cruises at speed and will find that the low gear on your G72 works just fine on a 3.27 axle ratio

A friend of mine sent his speedometer to Palo Alto Speedometer for recalibration after he did his rear end swap and had good results.

As for mufflers, I put a Timevalve system in mine about 14 years ago and it is as good as new. Mine is a little louder to begin with than a 280 SL because it is an early car with the split tube header, but my friend just put in a timevalve and thinks it is quieter. I think Borla also makes a system for 113s too. I had a Borla on my 66 E-Type Jaguar and was very happy with it. (The joke is that stock Jaguar mufflers rot out before the warehouse labels burn off, and as far as I could tell it was true).

Tom Hughes

[Benz Dr.]

Don't you mean .07 mm? .7 is .027'' of an inch.

You don't want ANY end play at all. Sometimes the large nut that holds the bearing tight will start to come loose. I've done a lot of these axels and several of these conversions and there's some misinformation starting to come out.

The auto trans is a poor choice for this conversion. It will work but drivability suffers around town and first gear starts aren't always possible. The trans kind of groans on inclines or hills. NOT GOOD.

There are no rings or grooves in the outer bearings. They sit in the axel tube and are held in place by the outer retaining plates. The axel is held in place by the bearing and the locked nut. Failure to use the proper bearing on the RT side can cause axel damage. The bearing can be removed using any standard shop press with the arms all the way at the bottom. Use new lock plates. You can drill and tap a hole for a grease fitting on the outer edge ( 45 degree angle area) of the axel tube and never need to pull the axels to grease the bearings ever again.

There is no snap ring inside of the slip coupling. The axel just slides into place and can be removed while the whole axel is in the car. The 4.5 axel may be different and it's been a long time since I had one apart , but frankly , I doubt there's any difference between it and a 280SL axel.

I like the cooling tube idea - that's a good fix.

I have a 3.27 axel if anyone decides to do this conversion.

Dan c
SL Barn

Daniel G Caron

[hughet]

I was wrong when I called it a grooved bearing. Earlier models used grooved bearings. For what it's worth, supplement 3 July 1973 Revision of the Big blue book details permissable end float and which bearing to use for replacement. Page 35-0/5 details that earlier cars used "grooved" ball bearings on both sides, later cars used grooved bearings on the left side and a self alligning roller bearing on the left.  Axles for the later V8 models used the self alligning roller bearing 000 981 05 06 on both sides. That is the bearing I used and I think that it is a substitute for all of the grooved bearings that were used in  previous models. The bearing is held in place by a retainer plate on the outer race and by the axle and nut on the inner race, but it is the bearing which determines end play. Or at least it was on my car.
The right axle on my 230SL had no groove and snap ring in the spline but the 3.27 axle did. I opened the manual to page 35-4/3 just to be sure that I didn't have some kind of crazy dream about doing that particular job.  The snap ring is detailed in fig. 35-4/6 in the blue book and the process of seating it is described in job 35-4B. Removal and installation of the right hand axle shaft is on page 35-42 and 35-4/3. I pulled the axle out with an axle puller and took it to my buddy here in town because he had a slot nut spanner and that crazy looking puller (136 589 20 33 00).   The Haynes manual is a little more user friendly and it describes the whole process of removal and replacement of the bearings. Fig. 8.1 shows a cross section of the hub, Fig. 8.2 shows the axleshaft and joint (they call the snap ring a circlip) and Fig. 8.3 shows that crazy looking puller.
The bottom line is that there is a snap ring on later axles and if you have to remove and reinstall the RT axle while it is in the car you have to remove the road springs, compensator spring, shocks and even the rubber axle stop bumpers on both sides in order to get the 22 degrees you need for the snap ring to snap into place behind the sliding sleeve.

Tom Hughes

[n/a]

The BBB 35-0/5 says the 280 SE 4.5 axle uses self-aligning roller bearings on both sides and that max end play is 0.7mm which is, indeed, .027 inches. On the 280SL (with the grooved bearing on the left) , they show max end play of 0.37mm.

I have a manual gearbox and hate 1st gear with the 4.08 probably more than 4th, although it's close. I'd almost rather start the car in 2nd and do, if there's any decline or forward roll at all.

I'm not tossing the original rear. If for some reason I don't like the change, I'll put it back.

Putting that grease fitting in sounds like a plan.

John

quote:Originally posted by Benz Dr.

Don't you mean .07 mm? .7 is .027'' of an inch.

You don't want ANY end play at all. Sometimes the large nut that holds the bearing tight will start to come loose. I've done a lot of these axels and several of these conversions and there's some misinformation starting to come out.

The auto trans is a poor choice for this conversion. It will work but drivability suffers around town and first gear starts aren't always possible. The trans kind of groans on inclines or hills. NOT GOOD.

There are no rings or grooves in the outer bearings. They sit in the axel tube and are held in place by the outer retaining plates. The axel is held in place by the bearing and the locked nut. Failure to use the proper bearing on the RT side can cause axel damage. The bearing can be removed using any standard shop press with the arms all the way at the bottom. Use new lock plates. You can drill and tap a hole for a grease fitting on the outer edge ( 45 degree angle area) of the axel tube and never need to pull the axels to grease the bearings ever again.

There is no snap ring inside of the slip coupling. The axel just slides into place and can be removed while the whole axel is in the car. The 4.5 axel may be different and it's been a long time since I had one apart , but frankly , I doubt there's any difference between it and a 280SL axel.

I like the cooling tube idea - that's a good fix.

I have a 3.27 axel if anyone decides to do this conversion.

Dan c
SL Barn

Daniel G Caron

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[n/a]

I think I'm just going to bend the dust shields roughly back into shape for the time being. I did a crude job and then tried putting the rotors back on. They seem to clear okay.

One new problem arose. It seems the 108 hubs have a locating pin that doesn't have a corresponding hole on my rotors. Is that pin something I should be able to pry out, or do I need to drill a hole in the rotor/drum to match the pin? The pin is midway between two lug bolt holes and is maybe an eighth of an inch in diameter and probably protrudes about the same amount.

John

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[Benz Dr.]

OK. Like I said , I haven't been inside of a 3.27 axel in a long time.

 What you have is two different types of bearings. On the earlier cars the right side has a barrel roller type while the left side has a ball bearing. I always use the barrel roller type on the right side even if they're had to find and pricey. The axel goes over centre as it moves up and down and needs this self alingment feature. The other side isn't as critical except for the 3.5/4.5 cars.

When I push or pull on the rear wheels to check for end play I better not find any. Bearings have almost no end play when new and .025'' is a lot of play. If your front wheel bearings had that much play your car would wander all over the road. They are completly different bearings but either way they'd be making alot of noise.

I've had to replace rear bearings because the were making noise and there was always end play and some radial play on the axel shaft. My car has none as do all the others that leave here. I check them as part of regular maintenance. You can have a little bit of play but you really shouldn't be able to feel it. There should no radial play either - in fact almost none at all ( .001 '' - you can't feel it )
Self aligning bearings have a bit more radial play and the end play is more than a grooved ball bearing but it's a realative thing. The radial play corrisponds dirctly to the end play. There needs to be some amount of clearance for grease to enter or the bearing would run hot and fail.
What you see in the book is simply the bearing manufacturing tolerance  stated as a maximum before replacement would be advised. Even fairly new bearings when run for a short time will be freer than new in the box bearings, and only an expert could tell you if they're any good or not.

 By their very nature , self alingning bearings are freer than ball or grooved bearings as you can turn the innner race completely around on the ones I've seen. Because there's only one U joint inside of the axel and the slip coupling moves with every bump on the road, the axel would knock due to the over centre effect because it needs to be longer at the upper and lower movement extremes.
You won't actualy see this end play because it's taken up in the design of the bearing as part of the self alignment requirements. In other words , it has end play because it needs to in order for the bearing to self align, but not in a way that lets the axel move in or out to any noticeable degree.

Not sure if I've explained this very well. I'm not an engineer and never went beyond high school. Did take drafting and machine shop for 3 years - comes in handy sometimes.

Dan c
SL Barn

Daniel G Caron

[n/a]

Dan,

I appreciate your input on this. The end play on my left-hand axle is about .008", so I'm a long way (it seems to me) from the factory's max spec. i realize no end play would be preferable, and I'll no doubt do that bearing at some point, but I'm hoping it's good enough to get the thing back together for the time being.

John

quote:Originally posted by Benz Dr.

OK. Like I said , I haven't been inside of a 3.27 axel in a long time.

 What you have is two different types of bearings. On the earlier cars the right side has a barrel roller type while the left side has a ball bearing. I always use the barrel roller type on the right side even if they're had to find and pricey. The axel goes over centre as it moves up and down and needs this self alingment feature. The other side isn't as critical except for the 3.5/4.5 cars.

When I push or pull on the rear wheels to check for end play I better not find any. Bearings have almost no end play when new and .025'' is a lot of play. If your front wheel bearings had that much play your car would wander all over the road. They are completly different bearings but either way they'd be making alot of noise.

I've had to replace rear bearings because the were making noise and there was always end play and some radial play on the axel shaft. My car has none as do all the others that leave here. I check them as part of regular maintenance. You can have a little bit of play but you really shouldn't be able to feel it. There should no radial play either - in fact almost none at all ( .001 '' - you can't feel it )
Self aligning bearings have a bit more radial play and the end play is more than a grooved ball bearing but it's a realative thing. The radial play corrisponds dirctly to the end play. There needs to be some amount of clearance for grease to enter or the bearing would run hot and fail.
What you see in the book is simply the bearing manufacturing tolerance  stated as a maximum before replacement would be advised. Even fairly new bearings when run for a short time will be freer than new in the box bearings, and only an expert could tell you if they're any good or not.

 By their very nature , self alingning bearings are freer than ball or grooved bearings as you can turn the innner race completely around on the ones I've seen. Because there's only one U joint inside of the axel and the slip coupling moves with every bump on the road, the axel would knock due to the over centre effect because it needs to be longer at the upper and lower movement extremes.
You won't actualy see this end play because it's taken up in the design of the bearing as part of the self alignment requirements. In other words , it has end play because it needs to in order for the bearing to self align, but not in a way that lets the axel move in or out to any noticeable degree.

Not sure if I've explained this very well. I'm not an engineer and never went beyond high school. Did take drafting and machine shop for 3 years - comes in handy sometimes.

Dan c
SL Barn

Daniel G Caron

John Livingston
Newport News, VA
1968 280SL 4 speed manual

[Benz Dr.]

You should be OK with that much play. This axel has things about it that are different than the regular 6 cylinder cars.

The book actually says this about axel pay:
''There should be no end play in installed condition between the outer race of the grooved ball bearing and the brake carrier plate; if so, place a pertinent compensating steel washer between the grooved ball bearing and the supporting tube.''

I take this to mean that any end play should be only that which is in the bearing and should not be very much.

Dan c

Daniel G Caron

[n/a]

Weekend Update:

I couldn't pull the locating pins on the 108 axle ends out. They went all the way through the hub, so I just hammered on them until they stuck out the back of the hub instead of the front.

I'm currently working on disconnecting the drive shaft (I like the Haynes "propellor shaft") from the transmission. The access plate is off (lord all those bolts seem like overkill), the mount is out, and now I'm contemplating removing the mount bracket to give me better access to the flex coupling bolts. Any tips on that procedure would be appreciated. I guess I'm going to have to break down and jack up the front of the car too, as it's a bit tight working under there with just the rear raised. Once the driveshaft is out, I'll probably have some questions on replacing the u-joints.

I'm waiting on the oil pan plugs to replace that transfer tube on the rear end. Plus I've got a couple of brake tools coming from samstagsales.com so I can get the hand brake cables transferred.

I'm a bit concerned that I'm not finding many rubber parts that look shot. The car was a bit creaky, so I was hoping that replacing mounts and bushings and the like would tighten and quieten things. Thus far, only the lower coil spring pads really looked worn. I'm replacing most everything anyway, but I'm beginning to wonder how much of a difference it will make.

John

John Livingston
Newport News, VA
1968 280SL 4 speed manual