rear axle trouble

[tomeo]

Thanks to all for your help.  For the life of me ( I am not a mechanic)  Ican't understand how a driveshaft could spin for 2 and half hours without bolts.  Maybe in fact there are no connections between rear failure and D/S bolts; Or lack thereof.

Now a mechanic wants to swap a sedan rear axle from same vintage?  Is this acceptable?  Brakes issue?

Again, thank you everyone..
tom

[ja17]

Hello Tom,

The sedan rear ends are virtually the same if you get the right one. Find out what your ratio is and what the ratio of the sedan rear end is.

You will have to keep the emergency brake cables with the SL since they are different from the sedans.

Joe Alexander
Blacklick, Ohio

[tomeo]

Thanks, Joe Alexander, and  to all others, for your invaluable help.  What a benefit to have these knowledgeable responses to questions about these beautiful cars.  There is nothing I like more than tooling around New England all summer long in my little 230 with the top down. Now I can at least ask my mechanics' the right questions, and hopefully have my little buggy ready for the summer.  Thanking all in advan ce for any help on these issues I am having...

tom osborn

[gary ensor]

tomeo,  i have a good complete 4.08 ratio rear end assy  from a 66 230sl that i will sell. i'm located in winchester, ky. Silverstar Motorwerks.

gary ensor

[rwmastel]

A 230SL should have a 3.75:1 ratio and drum brakes.  The 250SL and 280SL had various ratios, including 4.08:1, and they all had disk brakes.

Rodd
Pagoda Technical Manual
please contibute: http://www.sl113.org/wiki/pmwiki.php
1966 230SL
2006 C230 Sport Sedan

[graphic66]

My 66' 230SL has a stock 4.08 rearend with an automatic transmission and drum brakes.

[ja17]

Hello Tom,

OK, the 230SL has drum brakes on the rear. The early Mercedes finback sedans also had the drums on the rear and the same ratio. Some of the brake parts are different but intechangable.

Joe Alexander
Blacklick, Ohio

[rwmastel]

I am corrected!  Confirming what you said, I found in the MB book "Technical Data, Passenger Cars, October 1966", page 337, that the 230SL came standard with a 3.75, but vehicles sent to the USA or that were equipped with the 5-speed manual transmission got the 4.08 ratio.

I thought they were all 3.75, I learned something today!

By the way, this is a fascinating book with lots of trivial facts.

Number of teeth on 3.75 is 12:45
Number of teeth on 4.08 is 12:49
Both differentials take 2.5 liters of oil to fill.

Rodd
Pagoda Technical Manual
please contibute: http://www.sl113.org/wiki/pmwiki.php
1966 230SL
2006 C230 Sport Sedan

[Longtooth]

Rodd, regard's the 230SL rear end ratio's --- I came across the following info in Engelen's book Vom Barock zur Pagode.

There were 2 versions of 4 spd manual tranny's used on the 230SL's, the difference being primarily in 3rd gear, changing from 1:1.53 to 1:1.42 gear ratio, and in 1st gear from 1:4.42 to 1:4.05.  The change occurred starting with Chassis # 13876 on Oct 25, '65 (of 19,831 total 230SL's produced ---- 4752 of which were US export models, and approximately 2650 (or just over half of the US export models (~56%)) were built after the tranny change in Oct '65.  There was also a change in the gear ratio in reverse gear.

This change had the effect of increasing top speed in 1st gear from 45 km/hr to 50, and in 3rd gear from 135 km/hr to 147.  

The 250SL and 280SL manual 4 spd tranny's have the same gear ratio's 1st thru 4th and reverse as the 230SL post chassis #13876.

The 230SL standard rear end ratio for the 1st version manual 4 spd was 3.75, but there was an option to use the 4.08 rear end ratio for the 2nd version tranny in non-US models, and as you stated already the 4.08 was used with the 5 spd manual tranny.

For the 230SL automatic 4 spd the specification table in Engelen's book  p. 214 in hardcover book) is not entirely clear about the rear end ratio's though.  Both the 3.75 and 4.08 are shown with a notation "fur USA" applying to one of these ... which ratio this notation applies to, however, is not clear.

Point is only that there were 2 versions for the 230SL manual 4 spd transmission and that for the 2nd version both the 3.75 & 4.08 rear ends are shown for the non-US models... and both type rear ends are also shown for the 230SL automatic transmission.

Whether the 4.08 ratio rear end option was ever installed in any 230SL's is another question however.  

Also, according to the Service Manual (Big Blue Book, modification Oct. 67), no other passenger car used the 3.75 ratio rear end except the 300SE Sedan (standard and long versions), Coupe, & Convertable, which used this rear end ratio only on the 2nd version engine --- both the 3.75 and 3.92 were optional rear end ratio's for the 300SE with the 2nd version engine. The 1st version engine used either the 3.92, 4.10, or 4.08 rear end ratios in that model.  I'm not sure that the 300SE rear-end would mate into the 230SL though.. and even if it did, then the rear-end could as easily be a 3.92, 4.10, or 4.08 as 3.75.

Not that the above will necessarily help... and probably (certainly?) even adds some confusion, but it's important to realize, I think, that the 3.75 rear end was nearly exclusivly used only in the 230SL with the option of using a 4.08 ratio rear end in either the manual or automatic transmissions.

Longtooth
67 250SL US #113-043-10-002163
'02 SL500 Sport

[Longtooth]

Regards the observation of lack of bolts on the drive shaft coupling after the crash/bang/boom rear end failure:

From an engineering failure analysis point of view, if the bolts were loose or came loose before the rear-end siezed, and fell out one by one during the drive, when all but the last bolt or two had fallen out there would be an additional torque on the coupling due to the asymettry of forces now on the coupling.  That torque would shear the last remaining bolt (or bolts) off .... but if they were sheared off the other end of the bolt... the threaded end inside the tapped hole in the rear end side.... would still be in the hole... since there would be no force to torque it back out.  

Furthermore, if only one or two of the bolts were sheared off due to the asymettry as bolts fell out due to being too loose, the net effect would be to simply loose speeed, since no driving torque is being applied to the rear wheels any longer thru the drive shaft couple to the rear end... the rear end would simply be coasting as the rear wheels coasted.  The drive shaft would be wobbling / thrashing around since there's no longer any real support at the rear end coupling. When the bolts sheared free, the load on the engine would have had to drop to near nothing, so the engine speed should have rev'ed up suddenly when this occurred, as the thrash/bang/boom noises occurred due to the thrashing end of the drive shaft with no support at the rear.  

As to the damage to the rear end itself... I can't figure out how the thrashing rear coupling on the drive shaft could have severely damaged the rear end housing itself.  The only way this could occur, I think, is if the drive shaft were to have slipped to the rear, but this is unlikely unless it were not bolted into the transmission shaft as well.

On the other side of the possibilities, if the rear end siezed first, then the bolts attaching the drive shaft to the rear end coupling would have immediately sheared off, and for a fraction of a moment in time (less than blink of the eyes) the rear end would have resisted the motion of the axels (both rear wheels still be driven by momentum of car with friction from tire to road).  After that brief moment the same forces would have ground up the gears in the rear end and trashed it.... bang/boom... while coming to a stop. During the moment when the rear-end siezed and just before bolts sheared off the load on the engine would have increased dramatically... dropping rpm momentarily 'til the bolts were sheared off.


In either case though the threaded ends of the bolts inside the tapped holes in the rear end side of the coupling would still be in the hole.

The clue as to which occurred first -- bolts coming loose 'til last bolt or two were sheared, or the rear end siezing first --- is in the momentary difference in loads on the transmission and engine... one suddenly and momentarily increasing (bolts sheared first), with car coasting unrestricted to a stop.... the other causing the engine to momentarily drop in rpm as the load due to siezed rear-end increased momentarily before the bolts sheared, with car 'braking' to a stop as the resistance in the rear-end gears siezing or siezure having occurred.  

At first blush I'd guess that the rear-end siezed and that caused the bolts to shear, since I don't understand how the rear-end could be damaged severely (case, internals) just with the rear coupling on the drive shaft side were thrashing about after bolts fell out... nor how the last bolt or two remaining would not also have the (their) threaded end still inside the threaded hole.... i.e. there should be 1 or 2 remnants of the threaded end of the bolts in the tapped holes on the rear-end side of the coupling.  Otherwise, if rear-end siezed first, all the bolt's threaded ends should still be in the tappped holes.

Longtooth
67 250SL US #113-043-10-002163
'02 SL500 Sport

[tomeo]

  thanks Longtooth for your insight.  I haven't yet figured out what exactly happened.  As I think about it now, the bolts may still be in the rear hub, sheared off.  I honestly only saw the rear of the driveshaft when it was being winched up on the rollback.  
Another question then...
would the car still freewheel (Roll) up on the rollback if it had seized?  This question was put to me today by an old friend here in Jersey.  [the car rolled fine]

[Longtooth]

tomeo, I need to modify my analysis slightly, as the bolts at the coupling (drive shaft to differential housing) are thru-bolts... nuts on the other end.... not bolts into threaded holes in the coupling on the rear-end side.  Therefore, when the bolts sheared (regardless of which cause) it is unlikely that any of them would remain in the holes on the differential side of the coupling.

As to the cause, if the differential seized first (i.e. before any bolts came loose) you would have noticed a sudden momentary drop in engine speed (due to higher load on engine) and possibly a 'braking' feel as the rear tires were prevented from turning by the siezed differential.  After that moment, the bolts would have sheared free and the engine speed would have increased (before you had time to react by reducing pressure of your foot on the accelerator).  The car would then be restricted at least slightly from 'rolling' (free wheeling) by the mangled gears and additional friction in the differential.

On the other side (of cause), is the possibility that the bolts came loose during your drive and when the last bolt or 2 were still in place (loose or tight), the added asymettric couple applied a torque to the couple, causing the last bolt or 2 to shear off... freeing the drive shaft from the differential.  In this case, there are some tell-tales you can look for.  Most of the holes in the coupling on the drive-shaft side would not have any gross metal wear or deformation markes  on them --- these would be the bolt locations that vibrated loose and fell off over time of your drive.  The one or 2 remaining bolt holes should have gross damage on their edges due to the shearing action of the coupling on the bolts.... and this last bolt or 2 that were sheared off were also likely already slightly loose.. not tightly cinching the drive shaft end to the differential side of the coupling.

Whether the bolt hole edges are grossly damaged or not, however, you would have felt a momentary surge in engine speed (rpm) as the final bolt or 2 sheared off, and the rear end would not have momentarily "braked".  As the drive shaft was then loose, it would have possibly shifted backwards (toward the differntial) by a small amount, causing it to thrash/bang against the differential side of the coupling... both drive shaft side and differential side of the coupling are turning in same direction at that point, but at different speeds as the engine suddenly had no load on it after the last bolt sheared. I still can't understand though how the drive shaft coupling end could have moved back far enough to actually touch / bang into the differential housing itself though.... SINCE the transmission end of the drive shaft should have been bolted to the tranny... preventing the drive shaft from moving back toward the differential by more than a small fraction of an inch.  

Therefore, IF the drive shaft moved back far enough to slam into the differential housing itself (and break the case so that you found a ton of differential fluid all over the place), you should look carefully at the coupling of the drive shaft to the transmission... perhaps that's where the problem originated in the 1st place.  Are Any of those bolts loose?... or are the threads on the bolts damaged?

Longtooth
67 250SL US #113-043-10-002163
'02 SL500 Sport