Pagoda SL Group
W113 Pagoda SL Group => Drive train, fuel, suspension, steering & brakes => Topic started by: billhon on August 18, 2018, 17:57:03
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My 250sl rear axle is probably a 4.09. Does anybody know if it can be modified to say 3.6 or so. I've heard there are companies that do. But I've heard that sometimes the axles are very noisy. Any ideas would certainly be appreciated, thank you.
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Is the car a 5 speed ?
If no..... then it is likely a 3,92.
It is stamped on the lower left flat of the gear casing.
Check there before guessing.
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It's a 4 speed. Even if it's a 3.92 it really needs to be lower, say 3.60 or 3.27. Can the gear ratio be changed using the existing axle? Who does this and is it recommended?
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Hi,
e.g. have a look in the Technical Manual here: https://www.sl113.org/wiki/Main/Video (https://vimeo.com/18580672).
"Mercedes W113 rear axle 3.27 conversion: Joe Alexander describes procedures for replacement of stock W113 rear axle with 1972 or 1973 W108 higher ratio rear axle. Video by Dick Mentzer".
...WRe
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Thanks much! If anyone has done this I'd really appreciate hearing their results...
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... more info: https://www.sls-hh-shop.de/main/en/mercedes-230-280sl-w113-/35-rear-suspension/35-b-info-axle-ratio.
...WRe
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@billhon
Changing the 4.09 to a 3.27-3.69 rear axle is fairly well traveled modification, and there is a LOT of information on the forums.
I am starting this project on my 4-speed, having assembled the components including a 3.27 rear-end. This modification has proved successful over many years for 4-speed and automatic transmission w113s - thought the automatic can gain from a forced first gear switch in some case (different topic). I note a recent post of the SL market place values wherein it was stated that the 3.27 rear axle adds a decent amount of value to the vehicle. The following is what I have generally gathered about this topic:
1. Determine what you ratio have currently (just to be sure) - its is stamped on the left side of the differential casting forward of the driveshafts.
2. The most common modification seems to be a swap for a 3.27 axle from a sedan, as these still have some availability. This is generally a full rear end swap, end extensively discussed on the forums - I suggest you search "3.27" - let us know if you have no luck in the search.
3. Some members have swapped the ring and pinion in the differential with brand new items, but that takes a lot of experience to get right, and probably challenging to get aligned perfectly, even for a good mechanic not specifically specialized .
4. The rear-end swap is an opportunity to refurbish the axle, new boot, seals, etc. whilst it is out.
5. ** The rear end swap from a sedan comes with some key items to be addressed:
a) Use the same w113 compensator spring (that is straightforward).
b) Use the w113 parking brake cables (that is straightforward).
c) The 3.27 diff has a different vent tube location (on top on main housing rather, than on driveshaft side as in w113), there are implication from this, see below.
d) There is a rigid oil U-pipe across the top/front of the sedan 3.27 differential (most common) that interferes with the w113 bodywork, likely there for additional cooling from the higher torque V8 sedan. The consensus is that it not really needed for the lighter w113.
Options to address this include:
- i) Simply remove the rigid pipe and plug the openings - however this possibly/probably introduces very serious oil splash issues from the vent pipe 5.(c) in a significant proportion of installations (but note some members have had not problems with this approach after many years of use);
- ii) Remove the rigid U-pipe and plug the openings, but then relocate the top oil vent in 5.(c) via modest machining to the w113 location (it has been suggested this is perhaps best suited to a more comprehensive teardown due to the risk of shavings in the diff). This addresses the issue of 5.d(i): @Dr Benz developed this solution, and it is probably the cleanest non-invasive approach overall
[see https://www.sl113.org/forums/index.php?topic=9633.25] ;
- iii) Replace the rigid U-pipe with a flexible hose (suitable rubber or braided steel have been used) that then sits cleanly away from the bodywork. This is a straightforward and effective solution, assuming you can get the hose fabricated somewhere;
- iv) Retain the rigid U-pipe, but cut off its middle section and replace with flexible hose - this was proposed, but not sure if it actually proven in practice - easier than getting hose fabricated in 5.d(iii);
- v) Modify/bend/mold the (heavy gauge) rigid pipe so that is clears the w113 bodywork - this is a trial and error approach it seems, and likely requires a lot of lift the new axle in and out. It is not clear to me (yet) whether this is a viable approach. (A 3D model of a successfully modified rigid pipe would be great of course!);
- vi) modify the bodywork of the w113 to make space for the rigid hose. Mechanically this is the lowest risk, but does involve "permanent" changes to your w113. Many very experienced members have done this, and @stickandrudderman posted that this is his preferred approach.
To be honest, I have not finalized on which approach I will take with respect the rigid tube. It will likely be 5.d(iii) as I am not planning to disassemble enough to be comfortable with 5.d(ii) - but maybe others will advise me differently.
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Wow, thanks much for such detailed information. It seems that swapping rear ends is much less risky than changing parts in an existing 3.92. I have searched for 3.27's but not had any luck. Also how do I know the 3.27 I buy is in good shape? Also is there any demand for a 3.92 out there?
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I just did another swap to a 3.27 diff. for a customer. I deleted the rigid tube and used the Dan C. method of relocating the vent. Seems to have worked out well. No signs of any leakage.
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....Also how do I know the 3.27 I buy is in good shape?....
To start, listen what Joe is telling us here: https://vimeo.com/18580672
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Bill,
My 250SL has a 3.69 diff, which is said to be an optional extra.
I suggest you determine which diff you have before making your final decision. Crawl in under the car from behind the left rear wheel. The axle ratio is stamped underneath the diff housing. There is a flat bit at the bottom, possibly hidden under some grime... If not to dirty, it is quite easy to see.
Regards
Chris
Cape Town
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Hi,
If you don't want to crawl under your car you can determine your rear axle ratio with your speedo and rev counter, see sls-link above.
...WRe
https://www.sls-hh-shop.de/main/en/mercedes-230-280sl-w113-/35-rear-suspension/35-b-info-axle-ratio
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I second what Joe said. Plug the tube holes and move the vent.
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Joe / Shvegel - did you remove the left driveshaft housing in order to drill out the new vent location? I assume that fairly straightforward. If not, can you recommend how to address the risk of shavings dropping in?
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I have always done it with the axle apart and out of the car. Coating the drill bit or tap with grease and most of the shavings will get caught in the grease and stay on the bit or tap.
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Apologies for resurrecting old thread -
I have part disassembled my "new" V8/3.27 axle to replace seals/boot etc. The Dan C. approach to the vent issue is clearly most favored.
I have a couple of, perhaps dumb, questions:
(a) Could I reinstall the left half-shaft housing from my original W113/4.08 on the "new" V8/3.27 - I would thus have the correctly located vent hole already in place, and need just seal the one remaining U-tube opening on the diff housing and the original vent on top of the V8/3.27 diff housing. This would save me any machining of the half-shaft housing.
(b) In that case, should I still use the "new" V8/3.27 left half-shaft, with its more-substantial V8 roller bearing (as for sure the half-shaft splines matched the V8/3.27 diff) - or reuse the original W113/4.08 left half-shaft with a new ball bearing (as it matches the W113/4.27 left half-shaft housing)?
(c) I would assume that for the right half-shaft/housing it would be best to just stick with the V8/3.27 version, with new seals/boot.
--- Or ---
(d) Should I just keep the V8/3.27 "set" intact and just do the simple machining/tapping of one vent opening ;)
--Charles
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There is no way to know if the two left housings are machined exactly the same. You are much better off drilling and tapping the 3.27 housing.