Differential Ratio Swap on the W114

Hello to All,

Well after several weeks of no progress other than driving the W114 I finally did some more work.
I changed the rear differential from the 3:92 ratio to 3:07. I used a rear differential from a W123 300D turbo. The swap was quite simple and I did not remove the whole rear differential as the manual suggests. I parked the rear of the vehicle on ramps dropped the exhaust and the brace for the parking brake. I then disconnected the drive shaft from the differential leaving it in the vehicle. I then supported the differential with a jack, removed the rear mount and slowly dropped the subframe down. I then removed the rear differential cover and removed the two axle clips hold the rear CV axle in the case. With the subframe hanging down I have lots of room to gain accesses to the mounting bolts holding the rear differential to the sub frame. After the bolts where removed I then jacked the subframe back in to position and supported the subframe with jack stands and lowered the differential down from the subframe. The CV plunge joints allow enough movement side to side to remove one axle from the differential and then the other side and voila! The differential is out!

The only important thing I found is that there are axle spacers that look like washers on the splines of the inner CV joint. These spacers prevented the axles from fully seating in the W123 body differential; thus you can not install the retailing clips to hold the axles back in the rear differential. I removed theses and it solved the problem. Apparently, the W123 spline depth was 4mm deeper than the W114,W115. I don’t know if they used the spacers on all models.

The difference has gained 4 mpg and my current mileage is now 21hwy. My Speedometer is now off by 21.7 % and I need to change the speedometer gear to a lower tooth count….I just have to find out what I can interchange for the gear!

[Mark DiSilvestro]

Bryan,
What year 300 turbo diesel did you get the differential from? Do you know if all the 300 turbo diesels use the same ratio? (A friend has a 1985 300D turbo and a 1980 300D non-turbo and I believe they are different)
Thanks, Mark DiSilvestro

[ctaylor738]

Great post!

Did you take much of a hit in acceleration as a result of the new "cruising" ratio?

Chuck

[cth350]

I presume that you computed the new milage using something other than your odometer? It too is off by a percentage.

You can ask folks like Palo Alto Speedometer if they can reconfigure it for you, or just sell you the gear if you really want to DIY.

-CTH

Mark, The Ratio for 1985 was 2:88 and was available for only 85, the other years were all 3:07's All W123 of any year should work.

Chuck, The acceleration difference was not really that noticeable and I would recommend the swap if you plan on highway use over 65 mph! Made a difference in the engine noise level

CTH, The contact info for Palo would be great if you could email it to me!...and yes I used the factor backwards to calculate odometer mileage

Regards,
Bryan

[cth350]

Try http://www.paspeedo.com/

-CTH