Rear axle gear change from 4,08 to 3,27

[Peter]

I’m driving now half a year with the 3.27. I find it a good improvement. The car is still pretty fast and revolutions are 20% down! I also installed the “Gernold's magic button” (kick down button but then manually operated), but I never use it.

Van Dijk in Lisserbroek-NL, Pagode experts, do several swaps a year. Important is that the engine is good and still delivering the specified power.

I have an 280SL, how the performance will be on a 230SL or 250Sl I don’t know.

[teahead]

I have Gernold's magic button installed, and it works great.  It drops the transmission one gear when pushed, after which the trans will upshift depending on the throttle position.  It doesn't need to be held down.  It's nice because you can get a boost without flooring the throttle.

Man, can we get a formal writeup in the tech manual how to install one of these?

Be perfect with 3.27 (or even stock) rear ends for flexibility for our auto cars

[Benz Dr.]

It's not that hard to do if you know how and have the proper equipment. I've made my own install tools which really speeds things up.

[Garry]

Teahead,

As a Full Member you have full access to the Tech Manual and can add or amend a procedure for this or anything else and insert it in the Transmission and Clutch area.

The Group relies on all the Full members to fill out and add to the Tech Manual as we go along.  That is how we got to where we are now so feel free to do this. There is a ‘sand pit’ area for you to test how to do it before going live on the Manual.

 Others will appreciate your input.

Garry
Membership Administrator

[teahead]

Will do.

However, this particular request is because I know nothing how to configure this 1st gear switch magic

[Shvegel]

Wire a momentary button across the kickdown switch under the gas pedal.

[Shvegel]

There is a better way using the output from the throttle switch, a time delay relay  and maybe an RPM switch. Need to think on it a bit.

[teahead]

There is a better way using the output from the throttle switch, a time delay relay  and maybe an RPM switch. Need to think on it a bit.

https://www.holley.com/products/ignition/rpm_and_timing_controls/rpm_controls/parts/8950

[Shvegel]

Interesting idea.  What I realized is that any switching done based on throttle opening or RPM works in both directions.  Not only will it start in first gear but when decelerating it will force the transmission into first as well.  This is not ideal.  Having put a few miles on my car now with the 3.27 only once have I felt it was in too high a gear.  I simply pushed the shifter forward and manually selected a lower gear. 

[jeblack123]

I made the swap to a 3.27 from a 3.92 several years ago in my 280sl. Best modification that I have made to the car. Not sluggish, but I don't typically push the car hard from stoplight to stoplight. On the highway, the 20% decrease in RPMs (and noise) has been great!

James (Eddie) Black

[Ajcohndc]

Happy to receive emails on the subject but was contemplating making the switch any guidance on how much it might cost to replace the Rear Axle done by a reputable installer?

Alan

[Leester]

If you just swap out the old and swap in the new I would guess about 10 to 15 hours. However you now have additional work to do, brake lines, caliper change over, e-brake cables, drain and refill the diff. There will be two big bushings that should be replaced. Then you have to align the whole rear axle assembly. Maybe we're up to 20 hours now. I'm sure I left something out and others will chime in. But each of these additional items has additional sub-items like bleeding the brake calipers and new brake fluid.  The swap itself is not that complicated but it is heavy lifting of a heavy part and getting it all in place is hard physical work (at least that was my experience).  The additional activity isn't that complicated but its amazing how time flies. I would guess another 10 hours maybe. Not sure what shop rate around here is these days.

If you decide to have the parts powder coated or painted that's additional time. And if you open it up to inspect the innards that's even more time.  I disassembled mine and had the external parts powder coated. For reassembly and install, I had help from someone who I don't think wants to do another one.  In our area I would guess that the most reasonable cost source for expert work on 60s and 70s (and maybe 80s cars) is Chuck Taylor (ctaylor738) but I'm not sure if he would want to undertake this project.

[Cees Klumper]

When I had my differential swapped in The Netherlands, as I recall (about 20 years ago) it took the guy less than 8 hours all-in (which was longer than he had expected himself).