Getrag Transmission Conversion

[Jim Rosenthal]

I've decided to go ahead with converting my 1969 280SL over to the Getrag 5-speed transmission. My car is a factory four-speed; however a few years ago I had a 4.5 rear axle set fitted to it to try to make it less noisy at highway speeds. As you all know, this didn't improve the widely spaced ratios of the factory gearbox. Because my car has a 3.27 rear axle ratio, I decided to go with the Getrag 265 which has the 1:1 fifth gear. We now have the transmission, which was recently rebuilt by (I think) Precision Gear in CA, and I have ordered the kit and new flex disc from Mark Turnbull on this forum. While we are in there, I plan to replace the clutch, which is more than likely the one that was put into the car in 1969. If we take it apart and it's much more recent, then we may leave it in.

As far as matching the speedometer up to the Getrag gearbox, the best option seems to be to fit an electronic speedo drive which will convert the Getrag information and use it to drive the original speedo. If anyone has particular experience with any shops on this, please let me know in this thread. I'm all ears, as Ross Perot said.

My plan is to post photos of this as the process goes along. The shop where this is all going to happen is some forty miles from my house, but I am going to leave a camera up there and hope we can get photos of the relevant parts of the process which will be useful to other Pagoda owners who want to do this conversion. My aim is to make the transmission as good as the rest of the car- 113 SLs are wonderful cars, somewhat let down by their gearboxes, like many cars of the era, so if I can make the gearbox as good as the rest of the car, it ought to be a lot more fun to drive. And perhaps a bit quicker with close-ratio gears.

[pagoden]

Hi Jim,
I believe all the Z-F 5-speed Pagodas came with a 4.08 diff gear set.  "Garry" in Australia had that setup and swapped his axle for a lower ratio, then later concluded that he'd overdone it.  I'm not remembering just what ratio he put in, but surely no lower that your present 3.27.  I admire your ambition and think you'll love that Getrag, but fully expect you to be considering a re-swap of the axle in the fairly near future.  Garry's posts on the topic would tell you more.   Best luck with it, Denny (in Silver Spring) 

[stickandrudderman]

Pagoden, I think you've failed to pick up on the fact that Jim is fitting a "sport" box rather than the o/drive one so the 3.27:1 will be interesting.......

Because my car has a 3.27 rear axle ratio, I decided to go with the Getrag 265 which has the 1:1 fifth gear

I look forward to hearing the results.

[pagoden]

Uh, wellll, thanks, Stick.  I blush to admit ignorance of such a thing and did indeed soar right on over Jim's mention of it.  Silly old me.  It does then sound like just the thing.  In fact, I will follow with great interest.        [Can I plead having stayed up too late poring over this forum? ... again ... think that'd work for me?]         Sorry, Jim; all best luck with it, and TIA for your progress reports.

[Jim Rosenthal]

Denny, you may well be right. If I did convert it back, though, I would not go all the way to a 4.08 or whatever it was; it was entirely too busy at 70 mph. I would go to a 3.46 or similar.

The first gear in the ZF four-speed, which I think is nearly 4:1, is far too low; essentially the ZF box is a three speed with a granny gear for first. The first gear in the Getrag box is a 3.70, which is better. And then the ratios are spaced fairly closely up til fifth, which in this box is 1:1.

I'm very keen to see how this all works out. I have very little experience with BMWs (I've always been a Mercedes enthusiast, and any BMWs I wanted, such as the M1 and the 850CSi, were beyond my reach unless I was willing to let go of other cars) but I do know that this particular transmission is very well thought of for it's precise shifting and durability- they are said to be popular for BMW track cars. I don't intend to drive the 280SL that briskly, so in this application it ought to last me just fine.

And if it really turns out to be that tough, I've got a 6.3 that would be quite interesting with a five-speed manual gearbox.......

[Garry]

Jim,

As said earlier, I did the rear axle conversion to a 3.46 and followed a year later to the getrag as well.  Mine was the overdrive box and the revs ran at around 2200 for 60 mph.  it was too low for any reasonable acceleration in 5th on any sort of hill so I always thought it was a bit too much.

On the speedo, there is a mechanical worm drive made bu BMW that fits to the gearbox that will replace the electronic sender unit.  Quite an easy swap over and saves a lot of hassle. The only problem that that then gives is the accuracy of the speedo that needs to be re-calibrated by a speedo expert to correct.


I kept my 4.08 rear end and have handed it to the new owner who is also taking up my order on the new 5 speed ZF's being bult now.

Garry

[Jim Rosenthal]

Garry, can you tell me how to find the part number for that BMW item? That would be the way to go. Then I would just need to have the speedo recalibrated for the 3.27 rear axle ring and pinion, and get a speedo cable made up for the BMW drive on one end and the Mercedes speedometer on the other...

[Garry]

Jim,
I am away camping in my Kombi until the end of the week.  When I get back home I will see if I can find the details and let you know.

Garry

[Jim Rosenthal]

My Getrag 365 gearbox arrived- that's the good news. The bad news: UPS evidently dropped it, the side mount is broken off, also one of the shifter mounting bosses is cracked. Also it needs a throwout bearing sleeve. UPS has picked it up and I have been in touch with the seller. One way or another they will either replace the damaged parts on this unit and set it up again, or ship me another one. That will slow things up, unfortunately. Just as driving Gael's MB hotrod SL has really whetted my appetite for getting mine to shift like his. It won't be nearly as fast, of course (with half the torque) but the Getrag gearbox in his car was amazing. As good, I think, as the Tremec TKO600 I have in another car. So I am very keen to get this project moving and hope UPS doesn't gum up the works for too long. Meanwhile, the adapter kit is coming from Mark in the UK and we can take a look at all that when it arrives. Watch this space for further details.

I'd post photos of the busted Getrag, but that would just depress everyone..... so you are all spared that.

[Jim Rosenthal]

Not much to report- the kit from Mark arrived and looks fine, although they managed to mess up the packing enroute. But I think all the bits are there.

I could not reach a comfortable accommodation with the seller of the 265 dogleg box and have requested my funds back through eBay. I am waiting on those, and will try again to find a 265 dog leg box and proceed with the conversion. In addition to the shipping damage, there were other problems with the unit that should have been addressed in a rebuild- worn input sleeve, cracked shifter boss mounting. So back to the drawing board on that one. When I have a new unit and am ready to proceed with this, I'll pick up this thread again. I do hope this is not some kind of warning sign from above, but if so, I am too stubborn to heed it.