1975 450SL Distributor Problem...

[Jay Gibbs]

I thought I had gotten my 1975 D-Jet SL running pretty well over the last couple years...among other things- new trigger points, D-Jet harness, cap, rotor, plugs, cleaned injectors, etc, etc, etc. Fuel mileage went from 8 city and 10 highway to 12 and 14. Lumpy idle 98% better.

Just the last month or two I noticed every now and again it would have a sudden momentary "ignition feeling" stumble. It increased somewhat over time and occasionally I'd feel like I was losing several cylinders for a minute or two then it would be ok for a while. Just last week on a whim I tried to slightly push the distributor with a side load while the engine was running and was able to get the car to smooth out or idle badly at will with this applied side load. Removed the cap to check the rotor and found the end electrode is worn at an angle which I determined was caused by the distributor shaft having play and needing to be replaced.

Fast forward to this week...I decided to bite the bullet and called MB Classic Center to order a new distributor, which they said was available ($$$). It arrived yesterday (complete with new cap, rotor, points, trigger points and vacuum advance module) however I found a problem... The vacuum advance module only had one nipple (on the inboard side) to accommodate a vacuum hose. My current one has two- one inboard, one outboard. Also the green wire(s) from the points on the new one have plain circular "screw down" connectors at the far end while mine has a "coax type" push-on connector. Called Classic Center and they confirmed this was the MB Part number called out by my VIN, but we checked further by looking at the Bosch part numbers on the two distributors and found they were different! My old one is 0231404002 and the new one is 0231403007. The guy at Classic cross referenced the numbers and said my car was late production and had a newer style distributor which in fact is no longer available!

My question for you all now- As far as I can figure, the new distributor from the Classic Center is the older (up to 1974- pre-cat) "retard only" type distributor and the one on my car currently is the 1975-76 catalyst "retard-advance" style. So...is it possible to swap out my old 2-nipple retard/advance vacuum module and my old coax style green wire and put them on the new distributor? (Also- FYI my car has had the cats and air pump removed previously, so it is in essence a pre-75 non-cat car now...)

Is it possible to get this 0231403007 distributor to work properly in my 0231404002 car???

Thanks!

J.G.

[RadioTek]

I had wobble in my distributor shaft that was eating the rider on my points. Couldn't keep the dwell setting for more than a couple weeks.

I said "screw it" and went with the Crane/S&S retrofit unit to eliminate the points.

Haven't had any problems in 4 years.

You might be able to get your old one rebuilt. If it's the shaft wobbling, it should be fine after new bushings.

Scott

[meltedpanda]

Im not sure you can with assurance it will be better. Optical points solved my wobble issue . Wonder why they sent the wrong one?

[Jay Gibbs]

Originally Posted by meltedpanda

Im not sure you can with assurance it will be better. Optical points solved my wobble issue . Wonder why they sent the wrong one?

Apparently there were two versions of the distributor for the 1975 model year...my car was a very late production 1975 model (October 1975) and they no longer make the one for the late production cars (I even was in contact with Bosch in Germany and they confirmed that there was no replacement offered for the 1975 US late production cars.)

That being said, fast forward to today. I decided to see if the (early 1975) model distributor that MB Classic sent me could be made to work. The green wire to the ignition module was a simple fix. I simply unclipped the one that came with the new distributor and substituted mine with the coax end connector. Simple fix. I also decided to see what if any difference the different vacuum advance module would make. I installed the distributor and plugged the outboard vacuum hose that (I think) at one point somehow attached to the EGR system...(that no longer exists on my car anyway.) Plugged everything back together and twisted the ignition key...I'm happy to report the car started instantly, ran unbelievably smoothly and seems to perform perfectly! Took it for a 15 mile test run and can find no problems whatsoever. I'm going to fill the tank and see if there is any difference in gas mileage. Will report back after I run thru a tank of gas!

Thanks for all the help!

J.G.

[meltedpanda]

good news ! well perhaps you have taught us all a little something. Keep us posted

[Jay Gibbs]

Originally Posted by meltedpanda

good news ! well perhaps you have taught us all a little something. Keep us posted

Update on replacement distributor...

In short...it works perfectly! I checked the advance at the recommended rpm's and it is spot on. Over the last month, I have averaged 13.8 mpg's with an equal mix of city/highway driving, with a high of 16.1 for a 115 mile drive! I think she is finally dialed in perfectly. Nice smooth idle and flawless running. The original distributor (which only had a little over 50k miles) was clearly at fault on a number of issues. The slight shaft wobble clearly affected both the ignition and fuel injection timing, and neither could be resolved until the wobble was eliminated. At $1,100 from the Classic Center, the distributor was pricey...but when you consider it comes complete with new trigger points, new vacuum advance module, new cap, new rotor and new ignition points it becomes much more of a bargain. I also replaced the ignition control module with a remanufactured unit which has finally solved my ever-present jumpy tach needle problem!

The last item on the repair list was the car's stance. It always seemed to be too high in the front end, and I have noted many other 450SL owners have complained of this too. This situation was exacerbated when I relieved the engine compartment of over 50 lbs of catalyst manifolds, cats, air pump and assorted attaching hardware. I noted that the 380SL aluminum engine was approximately 80 lbs lighter than the 450's iron counterpart, (just slightly more than the weight I liberated) and decided to go with 380 front springs (114 321 05 04) They are slightly thinner diameter steel than the 450's but the length is longer which increases the spring rate. Bottom line is that they worked perfectly as well...front end drop was a little less than 1" with 4 bump spring pads, very slight nose down rake, and no noticeable difference in spring action from the 450 springs. Just what the doctor ordered!

[meltedpanda]

that confirms my belief and others that the "wobble" is an issue in these old distributors. Good job and now enjoy!