Highway RPM's

[Harry]

Hi.  My 1966 230SL Automatic is running about 3000 RPM at around 50 - 55 MPH or so.  Seems high to me.  Runs very smooth and actually pretty quiet but that just seems high.  Maybe I'm used to more modern cars that typically boast an overdrive?  Thoughts?
Also, the steering has a good bit of "play".  I read on the forum where the plastic bushing in the coupling is often the culprit and I have that new bushing to install.  I know the old worm gear VW sterring boxes had an adjustment for play.  Does this car offer a similar means to adjust?

Thanks,
Harry

[J. Huber]

Hi Harry,

Well, you definitely don't want to compare the RPMs to modern cars -- it just won't measure up. That being said, I think 3000 at 50 is a bit high, mine is more like 3000 at 60 or so I think. A lot of this has to do with the ratio of your (car's) rear-end... Mine is 3.75. I'll have to take a ride tomorrow to verify this...  

[66andBlue]

Harry,
if you have an axle with a 4.08 differential (as many later 230SLs have) then you are close to 3000 rpm at 55 mph (see attached graph). Especially if your tires are smaller?

[Richard Madison]

My Euro version 69 280SL has a 3.92 rear-end.

In 4th gear, the Tachometer and Speedometer needles move parallel to each other.

While tire size may make a small difference, my speed is just about double the Tach reading in hundreds.
So if the Tach is at 3,000 rpm, I'm going about 60 mph; 2,500 rpm is 50 mph. I don't have to look at the speedometer.

This is very handy in a car with a KM speedometer. A glance at the Tach tells me my approximate speed in MPH
without dong a KM to MPH conversion.

Richard M, NYC

[Harry]

Thanks very much.  I'll get firmer numbers on the RPM vs speed but it just seemed high the other day.  Where can the differential ratio be found.  I guess mt concern is whether its OK to drive the car at true highway speeds of 70-75 MPH for extended periods of time.  Back when this car was new the speed limit was 75 MPH though.

Thanks,
Harry

[thelews]

Thanks very much.  I'll get firmer numbers on the RPM vs speed but it just seemed high the other day.  Where can the differential ratio be found.  I guess mt concern is whether its OK to drive the car at true highway speeds of 70-75 MPH for extended periods of time.  Back when this car was new the speed limit was 75 MPH though.

Thanks,
Harry

Driving these cars at lower rpms for extended periods is bad for them.  You could drive it at 6000 rpm all day long.  It's what they were built for.  The Germans always drove aggressively on their autobahns.

[georgem]

That being said, when we first bought ours (4 speed manual) I can`t count the number of times that I found myself trying to change into "top" gear from 4th as the revs seemed high.

George

[thelews]

That being said, when we first bought ours (4 speed manual) I can`t count the number of times that I found myself trying to change into "top" gear from 4th as the revs seemed high.

George

You've gotten used to the non-interactive nature of many newer cars.  A Lexus is about as neutered a vehicle you can drive.

My 7 speed SL500 lopes down the freeway not much above idling rpms.  With my vintage cars, I won't drive them at any speed under 2K rpm.

[Harry]

I checked ain this AM - 2900 RPM at 50 MPH.  I recalled from my youth that these cars ran all day at highway speeds and seemed right at home.  I'll have to get myself "recalibrated".  Thanks very much for the advice and information.

Harry

[49er]

 My tach has always been a bit on the high side running about showing about 100rpm higher then actual. I Know the feeling about reaching for 5th or 6th gear. Never had a problem when the car was new as it was a jump up from my '65 VW Bug. But after owning a few cars with more gears (and not driving the SL for years) I got used to those low RPMs at freeway speeds.

John

[71Beige280SL]

My 71 280SL automatic runs 3000 RPM @ 55 MPH and 3500 RPM @ 65 MPH.

[DaveB]

Harry - there's a screw and nut arrangement on top of the steering box that looks like it must be for adjustment. But first have someone turn the steering while you watch the coupling between the firewall and the steering box, you'll probably find the play is there, and that the plastic bushings you mention are worn. There are two of them.

[Paul Robinson]

Harry,

Look for the ratio on a machined surface on the differential housing.  In the case of this 3.27, just forward of the axle on the driver's side.

Paul