Searching in google, I did find some specs on the W123 300TD turbo. It
should be able to pull a 3500lb trailer up an incline of around 14-15
degrees- better than my Volvo 740T, primarily due to a lower 1st gear.
Torque curve: http://www.zarnochwf1.com/node/18
I don't know the stall speed, but it's probably safe to say it's at
least 2000rpm, which would give about 177 ft*lb of torque for the turbo
engine.
The tires are the same as my 740, so 12.5" radius.
Rear axle ratio is 3.07 in '81-'84
(http://www.peachparts.com/shopforum/showthread.php?t=223884).
Curb weight is about 500lbs more than the Volvo, so say 7500 lbs total.
1st gear is 3.68:1 (http://home.comcast.net/~phantoms/vacuum/722_ratios.jpg)
Torque at rear axle: 177ft*lb*3.68*3.07=2000ft*lb
Thrust at stall: 2000ft*lb/1.04ft=1920lb
ramp angle = arcsin(1920lb/7500lb)=14.83 degrees
Tyler
tyler wrote:
Jamie,
I'm also towing a sailboat ('74 Catalina 22)- I highly recommend one
as it's cheap and very well made. It only weighs about 2200lbs, but
the trailer and gear bring it to about 3500. I'm currently towing it
with a beat up '87 Volvo 740 turbo wagon that tows it very well, but I
think the W124 would be more comfortable and fuel efficient. I am also
curious also about the Mercedes' ability to pull up a ramp. The Volvo
has been able to pull the boat up even the steepest of ramps without
issues. It has an automatic with 2.45:1 1st gear, and a 3.73:1 rear
axle with an Eaton G80 locker- and the engine makes 187 ft*lb (253 Nm)
of torque at 2900 rpm. Does anyone have the gear ratio and torque
specs for the W124? Is it available with a locking or limited slip
rear differential? I would assume if it has just as low or lower
gears, a locker or LSD, and as much torque then climbing the ramp
shouldn't be an issue.
I am mostly worried about the transmission or brakes in the W124
burning up going over mountains.
For pulling up a ramp, I think one could calculate reasonably well the
steepest ramp you could pull a given boat up given (1) the torque of
the engine at the stall speed of the torque converter, (2) the ratio
of 1st gear times the rear differential, (3) the tire outside
diameter, and (4) the combined weight of the entire rig. It's #1 that
I expect to be hardest to find...
Searching online, I found that my Volvo has a 2700rpm stall speed
torque converter and makes about 175 ft*lb of torque at this rpm - or
about 1599 ft*lb at the rear axle. With a 12.5in tire radius, this is
about 1535 lbs of forward thrust. Fully loaded will all of my gear,
the car and boat probably weigh 7,000lbs.
So:
Force = weight * sin(ramp angle)
ramp angle = arcsin(force/weight) = 0.22 radians = 12.61 degrees
So in theory I can probably pull up a 12.61 degree ramp. According to
BoatUS, most ramps are designed for a 6:1 slope (arctan(1/6)=9.46
degrees), so I have a good extra margin of ability, although without a
locking diff traction would probably come into play first. If someone
can help me find those same numbers for the W124 300TD, I will redo
the calculation for it.
Tyler
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