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I am new to this forum and after watching from the sidelines for quite a while, I recently took the plunge and purchased a 1985 230E automatic here in Singapore. I am presently a very happy and satisfied Merc owner and finally understand why you are all such enthusiastic supporters of these cars.

The car was imported used from the UK in 1991 and I've spent the last couple of months having various items of work done on it.

I have recently discovered that the speedometer on the car is optimistic by about 10%. At an indicated 120km/h (75mph) the true speed is about 110km/h (68.75mph). However more troubling is the fact that the engine is running at 3,900 rpm at this speed in 4th gear.

Based on my rough calculations, this would mean that the final drive ratio on the car is approx 4.16 (with no allowance for torque converter slip).

The car runs on the correct 195/70 x 14 types.

My questions are:

1. Is it normal for this model to be running such high engine speeds when cruising?

2. Can anyone advise me the factory spec final drive ratio for this car?

3. Could there be two separate issues here, the first being the incorrect final drive ratio and the second being excessive slip on the torque converter.

Look forward to any inputs you can provide on this. Many thanks in advance.

Choy
 

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200 -85 / 280E -79
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1,221 Posts
Don´t you got a 5´th gear also??[;)]

My 200 -85 runs at 3500 rpm in 120 km/h if i rememder right. It has a 4-speed manual gearbox.
In 160 km/h it runs in almost 5000 rpm.
I havent tried the topspeed since i got my tacho, but i think it must be running like 6000 rpm at the topspeed! [:0]
 

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200 -85 / 280E -79
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1,221 Posts
Sorry, i see now you tell it was a auto...no 5`th gear there[:I]
 

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1984 300CD
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2,679 Posts
Try this for gear ratio's...

http://www.benzworld.org/forums/forums/thread-view.asp?tid=1193747&posts=6&hl=gear
 

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1989 W201.029/M103 3.0
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244 Posts
Typically speaking manufacturers tend to place a slightly lower ratio diff gearing in autos compared to manual versions of a given model, to make up for the inherent slippage of torque converters, for fuel consumption considerations.

To compensate for lower torque ratings, manufacturers also tend to place higher diff ratios in lower engine capacity versions of a given model.

Factory outside tyre diameter sizes (to which the speedo is also calibrated) play a role to affect your final drive ratio. These will tend to vary between engine capacities and setups also. The larger diameter rims and tyres of a luxury make accompany a larger capacity engine and lower ratio differential, typically speaking, to dramatically lower overall final drive ratio for more leisurely cruising. Outright torque/horsepower figures make up for the inherent lack of accelerator response.
Even the 280E might have 15" rims as opposed to 14" rims on the 230E for precisely this reason (speculative, I'm only just getting into Mercs specifically...blame my two brothers in law).

3500 rpm at 100km/h (60mph) is pretty typical for a low capacity, medium sized sedan. 3800 or more for fours, depending on the weight of the vehicle. It's all about acceleration potential at overtaking speeds.
Add a couple of hundred revs for torque converter slippage when you get on the accelerator pedal...or in other words that engine speed will jump to 3650 odd as soon as you start accelerating hard and may drop to 3350 odd if you coast down a gentle slope.
This equates to roughly a 3.5 ratio differential.

I should mention, I think it unwise to rev the single OH cam 6 over 5000rpm too regularly. Valve spring rates, etc. aren't really designed to do that (probably redlines at 5300rpm from factory, giving max hp around 4700rpm...as opposed to up to 6000rpm for short throw, purpose built twin cams and a redline closer to 7000rpm or more). I'd not take it past 4800 myself, without modification, but I'm less familiar with Mercs than most around here.

Gives you a possible 130km/h cruising max in that car for good long term care, if a little high in the revs. Which is again, about typical for the manufacturer's setup. You can modify this by altering overall tyre height (up the rims to 16's and play around with tyre profiles to suit) and changing diff ratio, but keep in mind you'll have to modify your engine's torque and horsepower curves to not lose an already balanced, marginal performance range. You can do this with attention to head porting, camshaft grind and the exhaust system.

Don't forget a cruiser is designed by the engineers to bustle around at between 80 and 100km/h, hustle to 130km/h odd and crawl to 150km/h or more, depending on the model but that's where we get into performance salesmanship.
Mercs of all descriptions are better across generalized envelopes than most, but people wanting performance in the W123 went for the 2.8 litre twin cam, back when new.

Excessive torque converter slippage tends to become an issue with older, worn autos. As the clearances around the braking drums (ie. gears) decay, the oil starts to move around a bit too freely and the whole package starts loosening up. You get slippage both in the gears and at the torque converter, plus your gearchanges get thrown out in the hydrolic shift system (I'm not up on the tech specs of the mechanical injection in relation to gearbox shift kits, in electronic systems the engine management runs the shift points).

So get your auto serviced if your unsure (bands tightened and general cleanout and check).
 

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2008 PT, 1998 neon--1965 VW 1200
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2,533 Posts
i dont have anything to add to this post, but i did want to say hey van, you sound like you know that of which you speak! good for you! hahaha no joke, good post, man
 
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