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280SE 3.5
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36 Posts
Discussion Starter #1
Hi Everybody,
I have problem with acceleration. My 1976 450SLC does not accelerate more than 100mph even downhillI when pedal was fully pressed. Like speed limited at 100mph. I do not understand the reason. Problem with transmission or throttle linkage?

Thank you very much in advance
 

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w108 & w107
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146 Posts
What are your revs at 100miles per h?
Does the car rev higher than that in lower gears? You may need to hold the transmission in a lower gear to check that.
 

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2015 S550
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2 Posts
Even though it runs the same uphill and down my money is on a fuel starvation issue. The engine has to develop continuous power for the fuel to run low and it cannot supply more than 100 mph.
 

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Check the small plastic hiem balls on your throttle linkage. There's one on the firewall and one on the top of the intake manifold. If one or both are broken you will never get wide open throttle which is something you should be checking anyway.
 

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280SE 3.5
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Discussion Starter #5
Thank you very much for replies. Lower gears car accelarates normal without problem but I guess can be better. First second gears rpm reaches till 6000 rpm when kick down or manuel drive. But while driving 4th gear rpm does not exceed at full throttle 4000 at 100 miles. Downhill same. Engine temp increases as well due to driving like this. I was hoping about transmission but as Dr Benz said will check plastic hiems andas carock said will check fuel issue. But if fuel how can car revs at full throttle at lower gears.
Thank you guys will check tomorrow and inform you
 

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280SE 3.5
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Discussion Starter #6
Today I checked plastic hiems on throttle linkage (rods) they are available no cracks. I checked warm up regulator, I had two spares thought that i was not working properly. I had spare fuel pump, replaced and had a test drive. But no changes. Tomorrow, I will check injectors. But car acceleration is very bad. Hardly climbs 35% uphill even at gear L.Still did not find reason
 

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Did you check for wide open throttle? There's a place to adjust the linkage if it's not opening all the way. I've seen where some of the throttle linkage was installed wrong and it affected movement enough to cause problems like yours.
 

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'72 250C, '74 280C, '85 500SEL, '81 300CD.
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I might be "mis-remembering" but it seems to me the mid '70's SLC's had a rev limiter on them. They used either a fuel cut out on the fuel pump relay, a rev limiter on the distributor rotor or sometimes both.
 

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Rev limiters are more common on twin cam engines due to how quickly they can rev up. No indication from OP that the engine is missing and more like it won't top out. That's often a throttle linkage problem.
 

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280SE 3.5
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36 Posts
Discussion Starter #10
I found problem today. Came last my mind to check, catalytic converter was clogged. I removed from exhaust system and inside there was plenty of rust. Gases were not discharging sufficently. I had a test drive without converter. It runs excellent now
 

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More than just a possibility that it drank a few tanks of leaded fuel years ago. Remember those cheater spouts that you could stick on the end of the fuel nozzle because your fuel tank had a smaller fitting? Sometimes you ran out of fuel and sometimes that 5 cents a gallon less for leaded looked mighty tempting.
 

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Discussion Starter #14
Thank you very much all of you for comments. Clogged cat should also be considered or checked in the case of having poor performance issues which I noticed this case.
 
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