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Old 23rd November 2018, 09:11 AM
sean sherry sean sherry is offline
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Thumbs up Auto Transmissions

Having had a couple of queries on the subject
.........To set up any make of Auto Transmissions it is imperative that, firstly the Engine is in a good state of tune and in good condition, not with low compression. An Engine and an Automatic Box should be matching bed fellows ! With vacuum modulator pressure control units the vacuum reading at the modulator end must be the same as manifold reading. Say 16 to 18 inches and the pressure reading should flick up and down with a blipping throttle. This tells that the internal valves are not sticking. Most low vacuum reading are down to retarded ignitions, for what ever reason. Fix it ! A slow modulator reaction will never fix a problem. A weak modulator spring can be checked using a kitchen scale to read Lbs pressure before breaking. But when in doubt .just fit a new one. They work hard, in and out like a fiddlers elbow !
For instance in G M Cars, with non adjustable modulators and a hollow rod, just put a brake rivet down the inside to raise the pressure, works wonders at times.
Mercedes Modulators are like Hinz's Beans.. they come in 52 varieties. Fortunately they are easily adjustable and respond well to a full turn on the adjuster to fix mild flares., if you are lucky. But the vacuum must be right !
Any questions I will be happy to address, if I can.
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Old 3rd December 2018, 11:25 AM
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c107 c107 is offline
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Default Re: Auto Transmissions

Thanks Sean.
Interesting post.

Where you would you look if you had a car that will not exceed ~3500rpm unless you manually move through the gears with the shift lever.

Even if I floor the 450SLC, it will not move to redline (unless I use the shift lever). I had a mechanic look at it and he made some adjustment but it is still not revving out.

Kick down switch does work, but it is unwilling to kick down to higher RPMs.

Incidentally, I think my UK Spec 560 has an AU spec modulator on it. Not sure if this is a big deal?

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Old 4th December 2018, 06:57 AM
sean sherry sean sherry is offline
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Smile Re: Auto Transmissions

I would look at the linkage connecting from the Carb end running down to the Transmission. The modulator controls the Line pressure via the throttle Valve .
The linkage controlling the up shifts has it's built in limitations. Even in low gear it will up shift preventing the engine from over revving when using full throttle. It is not an uncommon problem to find that the accelerator pedal hits the floor before the carburettor gets full throttle. Wear and tear. Mostly this can be easily fixed by pulling the pedal up and bending it .
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Old 5th December 2018, 09:10 AM
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c107 c107 is offline
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Default Re: Auto Transmissions

Thanks - checking throttle linkage is a good place to start. Its an FI engine not a carby but the same would apply I assume.
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Old 5th December 2018, 01:33 PM
sean sherry sean sherry is offline
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Smile Re: Auto Transmissions

Yes, the principle is the same There would still be a mechanical linkage connection to the Transmission, with the non Electronic controller transmissions.
Helmet would know how the later Transmissions are controlled.
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Old Yesterday, 04:59 PM
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Styria Styria is offline
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Default Re: Auto Transmissions

Sorry boys, this goes beyond my feeble brain - but, keep it up as it makes good reading. Nothing like a brain teaser.........Regards Styria
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