On my 95 S320, I've noticed recently that the transmission upshift delay that keeps it in a lower gear when the engine is first started cold, doesn't hold it in the lower gear as long as it used to.

It's been colder here recently, and I would have thought that the upshift delay would delay longer - not shorter.

To test this I intentionally drive slow enough so as not to force it to upshift, and I travel about 1/3 the distance that it used to take before it first upshifts. The next few shifts are kind of rough too - which I attribute to a not-quite-warmed-up transmission.

Any thoughts on what might be going on?

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Dave

1995 S320

If it fails enough times it will set the check engine light.

The upshift delay valve on the transmission might be going out.

It works off of vacum, so you could have a vacum leak or the hose might be cracked or coming off.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Where is this valve and what does it look like?

Thanks

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Dave

1995 S320

Sorry, but I don't know.

I just know that mine went out and my mechanic replaced it.

He described to me how it works and what is involved.

You also have a separate part called an upshift delay valve that is mounted on your firewall behind the brake master cylinder. It has a black line (electrical) and a green line (vacum) going to it. This part could be bad, too, or the vacum line could be blocked.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

My car holds off shifting until I reach 3000 rpm when first starting up and driving off. Are you reaching 3000 rpm before yours shifts? I don't think the delay has anything to do with "how far", rather, how quickly.

Yes I know it will upshift if I get abouve 3000 rpm. It is upshifting well below 3000 rpm - sometimes...

The distance I mentioned basicly means 'how far do I go before it warms up to the point where the upshift delay stops delaying the upshift.'

I'll poke around a bit at the vacuum lines this weekend and see if I can find anything obvious.

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Dave

1995 S320

I live in the Tropics and get a similiar problem some times.

With mine its from 2nd to third. Obviously cold isn't an issue here, min of 24c overnight.

Did the fiddling with the vacum parts etc help solve the problem???

The upshift delay valve delays the upshift from 2nd to 3rd on both the W140 and W124.

And it is correct that it is not a function of "how far", but for "how long" it takes to warm up the catalytic converter. That is its only purpose - to warm up the cat. quicker.

The delay valve itself is on the side of the transmission, and it is operated via vacum. There is a switch-over valve that is mounted behind the brake master cylinder on the firewall, which provides the vacum to the upshift delay valve on the transmission.

95% of the time, when the delay valve starts acting up, it is the delay valve itself that is going out - usually because it doesn't hold vacum anymore.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

The delay valve that allows vac from the engine to the transmission is a switch-over-valve and is the Delay Shift Valve..
It, like all SOVs , is a Valve that , when electrically energized,
opens -allowing vac flow.
The working part on the trans is a Vac. Actuator [ sometimes called a vac element/servo]
It is not a valve in the sense that a valve allows flow...
The actuator mechanically moves a cable[ actuates] to a set position to retard the shift point.. and it does this when the Delay valve lets engine vac reach it.
So, if one test for vac on both sides of the delay valve, from there you can tell if the Acuator is getting vac and is at fault , or if the SOV is not allowing vac to reach the actuator....
This may help one understand the system...

thanks for the pointers, I'll get those areas checked out. I had the Gearbox fully serviced and was told no probles, clean as a whistle.

Suginami on a different tack, I was going to get a replacment gear shift knob, but was told that it was easy to get the old one out to put a new one in. The instructions I was given, simply push down hard, then twist, -- tried that and no luck. I would still like to get a new shift knob though. Sooooooooooo how to you get the gear shift out and put the NEW ONE IN???

I'll save Paul from telling you to use the search function...

Gear Shift Replacement

ooopss,

sorry for the faux pas.

Thanks for the tip

What are the symptoms of a defective upshift delay valve? Can it cause the trans to downshift after it warms up? My transmission is downshifting on my 92 500sel,w140 after it warms up.thanks Bill

I think your downshifting problem is completely unrelated to the upshift delay valve function.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

Suginami,thanks for quick reply. Any ideas as to what my downshifting problem is from.Thanks Bill