Mechanic says I need a transmission rebuild on my 300SDL
 

Yesterday, I had my transmission fluid changed. Found were black powdery stuff from the pan. My mechanic told me I need a trans rebuild.

I just got the car last November and the PO does not remember changing it in his 3 years of ownership.

I am experiencing flaring at 2-3 shifts when cold. Shifting is fine under operating temp. Also flares 2-3 at WOT. No shifting issues other than that.

VCV input from vac pump is 22" and VCV output after green damper is 10". My vac reading at idle is 10" to the transmission from a T after the green damper from the blue disk. It goes down to 0" at wot.

Do you really think I need a rebuild?

Would a K1 spring kit solve this?

How can I adjust the VCV output to 12" to put it up to spec?

Thanks for your time.

you dont say how long its been flareing for or how many miles its done. Once the trans starts to flare, its a fast down hill run for the trans as the clutch plates get destroyed.
It maybe easier to find a good second hand trans.

Thanks. Flaring started 3 mos ago after changing head gasket. I know its not related but that is when it started.

& the trans has done how many miles in total? 3 months of flaring is enough to kill the trans if you are doing driving with a bit of changing, especially if you dont drive in a way to minimize it.

If you changed the head gasket, it is likely that you had to disconnect some vacuum lines. My tranny shifted perfectly before I replaced my head gasket, and now I have flaring. I know it is vacuum related, but i haven't figured it out yet.

The K1 spring kit is a cheap $10 fix. Might as well try is. It made the difference on my two SD's.

The only people who rebuild working transmissions are prepping for Paris-Dakar.

Spring kit.

I have driven it about 1K miles already. It only flares in the morning, it does not flare when normal driving temp is reached. Also flares during 0-60 run. Did it about 10 times. Got 20 secs. But will try to tackle that once flaring is solved.

Precisely my case. I'll look for a K1 spring kit. But I still want to increase the VCV output to spec.

Check how much vacuum the VCV gets at idle and how much goes to the blue saucer. Check right at the VCV fittings. If you're losing 12" of vacuum at the VCV at idle, it needs a closer look. There are a couple of threads on reviving the VCV. In my case I happened upon a NOS unit on eBay and it improved the shifting situation more than the revived VCV did.

Sixto
87 300D

See my post in the SL forum. I had exactly the same symptom with a 2-3 flare and a highly trusted mechanic's recommendation for a re-build. He told me to drive it until it failed as the cost of a re-build was so high. Last week while poking around under the air cleaner shroud I discovered a loose vac fitting.

Reconnected line and the flare disappeared.

I also had a shifting problem on my 300SD with very HARD upshifts. In that case the issue was also a vac line - it was connected into an incorrect connector on that multiple vac connector thingy on top of the valve cover.

Your spring kit may be req'd but I've learned through the school of hard knocks that it could well be a vac issue and they can be annoyingly hard to locate!

The Higher the amount of Vacuum applied to the Transmission, the softer/more flary the shifts will be....
--This is how the trans 'Knows' how fast to apply the changes. The trottle-position varies the amount of vac applied At Idle, say around 10" dropping to '0' at WOT.

There are various 'Orifices' in the vac system on an M.B. it could well be that one has a partial restriction. Also well up on the fault-list are leaking vac-joints and hoses--those rubber joints may seem sound, but can easily leak--just enough to mess things up...

You could try altering the position of the VCV to reduce the amount of vacuum a little, say 1" to 9" At Idle.

At WOT, the vac top the trans should be '0' so thats OK....

My wagon suffers from the opposite. but its so slight I'm not too bothered. Its a little rough when stone-cold, smoothing out to perfect when hot....

I was able to purchase my car for cheap because the PO was told that it needed a new tranny. After I had the vac issue taken care of I didn't have much of a problem. But yes, tracking down a vac problem isn't fun.

http://www.continentalimports.com/ser_ic20242.html AUTOMATIC TRANSMISSION ADJUSTMENT ARTICLE

WIKI Transmission adjustment
http://www.peachparts.com/Wikka/TransVacTune

Transmission adjustment Thread
http://www.peachparts.com/shopforum/showthread.php?t=158216

If you were going to get a rebuilt trans they would just exchange it. In that case you might as well see if you can improve it or just drive it until it stops and get the exchange or a used one.

Also abnormal; at least on american cars to find particals in the Pan during a filter change. It is from the Bands and clutches and even on a new trans they wear and the particles have to end up somewhere.
I have read the Mechanics will often show what is in the pan to scare folks into replacing their transmission.