OK, I have two 300CDs. One of them is a 1984 and the other is 1982. They BOTH have a transmission flare problem. Shift from 1 to 2 is fine. 2 to 3 occasionally flares. The 3 to 4 flare is the most noticeable on both cars. What is the most common cause for this?



http://www.peachparts.com/shopforum/members/gregp1962-albums-repairs-picture6095-both-coupes.jpg

Subscribed as I no longer have all the ideas posted here over the years .

First and fore most : go under the hood and pull on each and every 3MM vacuum hose, oif any come apart without a serious tug and twisting, they're BAD and need replacing .

A tiny vacuum leak will screw up the shifting, make sure that's all perfect before adjusting anything else .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Here's something worth a quick check:

Transmisson Vacuum Valve Lever Replacement

Typically vacuum leaks won't cause flares as the vacuum has only ONE purpose; and that's to SOFTEN shifts. Small throttle = more vacuum = softer shift assuming throttle vacuum valve is operating correctly and scaling vacuum signal to throttle linearly.

For the most part, if any lines are leaking, you'll be getting the opposite effect and that's a hard/over firm shift or even a slam/clunk. Flares are always too slow or too weak of an application of pressure to the clutches in relation to the power being produced. A weak/tired engine or tune-up can cause shifts to all of sudden feel too firm.

Low fluid or a plugged filter can cause this. 2-3 shift is K1 clutch pack and 3-4 is K2 valve/clutch pack. So while in 4th gear, both are applied so if there is low line pressure due to worn pump or leaking seals in the pistons applying pressure, 4th is the first to show problems usually.

Does it flare when cruising around part throttle only?

Does it act right when you floor it?

Does it get worse when hot?

When I picked up my car with 255k on the clock, it wouldn't shift into 4th with vacuum hooked up and then would lose 4th entirely as it got hot and then eventually losing 3rd too.

After doing valve body springs (superior shift kit), replacing the plugged filter, filling with heavier viscosity fluid (Redline Racing ATF to account for worn transmission components), and making a few vacuum modulator twists to bump up line pressure, she's snapping off shifts at break-neck force. Feels like a freshly built TH400 with a shift kit now. You'd never know it had a 1/4 million miles of misadjustment leading up to my ownership!

__________________
{2010 Mazda 3 266,000mi} - daily since new, Airlift suspension + some chunky sway-bars: fastest pass 17.7@77MPH
{1987 300SDL 256,000mi} - stock turbo @ 22lbs straight piped + a whole bunch of pre-turbo water/meth injection, 722.3 with increased line pressure, special sauce, and shift kit: fastest pass 16.5@82
{1992 964 Carrera 4 Frankenstein ??,???mi} - 993 forward dated, Speedster conversion, GT45 + E85: fastest pass 12.5@113

Yes important to note that the Benz boxes shift firmer by design, as compared to US cars of the time. Many folks over the years had their shift quality "tuned" to reflect more of a soft, US type shift, which would be incorrect and lead to premature transmission wear.

The fact you claim the shift from 1-2 is "fine" seems to suggest the modulator is set way too soft. That 1-2 shift will be a little quick if you have the rest of the modulator and vacuum adjusted properly. 2-3 and 3-4 should be firm, but not jarring. If they're smooth and soft, you're destroying your transmission clutches. As mentioned in posts above, a properly tuned 722.3 should be firm, but not so firm that it feels like someone dumping the clutch. After you get it shifting nice and firm, you can soften it a bit with adjustments to the VCV, but don't go for smooth/soft or you're right back where you started. Contrary to what seems obvious, a smooth/soft/slow shift causes significantly more wear to the transmission than a quick/firm one does.

__________________
Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]

I should clarify that the shift from 1-2 is very firm. I'm ok with that if it's not bad for the transmission.

Transmission:

__________________
85 300d in progress

THANK YOU ! .

I need to test and adjust the tranny on my 1982 240D, it's shifting up to late .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Both of these transmissions are 722.3's, so the thing to check are the K2 accumulator springs. The accumulators "feather" the shifts, similar to the way you ease off the accelerator as you depress the clutch on a manual. If the accumulator piston isn't moving correctly, then the shifts will either be too hard or too soft. The K2 accumulator controls the 3-4 shift, and it's in the rear of the valve body. You can access it just by dropping the pan. Should be several posts here describing the job in detail.