'73 280 not shifting to 4th - PeachParts Mercedes-Benz Forum

Cephallus · #1 12-09-2006, 02:44 AM

I finally got the w114 road-worthy enough to take a spin on the freeway. Did the engine/trans service today...filters, fluids, etc. After doing the tranny filter/fluid, I drove about 20 miles around town, never exceeding around 45mph. Shifts great, smooth and on time. Sooooo, feeling adventurous, I took to the freeway to get a better feel for what I'm working with.

Around 80mph (on the dial, but seat-of-pants says it's actually around 70mph), I'm starting to wonder when it's going to shift to 4th. I lay off the pedal - nothing. Up to 85 on the dial...engine is whining...nothing. Edge close to 90 on the dial, and the car starts to bog like it's fuel starved. Never shifts to 4th.

The car had been sitting for 8 years or so - any advice jump to mind? Think driving it around town with fresh fluid might 'free up' 4th for me?

Other than being noisy from having no interior, not shifting into 4th, and wandering all over the road like the town drunk, she drives real smooth!

Mike D · #2 12-09-2006, 08:12 AM

You probably are in 4th. 95% of the time your car will never go into 1st gear or at least you won't notice it. 1st is a real "stump-puller" on those transmissions. Manual shift your transmission from "S" up and count the changes. You might also check the shift rod which connects the acc. linkage to the transmission shift point linkages.

Your ride sat for a long time so the subframe bushings are probably collapsed. That will give you the "drunk about town" feeling. The wander is probably more pronounced when the grade of the road changes or you change engine speed quickly. Spped bumps or dips should send it absolutely bonkers.

The lower control arm is not attached to the body frame as in American cars. The upper control arm is. When there is excessive play in the subframe mounts it changes the shape of the quadrilateral used in camber alignment. (imagine the four points. Upper ball joint, lower ball joint, center of a line drawn between the lower control arm bushing and center of a line between the upper control arm bushings). When the bushing shifts corresponding to grade changes or sudden differences in engine speeds (the engine mounts to the subframe but the tranny mounts to the body frame) you are altering the quadrilateral and changing the alignment. This also affects the toe-in as the idler arm is attached to the body frame.

They are an easy change and in fact I am doing mine this weekend. I'll post with pictures.

Cephallus · #3 12-09-2006, 12:54 PM

It's def. not upshifting to 4th...it does start in 1st with the kickdown engaged, and tops at 3. Plus, I'd find it hard to believe that a 4sp auto on an m110 would be designed to top out at ~80mph. Any tips for checking shift linkage? It's definitely in neutral on N, and tranny does not engage until the lever makes it all the way to D...so I don't see how I could be jumping over D to S. Any tips would be appreciated!

I was only being silly about the road feel of the car. In addition to the sit-time, I'm willing to bet that the soft bits of the car have never been touched. I'll go through the entire suspension bit by bit. Tie rod ends are all shot, bushings are crumbling and barely there, subframe bushings feel/look like old licorice, etc. Engine mounts are collapsed, tranny mount is toast. I've made my own tools for r&r of all of these bits, it's just a matter of the time it takes.

Pics of jobs are always appreciated! It's amazing how much head-scratching time a few pics can save...

Mike D · #4 12-09-2006, 04:42 PM

The linkage I'm talking about goes across the top of the engine and connects to a bellcrank on the passenger side of the engine. Not the gear selecter. It's some kind of gear selecter adjustment dowangy which works in correlation with the modulator. Make sure the linkage going down by the starter is not bound up on the ground strap, tranny fill tube or exhaust.

I was told the proper adjustment for this rod was, carb linkage at idle stop, linkage connected to transmission at full rear travel and the connecting bar going between acc. bellcrank and trans shift bellcrank adjusted to "zero travel snug fit".

Of course, I was also told if I was good then Santa would bring me a pony. Two more years and I'm gonna give up on that one.

Cephallus · #5 12-09-2006, 08:04 PM

Heh...never mind on this one. A little more gentle driving and the tranny is 'magically' shifting into 4th now. Guess it needed a little more flushing with the fresh fluid to get the rest of the nasty gunk that was passing as fluid in there before I changed it.

Now I need to do tranny mount, diff mount, and flex discs to smooth out the rest of the drivetrain.

The diff mount has almost no rubber left in it...