transmission fourth gear? - PeachParts Mercedes-Benz Forum

smartin · #1 01-30-2003, 11:11 AM

1985 300TDT (125K miles) At first, accelleration from zero very sluggish, with 3 "hesitations" until about 35 mph. Since then have cleaned ALDA line, diesel purge direct to IP, adjusted ALDA, changed return (diesel) lines, thermostat ( was'nt hitting 80 degrees), capped vac lines to EGR and recirc valve. The ALDA and recirc valve made the most noticeable difference. (I also changed the 2 fuel filters twice - once about 4 months ago, and after purge last week.) Car is a lot quicker from zero, but still has mini "hesitations" (versus before when they were a little longer causing car to "lurch forward" a little) I did notice that if I start in "L", and then shift upwards, finally to "D", - only a hint of these hesitations. Finally on the freeway the car feels like it is working a little too hard - revving 2500 PLUS at 55 to 60 mph. Is it shifting into fourth gear? There - I took long enough to get to my main question - but thought maybe they were related. I just received trans filter and gasket - (plan to do this weekend) Although earlier posts suggested I have a good mechanic do it the first time.

lrg · #2 01-30-2003, 12:55 PM

smartin,
That RPM seems about right for a California spec car. Mine hovers around 3,000 RPM at 70-75mph. The 85s have about the smoothest transmissions of the W123 series but you should definitely be able to feel it shift up the gears on hard acceleration. Remember you are starting in gear 1 (not zero) so you will only feel three actual shifts up into 4th gear.

#3 01-30-2003, 02:26 PM

smartin; sounds as though your rpm's are about correct for your 300d.............my 85 federal (asopposed to a california) version will tach out at aprox 3,000rpm at 70mph or so on level ground...these engines NEED to wind up a little bit to EXTRACT the necessary POWER!....remember that your auto starts out in 2nd gear unless you stomp down for the transmission to downshift into 1st gear.....try starting from a stop with the gear selector in 1st and then shift up into drive>then count the upshifts.best wishes always,spo.

smartin · #4 01-31-2003, 12:48 AM

Did you say start in 1 or L? The upshift to S then D? And then listen for upshifts? How many should there be? I know I am missing some general knowledge on transmissions, but I would like to know - does L, S, D count as gears?? Thanks.

lrg · #5 01-31-2003, 01:00 AM

My understanding is that L holds you to 1-2, S to 1-2-3 and D the whole range of 4 gears. I'm pretty sure that my car ('85 California 300 TDT) starts in 1st gear from a dead stop. I think the diesels start in 1st to give them a bit more go but I might be wrong. The easiest way to test is shut off radio, close windows and come to complete stop at the start of a highway on ramp some where. Then, as the English say, "Put your Wellie in it" or step on it (it's not necessary to floor it, just go at least 80% full throttle) and feel the shifts and watch the tach. You should see/feel three shifts, 1-2,2-3,3-4. If you are on it fairly hard the 3-4 shift will happend at about 4,500 and you'll be going 70+mph.

smartin · #6 02-04-2003, 02:17 AM

lrg - It sure seems like I get through all shifts by 20 mph! Is this right?

rwthomas1 · #7 02-04-2003, 10:57 AM

You have driven the car and it shifts 3 times and its into 4th gear at 20mph? Even when floored? At very light acceleration, the shifts will happen faily early but this shouldn't be happening with the pedal to the floor. Either your bowden cable isn't hooked up or it is in dire need of adjustment. Do a search on bowden cable adjustment and this should help you. RT

gsxr · #8 02-04-2003, 12:06 PM

I agree, the cable may be out of adjustment. FYI, there is no way to force the tranny to go into, or stay in, first gear as D/S/L are essentially 4/3/2.

At full throttle, your tranny should shift at 4500+rpm for each gear. It may shift out of first at a lower rpm, closer to 4000, at least some of the earlier 123's had this annoying "feature".

HTH,

smartin · #9 02-05-2003, 11:33 PM

In drive (from a dead stop) it shifts 3 times before hitting 20 mph. Tach gets up to 2000 at shifts. This does not seem right.

rwthomas1 · #10 02-05-2003, 11:41 PM

"In drive (from a dead stop) it shifts 3 times before hitting 20 mph. Tach gets up to 2000 at shifts. This does not seem right."

If it does this when floored your bowden cable is not functioning correctly or there is some other issue. This is your problem. RT

gsxr · #11 02-05-2003, 11:43 PM

If the tach never gets above 2000rpm before each shift, and only goes above 2000rpm in top gear, yes that is WRONG and you need to fix it....

NC240D76 · #12 02-06-2003, 07:33 AM

You might find some answers in this thread although the w115 and the w123 are different is some ways.

http://www.peachparts.com/shopforum/showthread.php?threadid=54196

Mine now runs like a new car although I may have it set slightly too aggresively, it is winding fairly good (no tach) when it shifts into 4th gear at 60 mph but it is smooth as silk and if I drive it easy it shifts into 4th between 30-40mph but it seems to have a relatively hard shift compared to the lower gear shifts when diving easy and all the shifts when driving hard.
Good Luck

lrg · #13 02-06-2003, 02:30 PM

I had my 123 out today and paid more attention to shift points. Around town with light/moderate throttle 1-2, 2-3 shifts occurred around 2,200 RPM. 3-4 occurred much later (not sure when exactly because I was going way above speed limit in town before it shifted to 4th. Under hard acceleration it holds the shifts much longer. I think this may help confirm that your Bowden cable is out of adjustment.

bjcsc · #14 02-06-2003, 02:49 PM

Regarding the shifts, it is unclear (to me anyway) whether he is getting the shifts at 2000 rpm under light pedal pressure AND heavy, or just light. 2000 rpm sounds about right under light accel, but I also see shifts around 4500rpm when zooming.

The "S" on the shift console stands for 'slope', and is both for climbing one and descending one, it was designed to and does work great as an engine brake in the mountains and saves front brakes from overheating.

I think a definitive answer from smartin as to the shift points under heavy accel would help everyone trying to assist.

smartin · #15 02-07-2003, 01:12 AM

The shifts under moderate acceleration occur at about 2000 rpm. Under hard acceleration - about 2200. Also - I am almost certain that I am in 4th gear by the time I hit 20 mph, I really do not detect another "shift", (even hitting speeds of 70 to 75 mph). Is this transmission that smooth that I cannot detect shifting into 4th, or is as I think it is with the 3 shifts happening before 20 mph? Bowden cable has slack no matter which way I turn it - either all the way in OR all the way out. Will this slack remain as part of he adjustment, the final tuning being a truly "FINE TUNING" adjustment, OR is ther another adjustment that I need to do. Thanks to everyone.