overhauled tranny, hard 3-4 shift - PeachParts Mercedes-Benz Forum

93300E · #1 06-08-2002, 10:51 AM

I had the tranny on my 93 300E 2.8 overhauled last December. I have a one year unlimited warranty on it. The 3-4 shift has been very rough on and off since then. The owner of the shop test drove it and declared it is shifting perfect and seemed offended that I have a problem (this is the same guy that flustered when I asked how much a repair he recommended would cost, saying "nobody has ever asked me how much it would cost" I guess all MB owners are made of money eh?). It only does it once in a while, and never when I back off of the accelerator (not that I ever accelerate very hard) right before the shift. When it does it the whole car shakes with a thunk. All other shifts are perfect, save for a long pause going into drive or reverse, and occasionally a hard thunk into reverse if I have been parked at an incline.
Thank you for any advice.

stevebfl · #2 06-08-2002, 11:36 AM

I suspect that the modulator pressure is too high. A large change should be tried to do some diagnosing. I would suggest two turns counter-clockwise. This takes about thirty seconds once on a lift.

If after this change you have shifts that flare while others are still firm then you have an internal problem. Its real concievable that you have a valve body problem.

From your technicians point of view its real hard to tell you, the customer, that a VB replacement might be the best answer. MB makes rebuilt valve bodies that are fairly cheap (less than $400) for many models. They have many corrections built in that take care of idiosyncracies that were discovered over time.

VB replacement after a rebuild is often the only answer for shifting irregularities. It is hard to make a technical case against the tech in these matters although not so hard to make a legal case. The tech is supposed to know ahead of times the costs and risks and is then held to his attempt.

We do lots of MB transmissions and occasionally get burned but not often as any problem not absolutely diagnosable will include the provision that shift quality of the final product will only be an issue after a rebuilt MB VB is installed. When these cases come up we loose as we wind up doing the VB install for no extra labor as we are committed to one price for the whole job (which by this point has proven to need the VB).

Boy, would I like to live in your neighborhood. I hardly ever see a customer that isn't interested in knowing the price.

jsmith · #3 06-08-2002, 12:02 PM

Steve,

If you do a VB replacement, do you include any adjustment that may be required or are the VB's already calibrated after the rebuild? I have had my "low up shifting" transmission in this very same model evaluated at a local MB specialist's and they recommended a VB replacement. I am aware that there is an adjustment that can be made in the VB to correct the full throttle shift point (mine shifts about 1k rpm too low at full throttle). I am concernced that upon replacement of the VB, there will be additional adjustments required anyway. Also, my tranny is a reman'd factory replacement 30k miles old (under warranty) and I discovered that the part number on the side has been ground off - so it is difficult to figure out exactly what transmission it is and what the corresponding VB will be.

93300E,

I had similar problems with the 3-4 upshift and I was about to make the adjustment Steve indicates but I found that moving the part throttle shift points higher alleviated this condition. This is done with the Bowden cable adjustment. I don't know if it is exactly the same condition but in my case low speed, part throttle shifts at around 2k rpm resulted in rough shifting. Moving the shift point higher to about 2.3k took care of the problem.

Cheers

93300E · #4 06-08-2002, 12:38 PM

Thanks for the advice, guys. It is sad that I am so hesitant to go and ask for help from the shop I have spent thousands at. I guess I am going to have to risk offending the owner and go back with your suggestions (as I dont have a lift and have no idea what a bowden cable is!)
Thanks,
Brooke
93300E

jsmith · #5 06-08-2002, 03:40 PM

93300E,

Check out this thread:

Bowden Cable Adjustments

We have the same model car so it should be exactly as shown in the pictures. The Bowden Cable adjustment is easily accessible in our car. It is in the driver's side beneath and to the back of the throttle linkage. It should have the characteristic orange bellows sleeve covering the end of it. I can actually turn the adjusting nut in mine by hand. Just keep track of how many turns you have made and in which direction. If you loosen the 13mm adjusting nut, it will delay the upshifts, which is what helped in my case.

93300E · #6 06-12-2002, 10:19 PM

Joe,
Should I try the modulator pressure adjustment first or the Bowden Cable, or should I just go to the shop with my warranty on the tranny and have them try it?
Since you have the same model, do you have these quirks, are they normal:
Overheats in hot weather at standstill when a/c is on, fans all working temp approaches the 120 mark and I have to turn off the a/c.
Idiot light for burned out bulb comes on with brakes occasionally, though no bulbs are out.
And lastly, I have been getting a trouble code 5 for EGR valve inop, but only occasionally...is this an easy fix? have you ever had this problem?
I love the car, it is a bit slow up hills (I dream of it being a 500e, oh well) Have you done any performance mods? I am too nervous of screwing it up, I have 160k miles.
Thanks for all your help, this forum is incredible, so many helpful people with prompt free advice, I almost feel guilty asking so many questions.
Brooke

#7 06-12-2002, 11:28 PM

I had the trans in my 87 300e rebuilt in november. the first shift is very slow wile the 3 & 4 shift are hard. I took it back to the shop last week and the tech turned the modulater adjuster one click clock-wise. It did not make much if any differance. Is there any long term problem with a hard shift? if I do nothing about it will the trans last?

jsmith · #8 06-13-2002, 12:02 AM

Brooke,

The Bowden cable adjustment is a lot easier to do - you just reach in there and turn the adjusting nut either by hand or with an open end 13 mm wrench if it doesn't turn freely. You want to turn it away from the end with the cable. It should hold the car in gear longer under partial throttle. The modulator valve adjustment is best done with the car in a lift. My mechanic started removing the cap but had trouble getting it off so I held off on it and haven't made any adjustments there all this time. The cap can break easily so it is best to have a replacement handy as you don't want to leave it open ($2 part). On PA_Joe's note, from what I understand, there is not enough of an appreciable effect if you just turn the cap even if you turn it all the way. You have to take it off and turn the key adjuster inside. Look for Steve Brotherton's posting on this - do a search on "flaring".

I have been watching temps very closely from the start and in anticipation of summer I changed the thermostat last week. I also have the resistor mod for the aux fans which keeps temps under 100, even with AC on in stop and go traffic.

I had that brake light problem and it drove me crazy for a while until I caught the third eye not coming on when the warning indicator came on. It was intermittent which made it hard to diagnose but replacing that bulb took care of that problem.

HTH

93300E · #9 06-13-2002, 10:21 AM

jsmith,
when I am accelerating hard and shifting at a higher point it still does a hard 3-4 at times, does that indicate the rpm's are not an issue, I am nervous about starting to mess with adjustments (I have bad past life memories about a volkswagen carb I adjusted until noone knew where the original settings where!)

Joe_PA (there sure are a lot of Joe's on this board)
I have been curious if I am hurting my tranny by letting this go for months as well, the whole car shudders when it starts acting up on the 3-4.

Thanks all!
Brooke

jsmith · #10 06-13-2002, 10:49 AM

Brooke,

What is "hard acceleration" for you? Is it wide open throttle? If it is shifting like this at 3K rpm, then maybe that's not the problem. Hold it in 3rd while accelerating to around 3k rpm then shift to "D" and see how the 3-4 shift feels (don't let up on the throttle). In my case, I did think that it was doing it even at harder acceleration but I think that it was shifting prematurely, because when I made the adjustment it went away. What I felt was a slight shudder, almost like running over 2 rub strips on the highway. If you do the adjustment, count the number of "flats" or sides of the adjusting nut. I had to go almost 2 complete turns before I felt the difference. If you go the wrong way, you will know right away because the shifting will get even harder at the lower shift point. Just remember to keep track of the adjustment...

Cheers