I'm back with a '92 300D 2.5 for my son, trans questions - PeachParts Mercedes-Benz Forum

muleears · #1 05-09-2016, 08:58 AM

I've been gone a while but you can see from my post count and join date I've been around these for a little while. Now on to the questions: Just bought the above car for my son. Has 253K, little known history. Problem is its upshifting quickly and consequently sluggish. Doesn't want to downshift either without hitting the kickdown. Haven't tried shifting manually yet. I plan to do the following, please share what else I should or shouldn't do. My memory isn't what it used to be...
First I want to adjust the Bowden and get the shifts at a little higher speed, then tweak the ALDA (if this model has one). Shifts are a bit harsh too so I may need to adjust the vac. modulator, correct? I'll also check all the vac lines for leaks, especially the one from the IM. I don't think(

) I have a boost problem but should probably look at that too. Anyone remind me how to check for a stuck wastegate?

It's good to be back, I'll be teaching my son all of these little mods and repairs as we fix up his car. First lesson this weekend will be new brakes (rotors, pads, fluid flush).

As always all input is appreciated.

babymog · #2 05-09-2016, 09:24 AM

I suggest your repairs in sequence, so that you don't adjust a dependent parameter only to find that your adjustment was un-necessary and needs to be re-done.

First is the ALDA. If you don't have boost enrichment, you will not have proper shifts, and you will not have power with your boost. Ensure that you are getting boost pressure from the intake plenum, through the hoses and switchover valve (usually blocked at the valve, WD-40 will clear it out). The fitting on the plenum also is sometimes the culprit, as is the orifice in the line.

Once you have verified (or cleaned) this path, apply light air pressure to the ALDA and check to see if it holds pressure (<1bar). If not, it needs to be disassembled and the O-ring replaced. If it does, and you still don't have any launch power (starting in 1st as it should?), start to adjust the ALDA screw (CCW is richer IIRC). You should be able to see just a light puff of smoke when you pop the throttle open each time. Go a bit further to a black puff and then back to leaner is my method.

Got enrichment? Good. A Mity-Vac is very useful for these tests BTW, buy the one that is pressure and vacuum, you can use the gauge to test for boost.

You should have a helper to check boost, put your mity-vac in the boost line from the intake plenum. You should be able to STAND BESIDE THE CAR while your helper gives it some throttle in drive, and see the boost built to ~10.5psi (not sure that is the '92 number, but probably close enough for this test). If you have boost and ALDA function you should have normal power. Always ensure that the filters are clean (air and both fuel), fuel tank problems are a different set of symptoms and tests.

If you are not getting boost, try running a vacuum line directly from the vacuum pump to the wastegate to bypass the emissions and protection circuits. If this restores your power then you need to troubleshoot your wastegate vacuum path, which is a whole set of subjects on this forum (including swapping to a direct/pressure actuated wastegate option). Good luck with that one, it's a project. Searches might include "vacuum wastegate" or ??

If this is all normal and shift points are still too low, check and adjust the Bowden Cable, be sure that it is not broken or binding, and ensure that the vacuum line to the transmission is also connected.

It is not common that the control pressure (modulator setting) is too high (unless it has been messed with), and causing hard shifts. More likely is that the transmission is shifting for the amount of power that it is expecting for the pedal position, but the power isn't there.

muleears · #3 05-09-2016, 09:55 AM

Jeff,
Thanks for the great and instant response. I will follow your directions and post back with the results. Glad you told me to do the ALDA first, I would have thought the Bowden cable, but I'll be the first to admit I'm no pro at these!

Maxbumpo · #4 05-09-2016, 09:58 AM

Sorry Jeff, I think you've got it backwards. All the symptoms (upshift timing, engine sluggishness, harsh shifting) _could_ be caused by the bowden cable. Upshift timing can _only_ be caused by the bowden cable adjustment.

I'd start there and fix the bowden cable adjustment (just slack or maybe a little tight at the engine idle position), see why symptoms still remain, and then progress through all the steps you wrote out.

vstech · #5 05-09-2016, 11:50 AM

rapid upshifting is most often the bowden cable broken or unhooked in the tranny...

however, HARSH shifts are common with plugged ALDA... so, are you getting BOTH symptoms? odd....

muleears · #6 05-09-2016, 02:32 PM

I adjusted the bowden and ALDA on my '87 124 but that had the 603. This has the 602, correct? Other than missing a cylinder whats the difference between the two? Again, I'm assuming here..... It has a 722.X?? transmission?

Maxbumpo · #7 05-09-2016, 03:39 PM

The waste-gate on your turbo is vacuum controlled vice pressure. Are the injectors the upgraded "inclined" or oblique version? I'm not sure on that one.

muleears · #8 05-09-2016, 04:02 PM

Quote:

Originally Posted by Maxbumpo

The waste-gate on your turbo is vacuum controlled vice pressure. Are the injectors the upgraded "inclined" or oblique version? I'm not sure on that one.

You got me there! I have no idea and wouldn't know how to tell the difference.

It seems to nail a little bit so I wouldn't be surprised if they were the original injectors, if that helps.

I'll take it for a drive and try to shift manually and see what I can make happen.

muleears · #9 05-09-2016, 07:57 PM

Here's some pics of what I've got:

The first shows the bowden cable unhooked from its linkage. When at idle and with no tension on the bowden they rest in the same place. In the pic I just popped it off and it stayed the same length. There is tension on the bowden when you pull on it so it is still connected inside the trans. This is proper adjustment for the Bowden, correct?

Second and fourth pics show the sliding linkage that connects to the CC and throttle linkage. It seems to be able to slide a fair distance without any change in throttle setting. The two pics show it at each end of its throw.

Third pic is just a shot of all the linkage, Bowden cable to the right of the pic and CC servo on the left.

Sorry for the orientation, for some reason the software here rotated them 90*...

As always any input is appreciated.

muleears · #10 05-15-2016, 12:09 AM

Well I finally got the chance to do a little work on the car. First I checked out the bowden, it appeared to be attached to something in the transmission and also appeared to be properly adjusted. Next I looked over the wastegate and everything seemed to be in order there. I have no idea what injectors are installed so I was at a loss on that front. Testing so far had provided little improvement. Finally today I removed the ALDA and opened it up one and a sixteenth turns. It was still sealed prior to my adjustment. This made a significant difference. It actually accelerates now when you step on the pedal, and will stay in a lower gear much longer. I have only driven it a small amount. Testing has to be done in the dark of night due to lack of proper documentation...

. I suspect I'm getting some smoke now which I did not before. I will verify in the daylight tomorrow. So far a successful modification, and I know the other items are in order too. Thank you gentlemen for the direction. I, and my son, thank you. Don't sit back yet though! Tomorrow we're doing pads and rotors on the front! Should be straightforward but with most of my projects it never is!

vstech · #11 05-15-2016, 06:46 AM

If you have a pull a part nearby, 94 and up 124 rotors and calipers AR a big upgrade...

muleears · #12 05-15-2016, 12:24 PM

Quote:

Originally Posted by vstech

If you have a pull a part nearby, 94 and up 124 rotors and calipers AR a big upgrade...

Are they just a bolt on replacement or will I need other parts as well? I do have a couple pic N pulls within an hour of me.

vstech · #13 05-15-2016, 01:22 PM

Should be a direct drop on. Same same.

92 has the deeper wheels that clear I think.

babymog · #14 05-15-2016, 03:27 PM

The '92 (through '93) sedan and wagon still have the 15hole wheels, I don't think that they clear.

You will most likely need new lower control arms, new heat shields, and new wheels to clear the new calipers on your '92.

muleears · #15 05-15-2016, 07:07 PM

Quote:

Originally Posted by babymog

The '92 (through '93) sedan and wagon still have the 15hole wheels, I don't think that they clear.

You will most likely need new lower control arms, new heat shields, and new wheels to clear the new calipers on your '92.

Thanks for the info. I just put new rotors and pads on it today. I guess I'll stick with them at least till they wear out.