Transmission flares on upshift from 2nd to 3rd gear - PeachParts Mercedes-Benz Forum

Diesel Dan · #1 03-16-2011, 02:47 AM

Anyone have ideas of why the tranny on my '87 300D would flare only during the upshift between 2nd and 3rd gear? I hope it's an inexpensive fix because it wasn't that long ago I had the tranny rebuilt.

kerry · #2 03-16-2011, 10:09 AM

Too much vacuum is the typical cause. Put a mity vac in line with the vacuum line from the VCV and modulator and see what vacuum levels you get at various accelerator positions. A simple test would also be to remove the vacuum line going to the modulator. The shifts shuold become stiff or harsh with no vacuum to the modulator.

Biodiesel300TD · #3 03-16-2011, 11:22 AM

When is the last time you changed the fluid and filter? That is always a good place to start with trans issues. Also a bottle of Trans-X can help when you refill the system. It will clean the varnish off any parts that have build-up and can help the situation too.

I'm not too familiar with the 124's, but shouldn't too much vac cause all shift points to flare? I would suggest the K2 spring. I has a pretty good flare in the trans on my 123 wagon, which I cured with a new K2 spring kit.

sjh · #4 03-16-2011, 02:05 PM

Having flaring or the opposite (hard shifts) in one transition (2 - 3) but not another is pretty common. People often go to kits to change components in the transmission.

At various times while trying to get my w124 transmission to function correctly I have encountered this. I considered getting a shift kit but kept on trying to get everything right with the transmission.

Now my transmission shifts incredibly well. I've never driven a 300D that shifts as smoothly.

The steps are straight-forward:

1. Vacuum must be right. Remove all extraneous components, replace bad tubing/connectors, clean out your over-pressure relay & then mity-vac everything. Make sure your VCV is set-up correctly. Make sure your vacuum amplifier (blur flying saucer) is set-up correctly.

2. Transmission pressure must be correct and vacuum modulator for the transmission must be correct.

3. All linkages must be set correctly. With light throttle pressure you can easily be in 3rd by ~23 MPH and 4th by ~30 MPH.

babymog · #5 03-16-2011, 03:38 PM

The K2 spring kit is a common problem/solution, and I believe it is around $15 dealer, easy to change with the pan off.

Don't let it continue, it will wear out the friction material.

Diesel Dan · #6 03-16-2011, 09:30 PM

Thanks for the replies everyone. As it turns out I'm going to need to get this fixed quickly and will not have time to mess around with it myself, so will take it to the shop. I'll print out your suggestions and leave them with the mechanic - maybe it'll give him ideas that will save time and save me money!

The shift from 2nd to 3rd was always a little funky even right after the rebuild (the previous mechanic will not be touching my transmission again), so I'm hoping it's just a simple mechanical adjustment. I've been driving very carefully and trying to avoid the flare. If I am accellerating lightly it is less likely to flare than if I'm accellerating normally or heavily. In some situations it's impossible to avoid, like having to accellerate up a hill from a dead stop. That's the worst.

I'll try to remember to bring closure to this post after the car is fixed and let you all know what the problem turned out to be.

Thanks again!

Dan

tangofox007 · #7 03-16-2011, 09:41 PM

Quote:

Originally Posted by Diesel Dan

I'm going to need to get this fixed quickly and will not have time to mess around with it myself, so will take it to the shop.

If your other shifts are okay, a new K2 spring assembly will most likely solve your problem. If you suggest that to the shop and they don't know what you are talking about, you are at the wrong shop.

JamesDean · #8 03-16-2011, 10:30 PM

You can also check out this spring kit. It contains the K1 as well as others. It also gives you the options of stiffening/softening the shifts as well by using different k factor springs.

http://www.superior-transmission.com/Product_Page.cfm?ID=19

I have one to put in my one 300SD, it has 2-3, and 3-4 flaring without vacuum.

Diesel Dan · #9 03-21-2011, 04:09 PM

As promised, I'm checking back to report on the resolution to the tranny problem. Turns out it was a vacuum leak at the transmission. I just spoke with the garage on the phone and they said something about a "vacuum cap" I think? They also made a few adjustments. One thing I didn't mention earlier (because I hadn't noticed it) is that there was also a slight flare between 3 and 4. I noticed this on my way to the garage. They said the car is shifting "much better" now, but the 3-4 flare still occurs periodically, and was "unfortunately something inside the transmission".

Say what?! They seemed to leave it that I should just drive the car until the 3-4 shift gets worse. Hmmm...

I think I'll try a different mechanic if the 3-4 shift gets bad enough to really bother me. I'll mention the "K722A-D Shift Correction Package" and see what their reaction is. Unfortunately, the better garages seem to all have these customer relations guys who aren't really mechanics, and say things like "I don't know what you're talking about, but I'm sure the mechanic knows about it..."

C'mon man, I'm paying nearly $100 an hour, I want my 10 minutes with the main man, just like at the doctor's office!

leathermang · #10 03-21-2011, 04:42 PM

Did you try the Trans-X ?

Cr from Texas · #11 03-21-2011, 05:09 PM

Quote:

Originally Posted by Diesel Dan

As promised, I'm checking back to report on the resolution to the tranny problem. Turns out it was a vacuum leak at the transmission. I just spoke with the garage on the phone and they said something about a "vacuum cap" I think? They also made a few adjustments. One thing I didn't mention earlier (because I hadn't noticed it) is that there was also a slight flare between 3 and 4. I noticed this on my way to the garage. They said the car is shifting "much better" now, but the 3-4 flare still occurs periodically, and was "unfortunately something inside the transmission".

Say what?! They seemed to leave it that I should just drive the car until the 3-4 shift gets worse. Hmmm...

I think I'll try a different mechanic if the 3-4 shift gets bad enough to really bother me. I'll mention the "K722A-D Shift Correction Package" and see what their reaction is. Unfortunately, the better garages seem to all have these customer relations guys who aren't really mechanics, and say things like "I don't know what you're talking about, but I'm sure the mechanic knows about it..."

C'mon man, I'm paying nearly $100 an hour, I want my 10 minutes with the main man, just like at the doctor's office!

Needs to be fixed, but I've lived with a 3-4 flare for a while. Around town, I drive in S. If I get above 40, I let of the pedal and manually shift to 4th - no flare.

tangofox007 · #12 03-21-2011, 05:12 PM

Quote:

Originally Posted by Diesel Dan

Turns out it was a vacuum leak at the transmission.

A vacuum leak and flaring is an unusual combination. There has to be more to the story.

Biodiesel300TD · #13 03-21-2011, 05:56 PM

Quote:

Originally Posted by tangofox007

A vacuum leak and flaring is an unusual combination. There has to be more to the story.

I agree. Leaks cause hard shifting. Too much vac causes flares.

Diesel Dan · #14 03-21-2011, 09:39 PM

Quote:

Originally Posted by leathermang

Did you try the Trans-X ?

I haven't had time to try anything myself, and I might consider the Trans-X, but it just seems unlikely to me that the transmission is in need of internal cleaning, since it probably has less than 5,000 miles on the rebuild. Would it really get gummed up that fast? The guy at the garage said they couldn't see anything that would be causing the flare, so they attribute it to an "internal" problem. One thing for sure, I have no faith in the guy that did the rebuild. Took him 3 tries to get it even close to "right". I had to cut my losses with him and move on.

leathermang · #15 03-21-2011, 10:49 PM

Quote:

Originally Posted by Diesel Dan

I haven't had time to try anything myself, and I might consider the Trans-X, but it just seems unlikely to me that the transmission is in need of internal cleaning, since it probably has less than 5,000 miles on the rebuild. Would it really get gummed up that fast? The guy at the garage said they couldn't see anything that would be causing the flare, so they attribute it to an "internal" problem. One thing for sure, I have no faith in the guy that did the rebuild. Took him 3 tries to get it even close to "right". I had to cut my losses with him and move on.

'Gummed up' is a loaded visual to me... the physics which might cause the varnish to build up in those tiny holes in which those tiny BB sized balls are used as gravity activated valves to channel the hydraulics has to do with oxidation rate.. which can be affected by things like the fluid level being too high or too low.. or high temperature... for instance.... over a certain temperature the addition of like 20 degrees F of the trans fluid HALVES the useful life.. thus something like rocking the trans from drive to reverse to get out of a hole has the potential for causing an immediate need to renew the fluid...
I suggested it because any varnish buildup has the potential for messing up the shifting since the speed of the clamping of the clutches in the trans are controlled by hydraulic pressure... so ' flaring' which I assume to be slipping can be the result of slow application of the transmission clutches..
Trans-X simply dissolves varnish... it is not some magic snake oil.... and it has saved me some big money on several cars since I first used it in 1975.
IT is relatively cheap to try it... if it does not fix it then it is a no harm no foul situation and you move on to check other potential causes....