'85 300D Slow tranny engagement
 

When shifting from neutral to drive (or reverse), engagement takes about 3 or 4 seconds...there is also no sound at all it is so soft. If I push the throttle down early, there will be a clunk to remind me I did not wait. the car drives ok, but the shifts feel softer than I'd like....after doing a search, it sounds like the symptoms match those with a broken tranny pressure regulator valve spring which Sonnax is selling....anybody have a similar problem? I also have an '84 300TD which works fine, and is where I'm getting my comparison.

Thanks

Awhile back, I test drove a 300SD that had this same problem, yet the tranny seemed good otherwise. I didn't buy it, but mostly for other reasons. That car had about 325K on it.

I rebuild GM 700R4's etc. as a hobby, but have not been into a MB 722.3/4 yet. But there are many similarities in operation.

If it is the pressure reg. valve, I think that would lower the line pressure and therefore cause slippage in all gears. Excessive clutch/band slippage = a short trans. life.

Transmissions have lip seals on the various apply pistons that get worn and stiff from age/heat. I suspect that fluid drainback/leakage is causing the delayed engagement. Some fluid leaks out, while not under pressure, and it takes a moment for the pump to fill the circuit/drum back up and build pressure to apply the friction element.

The "bad" news: I think a rebuild would be required to cure this.

The good news: I've heard/read that these trannys can work for a long time like this.

Perhaps an experienced builder of this specific transmission will post .

Thanks Brad,

Here is the link describing the spring. It seems to fit my symptoms, but I don't know anyone who has actually put one in.

http://www.transmissionspecialty.com/parts/parts/68942-01.htm

There seems to be excessive softness or slippage for all shifts,
as well as the engagement delay...but there are probably a few defects in the tranny that will cause both.

I drive the car carefully (with a light foot) because I know slippage means wear! It has about 200K miles on it. I changed the fluid and filter last year..did not see a lot of residue in the pan.

D

I have a similar problem but it only seems to do it in the morning with the car cold. Fortunately I have no slippage so I'm not worrying about it.

ds,

I read the sonnax info. sheet and your further description of soft shifts/slippage leads me to agree that this may be the problem.
I use a lot of Sonnax parts...great problem solvers.

I would recommend you try replacing the spring before you burn out the tranny. Spring seems to be replaceable without removing the valve body, and if VB removal is needed, it's not that bad...just messy laying on your back with fluid dripping on you.

You should also have a set of VB gaskets on hand and an ATSG manual to help keep track of any check balls, etc. , just in case the VB needs to come off. If you can do the fluid, you should be able to do this. If you need parts source info., let me know, I can get it or link you up.

I guess I'll give it a try. Do you have a source for the tranny manual? I've been looking for a while.

Thanks for the help,

D

D,

ATSG manuals - You could try Trans. Exchange Co. at 800-776-1191. Wholesalers that sell to tranny shops often have them also...Transtar, Dacco, etc. Should be about $15.00.

My 87 300D has slow engagement between neutral and drive too (about 1-2 seconds) and occasionally I have a slip if I don't wait long enough. Other than that the transmission behaves perfectly. Could it still be the spring?

DieselAddict,

Next time you are due for a fluid/filter change you could try to get the spring out to check it. It would be a good time to check the torque of the VB bolts also.

It would seem that you are getting some "bleed down" somewhere in the drive circuit, but 1-2 seconds doesn't seem too bad to me. I don't think you should be too concerned unless the interval gets longer , the shifts get overly soft or serious slippage occurs regularly...these last two are "tranny killers".

Wondering what the outcome was of the spring change?

I recently moved to an area where the temp is dropping into the mid 20's and now notice that it is taking 4 to 5 seconds for the trans to engage any gear. No slip, shifts fine, just slow to get into gear. Not saying it is the weather, quite possibly a coincidence.

Any help is appreciated.

Don

I got the Sonnax spring, and found it did not work with this tranny.
Sonnax has it wrong...their spring goes with a different tranny. I ended up disassembling the valve body and cleaning it. I still have a lag, but it is slightly improved.

Thanks for the reply....

Other than the delay...Should I expect the transmission to continue to function?.... or is it the beginning of the end?

I know that a lot of factors come into play...just trying to figure out if my wife can continue to drive it without my undue worry. About once or twice a month she takes it to visit family (about 300 miles each way).

If I had the funds (I don't at the moment) I would have it rebuilt or put in a factory unit. That being the case, my other option is to park it until the money is available.

Thanks again.
Don

Don,
Good to see you back. Hope you enjoy the new location. Missed you here in SoCal.

Bruce

Mine is slow to reverse, three seconds, 2-3 flares cold, 3-4 shifts, ah, not right. Anyway, it's worn out, those seals someone mentioned earlier. And I've put 40K miles on it, not babied, in the last year. Buy your wife a AAA card or something and a cell phone and drive it till it drops.

It's been quite a while since we have spoken. We moved to a small town near Yosemite National Park about 4 months ago, for a number of reasons and so far enjoying the change. Hope all is well with you and your MB.

Regards
Don