Transmission Quandry - PeachParts Mercedes-Benz Forum

mbboy · #1 01-18-2011, 01:26 PM

The 722.3 transmission on my 1981 380sl with app. 200k miles on it is starting to slip in reverse, and my research indicates that the slipping is due to a worn B3 clutch pack that has no external adjustment.

However, a local transmission specialist, who seems to know quite a bit about these trannies, suggested that he might be able to remove or significantly delay the problem by adjusting the "reverse servo," which can be accessed externally.

My question is "can reverse on the 722.3 be adjusted this way," and if not which of the following would be my best option:

1) Have him or another specialist rebuild my B3 clutch and inspect the rest of the unit for app. $750 including parts and a 6 month warranty; or

2) Replace the existing tranny with a used one with app. 100k miles on it from a local salvage yard for $400 + $350 for a specialist to install it. Although this used tranny would have a 90 day warranty, if it ends up being defective, I would have to pay another $350 to have it removed and replaced with God knows what.

Of course, the best thing to do would be to have the whole unit rebuilt for app. $1650, but the cost of doing that is prohibitive at this point.

Thanks very much in advance for your, usual, well-informed opinions.

Steve

loepke72 · #2 01-18-2011, 08:23 PM

There is no external B3 adjustment on the 722.3 transmission. The problem is normally a clutch pack where the friction material has flaked off for some reason. Also the reverse piston may have a crack in it and/or the piston seals have gone bad. Best thing of course is a full rebuild, but the B3 clutch can be taken care of by itself. The transmission has to come out for that.

The used transmission most likely will have a B3 clutch that's questionable, so that's a roll of the dice.

I think the transmission your guy is referring to are the 722.0/722.1 units which use a band for reverse that's at the front of the unit with an externally accessible adjustment. The 722.3 uses a multiple disc clutch instead of a band to do the same thing.

mbdoc · #3 01-19-2011, 08:15 AM

Stay away from that trans shop..no external adjustments on LB3.

ps2cho · #4 01-19-2011, 11:12 AM

Stick with your current transmission and just do the b3 bands. Go to another shop as mb doc said. No adjustments. The transmission must be removed.

A used transmission is a major gamble. One that in the long run may cost you more.

More info here:
http://www.w124-zone.com/articles.php?article_id=21

rs899 · #5 01-19-2011, 12:16 PM

What ps2cho said-

The B3 bands are really not that far in once you get the transmission wrestled to the ground. Problem is, at 200K you are about due for the rest of the clutch packs to be redone... although its really not all that hard to do the whole enchilada.

Rick

mbboy · #6 01-20-2011, 08:08 AM

After considering the amount of work doing the job myself would require, I opted to have the local transmission shop remove the tranny, and replace the B3 clutch pack and seals, along with anything else that needs replacing, in the hope that I'll be able to get another 150-200k miles out of it.

Although he evidently made a mistake about the possibility of adjusting the B3 on 722.3 externally with earlier versions, I still feel confident that he knows what he's doing, and his price -- $750 for r & r'ing the B3, and no more than $1350 for a complete rebuild, if necessary -- was very reasonable.

Of course, you never know what problems may arise, but the fact that his shop is local and has been in business for 20+ years without any BBB complaints gives me a sense of security that he'll stand behind his work for a reasonable period of time -- which is all one can really ask for in these cases.

However, thanks very much for the very helpful responses, as it helped me make a far, more informed decision than I could have made.

ps2cho · #7 01-20-2011, 01:29 PM

Make SURE he reseals the front pump. You do not want to have to pull it again if it starts dumping fluid everywhere.

B3 bands + reseal front pump is sufficient to keep you going. You can also opt to use higher quality transmission fluid since he will be completely draining it.

I highly recommend Redline Synthetic D4. It is the best fluid for the 722.3...hands down. I don't recommend synthetic for these older engines, but this fluid for the transmission is king

mbboy · #8 01-25-2011, 04:40 PM

Well, I just test drove my car after having the entire transmission rebuilt, and the problem I brought it in for is still there; namely, when I put the shifter into reverse when the car is hot, I can feel and hear the transmission whirring for a few seconds afterward. However, when the car is cold, there is no whirring, and the transmission goes into reverse as quickly and firmly as it goes into drive whether the car is hot or cold.

Now, the people that rebuilt the transmission are telling me that the whirring in reverse is normal, even though they told me that the car was indeed slipping in reverse when they test drove it. Am I wrong in believing that the whirring is not normal, and should be characterized as "slipping in reverse?"

In any event, I've owned this car for over ten years now, and I believe that the whirring, which only began a few months ago, was getting progressively worse -- which is why I brought the car in the first place.

Moreover, a number of threads in this forum revealed, or at least strongly suggested, that the problem was caused by worn B3 clutches. Yet, the rebuilder told me that he replaced those clutches, and that the old plates still had about 40% left on them -- in which case the problem, if it really exists, could be caused by a worn bearing in the planetary gear(?), which he didn't replace.

So, I'm left with trying to decide whether the whirring I brought it in for was in fact normal and was always there, but that I never noticed it; or whether some part of the transmission was indeed going.

In addition, I'm left with the problem of trying to decide what to do if the rebuilder -- who, at least, agreed to keep the car and look further into my complaint -- insists that the whirring is normal.

Thanks very much in advance for any additional advice anybody can give me on the best way to solve this problem.

#9 01-25-2011, 05:31 PM

Rule #1 You never take a mercedes benz transmission problem to a transmission shop, that doesn't totally specialized in mercedes benz transmissions. If you do you are going to loose every time. An honest transmission shop will turn the work away, because of the different intricacies of the transmission. A mercedes shop has all the equipment to hot test them, and there good before going back. The post that said bypass that transmission shop was giving the strait truth on the issue. Don't ask me how I know!

ps2cho · #10 01-25-2011, 09:42 PM

What Rebe said....

Whirring is not normal.

Also, why didn't you mention whirring in the initial post? All you said was reverse slippage. Our diagnosis was correct based on what you gave us.

mbboy · #11 01-26-2011, 07:57 AM

Quote:

Originally Posted by Rebe

Rule #1 You never take a mercedes benz transmission problem to a transmission shop, that doesn't totally specialized in mercedes benz transmissions. If you do you are going to loose every time. An honest transmission shop will turn the work away, because of the different intricacies of the transmission. A mercedes shop has all the equipment to hot test them, and there good before going back. The post that said bypass that transmission shop was giving the strait truth on the issue. Don't ask me how I know!

I don't know of any transmission shop in the Philadelphia/S. Jersey area that specializes in MB transmission, and all the shops I questioned said that they were familiar with them. Do shops that specialize in MB transmissions really exist, and if so, where?

I allowed this shop to rebuild it, because the guy who runs the shop assured me that he had rebuilt a large number of MB transmissions over the 20+ yrs he's been in business, and the guy who actually did the bench work convinced me that he was very familiar the 722.
In addition, the owner had test driven my car, and agreed that it was slipping in reverse, and the price he gave me for rebuilding it was so much better than anybody else's.

Quote:

Originally Posted by ps2cho

What Rebe said....

Whirring is not normal.

Thank you. I didn't think so.

Quote:

Originally Posted by ps2cho

Also, why didn't you mention whirring in the initial post? All you said was reverse slippage. Our diagnosis was correct based on what you gave us.

I said the transmission was slipping, because I believed that was the best way to characterize its failure to access reverse, and the whirring sounded like the whirring someone else explicitly mentioned and called slipping in this thread:

1992 500E - difficult to get reverse when hot

Moreover, since a number of other people had reported problems with reverse, but not other gears, in their with 722's, I concluded that I was having a similar problem.

So, now that you guys know that it's whirring when I put it in reverse when it's hot, but not when its cold or when I put it in D, N, or P, does anybody have any idea what it could be -- considering that the transmission was just rebuilt, and all the clutches were changed?

Your help would be greatly appreciated, as my car is still in the shop, and I'd like to have some idea as to what could be going on.

dpetryk · #12 01-26-2011, 07:15 PM

Did he replace the hidden O rings at the base of the clutch baskets? If you don't do that, the leakage will not allow the clutches to fully engage. To replace the O rings you have to drill out several rivets to get to the O ring. You then have to tap the rivet holes and put in a flat head screw. Ask him if he did that.

loepke72 · #13 01-26-2011, 10:05 PM

Quote:

Did he replace the hidden O rings at the base of the clutch baskets? If you don't do that, the leakage will not allow the clutches to fully engage. To replace the O rings you have to drill out several rivets to get to the O ring. You then have to tap the rivet holes and put in a flat head screw. Ask him if he did that.

Those O-rings are for clutches K1 and K2; they won't affect reverse at all.
Not all overhaul kits come with the K1 and K2 repair kits with the screws and O-rings. Really not sure what the OP is hearing in his transmission without seeing it for myself. Is it something that slows down as the transmission engages?

mbboy · #14 01-27-2011, 06:22 AM

Quote:

Originally Posted by loepke72

Those O-rings are for clutches K1 and K2; they won't affect reverse at all.
Not all overhaul kits come with the K1 and K2 repair kits with the screws and O-rings. Really not sure what the OP is hearing in his transmission without seeing it for myself. Is it something that slows down as the transmission engages?

The whirring occurs when I put the shifter into reverse when the car is hot, and it's more tactile than audible, though I can hear it. It's gone once the transmission engages, and as I mentioned, it never happens when the car is cold, or in D, N, or P.

So, my guess is it has something to do with heat lowering the viscosity of the transmission fluid, which is now Redline, or expanding something, making it difficult for the transmission to access reverse (?).

Thanks very much for the continued concern. It's greatly appreciated.

rs899 · #15 01-27-2011, 06:36 AM

Isn't there a seal around and in the middle of part #14 in this diagram?

http://www.jie.com/Mercedes/w4a020Sch1.htm

Anyway, there is a seal somewhere in front of the B3 clutches that actuates them- I have forgotten what works them, but I would guess that they didn't replace it and it's leaking when the fluid is hot and thin.