722.6 Sprag - PeachParts Mercedes-Benz Forum

Roncallo · #1 10-17-2008, 09:50 PM

In diagnosing the transmission noise I found that my 722.6, from a 1996 SL600, would make a clunking noise on start up and then under initial acceleration. Going under the car with a person starting it up on top I could definitely hear and feel the clunk was from internal in the transmission in the rear area. Considering that before this clunk started a week ago I did hear a very periodic once every 2 seconds rattle from the rear area, and that rattle is now gone the clunk is now present, I concluded rear sprag

My theory that the noise was coming from the rear F2 sprag. The sprag was engaging harshly on startup in park and slipping under load during initial acceleration. I felt that although the sprag has no real load during the start in park it will be capable of spinning and suddenly grabbing just from the clutch windage loads alone. During initial acceleration it slips and grabs.

I did a search on this sight and did come up with 3 threads indicating the early 722.6 had sprag failures.

In any case I'm going to pull the trans before any further driving. I have several questions.

1) Does this sound like a reasonably accurate diagnosis. I do have a 147 code.

2) I understand sprags and planetary bearings are week points. Are there updated parts for these.

3) Is it likely the sprag caused secondary damage to other nearby hard parts.

4) The VB is the original 1996 11/95 production date. This is the first VB and there have been several updates to both the VB and conductor plate. using a 1998+ VB will require a new computer. I am considering leaving this stuff as if can always be replaced later if need be. Is this risky???

Anything else I should know before going in.

whipplem104 · #2 10-18-2008, 02:31 PM

The sprag normaly does not do any damage as it is pretty contained.
You should still be able to get just the sprag but it will have more rollers on it.
The valve body is probably not an issue. The spring that breaks is easily repl.
All the updates where for shift quality. If you wanted to run a newer valve body you can. Just keep the large nag valve body in. They will all work.
The control unit updates were simply for matching the modifications in the valve body for shift quality. At the dealer I have done many combinations of repl. valve bodies and control units. There simply might be some harsh shifts at certain parameters. Which MB never actually perfected it before discontinuing it.
If you do end up getting a new trans in the future get the newest unit you can get your hands on no matter what it came out of as long as it was a v8 v12 etc. Swap the bellhousing and go.

Roncallo · #3 10-19-2008, 07:42 PM

Thanks Whipplem104

So far Iv'e gotten down to the major sub assemblies I've inspected both sprags they both look good and work fine on the bench. No surprise there, I still think the sprag is slipping, but no macroscopic signs of degradation.

So as far as overhaul kits are concerned I'm interested in recommendations. My ATSG manual references several upgraded seals. If I get the genuine MB seal kit will it have all the latest upgraded seals or will I have to order them additionally. There is also a front input shaft that ASTG insists I upgrade $400. Considering I do have this transmission apart, is this an important upgrade. Also what do you generally do about frictions I'm almost tempted to leave them as MB sells these 1 at a time or is there a recommended aftermarket kit.

I've attached my current parts list and some pictures.

Your thoughts and comments are welcome. This will be my first MB trans overhaul.

Benztech · #4 10-22-2008, 05:18 PM

Hi John: Your right about the input shaft update! quite expensive the reason is the early units only had a bushing between the input shaft and output shafts and after 100k they wipe out and the rear of the unit looses lube causing torrington bearings to fall into planet sets distroying the unit.The newer versions have a needle cage type.You can get the original bushing seperate for About 20 bucks! and replace those torrington bearings.Thats what I did on my 97 S500.
Good luck Tim

whipplem104 · #5 10-22-2008, 06:03 PM

I do a lot of rebuilds and so far not to many have needed new clutches unless there has been a seal blown and thats why I took it apart.
As far as reseal kits all the kits I have gotten are MB factory kits and have the new seals in them.
There is an alternative if you are going for frictions and that is IPT. They are building a super tough tranny for merc. and chrysler on this platform. They also sell a banner kit and valve bodies. Prices are about the same as mercedes but the clutches are kevlar and like the previous post said you can get new bearings and should. The one way was updated to have more rollers. Twice as many if I remember. The ones that I have seen fail recently look normal also but do not hold? It is hard to know what the right choice is though on rebuilds. They cost a lot and you can go get one already rebuilt with a warrenty for less than 2500. Not MB of course. To check the clutch packs it is pretty hard to do per the book without a lot of special tools. But if you get the specs you can just press down on the packs and check. This is a good indication of your clutch material.
As far as even doing the seals, you will need the special tool to take the pistons apart. Check out SG Motorsports. He is a buddy of mine and sells MB
shop tools from an aftermarket supplier. Good prices. j
I am getting to the point of just buying newer transmissions from the junkyard or off craigslist. I just priced out a 722.6 from a 97 e420 for 950.00
I can buy late model stuff for 1200 for small nag. and 15---1750 for large nag. That way you get all the updates and a good transmission.
Shout back if you have more questions.

Roncallo · #6 10-23-2008, 08:03 PM

Quote:

Originally Posted by Benztech

Hi John: Your right about the input shaft update! quite expensive the reason is the early units only had a bushing between the input shaft and output shafts and after 100k they wipe out and the rear of the unit looses lube causing torrington bearings to fall into planet sets distroying the unit.The newer versions have a needle cage type.You can get the original bushing seperate for About 20 bucks! and replace those torrington bearings.Thats what I did on my 97 S500.
Good luck Tim

For $20.00 I could be on the road for 100,000 miles in a car that really wont be driven too much. But when driven will be DRIVEN. That's going to be a tough decision.

Thank you for contributing to the fountain of knowledge.

Roncallo · #7 10-23-2008, 08:13 PM

Quote:

Originally Posted by whipplem104

I do a lot of rebuilds and so far not to many have needed new clutches unless there has been a seal blown and thats why I took it apart.
As far as reseal kits all the kits I have gotten are MB factory kits and have the new seals in them.
There is an alternative if you are going for frictions and that is IPT. They are building a super tough tranny for merc. and chrysler on this platform. They also sell a banner kit and valve bodies. Prices are about the same as mercedes but the clutches are kevlar and like the previous post said you can get new bearings and should. The one way was updated to have more rollers. Twice as many if I remember. The ones that I have seen fail recently look normal also but do not hold? It is hard to know what the right choice is though on rebuilds. They cost a lot and you can go get one already rebuilt with a warrenty for less than 2500. Not MB of course. To check the clutch packs it is pretty hard to do per the book without a lot of special tools. But if you get the specs you can just press down on the packs and check. This is a good indication of your clutch material.
As far as even doing the seals, you will need the special tool to take the pistons apart. Check out SG Motorsports. He is a buddy of mine and sells MB
shop tools from an aftermarket supplier. Good prices. j
I am getting to the point of just buying newer transmissions from the junkyard or off craigslist. I just priced out a 722.6 from a 97 e420 for 950.00
I can buy late model stuff for 1200 for small nag. and 15---1750 for large nag. That way you get all the updates and a good transmission.
Shout back if you have more questions.

Right now I'm leaning towards the build as originally planed, new sprags and input shaft. Things may change as I delve deeper into the sub assemblies. I see no reason to go with the high performance clutches for the moment as the engine will remain stock at least for the moment. I also expect to be experimenting with the PCS controller but let me walk first.

Thanks for contributing to the fountain of knowledge. I hope to contribute my self by posting pictures of the build as I progress.

Roncallo · #8 10-26-2008, 07:32 PM

In looking for the mysterious clunking noise I originally heard which made me take this trans out to begin with so far I have come up empty, with one remote exception. It turns out that the 2 sprags installed in this box are the updated 20 segment sprags. This car has an 11/28/95 delivery date with serial number 00010765 trans. Therefore I can only assume that the sprags have been replaced. What I did find was that one of the bolts holding in the rear piston assy was hand tight. For that reason alone it was worth removing the box and doing the disassembly, but I cant conclusively say that was causing the noise. I did order all new set of sprags and the front input shaft as well as everything else. The only real problem is I'm left with the feeling I did not find the real problem yet. It wont be the first trans I put back together with my fingers crossed, but at about $800.00 will be the most expensive.