R129 Transmission issues

[atlantimd]

Hi I have an Sl320 with 120k and good service history from MB dealers. The car is parked up a lot and used about 3 months a year. Last summer I noticed that driving slow the car would change to second but if left freewheeling engine Revs would not engage to move car unless given a good bit of acceleration then the car would lunge froward.
Second issue is when car is warmed up “ Cat up to temperature “ It goes over 4000rpm before changing from 3rd to 4th and then the charge from 4th to 5th is about 1 second later. I have checked fluid level it’s ok fluid is red but no history of a change.
I will be getting ATF flush done in the next few weeks and have got a filter and pilot bush.

Does this sound like a cable adjustment issue or vacuum ( it’s a 5 speed box) or valve issue.
I want to get to the bottom of it so car is ready for summer.
Also I am bit confused about getting codes from the ecu looks like my car is in that era between obd1 flash and obd2 reader, mercedes pre priority version.

 

[alexanderfoti]

What year is your 129?

 

[Steve@Avantgarde]

If we go by the ops profile its a 96 model so it will have 5 speed electronic box so no cables or vacuum control.

Have to say, it sounds like something is losing hydraulic pressure inside the tranny itself. If we assume the level is ok as he says it is, the only thing that causes a slip and lurch would be something like a K2 or K3 clutch pack failure.

I'd be draining the fluid and inspecting what debris there is!

 

[alexanderfoti]

Can't see it on mobile. Doh.

Would agree

 

[Blobcat]

Can't see it on mobile. Doh.

Would agree

Turn your phone to landscape

 

[alexanderfoti]

La de da! I have been enabling desktop mode this whole time.

 

[AndySlade]

Turn your phone to landscape

Here endeth the first lesson

 

[atlantimd]

Hi all thanks for the reply. Yes it is a 1996 model 5 speed. It does have cable back to transmission and also seems to have the green and purple vacuum pipes running back to transmission. I have atf and filter change planned with pilot bush.
I must say the thought of a k2 or K3 clutch pack failure is scarier than I envisioned.
I will report back my findings once I get it drained

Cheers

 

[LostKiwi]

1996 means it could be either the 722.5 (if it's a 1995 spec car registered in 1995) or 722.6 (if it's a 1996 spec car). If you post the VIN number we can confirm which it is though from your description it sounds like the 722.5 version which is largely hydraulic control.

This is the clutch/band operation diagram.


From this it looks like control of the K2 clutch and band B2 is the issue. Possibly check control valve (Y3/1y2). Do you any issues with Reverse?

 

[LostKiwi]

Found a thread about this problem. Pretty much as you describe.

Gearshift problem on 722.5 (5.speed)

My current problem applies to a 1993, E280 with M104 engine and 722.5, 5speed auto box. Auto box is misbehaving - Missing the 4. gear 1. Starts fine, up changes quite smoothly and at correct speeds. 2. At the 3 to 4 up-change point, it engages 4th for about half a second then changes to...

forums.mercedesclub.org.uk

 

[atlantimd]

1996 means it could be either the 722.5 (if it's a 1995 spec car registered in 1995) or 722.6 (if it's a 1996 spec car). If you post the VIN number we can confirm which it is though from your description it sounds like the 722.5 version which is largely hydraulic control.

This is the clutch/band operation diagram.
View attachment 84131

From this it looks like control of the K2 clutch and band B2 is the issue. Possibly check control valve (Y3/1y2). Do you any issues with Reverse?

Hi thanks for reply

Vin: WDB1290632F133489
I thought I had checked the fluid last summer and was ok? Obviously not!!
The car has done little mileage since then. Now today level is below hot band on dip stick at over 80C. I think the fluid also looks burnt I have attached pictures just for feedback.
It will be getting changed anyway but could this be the issue?

 

[LostKiwi]

Ok. Confirmed as 722.5 gearbox.
Here's the build sheet.

 

[LostKiwi]

Given you're taking the gearbox sump pan off to change oil and filter you may as well remove and check the Y3/1Y2 solenoid while you're at it. It mounts into the side of the valve body.

That oil doesn't look bad - does it smell like it's burnt?

 

[atlantimd]

Given you're taking the gearbox sump pan off to change oil and filter you may as well remove and check the Y3/1Y2 solenoid while you're at it. It mounts into the side of the valve body.

That oil doesn't look bad - does it smell like it's burnt? View attachment 84135

No oil does not smell burnt. I will do as you suggest great info on that car and Y3/1Y2. I am going away working for a few weeks but I will get it on a lift and tackle it. Car has 120k and was looked after loads of History but unfortunately I haven’t used it much just keep fluids changed and other bit that fail. Lol
When I was looking to purchase a R129 I deliberately avoided 1995 because of biodegradable wording harness but looks like mine is MY 1995 . At least Maybe I can use flash code reader anyway.

 

[LostKiwi]

Yes a flash reader will work with the gearbox.
The wiring harness issue isn't too bad - I had to do mine (1993). Sileck in Kent will do a repair for not too much money. Yours being a 6 cylinder is less likely to be affected. Heat is the killer and the V8 is very hot around the top of the engine. I had to do both main harness and throttle body. Easy to remove and refit. I used the fact it hadn't been done to beat the price down.