stuck in third gear

[Benz Dr.]

 OK, I have this really nice '68 280SL here. We found that the torque converter was leaking around the rivets so we changed it to the newer style. Then we found that the converter would drain after sitting so we pulled the trans again and replaced the pump. The car wouldn't move from engine start for about 20 seconds until the convertor filled back up! No leaks now, pulls like a freight train right from cold, so it's ready to go home.........not quite yet.

Although the trans had problems before all of this fiddling around it always shifted perfectly. Now it won't shift into high gear. I think it will one time from cold but after that it stays in third gear. I found a wire off last week and put it back on, figured I had it sorted out, didn't get a chance to drive the car again until today and it's doing it again.

I'm not really hearing the kick down linkage clicking like I think it should. It' moving, but not with a lot of force. Modulator linkage is moving freely and not tight.  Trans is up shifting but kick down is not working and I don't want to rev it that high. I had it up to 4,500 > RPM and it still wouldn't shift.

Anyone have a pic of the wiring harness on the trans? Something tells me that's where the problem is.  

[hkollan]

Hi,

Did you check the fuse for the transmission?
I had this on a 6.3 once, checked the kicked down switch, wiring etc.  before finally getting the bright idea to check the
fuse for the Auto trans.
Replaced the blown fuse, and car shifted into 4th again.

Hans

[ja17]

Hi Dan,

See if this is what you need.

[Benz Dr.]

Thanks guys. I'll look at it tomorrow.

[Benz Dr.]

Well, I looked at the wiring and it's not that simple. While some of the wiring colors are the same as shown in the diagram, some are completely different.
 My question is: which terminal should be live? I currently have the large and medium live as well as the teminal on the pressure switch. Something tells me this may not be right. I have no kick down function. I will pull the plug off of the switch tomorrow and see if I have power at the junction.

 

[drmb]

With the wiring disconnected from the solenoid the gearbox should move off in 2nd gear and change normally through to 4th at normal shift speeds,if so then the wiring when connected is the problem.
The pullback idle position only decreases the modulating pressure on the over run to prevent bumpy downshifts, and the fully forward position increases modulator pressure which in turn increases the
working pressure and activates kickdown or maximum speed upshifts. If your gearbox moves off in 1st gear when the wiring is connected the solenoid will be in kickdown mode.

[Benz Dr.]

Trans starts in second gear. I'm also reading where there can be internal problems with the trans. I hope it isn't any of those things.

I will try disconnecting the wires going to the trans and see what happens.

[Pawel66]

Your issue looks indeed similar to what I was facing. I mean I hope I was facing, I hope it is the past...
I am hearing in my case it was internal problem with oil pump after the converter broke open.
My car is being collected from the tranny shop Monday. I will write if I manage to find out more details of what was the issue in my case.

In my car the transmission indeed looked like it was stuck at 3rd gear, but then it did change the gear on a very high revolutions and in a very rough way.

[Benz Dr.]

Yes, I read where it will shift at 65 MPH into high gear which would put your RPM near red line. No thanks on that. Engine only has 300 miles on it.
We did change the pump and it sure could be an internal problem.

[Pawel66]

Aa a follow up: I have managed to resolve my gearbox problem (high pressure, late abrupt shifts, felt like stuck on 3rd gear until high revs, starting from 1st gear, could not bring pressure down). I returned the gearbox to the shop (guarantee). They said they fixed something with the pump, but not provided details. 

We put the tranny back into the car. We then managed to fine-tune the gear shifts so it is ok now.

Not very informative, I am afraid...

[Benz Dr.]

I messed around with the wires going to the kick down solenoid and now it works perfectly. One extra wire caused all of the problems so I left it unhooked.

[Pawel66]

Well, I have to confess: I also found one wire hanging there unhooked...

[Benz Dr.]

Maybe we should come up with a name for this mystery wire.