Hi everyone,

I'm currently experiencing an issue with my S-type that I hope you can help me with.

While driving in "Drive" the shifts start slipping. The first, second, all of them. Everytime it needs to shift they slip. Specially when the car needs to shift quickly. Almost impossible to drive the car.

However if I select the gear shifter to "4", the car runs smoothly and I don't have any issue. All the gears work as expected.

I've already changed the transmission fluid, but the problem is still there.
Of course the quickest explanation from the mechanic is "new gear box". Should I assume that or is there anything I could check?

Thanks a lot for help and availability

 

All 4 does is to tell the car not to use higher gears than 4 (there's only 5 on your car). (It would actually use 5 or rev limit if needs be, not sure which but it's not relevant here.)

So something odd is happening - maybe the cable is loose/stretched or ... well, see if anyone else has ideas.

 

Did the gearbox 'slip' prior to changing the fluid? If not, check that the fluid level is correct before going any further.

Is the vehicle a 3.0 or 4.0 litre?

The gearbox is a Ford 5R55N and has several issues that can lead to failure. One is wear in the piston bores for the servo units. If the bores are worn, the pistons cannot apply enough pressure to tighten the bands, or can cause the bands to break.

 

This is a good observation. I'm not very well versed on the innards of an automatic transmission, but I think this is a good sign. This would seem to indicate more of a control problem telling what internal bits to operate at specific times, versus a mechanical problem such as worn clutch packs, etc.

As previously mentioned, when shifting back and forth between D and 4, the cable doesn't move. There's just a microswitch in the shift lever assembly, sending a signal to the control module. When you put the shift lever in 4, apparently the logic changes for shifting through the lower gears. Something is taken out of the equation and the transmission behaves itself. What exactly that is, I can't tell you, but you're on the right track.

Working from potentially faulty memory, I could have sworn the 5R55N transmission is billed as a 5-speed, but it's really just a 4-speed and "5th" gear is when the torque converter clutch is electrically locked. If I'm out in left field, expect somebody to quickly jump in and point out the error of my ways. But IF I'm correct (a big IF), maybe you can use this info to help isolate the fault.

Not that I'd know how to interpret it, but does the behavior change when Sport mode is selected?

Do you have any fault codes present? For most of them, the check engine light will be illuminated.

Re: Your mechanic who wants to replace the transmission. Have you taken the car to a transmission specialist? Since the transmission behaves in 4, I suspect the problem isn't too difficult for a specialist to diagnose. I highly doubt you have to replace the entire transmission.

 

I think that's wrong as Ford 5R55N transmission shows 5th is a gear with a different ratio.

The tranny is controlled by the PCM so I expect it monitors that microswitch - maybe shown in the elec guide?

 

I neglected to ask in post 3 above if there are any DTCs stored. If so, please post them here.

Just in case anyone is bored with nothing else to do, here is a link to everything you ever wanted to know about the 5R55N gearbox, but were afraid to ask:

https://www.dropbox.com/s/gez4sqw92v...arbox.pdf?dl=0

 

Forgot to mention: Don’t let your mechanic convince you this is some rare, exotic transmission. It’s a variant of a very, very common Ford transmission, of which there are several bazillion on the road. Any competent specialist will be very familiar with this family of transmissions.

 

Hi everyone.

Firstly I would like to thank you all for all the replies and suggestions. I wasn't expecting such a helpful forum.

About the issue. It continues the same.
I'm just adding some specifications that you asked.

It's a 3.0
No error codes
The transission fluid was changed 2 months ago. It was the first thing I tried to see if I could fix it.

Shall I replace the gear selector before any other step? or it's way more probable to be the transmission.

It's so strange. In "4" or any other gear works perfectly. In "D" all caos breaks lose.

Thanks a lot.

 

You could do some checks in the area(s) mentioned already.

 

What condition was the fluid in when you drained it?

The most common failure of the 5R55N is loss of pressure to apply the intermediate and overdrive bands, which causes them to burn up contaminating the fluid.

As Karl mentioned, this gearbox is used in other vehicles and is well known by any competent specialist.