Transmission disengages between 1st and 2nd

[northern piper]

thanks Serge. I just added the proper fluid and took it for a quick drive. It drives ok but for just a second between 1st and 2nd the rpm jumps ever so slightly. This is the first time it happened so I'm going to keep an eye on it. It hasn't had a fluid/filter change in about 30,000 km so I think I should do that. Is a 2nd gear piston clutch crack common? Does it really mean we're soon to need a new trans?

[serge_saati]

No, actually cracked piston clutches are usually a problem of older Windstar (1995) because they were built in aluminium. They were redesigned for 1996+.

In newer Windstar, the most common causes are:
-worn trans oil pump shafts which is caused by poorly designed pump shaft bearing
-Cracked or Broken Transmission Case which is caused by the final drive differential which has a weak ring gear and causes a lot of trans fluid to leak out
-worn boost valves for main line pressure and torque converter clutch application

In your case, the most probable cause is worn main line pressure boost valve. This valve controls pressure within the main transmisson hydraulic circuits, so all gear shifts can be adversely affected. The valve piston is cylindrically shaped and is designed to fit snugly within an aluminum sleeve. Because the pressure valve is fairly short relative to its height, its leading and trailing edges tend to wear out the sleeve. The height to length ratio, known as aspect ratio, has a directly proportional impact on the rate of wear between the valve plunger and the sleeve. Assuming the height remains constant, the shorter the valve, the faster it wears out.

When you shift from 1 to 2, there's a lot more of engine breaking than when you shift from 2 to 3 and even more than 3 to 4. So when you shift from 1 to 2, the engine breaking require to the 2nd gear piston clutch a lot of force to engage which require more hydraulic pressure. If the valve of pressure line is worn, the pressure will not be enough, and pressure will drop when piston clutches is trying to engage so it will disengage, the pressure will increase cause the draw will be reduced and the gear will re-engage and so on...

[serge_saati]

When you shift from 1 to 2, there's a lot more of engine breaking than when you shift from 2 to 3 and even more than 3 to 4. So when you shift from 1 to 2, the engine breaking require to the 2nd gear piston clutch a lot of force to engage which require more hydraulic pressure. If the valve of pressure line is worn, the pressure will not be enough, and pressure will drop when piston clutches is trying to engage so it will disengage, the pressure will increase cause the draw will be reduced and the gear will re-engage and so on...

Unless if you press a lot of gas (at the moment where the gear is being shifted) to give more rpm to the engine, it'll be much easier for the piston clutch to push the clutch bands to grab the gear because there will be no more engine breaking if the rpm is high and you will have more rotary speed, more inertia moment. The remaining obstacle will be the heavy weight of the vehicle that will still require some pressure to activate the piston clutch. Which is not very important in 2nd gear.
Try that, press more gas and see if it still fall into neutral for 1 second or not.

[northern piper]

Hi Serge

thanks for the info. I left the van inside last night to warm it all up. I topped up the trans fluid. My wife is driving it today so I'll get the report from her... : /

I hope it was a fluid issue as it was down a bit and with the short drives, very cold days I'm really crossing my fingers that things are ok. I'll let everyone know.

IF it is the piston you refer to, I'm guessing that this isn't a do it yourself repair? I do have a 2 post hoist but have never done any ATS work.

[12Ounce]

A number of weird things can happen. I once had my Winny tranny operate only in 1st and reverse ... all of a sudden... while on a trip of a few hundred miles. I limped home, staying out of traffic, ... took the shift boost pistons out, and found a circlip had broken on one. Lucky find! I almost missed it.

[northern piper]

can you elaborate on the shift piston repair job 12ounce? I'm just trying to figure out my next steps. I plan on replacing fluid and filter this weekend so when the fluid's out is when I'd like to do work..if it's something I can tackle myself

[12Ounce]

The two servos are on the rear of the tranny ... the fluid does not have to out to service. Both servos have caps held in place by three screws. If you remerely remove the three screws ... spring loaded stuff will pop out and get lost. The original screws are just not long enough.

Remove one screw from each cap. Find longer screws, by an inch or so, with the same threads ... or longer screws/studs along with nuts. The idea is to provide a way to safely back the caps off ... without losing control.

One of the servos is a bit high up on the tranny ... lowering the subframe a bit might help. Inspecting the pistons and replacing the O-rings and seals ... reassembling ... a good days work.

[northern piper]

I'm betting we're talking about what's pictured in the following 2 diagrams right?
42155554.gif

42155553.gif

where did you get parts?

[serge_saati]

You can buy the parts from ATSG: https://www.atsg.us/atsg/

And from Sonnax: http://www.sonnax.com/quick-search

[northern piper]

so my wife reports that there's still the higher revs for 1/2 second as the trans switches from 1 to 2. I spoke to my ford service advisor today about replacing the 2 servo o-rings and gaskets. He doesn't feel that will have any effect at taking care of the apparent slip.

Can someone confirm this for me? I'll do the job if it'll help but don't want to if it won't. Serge, you spoke about the main line pressure boost valve.

Is this the same component? I'm kinda confused here...
Need some help here guys!

[serge_saati]

Originally Posted by northern piper

I spoke to my ford service advisor today about replacing the 2 servo o-rings and gaskets. He doesn't feel that will have any effect at taking care of the apparent slip.

Serge, you spoke about the main line pressure boost valve.

Is this the same component? I'm kinda confused here...
Need some help here guys!

No they're two different things. Don't confuse the main line pressure boost valve piston and the servo.

The first one is used only to regulate the trans fluid pressure into the main transmission hydraulic line of the valve body. The second one are used to actuate pressure to cylinder clutch to lock the clutches bands together to engage the gears.

[northern piper]

ok, so then what is the best route to take here? Replace the gaskets on the 2 servo piston clutches?

If so, and I know I'm asking a lot here, but what parts off the diagram would be needed? My parts guy at Ford while helpful isn't knowledgeable and will order what I ask for. He isn't offering ANY advice on which parts. I don't want to pull the whole thing apart and not have what I need, nor do I want to buy stuff I really don't.

Any help here really appreciated!

[12Ounce]

Since I had a Ford dealer nearby, I was able to remove the servo pistons first and then decide. But if you get all the soft parts for the two servos, to the right in your upper diagram, you should be OK.

[serge_saati]

Change also the main regulator boost valve along with its aluminium sleeve. They are inside the rear of the valve body. Or replace the entire valve body.
The boost valve is n°20 and is located in bore n° 37 of the valve body in the following pics.

main regulator boost valve.png

Valve body.png

The aluminium sleeve is located at right of the boost valve (n° 20).
The 3 springs you have to re install are located at left of the boost valve (n° 20).
The main regulator spring retainer is located at left of the 3 springs.

Fix also the fluid leak issue.

[serge_saati]

Figure 43 is actually my first pic showing the main regulator boost valve with its springs.
The main regulator spring retainer is located at left of the 3 springs.