Hello,

This my first ever post and I hoping someone can help. I'm going to include as much detail as I've got, so I apologize if this is a bit long.

I have a 1989 Aerostar 3.0 L, RWD with an A4LD transmission. This transmission has been replace/rebuilt at least once. It has had major service two other times. The last with in the past 18 months. The last service included new seals and replacement of several defective hard parts. It was performed by a transmission technician at a local dealership after I removed and tore down the transmission.

Currently, the van is on jacks. The transmission will not engage any forward gear properly (might creep forward at extremely high RPM's, but that's all). Reverse seems to work reasonably well, but is not completely consistent.

I did notice that the fluid level was too high and probably had been that way since the last service (12 - 18 months). I adjusted the fluid to the correct level, but no change. Before I did that, I took control pressure measurements at various RPMs:

Park Idle: 0 PSI
Park 1500+ RPM: 50 - 100 PSI, but jumps around
All other drive ranges were like this.

After I adjusted the levels and saw no change in performance. I did not recheck pressure readings.

I tore down the valve body and thoroughly cleaned it. There was a small amount of debris on the screen to one solenoids. Also, a couple of check ***** were missing (according to the ATSG manual).

Most of the valves came out and were installed without any problems. A few required real ingenuity to reseat. All valves except the Intermediate Server Accumulator Valve (Bore 216) moved easily. Bore 216 was a bit sticky and very hard to reassemble. There was no sign of any damage to any of the value body parts.

I checked the resistance on the two solenoids and it appears to be correct. I attempted to test them by attaching them to a 12 V supply and I can hear a small click (barely perceptible), but I can't see anything that says they're obviously working or not.


I reassembled the valve body (changing the transmission filter), making sure every part was absolutely clean. I cleaned the transmission pan. I cleaned the transmission cooler lines using a commercial product intended for that purpose. I reassembled and added new fluid to the proper level.

No change in performance.

Also, I have tested the vacuum modulator and it appears to be working. Put it under 18 in. Hg of vacuum and it held it. Vacuum (engine side) responds correct to changes in RPM (i.e., it drops under higher RPM).

I took new pressure readings as follows:

Park - Idle (800 RPM) - Varies from 0 to 50 PSI for no apparent reason.
Park - 1500+ RPM - Climbs to 100, but drops back to 0 sometimes. Sometimes it may stay at 50 PSI.

Neutral - Idle - Initially at 0, but may rise to 50 and stay there.

Reverse - Idle - Initially at 75, but rear wheels only turn sometimes. Pressure will also drop to zero suddenly.
Reverse - 1500+ RPM to WOT - Pressue will rise to between 100 - 200 PSI at 4000 RPM. However, pressure jumps around (even at relatively stable RPM) and the transmission seems to "miss" at points, causing pressure to drop suddenly.

All other drive ranges are similar to above, with little or no turning of drive wheels.

I removed the transmission from the vehical and have removed the bell housing and oversrive assembly. Here's what I found:

- No obvious leaks from torque converter to bell housing.
- No obvious damage to any parts. I carefully inspected all shafts, splines, gears, and surfaces. Only minimal wear apparent.
- Pump appears to be good. No damage to either internal gear.
- All seals appear to be good.
- The only thing that was even remotely worrisome as a small sliver of metal that lay just in front of the overdrive's sun gear. It is possible that this was airborne or some other external contaminant.

Bands on overdrive look okay, but I'm no expert, so I may not be viewing them correctly.

With the pump appearing to be sound and the pressure varying for no reason, my only thought is that it's the torque converter. What I can't understand is why Reverse would work as the converter only turns one way.

Here's a summary:

- No forward engagement.
- Reverse usually works.
- Pressure tests (with vehical on jackstands) show widely varying, inconsistent pressure.
- Valve body has been cleaned, but not 100% sure if a problem is there.
- Solenoids, based on resistance, appear okay.
- No apparent damage to any parts from overdrive assembly to torque converter.

I'm not a mechanic, but I think I have every know reference on this transmission including the Ford shop manual, ATSG manual for this model, Haynes Ford transmission manual, and stuff from the web. I don't want to just start replacing parts and am hoping one you far more knowledgeable type can point me in the right direction.

Thanks for reading through this and any help you can give me.

Michael

 

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The converter has small fins that control flow rate, You could be getting just enough for reverse to work.

 

Welcome!


I agree with muffinman, it sounds like your TC is on the way out.

 

Thanks guys. I have also discovered that the overrun sprag clutch is slightly damaged.

Anything I should check in particular (e.g., valve body functions, etc.) A bad TC would certainly explain widely varying control pressures.

Am I correct in assuming that at idle, in Park there should ALWAYS be control pressure of some sort. In other words, if the engine is on, should there be control pressure?

 

Oh year, by the way. Got a good source for the parts I need?

 

Michael:

Since you had the thing torn down already, replace the sprag, the clutches and all the piston seals. If the piston seals leak, the clutches won't engage. The sprag is a known problem so that should always be replaced. The intermediate and overdrive bands should also be replaced, but the reverse band almost never wears out. It's also a good idea to replace the thrust washers.

Transparthouse on Ebay sells the entire kit for about $130, or you can go to www.bulkpart.com. Prices are comparable.

As for the missing *****, I won't worry about those if the van was running before. The valve body has gone through some evolution. As a result, the location and number of ***** also changed around. If you look at the ATSG manual, there are several configurations. You must look for the one that corresponds to your specific year and model.

Good luck

 

copper,

Thanks. Sounds like great advice as it's not trivial to get this thing in and out.

Michael

 

Hey Guys,

One thing (I cringe)... I took the pump off to inspect it (it was perfect). I put it back on in what I believe to be exactly the same spot. From your experience, am I going to have to go out and get this pump alignment tool I've read about (at least $ 100). Is this one of those "you'll be really sorry if you don't..." situations or is there another way to ensure alignment?

Thanks again for the great help! I appreciate having experienced hands "looking over my shoulder". I'm almost getting to the point where I understand this little beast.

Michael

 

After you bought the kit, take the pump off again to help knock the front seal off. It's a whole lot easier to remove and replace the front seal with the pump out of the way, well worth the cost of the pump alignment tool, in my opinion.

The pump alignment tool can be bought from TCS for $59+shipping

http://www.tcsproducts.com/products/...t=5&validate=1

Anyway, there was a lengthy post on the A4LD rebuild, you might want to check it out.

https://www.ford-trucks.com/forums/s...d.php?t=354207

 

Thanks. I'll check it out. Sounds like I need that alignment tool.

Michael