A4LD No 4th gear

[Nuggethead 420]

Have read the forums on this issue and I would be working for a year to do all the things it could be but want some input from the experts.

problems: No 4th gear
No cruise control
Bouncing speedometer

Answer: speed sensor!!

From the forum this is the answer I cam up with and would like some of the experts to chime in.
I am however going to clean the screen and clean out the solinoids to make sure while I am at it.

I have found a speed sensor at autozone...good/bad idea???

Feedback please.

 

[MrShorty]

Sounds logical. Before I went and bought the speed sensor, I might do a few things:

1) pull codes to see if the computer sees a fault. Haven't toyed with the speed sensor codes much, but I suspect that the only faults the computer may see is a full open or a short to ground in the VSS circuit. By itself, not definitive, but it would be interesting to see if the computer can see the fault.
2) might be interesting to hook up a voltmeter/frequency counter to the VSS output, just to see what kind of signal the VSS is sending out. Is the VSS signal erratic like the speedometer (remember that the dash speedometer is cable driven where the computer sees an electric signal from the VSS)? Like I said, haven't played with a VSS really, so I'm only talking in generalities. Don't really have specifics.
3) Might pull the VSS out and inspect the speedometer gear. The problem may be that the speedo gear is stripped/partially stripped and is being driven erratically. In this case, the problem may not be in the VSS itself.

 

[Glacier991]

The speed sensor is involved in all 3 (well involved in that the speedo cable plugs into it) so it is a good guess that when all 3 are absent to look at the speed sensor. It's the thinking man's call. before I dropped the tranny pan to clean the 3/4 shift solenoid, I'd see if a new sensor doesn't bring back 4th gear. Your speedo driven gear could have buggered things up, you should see if the gear looks ok when you remove it.

 

[Nuggethead 420]

Thanks for the input I am going to start with the speed sensor and the connection.
I lind of searched as I tend to do and took all the info for similar but they all point as a whole to the speed sensor. It is an external fix and easily replaced so I will start there.
I am hoping it brings 4th gear back but ready for more if that is what it takes. I have a second valve body that I am rebuilding right now but not quite ready to drop the pan.

You are the two I would have hoped to get input from. I really appreciate the info.
I drive about 70 mile a day just back and forth to work and need 4th running about 16.25 mpg right now but need more. Gotta love the oil companies hey!!!

Thanks I will post after I change the speed sensor.

 

[falls guy]

Lockup torque selenoid?

 

[BrooklynBay]

I once saw an interesting article in Gears magazine about a lady that had an intermittent problem with her speedometer, and her transmission changing gears erratically at highway speeds. She went to several shops, and they told her that it's the VSS. She had it replaced, and it didn't solve the problem. They changed some sensor on the differential which they thought was an additional speed sensor. She later found out that it was only a sensor for ABS, and had nothing to do with the transmission. Finally, somebody from Gears magazine got on the case. They checked the wiring harness inside the steering column to see if there was some sort of problem, because they opened the dashboard and got an intermittent reading on the speedometer gauge, and they finally found their problem! It was some wiring in the tilt column that was pinched every time the column was tilted. This was causing intermittent shorts as she was driving, and affected the speedometer gauge, and the signal going to the computer, which was controlling the shift points. It was in a motor home, but I guess it could happen to other vehicles as well.

 

[Glacier991]

GEARS is always worthy reading.... and many is the time it shows that in computer controlled trannies the problem is NOT in the transmission, but in the inputs to the computer controlling it.

Welcome to the Forum BrooklynBay! You sound like the knd of guy we need more of !!! (anyone who reads GEARS is ok in MY book!)

 

[Nuggethead 420]

No luck so far

All I had time for was the speed sensor and it did nothing.
Goint to try the valve body but I just rebiult it about 6 months ago and remember no screen in the 3-4 shift bore. put in new TC lockup and 3-4 Shift solenoids. This problem is getting very anoying. I put dextron/mercon III in would it be better to run Mercon V instead just for cold weather running?
Any tips on that? If I drop the valve body I will be dumping alot of fluid should I replace it with Mercon V?

 

[Nuggethead 420]

I do not believe I have a antilock break sensor on the 91 I have never noticed one before when I had the breaks or bearings or front end apart?

 

[MrShorty]

'91 only had Rear Anti-lock brakes (RABS), so your only ABS speed sensor is in the rear differential. And it was only used for the RABS system. Cruise control/EEC-IV system use the vehicle speed sensor in the transfer case (4WD)/transmission (2WD).

Since replacing the VSS didn't have any effect on the problem, then I would back up to some of the things I suggested earlier: namely, pull codes and check VSS output. Remember that there are several feet of wire between the VSS and the cruise control computer and EEC-IV computer.

 

[Nuggethead 420]

Going to checker to have the codes read and see what it says.
I am still going to put in the rebuilt valve body when I'm done.
What about the Mercon V question?

 

[Glacier991]

Stick with Mercon III or go to a full synthetic. I do not recommend Mercon V in an A4LD.

 

[Nuggethead 420]

Where in the rear end of a 91 is the sensor located? When I pull it in tonight I want to have an area of focus. I have done the back brakes and do not remember it.

 

[Nuggethead 420]

So the overdrive or 4th gear will not work if the electrical is somehow compromised? whether it be the RABS or th wire to the computer from the speed sensor these would not allow overdrive?

 

[MrShorty]

RABS speed sensor is in the top of the differential housing. There's a toothed gear mounted to the carrier behind the ring that the sensor is monitoring. RABS speed sensor has nothing to do with the EEC-IV system, so it won't effect the computer's decision to shift into 4th gear (or engage the torque converter clutch). I wouldn't spend any time with the RABS speed sensor.

However, there are electrical faults that would prevent 3-4 shift from occuring. As has been noted many times before, 3-4 shift is electronically controlled by the EEC-IV computer. The EEC-IV computer receives several electrical inputs (VSS and TPS are probably the most important inputs for deciding when to command 3-4 shift). Faults in those inputs could cause the computer to not command the shift into 4th gear. Faults in the wiring to the 3-4 shift solenoid can adversely effect the command to shift into 4th gear. Do you have a wiring diagram so you can see how it's wired in? Did your trip to Checker yield any useful information, or did you get all pass codes?

 

[Nuggethead 420]

It is all going south in a hurry. It was about 20 degrees yeasterday in the great state of wisconsin and I started my ex up and let it warm up for about 10 min in the lot at work. Got out to go home and saw about 2 quarts of tranny fluid.
I have recently replaced, Rear main seal on block, front seal on tranny, both servos, pan gasket and have had not a drop drip since then.
I went home and on the way put in 2 fresh quarts. No problems on the way. I put it in the garage cleaned everything up checked all over the tranny........NOTHING!!!
I let it cool down to air temp and resarted it.......Nothing.
Let it sit overnight, started it up this morning to go to work, nothing.
I am very confused.
I did find the speed sensor in the back in the differential in my travels under the ex.
I need help this tranny is killing me and I cannot afford a $1000.00 shop charge the truck is only worth, $1600.00 total.

 

[Nuggethead 420]

I'm Screwed, Need this thing to run and it is now making a loud ticking noise from inside the tranny. I have a baby due in 2 months and need it to run but don't have a lot of cash to take it in and not alot of time to fix. Looking for specific fixes. I thingk I will have to take it to the tranny shop to have them figure out what is wrong with it and try to make something work. I am still leaking in the morning noticed another puddle about 1/2 a quart inder the ex but in work cloths could not get under it to see the leaking area.

What is the purpose of the hose off the transfer case that goes up to a bracket and the end is pluged?

 

[Nuggethead 420]

No computer codes. Must be a hydraulic or internal problem........

 

[MrShorty]

It appears you may have several problems developing all at once. However, just because there are no codes doesn't eman there aren't electrical problems. EEC-IV computers just aren't 100% at detecting all possible faults. The electrical only effects 3-4 shift and TCC lockup, so it won't have anything to do with the intermittent leaks. I would still double check the electrical. I know I have posted more detailed instructions before. Start with a wiring diagram and a voltmeter, then use the output state test to verify that the computer "can" command the 3-4 shift, then a driving test to verify that the computer "chooses" to command the 3-4 shift. Then you will know if the transmission isn't responding to the computer's commands or if the computer isn't telling the transmission what to do.

BTW. As a father of 4 (including 14 mo old twins), congratulations on the pending bundle of joy.

 

[Glacier991]

That hose is the vent tube. designed to let the internal case operate at atmospheric pressure, and overvent boiling fluid rather than build up some case pressure. The end is plugged ?