No Reverse - Foward OK

[Digger_ib]

Hi, Thanks to everyone for a great forum - I have used it a lot but this is my first post.

I have a 91 explorer with the A4LD tranny. The person I got it from had a slipping problem in drive and they dropped the valve body in an attemp to fix it. I was told they found a broken pressure relief valve spring and replaced it with "something close". Afterward it did not have reverse. The truck drove ok on the way home, only 2 miles and I did not notice any slipping issues. In my great wisdom and effort to save a dollar (its my sons truck). I bought a rebuild kit thinking possible broken reverse band or most likely the valve body put back together wrong. Since I had some time, I decided new cluches would be a good thing.

I checked the valve body, replaced the broken pressure relief with the correct type spring from a local shop. I also noticed one hockey puck missing and one of four check balls in an obvious wrong position.

In the Trans, I replaced the cluches and O rings I came across. I did not disassemble the Drum assemblies - possible big mistake - however I did not think this was the problem since the truck drove OK and it had reverse before they messed with it.

Both the Intermediate and O/D servo pistons seemed damaged and I replaced them with new parts. I put everything back together. Added a checkball to the valve body for a total of 5 checkballs, as I thought was correct, and tested the unit.

Everything worked except for reverse. I did some more reading and dropped the valve body again. I decided from what I read that my valve body must have a reverse engagement valve (even though I expected something easier to identify) and thus should only have 4 checkballs as I orginally found, so I made the change, checked the spool at the reverse engagement valve to make sure it was moving freely and put it back together. Still no reverse.

I'm basically an electrican with a set of tools and not enough sense to back away from a problem. Most of the time, I am sucessful. I hate to pull the trans again, especially without a good game plan. However, its not a daily driver and I have some time to get it fixed. Any help with this problem would be greatly appreciated.

 

[BrooklynBay]

Welcome to this forum! Did you check the tip of the low/reverse servo to see if it had a chip? Did you replace the 2 "O" ring seals on that servo? Did you check the rear one way sprag to see if it's only capable of turning one way? What shift kit did you use on the valve body? Did you use a 1/4" drive In/Lb torque wrench on the valve body bolts? Do you have manual 1st gear?

 

[Digger_ib]

The Reverse Servo looked OK and I didn't notice any chips. I did replace the O-Rings. One thing I noticed was that it did not come out on its own, I had to pull it out, is that normal? I did not test the sprag - another mistake on my part. I did not put in a shift kit - everything left stock and used an in-lb torque wrench. When I put the shifter in 1, 2, or Drive the trans works, I assume this is what you were asking.

Thanks.

 

[BrooklynBay]

The O rings hold the servo in position, so this is why it felt stiff to pull out. The old O rings were probably good since it was firm.

 

[Digger_ib]

I guess I'll be pulling the trans back out - I may have been told some bad info - I know the truck drove ok but I'm not positive about the reverse. It may have been working but I'm not sure since we got the truck over a year ago and my son has been driving it in forward only for the whole time (on our land). I thought the slipping problem would be only when its hot which I could not really test since its not legal for the road. Sprag sounds like the most likely problem. Thanks again.

 

[BrooklynBay]

Check the sticky thread called the A4LD rebuild diary for more information before you open the transmission again. Is this a 2WD or a 4WD? A broken shift fork in the transfer case is another possibility.

 

[Digger_ib]

I actually printed the whole rebuild diary before I started this project - great info. The explorer is a 4X4. I also have a 4X2 with a manual that I thought I could swap. But thats not going to happen with the parts that I have. Plus I'm told that I would end up with computer problems. Back to the real issue... A broken shift fork was a great idea, I never thought of that. From what I read, I put the trans in reverse and checked the reverse lights. They worked. I assume this means that the shift fork is in good condition and activating the switch properly.

From what I understand, pressure checks would not help me since the trans works in all forward positions. The rev bands must be in good condition since it works in manual 1 position. Not sure if the valve body could be causing this problem - but I believe it is assembled correctly now.

 

[BrooklynBay]

The reverse lights are controlled by the neutral safety switch, and is not connected to the transfer case.

 

[Digger_ib]

Thats good news - there sure are a lot of people using the rev lights as a test - I am a serious newbee to 4 wheel drive. What would you suggest to check the gear box? Thanks.

 

[BrooklynBay]

You would have to open the transfer case to check the shift fork.

 

[Jack Flash]

the A4LD has a rather large spring that usually pushes the servo out when you remove the 4 bolts. was this spring missing or was it in there ? could be causing your problem.

later trannys (4R55E & 5R55E) don't have this spring and an unknowing mechanic could have left it out.


just a thought.........jjf

 

[Digger_ib]

That was my qustion earlier - I thought that the reverse servo would have came out on its own due to the spring. It has a spring but the o-rings held the servo in place.

I just pulled the transfer case. When I turned it by hand it seemed to work fine in both directions. I did not spilt the case because I don't think this is the problem - but I could easily be wrong.

I ran the trans with the transfer case off - It rotated CCW in forward gears, and CCW in reverse and neutral. I assume without any load on the trans it would continue to rotate, but when I put it in reverse, it should have changed direction.

From this I'm still thinking Sprag or valve body. I don't have either part so it would be cheaper for me to check the Sprag, but a whole lot more work. You can bet that before I pull the trans I will inspect the reverse servo very carefully.

 

[Digger_ib]

I just wanted to post what the problem was in case someone else ever has this problem. The o-ring on the reverse servo had been replaced with a thicker o-ring. When I rebuilt the trans, I replaced it with another o-ring that was too thick. (Strange that the kit had an identical o-ring as the one I pulled out.) When I bench tested the servo, I found the O-ring problem where reverse would not engage. Now reverse works like a charm. I guess hard lessons are the easiest to remember. I learned a lot from this project, thanks for everyones help.

 

[BrooklynBay]

Thanks for the update! If you want to install something a little better than an O ring, Transtec makes a Viton D ring kit which makes a better seal than a standard O ring.