lost reverse

[chazoz]

first off awesome forum, I've had my 6.5 for a while and have been a lurker, and finally decided to join up. well heres what I have. 1992 3500 2wd. today on the way home I went to back in my drive way, and then drove forward to get the newspaper from the box. went to back up again and all of the sudden no reverse....none at all. you can put it in reverse, and there is no sign of engaging, no rpm change no lunge no nothing. I'm not really familiar with this trans, but I'd imagine if reverse was getting ready to go there would be some sign right?? like slipping or delayed engagement? the fluid is red not burnt, no sludge in the pan, and I have every gear, but reverse. as far as i know If I have 1st I should have reverse right?? is there any electronic controls that would do this?? any ideas?? thanks in advance

chuck

[Sasquatch]

I would guess you have a TH700R4. Do you know if the filter had been changed recently? Maybe before you’re bought the truck. You could have some trash blocking the fluid passage.

[Sundance]

I recommend a trany flush and filter change. It may
not work, but at $100 or so it's worth a shot. My
'96 I had developed slipping...... did the trany flush
and problem solved and ran like a top until I sold it
over 50K later.

[grancito]

Check the oil pressure in reverse, there is a plug half way up the side of the trans, drivers side near the bell housing. minimum pressure at 1000 rpm in reverse 632, or 742 psi depending on the model. Reverse uses two clutches, 1st and reverse clutches together, the reverse one may have damage. There are a lot of causes of no reverse.

[ZiGBlazer]

I had your problem in January and did a bunch of looking. I found out a good way to check it and what the probable problem is. Mine ended up being the reverse band, so I am still working on getting the reman trans in, almost done. The only problem is which transmission you have, as far as I've seen the 1-tons only used the TH400 and 4L80. The TH400 is a 3-spd no overdrive, the 4L80 is a 4-spd with overdrive, almost the same trans with an extra overdrive at the rear. I can help you if you have a 4L80.

Checking is easy. As long as you can take a short drive without backing up.
- First check fluid level - very important and often over looked.
- Next drive and see if you have engine braking in ******* gear.
- if it has no engine braking (down shifting doesn't slow vehicle) then the rear band is not working.
- if it has engine braking it should be missing or have a weak 3rd gear, then it is the direct clutch that has gone.

The causes are the simple low fluid pressure (not so likely, will still feel engagement), low fluid (starves rear passages first), clogged passages (will be most like low pressure. These could be possibly fixed by a fluid flush.

If the rear band isn't working here are the likely causes in order of likelyness.
1. Broken band
2. Broken band anchor pin
3. Broken actuator piston
4. Broken actuator piston rod.

The piston is not that bad, can be checked and replaced by removing the pan and then the piston.

If it is the band or pin then you will have to remove and disassemble the transmission completely as it is at the rear. It is called the rear band and is a common problem for the diesels (too much torque on engagement). There are a whole bunch of stronger rear bands available.

If the direct clutch isn't working then the trans will have to come out and be taken apart.

If you don't have the 4L80 then let me know and I can try to find how they work.

I purchased a beefed up 4L80 from a company in Florida with all the strength components upgraded. It cost me $1800 with shipping and core charge of $300, I just kept the old trans because it would take me too long to get it back to them, plus cost me about $200 to ship it back. That way I can fix it and sell it when the weather is warmer, I get a cleaner place to rebuild it, and get my wrist problems fixed so I can.

You also might try a subscription to All Data at www.alldatadiy.com, it is fairly cheap for a 3 year subscription, a second vehicle is a bit more. They have almost any information you need for whatever vehicle you are working on. It is the single user version of what a lot of independent shops use for all their information.

[grancito]

I checked the year, it should have the 700R4, if it is a TH400, most of the parts are the same as the 4L80E but no electronics.

[Sasquatch]

If it is a 700R4 find a different trany. Or by one that is beefed up from B&M. Those things shouldn’t even be behind a 6 cylinder.

[grancito]

GM made upgrades for the 700R4, so the later trucks should have them. I had my 82 Chev 700R4 upgraded in 1993 and it has done 180,000 miles on it and still going.