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Old 11-18-2012, 06:20 AM
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700R4 troubles

Hello everyone!

I will keep this short. I have a 1990 K1500 4x4. The 700R4 lost 3rd-4th randomly one day. I pulled the transmission and ordered an ATSG manual along with a rebuild kit from TransTec.

My conclusion was the the 3-4 clutches were toast along with the input drum piston seal (common problem I hear). I made use of all the information floating about the internet.

Now here is the problem:
After the rebuild I installed the transmission and got a similar problem that I started with.

Rev: Very Strong
1st: Very Strong
2nd: Very Strong
3rd: Won't Shift Into
4th: Won't Shift Into

I have adjusted the TV cable with no luck. When I place the gear selector into "OD" I get no response from the transmission (like it's still in Neutral). When I shift to "D" it will engage.

During the test drive it will shift from 1-2 no problem but when it comes time for 3rd gear to engage the transmission does nothing but hold 2nd gear. If i let off the throttle it will engine brake (like it was in "2" at high RPM's).

I am looking for any and every possible problem. So far my list of things to check are:

Servo - bad 3/4 seals (although all new), possibly assembled wrong?
Pump - has something in it for the 3-4 shift
3-4 Accumulator - This seemed fine during reassembly
Input Drum & Pump Seals - I ended up using the scarf cut seals.
Input Drum - I did air test the piston, seemed fine. I did have some confusion with all the steels since all the plates feel out of order during disassembly. Clearances measured out in the end.
Sprag/Low & Reverse Roller - Pretty sure that I got these installed correctly (the Low & Reverse Roller for sure).
Valve Body: Didn't check every item on it. I am sure the check balls are installed in the right locations.

Any and all help is appreciated by this veteran! Cheers!

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Last edited by 90K1500; 11-18-2012 at 06:26 AM.
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Old 11-19-2012, 03:45 PM
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I am a novice when it comes to transmissions. I have my own 700R4 torn down right now and have a question posted here concerning some performance mods I'm considering. Having said that, one thing I can think of that might cause your trouble would be a stuck 2-3 shift valve train. This is a valve set in the valve body and it may have debri stuck in it from the 3-4 clutch failure. There could also be a check ball out of place I suppose. The 2nd clutch and 3rd clutch check balls are the two close together, about the center of the separator plate. These are just slightly educated guesses.
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Old 11-20-2012, 04:39 AM
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Thanks for the suggestions. I am hoping that it is the Input Assembly Sprag that is causing all of these problems. I may have taken it apart and put it together backwards. Should have an answer in a day or two!
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Old 11-20-2012, 08:58 AM
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Lol. It's funny you mention the forward sprag. I had mine apart for cleaning and had to go back and check it later to be sure I had it right. That would cause problems wouldn't it. But wouldn't that cause no 1st gear? Im not sure. Hopefully someone with more knowledge will chime in here.
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Old 11-20-2012, 10:50 AM
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Quote:
Originally Posted by ASE Doc View Post
Lol. It's funny you mention the forward sprag. I had mine apart for cleaning and had to go back and check it later to be sure I had it right. That would cause problems wouldn't it. But wouldn't that cause no 1st gear? Im not sure. Hopefully someone with more knowledge will chime in here.

As far as I understand, no it will not cause a no 1st issue since it is tucked away between the forward and 3-4 clutches. I am assuming that the sprag is free-wheeling in the direction that it should be locked to make forward movement. This could also be the reason that I can not get any 3rd gear action in the "D" gear selector position (not overdrive). The transmission gets from 1-2 no problem but holds 2nd no matter what I try and "OD" just acts like neutral.

Basically it is acting like the opposite of what it should.
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Old 11-21-2012, 10:52 AM
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Quote:
Originally Posted by 90K1500 View Post
As far as I understand, no it will not cause a no 1st issue since it is tucked away between the forward and 3-4 clutches. I am assuming that the sprag is free-wheeling in the direction that it should be locked to make forward movement. This could also be the reason that I can not get any 3rd gear action in the "D" gear selector position (not overdrive). The transmission gets from 1-2 no problem but holds 2nd no matter what I try and "OD" just acts like neutral.

Basically it is acting like the opposite of what it should.
Forward sprag in backwards will provide no movement in OD... shift to "D" will apply over run clutch, vehicle will then move from a full stop

Clean the v-body. DO not remove all valves at once. Do not flip over the aluminum sleeves , watch how they come out and where pins install. Some folks re-install incorrectly.

ALL shift valves must move fully for the trans to operate - shift correctly
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Old 11-22-2012, 09:06 AM
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Good News! The sprag was the problem. Now I have another problem. First the transmission was shifting just fine, then it wouldnlt leave first. Then after a couple WOT runs it finally went into 2nd, then repeated the prcoess for 3rd and OD. I have a feeling that the TV cable and/or the small amount of engine assembly lube I used to retain the balls in the valve body while assembling have something to do with this. My last resort is going to be a bad valve body.
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Old 11-23-2012, 01:42 PM
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I have always used transmission assembly lube and ATF for assembly. Trans jel as the assembly lube is also known is a thick, tacky grease that works great for sticking thrust washers in place so that they don't drop out of place during assembly. I understand that petroleum jelly also works well for this. The thing that would concern me about using any other material is how quickly that material dissolves in ATF. I would think that you need to use a product that dissolves almost instantly. Otherwise, you will have globs of the material clogging orifices and sticking valves.
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Old 11-23-2012, 06:35 PM
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Somehow it is all working now! All good, for now! Thanks everyone
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Old 11-26-2012, 11:48 AM
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Whatever was sticking must have broken loose. That's always good. One product I have had great luck with that helps keep things lubed up and prevents sticky valves is Lubeguard Red. Others may chime in on this but Ive used it in every GM transmission Ive ever had apart. I even used it to unstick the 1-2 valvetrain on a 700R4 that was having trouble shifting out of first. You may want to add a bottle to your fluid.
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