L-EATER

iTrader: (2)

I am having a weird problem with my '80e and I hope someone on here can point me in the direction of where to begin diagnosing. Please bear with me as I try to explain what its doing.....

Around the end of last season I decided to make a couple passes at the track in my truck just to get a baseline for a before and after comparison, knowing I was going to turbo it over the winter. I left it in OD as I always have, and it took off in first gear then when it hit about 15 or 20 MPH it shifted to second and stayed there til like 45 MPH then downshifted back to low where it stayed til the normal shift point of around 62 MPH. Through experimentation I found the following: If I pull it down to manual Drive instead of OD it would perform flawlessly. Also if I floor it from around 12 MPH or higher roll it would downshift to first and stay in first til time to shift.

So all winter I just pulled it down to D if I wanted to take off from a dead start and wind it thru the gears.

I got the front mount turbo up and functioning a couple weeks ago and the tranny has been working fine by pulling it down into D. Tonight on my first pass down the track it shifted to second when it was supposed to, but then almost immediately went on into third. It only stayed in 3rd a very short time then downshifted back to second. The next pass I tried pulling the shifter into manual 2nd as soon as it shifted to second to try and force it to hold second but it still did the immediate 2-3 then back to 2nd thing. I really didn't want to keep beating on it but I decided to try and manual shift it from first to second so I made a pass leaving the line in manual low then shifting to second and it functioned correctly and stayed in second like it should.

Months ago we hooked a scanner to it and everything looked good as far as the electronic part-no codes, nothing weird showing on any of the trans readings. I am thinking it is a VB problem or maybe some kinda cross leak between the VB and the case?

PS this thing has the transgo shift kit and a Precision converter. It has the blue clutches and has been together and working fine for probably 5 or 6 yrs. Anybody have a clue???

jakeshoe

iTrader: (14)

The fact that pulling it down to manual 3rd helps alleviate some problems tells me that is may have an issue with the OD sprag.
Pulling it into 3rd brings on the over-run clutches and takes the load off the sprag.


The oddball shifting issues are most likely caused by a crossleak.
It sounds like you are using the old version of the TransGo HD-2 kit and that version still used the "sandwich plate" and the maze of drilled passages on the backside of the VB.
I think this causes issues when you do it with more than one circuit and you don't have a positively sealed plate to VB.
This is what I've seen.

A solenoid feed hole that is too large (some hack rebuilders think this fixes problems) will also cause similar issues.

L-EATER

iTrader: (2)

Yes, its the old Transgo kit with all the crazy angled holes etc. I forgot to mention that it will act normal until it comes up to operating temp.

I have the pan off right now, just got back from picking up a filter and some fluid. Gonna drop the VB and inspect things then put it back together with some new gaskets and see what happens.,

jakeshoe

iTrader: (14)

A couple of tips..
Flat sand the back of the valve body and the TransGo sandwich plate.

Drill all the passage holes out larger. If it goes through the VB drill it to .156".

If you have a mill you could cut o-ring grooves in the VB and put o-rings between the VB and plate

L-EATER

iTrader: (2)

Ok, I have an update. I pulled the VB and sanded the plate, cleaned everything up really good and buttoned it back up on Saturday (before I saw the tip about sanding the VB and drilling out the holes.

Drove it around for an hour or so to make sure it was fully heated up then tried a full throttle pass with the lever in OD. It shifted perfect 1-2 and 2-3. Did this several times and it worked great so I called it done.

Drove it to work Sunday and was making some HP Tuners logs on the way home, still working on the tune for the turbo, and it did a short shift from 1-2 once. It stayed in 2nd-didnt kick back down to first at 55mph like it used to. Then on another run it "neutraled" in the middle of second gear under full throttle probably around 5000 rpm. It was pulling fine then it just went away and the motor bounced off the rev limiter.

Since then it has been shifting fine if the lever is in drive instead of OD. Normal everyday driving is still perfect. I am about to just get another trans and smash this one with a sledge hammer !!

L-EATER

iTrader: (2)

GRRRRRRR!!!! Today I punched it down from a 30mph roll and it didnt downshift to first. When I floored the pedal it was either in 2nd or 3rd and just stayed there. I slowed down to 20mph and tried it then to about 10 then finally from a dead stop but it wouldnt downshift. So I didnt try anything else right then since I was about 20 miles from home.

Once I got close to home I started putting the lever in different positions to see what it would do. If I put it in OD or manual 3rd it only has one gear (I cant really tell if its 2nd or 3rd) If I put it in 2 or 1 it binds up. From a dead stop in manual 1 or 2 it will roll if you get it heavy throttle but its like the emergency brake is on. It has no reverse at all-if I bring the RPM up to 3000 or so it will act like it wants to move backwards but it doesnt go anywhere. Also the converter wont lock.

I scanned it real quick just now and it has codes 706 (trans range switch) and 756 (2-3 shift solenoid valve) It shows being in gear 1 when in OD or D then as I drove down the neighborhood it showed shifts to 2,3 and 4 but it just stays in whatever it is stuck in. I know limp mode is 2nd and reverse only but I dont have reverse. I am thinking this is something broken,,,,,what do you guys think?

L-EATER

iTrader: (2)

Anybody?

Predator T/A

iTrader: (7)

reverse is a non electronic function I would suspect that there is a problem going on in the direct drum being that reverse is ran off the direct drum and the reverse band. remember the sprag is also on the direct drum and as jake said you may have a sprag issue. hope this helps.

blown99bergerssclone

iTrader: (13)

jake knows his stuff

Predator T/A

iTrader: (7)

^werd

jakeshoe

iTrader: (14)

Thanks guys!

It sounds like lots of different issues going on.
It does sound like it needs to come apart and be rebuilt/repaired.

The OD sprag could be lunched and if so you won't have reverse because it locks in reverse (and 1,2,3) to give forward motion to the forward drum. it overruns in OD to allow the OD planet to overdrive the forward drum.
All the reverse function happens bheind it in the rear planets but if it's damaged or left out on rebuild (don't ask...) you won't have reverse.
You also wouldn't have any forward drive in the OD position, but you would in manual 3rd, 2nd, and low.


I would rip it out and go through it. If you have any questions post them up, I'll try to help out.

L-EATER

iTrader: (2)

Thanks guys. I started pulling it after work today. Should have it on the bench by this time tomorrow eve. I am going to replace the valve body and start with the new style Transgo shift kit since the consensus seems to be the old style like I have is troublesome. I am hoping the damage isnt too bad but my default luck says otherwise.....

On a positive note this gives me the chance to get my converter restalled !!

jakeshoe

iTrader: (14)

You don't need the TransGo kit if you are doing a rebuild.
Re-use your TransGo boost valve and PR spring, HD intermediate snap ring if it's there, and get a stock VB.

You can do all the mods you need internally and save the $.

Now would be an excellent time to install a trans-brake

L-EATER

iTrader: (2)

Well, I pulled it apart last night but I was pressed for time so I didn't get a chance to really look things over yet. The forward and direct clutches look brand new but 2nd gear is toast. The front band is cracked and looks smoked. The intermediate piston looks "bent up" and like its been rubbing on something. There are some bushings and thrust washers ate up down there too. The main shaft is worn down a LOT in the area where it passes thru the center support bushing-looks like someone reduced the diameter of it by at least 1/8" using a hand grinder lol.

All in all there is more carnage than I expected. I am considering getting another complete tranny and starting overe.....

Predator T/A

iTrader: (7)

kinda sounds like the endplay was too tight

L-EATER

iTrader: (2)

The overrun clutches are fine also. The rear planetary gears are locked up and stripped of some teeth and the sun gear is missing some teeth too. The thrust washer between the output shaft and the case looks good but the output shaft itself looks like it has been rubbing on something (inbound of the outer edge where the snap ring holds it in) I didnt put it back in the case by itself but to see what it could be rubbing on but I dont see how it could since the thrust is ok?

Any more theories?

jakeshoe

iTrader: (14)

Sounds like a loss of lube flow.

Is this an early unit with both lines up front or later center lube?

I see this more frequently on the "improved" center lube units as odd as it seems, and if it is the center lube style, if it has the wrong rear fitting, it's a gauranteed failure.

You probably are best to start with another core.

L-EATER

iTrader: (2)

Yes this is the later style-I think it came out of an '01 truck. The rear fitting is the one that came with the trans when I got it.

I have been trying to recall my long term memory and I think I bought this tranny at a salvage yard back in like 2003 and it was supposed to have about 30,000 miles on it. I put the transgo in it and put it in my '02 truck. When I broke the input shaft I pulled it out and went completely thru it and put it in my '94 truck at that time...probably in 2005. It has worked great until last yr when it started doing the weird shifting stuff.

I have found a '97 core....is there any problem with using the internals from the 97 in my 01 case? I haven't laid eyes on the 97 yet but I believe it is supposed to be the center lube style.

L-EATER

iTrader: (2)

I have the '97 trans stripped down and most parts cleaned and ready to be reassembled. I am waiting on my seal kit and some bearings and then I am going to put this thing together, hopefully in a couple days. Then I will just be waiting on my conveter to come back.....