Hi all. Sorry for the really long post but I felt like I should share my problem and how I figured it out. Thats what this site is all about. I really appreciate all the info here. I recently rebuilt the trans and engine in my 03 2500hd farm truck. I referred to this site along with a few others for much of my info in addition to a couple of shop manuals borrowed from a friend. I completely went through the tranny and replaced all the clutches, seals, bushings, and bands. Checked over all parts and went through the valve body. Put some of the hd2 kit parts in the valve body and pump housing. I dual fed the direct clutch internally like most do. Got it all put back in the truck after I got the engine done and fired it up on the jackstands. It started out in third gear in drive and seemed like it was in a little bit of a bind. It would run up to 50 mph with little effort though. So I dropped it into 3rd and the wheels slowed down and stopped spinning. I let it idle and went into 2nd and then first. I could feel it jerk slightly each time I shifted it until I went to drive and it started spinning again. Reverse worked but there was a 5 second delay in engagement. So I connected a pressure gage and ran it though the gears again. Pressure was around 50 or so at idle in neutral. In drive it was 125 around 1100 rpm 15 mph. In 3rd it jumped to 200 no wheel spin. 2nd and 1st jumped to 150-175 psi. Reverse was around 165. I have the HP tuner software so I tried commanding each gear to engage and I could feel it jerk slightly in the three lower gears until I commanded fourth and then the wheels started spinning again. So I decided to lower the pressure in the pump and see if I could make the wheels spin in the lower gears. I could get it to spin to 25 mph in third but not in 1st or 2nd. Complete bind in those 2 gears. I decided to pull the valve body out and see what I screwed up. Looked it over and everything looked good. So I decided that wasn't the problem and pulled the trans back out and tore it back down to the bare case. Looked over everything and checked each clutch pack for burnt color. Found a couple 4th clutch plates burnt pretty bad. When I first fired up the truck I ran it through all the gears and tried to get it to shift and some smoke came out of the fill tube. Trans was about 6 qts low so it burnt those plates. I did a lot of reading and staring at flow charts and decided to look at the valve body once again and thats when I saw it. DUH!!!! The 3rd reverse check ball seat wasn't seated all the way in the body.


I didn't install it right!

Now its right. It was trying to engage 3rd and 4th at the same time with this not being seated all the way in. I'm dumb. Lol

Corrected now

 

That was a Bummer of a build mistake... Such a small part can cause a big problem (especially when you introduce a leak into a hydraulic circuit LMAO).

Congrats on finding the problem and you are quite fortunate that this was nothing major and didn't waste too much $$$ when all is done.

 

Yeah I was pissed. I told my old man if I hadn't put that together wrong it would have worked right the first time or so I hope. Still putting it back together now. I replaced the two clutch plates that were burnt. Everything else looked alright. I will soon find out how she works!

 

Good Luck! :-)

 

Well I got it back together yesterday and took it out on the road. Shift points are a little off but other than that it shifts fine. Pressures look good. No leaks always a plus. I'll probably readjust the shift points cause the factory ones drive me nuts. I need to retune the engine since I changed the cam and got rid of the stock exhaust.

 

Well I was backing a trailer into the shop today and I felt reverse start shuddering a little. I did manage to get the trailer in the shop. Went out on the road to see if I still had low gear and engine braking. It seemed fine so I tried backing up a hill with no trailer and no reverse at all. Revved it up some and it slowly crept up the hill and then there was smoke. Blew front pump seal. So now its in the shop. I have too much other stuff to work on for this to be happening right now. I farm for a living so we'll be in the field for the next 2 months. Hope Its nothing major. Any ideas as to what it might be? Thanks in advance!

 

The band apply pin is too short. A lot came straight from the factory barely long enough to work. This can also break the reverse servo piston because it slams against the case.

And/Or it could be a worn boost valve, caused high line pressure and broke the reverse servo and possibly blew out the seals in the direct drum.

 

When I measured the reverse servo travel it was at .150" if I remember correctly. I thought that was within spec. I did replace the boost valve with one that came in the transgo kit. My reverse pressure was at 300 or so after I got it going good last month. Ive put close to 1000 miles on it since and it has been working great until today. Dad pulled our skid loader with it a week ago and he said it was a whole different truck from what it was before. It was pretty gutless.

 

"in spec" doesn't always work.

 

Jays is absolutely correct, the low/ reverse band servo travel is most likely excessive... as he states there are cases of this...
All though, with a good band and good reaction carrier... 0.1875" is considered max travel by GM/ Hydra-Matic. I do not recommend this.
I would aim for 0.1250" instead.
Other times I have seen the reaction planet carrier be installed under specification (diameter too small), or have the incorrect design low/ reverse band installed.

Search for this subject with "Sonnax" in the search terms as well via google. You will see some decent articles on the subject from Sonnax.

In regards to the front pump seal blow-out... The front pump seal drain-back passage should be enlarged over the stock dimensions to 0.2500".
Clean out the pump half completely with brake parts cleaner and compressed air.



Then ideally install a new pump bushing (Teflon lined ideally) with red thread locking compound. Last install a new pump seal (pack the inside of the seal and cover the coil spring with Transmission assembly lube. If you do not have any, purchase a small tub of Vaseline, to use instead. Apply red thread locking compound to the O.D. of the seal).

Excessively high line pressure in reverse may also be a problem. I usually delete the reverse boost circuit in these transmissions anytime I raise the line pressure.
Should you like to discuss this further, please message me and i will go over photos and instructions with you.
This procedure also helps to prevent the "late model" low/ reverse servo piston failures.

 

Thanks

 

No need to have more than 180 - 200 PSI in any gear range unless the engine is over-powering the transmission and causing clutch slipping.
Some what less pressure is even fine for stock.

In the reverse gear range, the line pressure can be up in the 300 PSI range. Which is no good and causes parts failures.
Line pressure of over 600 PSI has been regularly seen in reverse, usually when there is excessive pressure regulator boost valve wear.

 

I got it tore down and found a lot of metal flakes from the bushings in the fluid.

 

Looks like you had some torque converter/ transmission misalignment going on.

How did the oil pump gears look?

What were the line pressure readings like before this just happened???

 

The pump gears...

both sides look the same. Ive never had trans alignment issues until now. What would have caused the misalignment? I don't know what the pressure was cause I didn't have a gage on it at the time and the fluid was pouring out of the front of the trans.

 

Are the alignment dowel pins still in the block, or pushed in flush with the block?

 

They are in correctly. No cracks around them or anything unusual. The one dowel had some paint on it so I wonder if that was an issue. When I got everything buttoned up after I put it in the last time I didnt see a gap between the bellhousing and block. I did have a little trouble getting the two split apart when I pulled the trans out though.

 

Where can I get a decent bushing install tool online? Any recommendations?

 

Most DIY'ers have good luck with something like this.
TAKE CAUTION to drive bushings in square. Alot of times it is best with a press, but you can hammer them into place too if you don't have access to a press.

 

This tranny has been kickin my butt. I got it put back in back in July and it worked great for about 400 miles and started losing reverse again. Another thing I noticed is it would take awhile for it to engage in gear after start up. Longer when warm than cold. Pressure ran around 25 psi at first and 60 psi at idle once it got the pressure built up. Ran around 145 psi going down the road and 250 to 300 plus in reverse after I first got it put in the truck and now it doesnt get past 280. Could the high pressure be blowing the gasket out in the low reverse servo cover? I'll be pulling the trans out soon.