[ckucia]

This will probably be a bit long, but I want anyone who may be able to help to have all the details...

Vehicle is a 2000 GMC Sierra 1500 4x4 extended cab pickup.

Trans was rebuilt (professionally) about 30k/4 years ago due to a broken sun shell.

Last few weeks I've been getting a delayed or harsh or just erratic 1-2 shift, especially when cold.

Searched the web and figured it was probably a problem with the 1-2 accumulator piston.

Dropped the pan, pulled the accumulator cover off and, sure enough, the piston (plastic) was cocked in the bore with fractures around the pin bore. Took it off to find the outer spring broken with bunch of plastic bits inside the bore. Not sure if the broken spring caused the piston to tilt and crack, or the broken piston cocked and snapped the spring.

I took the broken spring out, cleaned out all the plastic bits I could find, changed the fluid and filter, bolted it back up and drove it gently for a week while I ordered some parts.

I ordered an aluminum 1-2 accumulator piston, and I figured I'd better pull the valve body and clean it well in case any plastic bits had gotten into the bores.

We just bought a small travel trailer, so I thought while I had it all apart, I'd put in a very mild shift kit - I settled on the Transgo "orange box" SK4L60e.

When I got the valve body apart, I discovered that the rebuilder had put in "most" of the same Transgo kit. All the springs were exactly the same color, and the ISO-CONV valve had been replaced. But, there was a different spring on the accumulator bushing, and none of the holes in the separator plate were redrilled to Transgo's specs. The servo was also left stock.

More importantly, there was an oversize 1-2 shift ball installed and it was nearly through the hole.

So, I ran to Summit racing and got a new Transgo separator plate. Dad had a few stock check balls so I took out the oversized one.

I basically followed the Transgo instructions exactly as if I was on a stock trans - replaced everything with new parts from the kit based on the kit instructions. There were two areas where I had to make some decisions. I drilled the 1-2 orifice in the separator plate to .070 for a firmer 1-2 shift. I used the spring recommended for the 1-2 accumulator bushing (rather than going up one size that would have given an even firmer shift), and I left the existing 2-3 orifice which was at about .075 on the new separator plate.

I also put all the electronic components on an ohmmeter and verified they were in spec.

So, I got it back together and it works OK - gets me to work and back but...

The 1-2 shift is great at light throttle and heavy throttle. A little harsh at a medium throttle. It will softly chirp the tires going around a corner agressively. I wouldn't mind softening it a bit since my wife drives the the truck occassionally, but I could live with it.

3-4 is awesome. Like clockwork.

2-3 leaves a lot to be desired. Light throttle is nice, but a bit on the slow side after a crisp 1-2. The heavier the throttle, the longer and (it seems) later the shift occurs. This is prime freeway entrance ramp territory so I think this is an area I need to address. The 2-3 shift takes about 2x to 3x as long as the 1-2 and there is sometimes a noticeable delay and very slight rpm rise before it occurs.


I have not pushed it hard because of the soft 2-3 - don't want to burn something up until I get it a little tighter. Plus, I think i'd chirp the tires pushing the 1-2 shift harder and that can't be all that good longterm either (although it would be fun)

This weekend I'm going to try to fix it. I have another seperator plate ordered in case I need to start from scratch. Also ordered new solenoids (should have replaced them when I was inside just as a preventative). Also ordered an aluminum forward accumulator piston as I found mine was plastic (was in OK condition, but it's a fail point).

I will probably give Transgo a call and see what they think.

Also have an ATSG manual on order.

So...

With the 2-3 shift, my guess is that enlarging the orifice hole a bit might firm up the shift. Any thoughts on this? Maybe go with .093 like most of the other holes? .093 is recommended for some of the other servo pistons (I have the 8642553 piston and the DX accumulator bushing) I've seen some on the web recommend over .100 on this orifice.

With the 1-2 shift, since I'll have the trans open and I installed the special Transgo pin to make it easy to change, I thought I might put in the next softer spring in the 1-2 accumulator bushing (I used the yellow 72oz spring - thought I'd try the white 56 oz). Just to take the edge off the 1-2 shift. Or, I could start with a fresh separator plate and use a smaller hole in the orifice. .063 was preferred, but I used .070 for firmer 1-2 shifts, maybe that wasn't the best idea.

Any thoughts? Am I on the right track? Other than the 1-2 accumulator problem that is now fixed, the trans has been great up to now. I don't have any reason to suspect abnormal wear inside the main case or pump. This is my daily driver and I don't beat on it. The hardest work it gets is towing a ~4000lb trailer and hauling my wife's plants.

I really don't want this to be a radical performer - just be reliable and dependable and on the firmer side of the stock parameters. I'm willing to do a bit of experimenting if it will pay off in a nicer shifting truck, although I'd rather not drop the trans and get inside the main case unless absolutely necessary.

Any advice would be much appreciated. I do have a pressure gauge, although I'd have to fab up a longer line in order to read it while driving. I could get some figures if that would be helpful.

[Crosley]

Did you check the gaskets to see if they covered the 2-3 shift hole in the separator plate?


Early design gaskets for the year 2000 trans have a smaller hole at the 2-3 shift location.

[ckucia]

I did check that no holes were covered by the gaskets before assembly, but I suppose I could have missed one, or not noticed if it was there but smaller.

I won't have any of the parts I ordered until Monday - I wanted to have some before doing anything else in case I changed something and made it worse. However, I have nice weather expected this weekend, and re-checking doesn't hurt anything, so I'll make some time to tear it back down and doublecheck the gaskets.


Thanks for the suggestion. If the hole is partially covered by the gasket, I assume I can just open it up a bit - maybe make a punch out of some small diameter tubing?

[ckucia]

Been quite a ride...

Never got the chance to check anything. On a trip to the part store to fix the wife's car, I had a really hard 1-2 shift and a pop, then no reverse, 2nd or 4th. Another sun gear bit the dust. I bought a Beast from TCI.

Anyhow, I pulled it and opened it up. Found I had the 1-2 accumulator bushing in upside down. Dumb mistake - I matched the picture of the bushing in the install page, but my valve body was oriented upside down.

Also took a look at the plate gaskets and the 2-3 hole was tiny. I'd be amazed if I got it aligned right putting it in from the bottom as before.


This time, I used another vendors gaskets with larger holes, and assembled it on the bench.

To make a long story short, the ATSG manual has a misprint and I mistakenly thought, based on that, that my clutches were worn beyond spec, so I bought a rebuilt kit only to find that mine were OK, but on the low side. Went ahead and replaced all the clutches and steels, verified the clearances, changed what seals I could. Also changed out the plastic forward accumulator piston since I had it apart.

I also had to replace the bushing at the back of the case and the part (sun gear support?) that went through it. This may or may not have been what fixed the deceleration clunk that I have been trying to find for years (apparently not the driveshaft yoke). This is odd, because the xfer case is behind that. My best guess is the sloppy bushing allowed the output shaft of the trans and the input shaft of the xfer case to bind up within the slop of the bushing and clunk, but it's just a theory.

Made another dumb mistake and broke the pump impeller installing the TC wrong, then busted the TC solenoid taking the pump off w/o opening the pan. I have new respect for you guys that do this full time for a living - I work behind a desk most of the time. Wrenching for three days straight can really take it's toll on you.

I put in a stock, non-drilled Transgo plate, and a Corvette servo. Also added an electronic trans pressure gauge and sender so I can monitor things. Most of the clutch clearances are on the low side of the ATSG manual, except the 3-4 which I went tighter.

Anyhow, it shifts very well now. Pressures are good. I'd like a little firmer shifts and I may play with the orifices a bit on the 1-2 and 2-3. If I get on the 2-3 I get a slightly perceptable hickup, which I think is due to the orifice being undersized (I wanted to start off with a stock plate and drill from there and Transgo recommends drilling the 2-3 out a bit with the 093 servo. The 1-2 is also on the lowest side of V8 recommendations).

Just for my own interest, I also measured all the orifices of the stock plate to see how they compared to the Transgo and their recommendations. The 1-2 orifice was much larger on the stock than on the Transgo. I can't recall the size but I have it recorded.

I sure have learned a lot. If this wasn't my daily driver, and I wasn't in a hurry to have it back on the road, it would have been almost fun.