The_Hamster

Having seen how helpful you guys can be with these 4 speed autos I thought I would drop a line here.

I have a 2005 Silverado with a 4L60E in it. The original one failed and a GM 'goodwrench' rebuild one was installed that had low mileage on it since the rebuild. Since day one it had a harsh shift between 1-2 gear. It holds 1st too long then hits 2nd pretty hard. Would shift smoothly for the first couple of shifts, then go harsh until it cooled off completely overnight.

That was a couple of years ago, now it slips in second gear. It gets up to about 3000rpm in second and then slips up to about 4k and hits third. I haven't noticed any issues with fourth gear slipping.

I pulled the 1-2 accumulator out to see if the piston was cracked or the spring broken as I saw mentioned a few places and can't see any issues with it. Piston looks solid (is white polymer of some sort) and both springs seem fine (green springs).

Any suggestions on what I can check next while the transmission pan is off?

Thanks;

2018 Edit -I see that this has gotten a few hits. I have re-hosted the photos on Imgur so they can be seen. Unfortunately I didn't take any photos of the new pin or Sonnax kit it seems. Also this has been working for about 40,000 miles and 4 years now. Not bad (knock on wood). I am not certain how much of the success can be attributed to the 'super hold kit' or if it's singly due to the longer pin.

mrvedit

This is very similar to a recent thread about not shifting into 2nd:
https://ls1tech.com/forums/automatic...-into-2nd.html

I am repeating my post in that thread:
----------
Another possibility is that the band is very worn. While the band is used for both 2nd and 4th gear, usually (not always) you lose 2nd gear before you lose both.

It is useful to know the endplay of the servo; and relatively easy to check.
With a crowbar, press on the trans servo cover and estimate how far it moves.
Ideally it is only between 1/16 and 1/8". Around 3/16" is too much and around 1/4" the band will begin slipping.
------------

Other related threads:
https://ls1tech.com/forums/automatic...t-trouble.html
https://ls1tech.com/forums/automatic...nead-help.html

---------------
On the issue of the 1-2 shift, you correctly determined that the piston or springs in the 1-2 accumulator are often the culprit. Since you checked them, the problem must be elsewhere, but I'm sure the slipping 2nd gear is now the priority.

The_Hamster

Sorry to sound useless, but which part (where) is the servo cover that I am to press on?

The_Hamster

A quick google shows you are likely talking about the servo cover on the side of the transmission? The round cover on the RH side?


I'll go give it a push in the morning, I've cleaned myself up for the day and am preparing a rotisserie turkey. I'd share if I could, I swear....

Thanks for the help thus far.

mrvedit

10 seconds into the video he points to the servo cover.
The "boxWrench.net" are very useful basic videos btw.

bbond105

I don’t think this is why your trans is slipping in 2nd but it sounds like your line pressure is high. That is most likely why it is shifting hard. This is strange that it is sipping in 2nd and not 4th.
As mrvedit checking the servo endplay would be a good place to start. Another way to check the band clearance would be to wiggle it front to back on the drum. With the pan off you can see how lose the band is on the drum. TransGo 4L60E-HD-C instructions say that ideally the band should move around an1/8” front to back on the drum. I would think that with use you would have more than the 1/8” but not a lot more. The way mrvedit is saying to check it is more precise though.

mrvedit

bbond105 is probably right that your line pressure is too high; you will need to hook up a pressure gauge to check that.
Based on what trans builders have told me and my experience from helping people with this problem, 2nd gear typically starts slipping before 4th gear, even though both use the band.
Measuring the servo pin end play by pressing on the cover does not involve the mess and trouble of dropping the pan.
When the end play was too much, I have had several OPs lengthen the servo pin by welding a blob on it and they got another 5000+ (10,000?) miles out of the trans before it needed a rebuild.

bbond105

He did ask what he could do while the pan was still off.

Quote
Any suggestions on what I can check next while the transmission pan is off?

The_Hamster

Ok;

I went and used a prybar to push on the servo cover. Took a bit of force, was only wiggling 1/16" at first. Then suddenly it got over whatever was holding it back and probably went in 1/4" or more. Didn't come out again to do the test again, stayed in almost all the way that it traveled short of a small bit.

So, this means my 2-4 band is worn and the 'weld a blob' option is a possibility? How much does one normally weld on? All I have is an arc (stick) welder. Could be difficult to do with precision. Should I do the 'corvette servo' while I am at it, or is it a waste of time at this point?

bbond105

You can pull the servo cover, pistons and pin and weld a few blobs on the end of the pin then grind pin tip to get the correct pin travel. Or you can just buy the Sonnax Extra Long Pin part #77787-02K. Either way you most likely will have to grind the pin tip to get the travel you need. This may get you some more life out of your trans.
See attacked instructions on grinding pin tip and checking pin travel.

http://www.sonnax.com/parts/2477

The_Hamster

Thanks for the info. I will call the local supplier for pricing.

However, how do you know how much to weld onto the original pin?

Can the spring to soften second gear be installed at this time with my original pin?

What benefit would a corvette servo bring at this time?

bbond105

You need to add enough weld to make the pin longer to decrease servo travel after grinding the pin tip to achieve .075"-.125" of servo travel.
I have not done this before but in theory it should work. Measure the servo travel before disassembly and write that number down. Subtract .075 from the number you wrote down and what you get is how much longer the pin should be.

The springs that control the shift firmness are in the 1-2 accumulator. The stock spring is not the problem. You will need to hook up a pressure gauge to check the line pressure. I am thinking it is too high. At idle in park it should around 90psi.

The corvette servo will add more holding power of the band, but will also make it shift harder.

I would correct the servo travel first and see if the trans stops slipping and if it does then deal with how hard it shifts.

The_Hamster

There was a lot of travel in the servo. Solid quarter inch.

I have disassembled it. I can throw it back together to measure the travel more precisely, but like I said before it didn't come back out on it's own. I had to pull it back with channel locks which makes it a challenge.

I notice the pin doesn't have any o-rings or anything on it. That normal? The 'extended pin' mentioned earlier had o-rings on it.

Everybody likes pictures?

The Patient
https://imgur.com/YDC73Ok

The trans pan
https://imgur.com/Zu8DUMU
https://imgur.com/STEih2D

1-2 Accumulator
https://imgur.com/rflqnKo

1-2 Accumulator Piston
https://imgur.com/x700kcV
https://imgur.com/hpyEAhg

Accumulator Springs
https://imgur.com/KYuVdbE

Accumulator Bore
https://imgur.com/fFq9QNN

Servo Assembly
https://imgur.com/2fZZOPJ
https://imgur.com/3juD37Z
https://imgur.com/vASdeaE
https://imgur.com/V2KMMSt
https://imgur.com/xTjTO8b

The Pin
https://imgur.com/dEJZGDh
https://imgur.com/S1UcGE7
https://imgur.com/RT9COfu
https://imgur.com/TWGVmNf
https://imgur.com/JeQqNrQ
https://imgur.com/LqqpMf5
https://imgur.com/LmXvwms
https://imgur.com/oJffXfB

mrvedit

Mr Bond (007?) is giving you good advice. A longer servo pin from Sonnax is probably the best way to go. I think GM has one too, but I don't know the part #.
Here are some threads where people (mechanic that knew how to weld) has luck with lengthening the pin:

https://ls1tech.com/forums/automatic...t-trouble.html
https://ls1tech.com/forums/automatic...-gear-all.html
https://ls1tech.com/forums/automatic...ckup-help.html

While your 1-2 accumulator looks perfect, I would suggest getting the GM aluminum piston for it. Or if you are ordering Sonnax parts, get their pinless piston ($15).

Mr Bond mentioned 95psi at idle; that is with a bigger boost valve installed. With the stock setup, it will be more in the 65-75psi range.

You are "lucky" to have a truck where it relatively easy to remove the servo.

bbond105

This is normal. The stock pins do not have seals on them. It is also normal to have to use a little force to pull the servo out. If you put it back together to check the travel don’t install any of the seals and o-rings. This will make it easier.

If you have a ¼” of travel and an 1/8” and recheck.

Jake's Performance

iTrader: (2)

I'm not a big fan of the pinless accumulator pistons. But as stated a new aluminum would be worthwhile.

The_Hamster

I have acquired a Sonnax 'super hold second gear kit' which comes with the longer pin. Also a new aluminum OEM accumulator piston, and filter etc. Just need to pick up some dex 6 and a new o-ring for the servo cover. They will likely go in on Saturday. I will update you guys with the results.

Thanks!

The_Hamster

Should the 1-2 accumulator be filled with trans fluid before being re-installed, or installed empty, or does it matter?

bbond105

It doesn't matter so install it install.

The_Hamster

Operation was a success. Holds second at full throttle now to redline. Sonnax kit was a breeze to install. My band however is so worn that no grinding was required on their extra long pin. Oh well. Hopefully I get 15-20k km's out of it of light use.

The 1-2 shift is improved but not great still. Less hang time before second engages than before. A more positive engagement as well.

Thanks for everyone's help.