4L60e 1-2 issue - Accumulator?
 

My 4l60E has a new issue. Under higher loads (3/4 throttle to WOT) the 1-2 shift is a bit juddery and feels like it slips a bit before 2nd gear engages. Anything less than half throttle and its mostly fine, but sometimes feels a bit hard when it shifts.

My research points me to the 1-2 accumulator. Do you gurus concur? or am i looking at something bigger?

Thanks

when i say it feels like it slips a bit, i don't mean that the revs go up and bounce the limiter for a second, its like theres two stages of the 1-2 shift..the revs will increase to 6000rpm, the shift begins, revs drop to say 4000rpm, feels a bit juddery and then the revs will drop again to 3900 and I'm in second gear and its fine. It almost like the shift is happening in 2 stages. Thats at 3/4-WOT.

You can drop the pan and pull the 1-2 accumulator out and see if the piston is cracked also push on the servo cover and see how far it goes in. It should only go in about .125".

I would guess your 2-4 band is toast

Ahhh shit

Don't take my post as fact..... just a starting point.

Rare to see a burned band.
any info? Stock, built, whats the story?

What you're describing is an accumulator problem, broken spring most likely.

A transgo sk kit with a .500 boost valve (doesn't come in the kit) or hd kit would give you the parts to fix it. You would have to get an aluminum accumulator piston. It's real easy to make the 1-2 brutal.

And of course others will chime in with the 100 other guesses and cures for the problem.

Then to be honest I've seen worn forward clutches cause this problem. Just worn to the point where they can't hold the step up in gear ratios from 1st to second.

You Can make the 1-2 shift brutal, but there is no good reason to. Any spacers in the transgo kit, get thrown in the trash where they belong. Unless you have an old casting accumulator housing, then you use 1 as a spring seat. All they do is created very harsh part throttle shifts which may have the placebo effect of thinking you have a really built trans...but it's really just shocking the hard parts with no real benefit at the upper rpm WOT shifts. If you want hard shifts, then yea...you can make it happen pretty easily with a 60e. But in my opinion there's really no logical gain from it.

Check the accumulator and band endplay just like Cayenne advised. Very good starting point.

I definitely don't want the shifts to feel brutal, and normally they don't.

I am not sure what is in this 4l60e, speaking to previous owners of the car and non of them have the full story of what was done.

all i know is that in the past it did indeed have a Transgo HD2 kit fitted, i even have the receipt in my cars folder for it. However, one of the previous owners says the box was rebuilt and the kit was dumped...but i can't verify that. Unfortunately, the same guy said it was rebuilt with alto red eagle clutches which i have read about and not happy that they're in there...but i wouldn't be stripping it down for a rebuild just to replace them unless it actually takes a dump.

It also has "corvette servos" from what i gather, a "Sonnax Beast sun shell" and a "Sonnax Alto extra wide intermediate band 77700-01K" if that makes sense to anybody - have the receipts for these too.

Other than this 1-2 issue, it seems healthy. i can manually select 2nd gear and it will pull solidly unto the rev limit - no slipping, and 3rd and 4th also no slipping. no strange noises, clunks or similar. The only issue is this 1-2 strange behaviour and it only started this week.

I'm no good with transmissions, so ill probably take it to a local shop and ask them to check those things out that have been recommended.

If you leave it in manual 1st, and go WOT then manually shift into 2nd, does it have the same issue?

Then I would still advise to follow Cayenne's advice and drop the pan to inspect the accumulator and also check band clearance while you're under the car

MEANING.....if it's weak theres a problem thats going to be extremely obvious when found.

Where the broken accumulator spring will be found.

If spring is broken, do what FourthGenCamaro suggested and get a shift kit. Go with the Transgo HD2 + aluminum piston + .500 boost valve. Check the existing plastic piston for cracks and pin bore wear.

The HD2 comes with the .500" boost valve. The band sounds as though it is going away, if you do not find any problem in the 2nd accumulator setup. Most likely you will be going into the transmission to solve.

My mistake. I originally bought the boost valve separately and forgot it comes in the HD kit.

If it's the band, would the Sonnax servo pin solve the issue? I guess that would be more of a band-aid than a fix.

Ok so my cars at the automatic gearbox shop.

Had a phone call this afternoon to say they had removed the accumulator housing and found something they've not seen before...bear in mind theres not many of us over here running tuned up Pontiacs!... although they are very familiar with stock 4L60E

They say the accumulator has a standard piston and pin, but has 2 springs and a washer fitted (this is the bit they've not seen before). There is a washer and blue spring below the piston and an orange spring above..the orange spring is snapped and the piston is sloppy on the pin also.

The servo moves inwards by 0.090 inches.

Question is, they want to replace the accumulator with a new housing and stock springs etc...where could i get a replacement transgo spring on its own? as it appears as though the transgo kit is still fitted! I hope transgo sell them separately.

That's the transgo hd2 kit set up.
Spring broken you say? Hmmm. Who would have figured.
need a short stock spring or go back to the stock set up.

You could always go with the sonnax enhanced performance spring

https://www.sonnax.com/parts/2433-enhanced-performance-accumulator-spring