James0919

Hello:

I hope someone can provide a bit of insight as to what's going on with my transmission.

I bought the car with 79k on it (Dec 2012) and now have 85k on it. DD but, I don't put a lot of miles on

The Car:
2000 Firebird Formula NHRA Ed 5.7 V8

Mods:
Long Tube Headers, SLP Lid, 90mm Throttle Body, FAST Intake Manifold, Speed Density Tuning, NO MAF , prob other stuff that was done before I got it


The Good:
Trans fluid is full, pink, no burning smell
At normal speeds (not hitting it hard) the car shifts just fine through all the gears, no issues at all

The Problem:
Over the past two weeks, I've noticed that if I hit it (either off the line or in 2nd, 3rd gear while moving) the RPMs shoot up to around 5 or so and then the car "slingshots" into gear. If I do this off the line it shoots up and then during the shift to second, I get a wicked screech of the wheels

Clearly, I am going to take the car in and have it looked at, however I'm trying to get some advance thoughts prior to doing so.

Any thoughts or comments are greatly appreciated.

James

mrvedit

The "shoot up" is either the trans or the converter slipping.
Is it slipping in 1st gear too? Since the 4L60E rarely slips in 1st, I would then first think about the converter.
If it only slips in 2nd, 3rd and 4th, I would first suspect low line pressure, possibly due to a marginal EPC (Pressure control solenoid).
If it only slips on the 2-3 shift, then it might be the notorious 3/4 clutch and require a rebuild.
I assume you have check fluid level and know that it has to be checked with the engine running.

If you take the care in, report back what they checked and what their diagnosis is. I would especially want to know if they hooked up a pressure gauge and made other tests that any competent and ethical shop should do.
In case it does need a rebuild, don't let any old local shop do it! Since you are in Chicago, you are near FLT (finishlinetransmissions.com), both a sponsor and one of the best performance trans builders anywhere.

I'm not a pro, so these are just my opinions; hopefully others will give you theirs.

James0919

Thanks, MVE! I appreciate the feedback.

I took her out again today and, again, it feels like it's running fine until I floor it then the RPM shoot up and I get the rubberband effect.

I honestly think it only slips on the "downshift" - it doesn't slip when actually going through the gears normally, even at a pretty heavy throttle...

Any other thoughts?

sick98z28

could be the seals have shrunk due to age... loss of pressure causing it to slip

James0919

Is AAMCO a decent place to have it checked out? I would definitely consider the local shop as that's the second time they were recommended for the work,

mrvedit

I think AAMCO is a franchise, so the competence/honestly will vary widely. But nothing wrong with having them put a pressure gauge and tester on it.

James0919

Sounds good, thanks for the messages.

I have a friend who works at Goodyear and they can do a lot of the testing (although the don't fix transmission problems...rebuild, etc) so I am going to take it to him since the trust factor is not an issue.

Anything beyond what was listed here (pressure gauge, etc) I should ask them to test specifically?

Thanks again for the replies!

James

jimmyblue

iTrader: (11)

First off you ought to figure out what kind of converter.
Mine "slingshots" similarly as you describe. The low STR
makes the coupling more "elastic" while the moderate
stall speed plus the "stretch" lets it wind up to near HP
peak (the point of it all).

But the key is not that RPM rises - it's that doing so,
gives you torque multiplication as well. If you have
RPM rise without increased acceleration, that's bad news -
nothing but heat and wear comes of that "flare". You
need to discern, which is going on (and it could be both,
like multiplied torque outrunning the clutch & band holding
torque capacity, due to crappy stock line pressure profile
or some such; ghetto mods or plain old crust can make
that worsen too).

Oh, and stay the hell away from service chains that get
paid for selling rebuilds. One, they're perversely incentivized
and two, they're not good at it.

James0919

Thanks, jimmyblue!

Well, I went for a ride today with a co-worker so he could see what I'm dealing with and, of course, it drove perfectly...even when floored.

The only thing I did was put Fuel Injector cleaner in a few days ago, not likely that would make a difference.

My plan right now is to chill and then take it in on a Sat when it's more convenient for me, and see what they have to say.

Weird though....

James

James0919

Well, the general consensus is that I'm crazy... There seems to be nothing wrong (to everyone who drove the car) however I KNOW that something is different.

Question: Can a tune "lose" it's shift points? Not sure if that is even an accurate question, but I appreciate any thoughts

Have a great weekend!

jimmyblue

iTrader: (11)

Tune will not lose shiftpoint data. But there is stuff
like adaptive shift pressure for "desired shift time"
which can make the PCM "learn" like you wish it
didn't - it tries to be "just good enough" and that
can make it "think" less line is OK, based on today's
weather and so on, and then be oppositely wrong
tomorrow. Comes, goes, makes stuff slip until it gets
its "mind" right again, on and on. Bad news especially
when you start to throw more power through it.

Whether the tuning to date, has left that in play or
not, I have no idea. But it's a possibility in all this.

RevGTO

iTrader: (12)

I don't mean to ask a really stupid question, but ... are you sure it's not your tires spinning? I ask only because it happened to me: "Whoa - my tranny really slipped during that shift!" only to realize that it was my tires that were doing the slipping. They spun so quickly that there was no noise and no smoke - just an rpm flare.

performabuilt

iTrader: (25)

I have seen also where on the kick down the car will go to first gear for a moment actually commanded but just a moment then you get a sling shot effect to 2nd or even third (My own car did this many years ago but with a 700r4 it was actually kinda nice IMO made for a nice kick forward ). Also as mentioned Tires spinning can give a similar effect , I actually had a guy once swear a trans I build for him slipped in second gear I met with him and drove the car in fact he had a bad posi so only spun one wheel and that is what he thought was a slip it made no squeal only a slight almost brushing sound .

James0919

Thanks everyone! That's a really good point regarding wheel slippage - I would expect to have some sliding as well, but having said that I have 315s all around so I really don't slip.

I will keep an eye on it and report back. Thanks again for all the suggestions!!!

savage388

Sub'd. mine does the exact same thing, goes great through the gears, chirps 1-2 is fine everywhere but on a 3-2 or 4-3 almost wot downshift, its like it slips for a second before upshifting. the car just had a 2400 stall along with a shift kit and full rebuild 2 years ago by the previous owner from a good shop.

James0919

Hey everyone:

Just a thought... Would the p0332 (knock sensor low voltage) code, perhaps be messing with the way the car shifts and, more specifically, downshifts per the original problem above?

Just looking for thoughts since even AAMCO says the trans is fine....and I fully expected them to push for a new trans...

Any thoughts are greatly appreciated!

James0919

Bump...

mrvedit

As far as I know, only the MAF, TPS and MAP sensors and PCM calculations for misfire and trans/converter slippage will affect how the PCM changes the transmissions line pressure. I'm no expert, but I have never heard of knock sensors affecting the trans.