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Discussion Starter · #1 ·
Hello all,

Please be patient with me, I am not a transmission expert.

I have a 1995 Pontiac firebird formula, LT1, 4l60e trans. 128k on car.

When driving, first and second gears work great. seems to never really shift into third, but sometimes it seems like it does, but then struggles getting into fourth. It seems to slip occasionally in 3rd gear and sometimes even second, but even then, the car still pulls so it isn't really like a slip?

When cruising at higher speeds (e.g. 50 mph), even when I slightly press gas, the rpm's raise quickly and car pulls like it is in third (or second, I don't know). When I let go of the gas, the rpm's drop, and the car seems like it is in fourth until I hit the gas, then the rpm's raise and car pulls like it is in third again. At higher rpm's, a whining sound sort of happens, but my vacuum check valve is leaking, so it may just be that.

Honestly, it is a weird issue and it confuses me, and I am sure a paragraph about the issue will not enable anyone to help me. My real question is what are some easy things to try before I resort to rebuild. The transmission fluid is not burnt, does not have chunks of gear in it. Trans fluid and filter were just replaced 300 miles ago. Also, no smells or sounds. Fluid level is good too. (at least I think so). No check engine light is on.

So far, I replaced the TPS hoping for a quick-fix and this did not resolve the issue. I have ordered 2 shift solenoids to replace the 1-2 and 3-4 solenoids. Is that a reasonable attempt to fix my issue? Figured it was worth a shot since they were only 12 dollars a piece. While I am under the car doing the solenoids, I will look for any bad connections or anything like that.

I would greatly appreciate any suggestions before resorting to a rebuild. Thanks in advance for any help.
 

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When in first gear, the 4L60E has the forward clutch applied, and both shift solenoids are ON. In second, the band applies (forward clutch still holding), and the 1-2 solenoid is OFF. In third gear, the 3-4 clutch pack is applied (forward clutch says applied as well), and both solenoids are OFF. In 4th, the forward clutch, 3-4 clutch, and band area all applied, and the 3-4 solenoid is off. Using this information, and what you said above, we can draw some conclusions.

1) Since you have first gear, both solenoids are working.

2) Since you have 2nd gear, the band is grabbing OK (at least when the second apply piston pushes on it)

3) Since you have 1st and second, the forward clutch pack is grabbing OK.

From what you are saying, it seems like the issues start when you shift into 3rd, and 4th. The common element, for third and forth gear is the 3-4 clutch pack. A toasted 3-4 clutch pack is a very common problem with the 4L60E.

While the pan is off, I would make sure all the valve body bolts are tight, replace the pump boost valve, and give the torx head screw on the back of the force motor a 1/4 turn in. This will give a bit more line pressure that might help in the short term, but if the 3-4 clutch pack is toast, all the line pressure in the universe will not make up for a burned up 3-4 clutch pack. Something else to consider, is there is a fitting just above the gear selector shaft that you can hook a pressure gauge to and see what the line pressure is in different gears (and throttle angles....the TPS tells the force motor to increase line pressure as the throttle is opened). Good line pressure, and higher line pressure when you power brake the car shows the pump and force motor are working good. But since 1st and second work OK, i'd say the pump is OK....still sounds like a burned up 3-4 clutch pack.
 

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Even though your problem sounds like 3-4 clutch pack being toast,you can use GaryDoug scan program called "scan9495" to check the transmission actuators in your car. That way you will know for sure they are all working correctly. I am including the program in this post. It is a winzip file so you need winzip to unpack. You should be able to get a trial version for free.

Scan9495 checks for regular codes, ABS & SIR codes. It does running sensor data scans and will save data for later playback. And tests engine & auto trans actuators. It will turn any pc based computer into a powerful scan tool.

However, you will need a 16 pin obd 1 cable for your 95. This will connect car's aldl to usb port of pc. Get cable at

http://www.aldlcables.com

or http://www.tunercat.com

don't buy an obd 2 cable. They have 16 pins also but won't work on your car.

You will also need microsoft net framework to use program. I believe the read me file will tell you what version you need. It's a free download at microsoft website.

You can get help from GaryDoug if you have problems with program. He wrote the program for our lt1 f-bodies.

One more thing, if you base a no code conclusion on the check engine light being off, this is wrong. There are codes that don't light the cel when they set.

And I hope you based your not being low on fluid by actually checking fluid level with engine warmed up and running when you checked.
 

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']['exXxas']['itan
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I agree, probably the 3/4 pack. There is an upgraded kit called a Zpac that corrects the flimsy 3/4s if a 700/4L60E. They are used in all of the 4L65E's now. I have one in my 700...bangs 3rd like a sledge hammer.

Now I do have a question. You said the fluid was just changed 300 miles ago. Was this because of this problem, or did the problem arise AFTER the trans service?
 

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Discussion Starter · #5 ·
Thanks for all the good help. I will look into the pump boost valve and tighten that screw and check the valve body bolts. I know no check engine light does not mean no trans codes, or anything like that. I just wanted to include the no check engine light in the description. The fluid and filter was changed before the problem. This problem seemed to occur around 300 miles and 1 month after the service was completed.

Really, I appreciate all the help here, I was really hoping it wasn't the 3-4 pack. Does a new 3-4 pack come with a rebuild kit? I will probably get an upgraded one anyway though.

I will keep you updated. I will be switching the solenoids out, tightening the bolts/screws, hopefully replacing the pump boost valve, and inspecting everything Wednesday hopefully.
 

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Was it one of those flush services or did they just drop the pan, replace the filter and 6qt of fluid?
 

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Discussion Starter · #7 ·
They flushed all of the fluid and replaced the filter.

I also just checked the transmission fluid again, this time letting the car get hotter as advised in an earlier post, and the level does appear to be just a little higher, definitely out of that crossed area. Still, only a little above it though. maybe 1/8 inch, or little less.

I apologize for not checking the fluid correctly the first time, I'm not sure how I checked it before to make me feel like the level was okay.
 

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']['exXxas']['itan
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Flush = bad

Pan drop/filter swap/6qt = good

The flush type stir up all kinds of trash in the valve body causing all sorts of problems. Not to mention introducing that much new fluid (detergent) will cause a weak lining on a clutch to come loose. I was a transmission builder long before I became a couch potato lol.
 

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Discussion Starter · #9 ·
Well that sucks. Wish I knew that one before.

That being said, I am still going to do the solenoids today and tighten up everything, etc... By any chance if for some strange reason this fixes it, is there anything I can do to stop the new fluid's damage? or is the damage already done? I realize this stuff today is probably going to do nothing, I am just trying to stay positive.

Also, If I need a rebuild...

Would it be substantially cheaper to remove the trans myself and then have a shop rebuild?

Any chance I could just replace the valve body? or rebuild the valve body? could that be done without removing the trans?
 

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With the time your going to invest into any sort of internal work, be it valve body or trans R&R, it would probably be best to find a working unit at a salvage yard. That will be your cheapest solution.

With your car being a LT1, its no slouch. So to build one, all of the updates would need to be done. This would yield around $1,600-$1,800(not including converter) if you pulled it and that would most likely land a 12mo/12,000mi warranty. Thats what most shops do these days.

Recommended upgrades:

Hardened sunshell+rear planet input collar

10 or 13 vane pump rotor/assy

HD wide or HE band

New 2nd/4th drum to match ban

Billet or Corvette servo

Shift kit

PWM pump valve upgrade (improves lockup apply to avoid P01870 code, 95 was first year of PWM style lockup)

New internal harness and pressure manifold assembly, harnesses connectors are crap and cause all sorts of issues so this is a must

Zpac 3/4 upgrade (9 clutch assembly with hardened apply piston and heat treated steels)

hardened OD sprag assy

4 or 5 pin planetary assembly with flinger ring installed (from late model 4L65E)

Milled LR center support for additional clutch/steel

New EPC/Force motor (OEM not some chinese knock off)

New shift solenoids (OEM Delco/Delphi)

Rebuilt converter with Kevlar "fuzzy" lockup clutch

We did this to all "hi-perf" type vehicles when I built them for a living. My 68 has all of this + a billet 3500rpm converter with anti-balloon outer shell, and a complete shift reprogram type kit (lightning fast shifts). I plan on shelling it out with a couple N2O kits :)
 

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Wow, I really thank you for all the help! that's a sweet list. If it comes to that I will definitely get a junkyard trans and take it from there. Although I am not going for the awesome build you certainly have going there, It will be nice having at least the opportunity to pursue that in the future if I wish.

But, for now...

If the new fluid messed up the valve body, is there anyway I can try dropping the valve body. And then replacing the valve body along with all the gaskets and solenoids I can? I'm sorry for being in denial, I know I am not a trans expert, but anyone who drives my car refuses to believe the transmission is going since it always pulls, just can't really seem to shift into 4th and occasionally maybe 3rd. Now, I realize these people aren't 4l60e pro's, but I am still holding onto any hope that I won't need to drop the transmission and replace. I mean if it is an internal transmission problem wouldn't I be having leaks? burnt fluid? sounds? I don't have any of that.

Just curious If a valve body replacement is something to pursue for now. This car isn't a racecar for me. Just a fun daily, so I would like to get it driving right again. Obviously, you all know more than me, so if the valve body thing is a waste of my time, I'll have to pursue a new transmission or a rebuild.

Also what about the PWM TCC solenoid? is that worth a shot?
 

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It is not that big of thing to remove the valve body. Just make sure the bolts go back in where they came out. Especially the three 8mm bolts. If you are going to take out the valve body, you may as well get a new separator plate when you get the valve body gaskets. Watch out for the checkballs as you remove the valvebody and you may want to get some trans jell to keep things in place when it is time for reassembly. While the valvebody is out, you can do some basic inspection to make sure all the valves move free, give it a good cleaning, and see that there are no broken springs. I recommend doing one valve line up at a time and lay the parts out in the same order and orentation. You can substitute any new parts in as you go. Keep everything very clean while you are working on the valve body (like you would if you were rebuilding a carburetor). I think a '95 4L60E is a unique year if you do get one from a junk yard.
 

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Discussion Starter · #13 ·
okay awesome! So if these solenoids don't do the trick, I'll remove the valve body and spend some time taking that apart. Then I will proceed to rebuild/replacement. Thanks for the insight.
 

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Joe is correct. The 95 was the first year of pulse width modulated lockup but retains certain features of the non PWM 94 style. 96 went to a later style pump and different valve body programming. Essentially, a 96 would work as long as you got the converter with it. The ECM logic should be common between the two but would need to confirm.

If it was up to me, and $$$ was tight, I would recommend swapping the whole thing out from a salvage yard unit. Jasper has some fair prices on their pull outs.
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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There are a couple electronic issues 96 and up the preclude use in a 95. A 94 switched lockup trans can be used by flashing your 95 PCM with a 94 program, and minor rewiring of the harness. 94 and 95 PCM's are the same part #.

When I get back to my PC I can post a link to a thread on LTxTech.com that explains the details of the various versions of the 4L60E, with respect to the various versions of the PCM..
 

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Discussion Starter · #16 ·
Hello,

Thank you to everyone who spent time on this forum and trying to help me out! I appreciate it. As expected, the solenoids did not fix the problem. So I am off to either rebuild or replacement stage. If I decide to replace I will go with a '95 trans to keep things simple.

Thanks again!
 

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1994 Firebird Formula 381ci LT1 / TH400+GV O/D
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