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Discussion Starter #1
Hey guys. I know I haven't posted in awhile, but my car has been acting funny lately...

The 1-2 upshift on WOT, the trans feels like it slips between gears, like it's not making a solid transition into the next gear.

Also, on the 2-3 upshift under normal accel. and WOT, the RPM's flare up when the trans shifts.

Is my trans taking a crap, or something else? It only has 67,000 on it... and especially since it's behind an underpowered L99, I'd think it would last longer than this...
 

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Might try cleaning the EPC solenoid screen. Bet Google will turn up instructions.

Since the problem is presenting in multiple gears it makes sense to look at an issue that would affect line pressure. This is a pretty cheap and easy thing to do too.
 

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Discussion Starter #3
I forgot to state that this issue only presents itself when the car is up to operating temp. And that after driving the car for awhile, and the fluid gets hot, it seems alot more hesitant to get out of second gear, but I guess that's normal for any auto trans that gets hot.

Would switching from the smaller L99 servo to a corvette servo help at all? Maybe it's just natural for the car, and it doesn't produce enough clamping force on the bands?
 

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You might consider calling pro-built.net and ask him about the servo, maybe even a Transgo kit with the servo, new boost valve etc.

He helped me with some issues I had with a locally built tranny before it blew and onc3e it did blow I ordered the current one from him, that was 8.5 years ago when my goals were much milder like 150hp less than the car has and all he had me do is redrill one single hole when I added the power and it has been great.

At any rate he will talk you through things even if you aren't buying anything right then, the service and support ensures that later when you do need something you think of him.
 

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Discussion Starter #5
Just an update on the issue. I found a TSB for 1995 L99 cars with 2.93 gears and 4L60-E trans. Its says that the PCM needed to be reflashed. I took it to my local Chevy dealer, they loaded the newest PCM file in, and now... It shifts perfectly.

Here's the TSB I read on MotorAllData...

FILE IN SECTION: 7 - Transmission

BULLETIN NO.: 57-71-05

DATE: February, 1995
SUBJECT:
1-2 Upshift Run-through with End Bump and 2-3 Upshift Flare
(Reflash Control Module)

MODEL:
1995 Chevrolet Caprice
with 4.3L Engine (VIN W - RPO L99), 4L60-E Transmission (RPO M3O)
and 2.93 Axle Ratio


VIN Breakpoints:
SOP - 134648 - Federal
SOP - 134795 - California (Export)

CONDITION
Some owners may experience a 1-2 Upshift run-through with end bump and 2-3 Upshift flare.

CAUSE
Change in power level.

CORRECTION
Reflash the Powertrain Control Module with the appropriate part numbers below.


Refer to your Service Manual for proper procedure.

PARTS INFORMATION
NEW FILE # DESCRIPTION VERSION16220821 Federal March16220831 California March (Export)


This new calibration will be available starting with the March, 1995 CD update.
 

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How much did they get you for that? You know you probably could have done a custom tune resolved the TBS and gotten some other improvement.
 

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Discussion Starter #7
Luckily, my best friends dad is the parts manager at this particular dealer, and was able to have the tech do it "on the side".
 

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Just following this thread and saw someone with an L99 motor,is
that motor the same as the LT1 except for cubic inches displacement?
If so its always interested me,I would think that little motor could really
pump out some horsepower especially in class type racing like
stock or superstock. ed
 

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Discussion Starter #9
Besides the fact of displacement, they have different cylinder heads. But it has the reverse flow cooling, cam, intake just like the LT1.
 

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Tryin to build an L99 is an even worse idea than building a 305, just get an LT1.
 

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On another forum one of the creative and quick guys even tried my old L99 crank and rods with LT1 pistons in an LT1 block to build a 302 with hopes of fuel economy. Don't remember which heads he used. At any rate I think he pretty much branded the project a failure. The lack of stroke meant no torque and no torque meant the converter was always unlocking and it was always downshifting, it was pointless, and that was a 302.

Oddly the L99 rods are a goofy length so the L99 and LT1 pistons had the same height which is why he was able to just use stock LT1 pistons on the L99 crank and rods.
 
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