Ls2SilverBullet

I have a ls2 swapped z28 with a built 4l60 with a 3500 stall with full lock up(car in sig). Been having issues with wot shifting and a vibration/jerking that only occurs during full lock up.

So, #1...
The car is having issues shifting from 2nd - 3rd at WOT. When it was on the dyno my tuner said he thought my clutches were slipping past 5k rpm, but it still made 427/371 at the wheels. I would like to think its not slipping but I cant tell for sure.. At WOT the car will just bounce off the rev limiter until I let off some and then it shifts. I dont know if this is due to a slipping clutch or poorly set shift rmp and mph. I would like to think its in the tune, but IDK and i want to get to the bottom of it so I can run the car all out. This has been going on for a long time now but I rarely acutally put the pedal to the floor so I've just put up with it for over a year.

Tell me what you think

#2...
When I'm just cruising at a given speed with the converter in full lock up (converter locks up at about 40mph and the problem is worse at lower speeds close to 40 than it is at higher speeds) I get a vibration/jerking front to back if the car begins to slow down. It only happens when the TC is locked up, and occurs when the car begins to gradually slow down (very noticible on highway with cruise controll when I go down the slope from an overpass .It will feel like its jerking back and jumping forward slightly and I hear a chattering noise. If the TC unlocks when i begin to slow/let off the gas the vibration and noise do not happen and the car rolls smoothly.
Maybe rear end problem? My best visualization in my head of what could cause this is the there is "play" in between the teeth of the pinion and ring gear, when gas is applied they lay properly, but when the car begins to slow they may bind causing the vibration? What you think?
ALso, SOMETIMES when the converter locks up I hear a pop from the rear of the car.

I know these type of things are hard to to diagnose through my explanation but any advice or ideas are appreciated.

I'm putting on new rotors and pads today so when the rear is up I plan on checking the rear end pinion bearing, ujoints, , trans mounts, and tranny output shaft bearing/bushing... Is there anything else you guys would check out while im down there that may cause this?

THanks Y'all

Gilbert@Ace Racing

If the transmission fluid looks and smells good then the 2/3 shift issue is in either the transmission itself or the tune.

The second condition you are referring to is what is commonly known as "cam surge". Have your tuner move the converter lock up to somewhere in the 48 -52 mph range and you will not experience that. It is the exact same condition that can be felt when shifting a manual transmission into a higher gear at too low a vehicle speed.

g

Ls2SilverBullet

Thanks for taking the time to read and reply.

I keep the fluid really fresh, it looks and smells good. In the tune, what does the shift depend on? RPM, MPH, and TPS %. Anything else?

As for the "cam surge," would it still happen at higher speeds like 60-75? Because mine does it then also, its just more noticible/louder at lower speeds.
What causes this? A slight but rapid increase and decrease of power through the drivetrain?

Thanks again

Gilbert@Ace Racing

Yeah something like that.... it's very relative to the cam vs. torque converter vs. rear axle gear ratio. So to say that yours does it at higher road speeds but it is more apparent at low speed tells me that it most likely occurs at very light or <15% throttle.

It is merely a function of the engine power pulses. A word of caution though... if it is allowed to continue converter clutch failure can occur. The only thing that can be done to alleviate the symptom is to have it tuned while driving... meaning a dyno tune will never solve the issue because a dyno cannot simulate the same load that the vehicle weight itself represents.

Hope that helps to explain it.

g

Ls2SilverBullet

Yes, it definitely helps, thank you. And you're right, it happens under very light or 0 throttle. Makes sense about needing an open road tune, car hasnt one since I've owned it.

It has done it since I bought the car almost 2 years ago. And has recently gotten a little louder/clunkier. Not a good sign I'm guessing...?

Thanks again

Gilbert@Ace Racing

You're welcome, glad I could take some mystery out of it. Many Tuners preoccupy themselves with maximum power and don't really consider driveability. Not all tuners take that approach, but in my experience many, many do.

The clunk / noise that's changing is most likely excessive play or slop at the ring and pinion, maybe worn u-joints. But if the converter clutch is holding and the tranny is solid... the drive line slack you are feeling is in the driveshaft or axle.

g

Ls2SilverBullet

yeah, hopefully its not trans related. I'll rule out the driveshaft, ujoints, and gears before anything..was supposed to do that when I installed my new rotors yesterday, but after breaking a bolt and having to go to the hardware store I didn't have time before i needed to be back at work.. guess ill get under there and make sure there is no play in anything

I want to get a copy of my tune to inspect also. might as well rule that out also before I drop the trans.

i have a good understanding of engines but trannys, not so much. how difficult is it to change out clutches in one? I've been told if you let the wrong person touch you're 4l60 it will end badly