I've got a problem with my transmission. (duh) Anyways, I took a trip to Nebraska on friday afternoon. I'll be going along at about 70-80 MPH, and I'll try to accelerate to go up a hill or something, and it'll downshift out of overdrive like it should, but the whole car will start shuddering pretty hard. I'll put more foot into the gas and the problem will go away. I'll drop back down into the same RPM band (20-25k) in the same gear it will be fine. At first we thought the problem was just at high speeds, but it happens at 50-60 MPH too. Any ideas on what might be wrong?

Oh yeah, Stock305, stock 700R4, 146,000miles on both.

 

Need more info.
Do you feel the shuddering throughout the whole car?
Can you feel it in your seat, or do you just see the dash shaking?
Is your engine stuttering/missing at all at the same time?
Is it just in one gear? Second? Third?
It only ever happens at part throttle?
Does it always happen between 20-25k?

 

Shuddering throughout the whole car, like I'm hitting bumps.
Can feel it in my seat
No studdering/missing.
I think it's when it comes out of OD into 4th at around 75-80 MPH but it's done it after the OD to 3 change at 55-60 MPH also (It could quite possibly be the same gears though). Only at part throttle, if I put my foot into the pedal more, it comes out just fine into the gear. Also, it seems to only do it when it's hot or been used for awhile.

 

I would put my money on torque converter clutch. When it starts doing it again, tap the brakes enough to make the brake lights come on. If it stops, it is most likely the TCC.

 

I'll have to check it out. I'm stupid with transmissions, so tell me what it means. Thanks!

 

Guess nobody else knows? I read a couple of other posts and they had the exact symptoms of mine, but nobody replied.

 

I've been researching this a little, and it loks like it's TCC related. I have no idea what I'm talking abut, probably I'm wrong. this is my only driver, and I'm gonna have to take it to a shop.

 

I put some transmission treatment for cirs with 50000 miles or more on their fluid. Thick as syrup. Haven't driven it yet, I'll y'all know.

 

I'll agree that it could be lock up torque converter related, it definately sounds like a balance problem: i.e. tire/wheels, driveshaft, flywheel, torque converter. By tapping the brakes, the electric solenoid which causes the torque converter to lock up for a false 4th gear which improves gas mileage will receive a signal from the computer that you are slowing down and it should unlock the torque converter, though it should unlock when you put your foot into the gas pedal anyway. Sometimes with these electric lock up tc's the solenoid fails to unlock. Then when you come to a stop from driving a distance and speed that would call for lock up, the car will stall as if you were driving a standard and didn't clutch as you slowed to a stop. If your solenoid is failing, you can simply unplug it and it will drive fine for a while...you can even do this to test the lock up tcc...but beware, highway driving for a tranny with lockup tcc REQUIRES lock up because it is relative to the fluid pump for your tranny, which will not be operating per design when you unplug the solenoid, thus burning up your tranny. I know all of this because not only have I been to school for transmissions and worked at a tranny shop in houston, but because it happened to me on my old `91 grand am. After mine went out I had to drive from houston to san diego with it unplugged, and then at least 60 miles a day if I kept the car (120 if my wife kept the car) for an additional 15 months, due to lack of money (military).

 

I don't believe it's a balance problem now. I thought I had it fixed, I put some tranny additive in it, and it did help immensely, but it didn't fix it. I was playing around on the highway today at some relatively high speeds, and I was giving the tranny a really good workout. When I got back to where I was coming from, the shuddering had shown up again. Seems as if when the tranny heats up, the problem shows up.

 

Ok since you have a similar setup to me, I'll assume you have a steel driveshaft. The critical rotational speed of a steel driveshaft is around 7100 RPM, but at half that, around 3550 RPM vibrations will occur. This is different for everydriveshaft though, more for some less for others depending on how well it was balanced and initially forged. This is only aggrevated by age and condition of the driveshaft, where it drops over time as corrosion will alter the rotational characteristics of the driveshaft. Since I changed out my differential, the speeds at which this occurs is different, but the RPM is the same. For me this occurs at around 3400 in 3rd gear and 2400 in 4th gear. Notice with a 700 r4 2400/0.7=3428 where 0.7 is the tranny ratio. The speed this happens at is roughly 100 mph with my old 2.73 gear, but with a 3.23 in, its like around 85 mph. If the vibration is as consistent as you say it is and always happens at those RPM, then that is most likely your problem.

To determine if its your TCC, you can jury rig your TCC to lockup as early as 2nd gear and stay locked up for 2nd third and 4th. If the vibration is constant while the TCC is on, then get that fixed/replaced. If not, your driveshaft may be the issue. This site has a guide to making a TCC lockup switch via the ALDL.

https://www.thirdgen.org/newdesign/t...ueswitch.shtml

The only way to get rid of that problem is to put in a better driveshaft. It has to be stronger and rated to higher RPM. An aluminum 1LE driveshaft is a quick drop in part and cheap. Also have carbon-fibre ones, but that also runs up in price. Good luck.

 

The vibration comes and go's depending on the tranny, not speed. If the vibration was always at 90mph or something like that, then sure it could be a driveshaft. Unplug the tranny and take it for a drive--see if it still does it. Plug it back in when you are done.

 

You know what it sounds like? Torque converter clutch chatter.

I had a friend of mine whose TC was doing that. Have you ever been in a stick shift car that had clutch chatter? It feels similar with an auto but nowhere near as bad. And with the auto it seems for some reason that shudder on RELEASE is more common than on apply (opposite a stick shift). It almost sounds like when you give it a bit more foot the TCC unlocks and the vibration stops.

 

yeah, when i give it more foot, the vibration stops. It's progressively gotten worse, and I know it can't be the driveshaft, because it'll run fine in the 2200 range just on normal driving, but when I get out on the highway, I really notice it in every gear transition, no matter what gear. I DO think that I might need new u-joints because they make a small amount of noise when I hit the gas, but no thuds or anything like that, just noise, which has always been there. Like I said, this all started when I took a long trip in the car ~400 miles.

 

Consider the relatively lost cost option of having the fluid completely changed using the T-tech (or similar) system. I've experienced this same condition (attributed by some to cavitation in the torque converter) disappear completely with a fluid flush.
Can't explain it myself but have felt it suceed. Not a substitute for replacing worn/damaged parts but a simple place to start.

Tom

 

What is the T-tech system?

 

T-tech is one particular brand of a system which flushes the fluid from an automatic transmission system. It ties into the fluid cooling lines and uses the transmission's own pump to remove all old fluid and replace it with all new fluid. You can watch the color improve while it works. Many oil change places have this and the service typically costs around $60 to $70. Since fluid change is smart maintainance anyways, might as well do this. Much more effective than just dropping the pan.

Tom

 

What you're having is called converter-clutch shake. I have the exact same problem. I had my trans pan dropped and the filter and fluid changed, which made the problem go away for about 5,000 miles and now it's back again....and like yours, only gets worse the warmer the transmission gets. I just have to baby it for a little when it starts to happen and not remain in the RPM zone. What it means (or so I've been told) is that the convertor is starting to go out, which means your transmission is going to have to come out.......yeah.....time for a rebuild.

As far as the T-tech system; I don't recomment it at all. I used to work in a grease pit with this system, and I do not recommend it for a high milage tranny. My transmission guy (who has been working on trannys for 30 years) refuses to use the system, but likes it because of all the business he gets for having to fix the all the problems they cause other people.

My recommendation if you have that many miles on it, is to get it rebuilt. And on the bonus, while it's being rebuilt you can throw on a transmission cooler , a corvette servo and a trans-go shift while it's all apart.......or you can just order a stout tranny from Pro-Built for about the same amount of money.