Recently, I have noticed a shudder in my 87 Coupe. It has a stock 400r7 tranny. It shifts smoothly from 1st to 2nd and to 3rd. But when it shifts into 4th, it shudders slightly. Now, when in 4th, if I accelerate, the car it begins to shudder badly. Some friend told me it was probably the converter lock-up is not working properly, but I don't know the first thing about auto trannys.
The engine is basically stock with a few bolt-ons: Hypertech thermomaster chip, air foil, Dynomax high performance mufflers with Y-pipe and crossover.
Is the tranny giving up or is it a minor problem easily fixed?

 

I am dealing with the same exact problem with me 87. Pete K is the man to ask.

 

OK, PETE K. HELP US OUT PLEASE.
Thank you.

 

ODIVETTE, read on. This was sent by a reader in another forum. I will try that soon.


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Hi there,
One way to make sure its the converter.
Simply touch your brake pedal while you are steady cruising or when the shudder occurs, while keeping your foot on the gas.
This will disable the TC clutch and tell you if that is what is causing the problem.
Allthebest,
__________________
ALMOST GM world class certified! 7 down, 3 to go. Chevrolet Professional service guild NCM#7993. FIX IT RIGHT OR DONT OPEN THE HOOD! My greatest asset, my daughter. http://www.corvettemechanic.com

 

I never tried that....but I will. If that eliminates the shudder...what needs to be done/bad torque converter (anyone know)?

 

Just off the cuff, it sounds to me like your coverter is trying to but not locking up. Pete K will have the answer for sure.

 

ODIVETTE: Read on.

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I just checked it. When shuddering started I kept my foot on the gas pedal & touched the brakes and the shuddering stopped.
Thank you very much.

 

Hmmmm.....so, how is this problem fixed? What exactly is the problem?

 

Maybe when Pete K reads this he can tell us.


HEY PETE

 

What you guys are describing sounds like a classic case of torque converter shudder. Inside of the torque converter is a large diameter plate with a thin ring of friction material bonded to it. When the solenoid causes the valve to move, fluid forces the lock up plate against the rear of the torque converter, thus locking it up and allowing it to go 1:1.
If the friction material is glazed, worn or peeling, it will cause shudder.
The only way to fix this is to rebuild the converter and rebond new friction material. The company I use bonds raybestos 500 hp friction material. It lasts a very long time.
If the converter needs replacing, the good news is that the time is right to install a higher than stock stall rated unit, if you choose to do it. If you need one, I can hook you up.

 

i am having the exact same problem. dam time to yank the trans,

hey pete, how much for a new high stall converter from your source?

 

The place I use charges $300. No core required. Actual shipping from pennsylvania would be extra.
They can add anti balloon plates for $50 more. Most of us do not need those, but it is a nice service that they offer. They also beef up the guts and use the 500 hp raybestos friction lining I mentioned.If you need one, pm me and I can help out...

 

Pete, why would the shutter occur only in OD? And, in my case, later start in D? Also, anything else we can do to confirm that it is the torque converter and not something else? Dropping the tranny is going to be a pain in the a$$ and, with my luck, I'll go through all of that and it will do the same thing.

Also, what stall speed would you recommend for a daily driver that gets some track time?

 

Usually, the torque converter chatter will start in 4 th gear and as it worsens it will occur in third gear as well. Some will even do it in 2nd gear, if the trans is wired up to allow lock up in 2nd gear. As someone else mentioned, unplugging the lock up connector will stop the converter from receiving the ecm trigger to lock. Unplug it and go for a ride. If chatter goes away, there is a 99.9% likelyhood it is the converter. This will save alot of time testing components.
On a street driven, mild modded l-98, I like 2000-2500 stall, depending on needs. If you change converter, we can discuss it in detail to be sure you get what you want/need...

 

also, before you are committed to a trans removal, check your u-joints. I was in the process of removing my trans, looking over my marvelous aluminum driveshaft, when I noticed the ends of the u-joints look like they had gotten warm.
Popped the caps, and they were as dry as the sonoran desert complete with metal dust inside.
I changed the u-joints, and vibration gone......started at about 40 and just got worse. the faster I went, the more the vibration.
Since the torque arm ties the trans to the rear end, they don't move very much, and the rollers wore grooves into the caps,
but that was my particular instance.
after you change 6 u-joints, you kinda get to be a professioal u-joint remover and installer

 

I have the same problem in my '88 and found this thread very informative. Given that there is chatter in both third and forth gear, how much damage to the trans has been done or will be done with continued driving?

 

Because the lock up feature reduces heat substantially, continued driving is not good. Also the chatter will pound the front pump bushing(and others). Always wise to fix a lock up problem quickly.

 

What you are describing is called Pulse Width Modulation. This actually happens in the converter from day one when you buy the car itself. The stock converter uses a clutch that is built to allow slipping in the converter. However, considering the amount of abuse that transmissions and their components take, 20 years can take its toll. But it is not necessarily actually the converter itself. If the valve body has excessive wear, these exact symptoms can manifest themselves. Before you take the jump to a new converter, I highly recommend confirming that the converter itself is the problem. This is pretty easy to do. There is a small round cover on the bottom of the bellhousing that can be taken off to see inside the converter itself. Shine a flashlight up there and look at the front of the converter (the part that faces the engine, not the transmission). Look for any darkening on the converter. If a clutch is going out, there will always be a ring of darker material created from the heat on the front cover. It will look burned. If everything looks okay, you need to rebuild that area of the valve body.

I highly recommend, if you decide to swap the converter, not going to a restalled/reworked stock unit. For the cost, it isn't worth the end result. The restalled stock units don't save you any weight and aren't much less expensive than a high quality smaller diameter. A small diameter converter will give you considerably more performance as it allows the engine to spin a lot faster. If I can help you in any way, please feel free to shoot me a PM, or give me a call at (801) 368-9655. That is my cell and I'd be more than happy to answer any questions you might have.

Thanks,
John Cameron
FuddleRacingTorqueConverters

 

Pulse Width Modulation started in 1995. Prior to this it is a on-off switch that controls the TC lockup. When installing a TransGo Performance Shift kit, this will eliminate the PWM, and bring it back to a on-off setup. In theory the PWM is supposed to make things a little smoother, but in reality it has been a headache.