Hi, I'm new to this site but can see it is very informative and staffed by knowledgeable people. Here is my situation. I have an opportunity to buy a friends 1996 Bonneville SE. He has owned it since new. After testing driving the car for a few days I dicsovered a very severe vibration/shudder coming from either the engine or transmission. It seems to happen only after the engine has reached operating temperature. The vibration/shaking seems to occur when in overdrive at highway speeds when the engine is trying to maintain speed on a slight incline. It does however occur at other speeds too though the vibrations are not as prominent . There doesn't seem to be any "slipping" happening and it seems to shift smoothly between gears. My friend has offered to buy the car back if I want or he will split the cost of any repairs. He was not aware the car had these problems. I have been talking to mechanics for ideas as to what could be causing this problem and so far I have been told to change plug wires, which I did, but no change. I changed plugs, no change, but they were very white in color. I cleaned the mass air sensor, no change. I tested the primary and secondary ohms on the coil packs, all were in proper ranges. I was also told to change the oxygen sensors. I have not done this yet as it seems to be a stretch. I'm thnking maybe something is going on with the torque converter. The car does not stall when slowing, starts very good and idles very smoothly. The vibration/shaking is bad enough that it shakes the dash and makes anything in the glove box bounce around. It is similar to driving over a gravel road that has a very bad "washboard" surface. Does anyone have any suggestions as to what the problem might be. Can a qualified mechanic detect the specific problem so that I'm not paying for unneccesary repairs in a process of elimination? Thanks for any insight.

Welcome to the club. Don't let this completely make your decision against the buy. I have two Bonnevilles one which I just bought. They are great reliable cars and very much fun. The first thing that comes to my mind here with everything you have tried is injectors. I had the same problem and it turned out to be an injector that was the wrong injector completely. I replaced the one that was different with one from the local Pick N Pull and it runs like a dream since. There are other things that I will let the resident gearheads tackle, but I did have the same shuddering when the lockup kicked in.

What you describe sounds like chuggle. And the suggestions given to you so far are good. Typically chuggle is ignition related.

This issue is only when heading up a slight incline in OD? Doesn't happen at certain speeds all the time?

Billboost, Oh no, not the dreaded CHUGGLE! : < ) I like it. "This issue is only when heading up a slight incline in OD? Doesn't happen at certain speeds all the time?" No, at times there is a slight vibration/shimmy/chuggle during acceleration from a stop. It seems the lower the rpms, the more noticable the shimmy/shake is. Now I'm also leaning towards an ignition or electrical problem since the engine needs to be at operating temperature before the problem shows itself. Maybe there is a component that works fine until it gets hot, then malfunctions. Anyway, I'm taking it to a shop on Tuesday. Hopefully they can pinpoint the problem. By the way, if you had to take it in for work, would you take it to a Pontiac dealer or a reputable transmission shop?

jed

Why would you consider a tranny shop for whats usually an engine ignition problem?
Is this a multi-taleneted repair center or something?

imo, the dealer would be more familiar with the chuggle problem as it affects other vehicles also.

popatim, maybe I was ahead of myself alittle. My thought was, If it were a tranny issue, then dealer or tranny shop? BTW, it is going to the local Pontiac dealer on Tue. I'll update as to the finding.

jed.

Jed...let the barrage of questions continue

Have you noticed any coolant loss lately?
How many miles on the car?
Has the upper intake manifold ever been replaced that you know of?


Take a look at this link for informational purposes only at this point. Sometimes..the beginning of a failure can show itself this way..but not usually..
http://www.bonnevilleclub.com/forum/...e=article&k=38

if it turns out not being the ignition system, smell the trans fluid. TC shudder is caused when the trans fluid reaches a certain temperature(too high) at which time the fluid actually breaks down. I'd follow the other advice on the ignition systems, but what I mentioned also popped in my head. I suppose I should ask, is it a very consistant vibration? Is it sort of like a pulse that gets stronger and weaker?

BillBoost37, No coolant loss, the car has 184,00 miles on it and if the upper intake and the plenum are the same thing, then yes, it was replaced less than a year ago.

MyLittleBlackBird, I considered changing the fluid and filter but according to the owner and the maintainance records, the tranny fluid was changed about 2 years ago.

The fluid definately does not look as red as new fluid, it also isn't real dark in color either. I did add a bottle of Dura Lube for Dexron III tranny fluid but it made no difference.

It is not a constant shudder/vibration. It does not get stronger and weaker. It is either shaking or it isn't, there is no in between. It only happens after the car has reached operating temperature. The violent shaking happens at highway speeds in OD when the engine has to work slightly harder to maintain speed, such as traveling up a very slight incline or against a head wind. As soon as the engine drops out of OD it quits. That'* not to say it doesn't do it at other times though. I've noticed a subtle virbration at times upon acceleration from a stop also. But as far as shifting from gear to gear, its smooth as silk.

Thanks everyone,

jed