sohofisherman

Hello All. This is my first post to the yotatech forums. However, I have been reading these posts for years now. Usually, my problem diagnosis is resolved by consulting the forums, but I haven't been so lucky in regard to my current issue.

My Truck: 1998 Toyota Tacoma V6 4WD SR5 199K miles. I'm the second owner beginning at 65K.

Original Equipment: Suspension and all steering components, drivetrain (except for a rear u-joint replacement in 2014), differential components, transfer case, transmission, wheel bearings, etc.

Recent Maintenance: Replaced all six fuel injectors, spark plugs and wires, and some ignition coils after misfire detected on engine cylinder 5 (injector solenoid was faulty). Changed/replaced front and rear differential fluid, power steering fluid, transfer case fluid, and automatic transmission fluid (including transmission filter).

Problem: When at highway speeds, a clunk or sound can be felt and heard from the rear of the vehicle. The feeling and/or sound can be mild, moderate, or more severe. Mild symptoms are difficult to feel/detect while moderate sounds are more noticeable. Severe symptoms can be felt through the entire drivetrain leading to vibration in the transmission and sometimes both the transmission and the engine. A loss of power of approximately 5 mph and a jerk is not uncommon with severe clunks/sounds/symptoms. Mild and moderate symptoms are not accompanied by a loss of power. Instead, there is a definite skipping or slight hesitation while driving. I have noticed that these symptoms are more pronounced when driving into an intense headwind or approaching cold front. I originally thought that wet conditions were also more conducive for exacerbating the issue, but I recently experienced the same problem while on dry pavement. Mild and moderate symptoms are more common when the vehicle is warm (~1 hour or so of highway driving) and severe symptoms are more common on longer road trips when the vehicle has been driven for 250-500 miles. A range of symptoms are also felt on these trips. When the truck is cold, clunking is nonexistent. This problem is always felt at highway speeds in overdrive (4th gear). I'm not saying that it doesn't occur in lower gears. If it does, I just can't feel it or hear it. Symptoms can occur while driving up a hill/mountain, but more often occur while coasting at speed on straight-laned highway. It depends on the day, but clunking will probably occur 2-3 maybe 4 times on a good day for every hour of driving. On longer drives, clunking can occur 10 times or so with at least a few moderate clunks and one good jerk. Folks that ride around with me frequently are provided with opportunities to experience the issue. Others that don't simply don't get to. The clunking issue isn't really annoying to me as much as it is discerning to both my wallet and perception of safety. It's only annoying on longer drives when the truck acts like it's sick and has the hiccups--no kidding. I'd like to diagnose the problem to save money on a rebuilt transmission (if it comes to that) or if it is a drivetrain issue to prevent hazardous driving conditions associated with drivetrain failure.

Originally, I had thought this issue was part of an ongoing engine misfire spat during which the truck visited four different repair shops (dealership included) after I couldn't locate the problem myself. However, it definitely seems as if the engine misfire and the current issue were two unrelated problems. No Check Engine Light while experiencing the above symptoms, and I can't hear a misfire either. Engine was also misfiring at idle when CEL light came on although I'm sure there was a misfire under load at some point. I have shifted my thinking to either an automatic transmission issue or drivetrain issue. I drained and replaced about 5.5 qts. of transmission fluid and changed the filter. To my knowledge, the transmission fluid and filter had not been changed in at least 100K+ miles. That's my own fault. However, the fluid was dark reddish orange/slightly brown in color and did not smell burnt (normal ATF smell), so I don't suspect any overheating or burnt internal parts (clutch). There was some sediment/gunk in the bottom of the pan and a few (4-5) metal flakes on the magnets. I cleaned the magnets, wiped down the pan with brake cleaner, and resealed with RTV. I replaced approximately 1 qt. of transmission fluid with Lucas Stop Slip, but I'm still experiencing the same symptoms (Lucas can't fix broken internal or electrical components). Shifting between park, reverse, neutral, and drive does come with slight movement (I guess that might constitute as hard shifting) when the vehicle has been sitting for a few days in cold weather. Occasionally, symptoms occur when easing off the accelerator slightly and then accelerating again. However, most of the time symptoms occur and are more noticeable when coasting around 65+ mph on straight, level stretches of highway. Could my highway symptoms be the result of a faulty shift solenoid or shift sprag/sprag clutch not disengaging when letting off the accelerator and subsequently regaining speed by pushing the gas pedal? There is some vibration in the steering wheel and while pressing on the accelerator while driving 45 mph+. This vibration is less common at lower speeds and gears. Truck had a courtesy wheel alignment and balance performed today (2/7/2017), which did not solve the vibration issue. To be honest, 19 year old steering and suspension components probably aren't helping either, and for a little while I even thought that some potholes and bumps I hit accidentally were making the noise/sound. However, symptoms are definitely felt/heard on what appears to be flat highway road surfaces in the absence of dips, holes, and cracks. I had never felt vibration in the gas pedal until the clunking problem began. Does anyone think that the vibration and potential transmission issue are related? There is no play in the drivetrain that I can feel by hand, and I personally lubed the entire drivetrain (zerk fittings) and front end with grease last weekend. I'd like to be able to determine whether or not the symptoms I am experiencing are transmission or drivetrain related or neither before taking my repairs any further. I'm better than the average Joe when it's time to be a mechanic, but I'm not a mechanic. I'm not skilled enough to rebuild a transmission, but I don't have any help to install a new one, unfortunately. So, please keep that in mind when responding.

Also thought that the front brakes and/or rear parking brake bell housing was sticking. This is not the case either. Wouldn't that have been nice. Truck's rear main seal is seeping (not bad). Could any engine oil pass the fly wheel and mix with transmission fluid? Motor oil would only increase the heating capacity of the AT fluid, but lack chemicals necessary for AT functionality. Still not sure a little transfer would be causing my problem but who knows.

All the best,
Matt.

^^^Note: Problem existed before misfire diagnosis and above maintenance. If anything, the problem seems to have gotten slightly better with fluid changes but that could simply be my imagination. Regardless, it still exists.

83

Well I don't have much advice except it sounds a bit like a transmission issue. I don't know anything about auto trannies, though.

My only advice, because I feel bad just leaving your thread hanging out there with no response: We're very helpful around here. And we are literate, I promise. But we're busy people, most of us, and we don't come here for our reading. I'm still finding the right balance for this myself, so I'm not saying I know the right way to post, but you have to find the balance between describing the issue and what you've looked at, and keeping the post brief. The first time I opened your thread, I closed right back out without reading it, because I just didn't feel like reading so much text.

Hopefully somebody has some info for you, though.

Good luck!

sohofisherman

Thank you for the response.

I, too, think it is a transmission issue. However, the problem has been around for a couple of months, and it doesn't seem to be getting any worse. Therefore, I'm assuming that there is a slight chance that the problem could be in the drivetrain. I'm also fairly ignorant in regard to how quickly potential transmission issues become more servere.

I realize that my initial post was quite long, but I was trying to be as comprehensive as possible. Many of the threads that I read on Toyota and Tacoma forums are resolved after a few responses where the author simply isn't as detailed. I was trying to avoid having to answer questions about the problem/symptoms, previous maintence, and fixes that I hadn't considered.

I didn't post with the expectation that everyone will read and comment on the post. I did so in hope that the right person is out there with the correct knowledge to help solve/pinpoint the problem. I'm very busy myself and having used a good portion of my afternoon that day writing up what I wrote is certainly a testament to my desire to fix the problem and seek advice.

Regardless, does anyone know what might be causing my symptoms?

Malcolm99

Where did you get the transmission filter, they should be a reusable screen. And what ATF are you using, if the issue is during overdrive it is related to the torque converter., maybe even a bad flex plate attached to the torque converter, they stress crack and make a clunking sound,.. Also, it is common for the rad to fail mixing rad fluid into ATF, some flush the hell out of them and sell them afterwards knowing there has been damage done to the trans, not honest but it happens. These transmissions are a bit clunky at highway speeds if you let off the throttle and get back on right away it may result in a clunky shift out-in-out of overdrive and is normal if the kick down cable is set to tight, you can adjust this on the kick down cable on the throttle linkage. And yes, I'll admit I closed this post a few times due to the info overload., infact I still haven't read it all just quickly scanned over it, so perhaps I'm missing something. And there is no way for engine oil to get in the tranny, and brown ATF, gunk in the pan and metal shavings are all very bad for the transmission and can cause internal damage, 100,000mi is way to long between flushes.

83

I've been through the same thing. Wanting to avoid the follow up questions, I put everything in the thread. Then look back and see that I've written a novel. Like I said, it's a balance. Sometimes you've got to just keep it brief and get a conversation going, even though your natural instinct is to be exhaustive.

thefishguy77

iTrader: (1)

Could it be the output shaft on the transmission wearing?

sohofisherman

Malcom and Fish Guy,

Thank you for the suggestions. I'll put kick down cable adjustment, torque convertor, flex plate, and transmission output shaft on the list of potential causes.

AT filter came straight from Toyota as did the AT fluid (Dexron). I had actually considered coolant loss. Tell me more about what might be happening here? I have been loosing coolant, but I don't think its that serious. Maybe I'm wrong. Perhaps a pint every 25,000-50,000 miles.

I will also say that the clunking that I feel is most often in the rear wheels or rear diff, which then (if bad enough) will vibrate through the drivetrain to the transmission and even engine. Rarely, the problem begins at the transmission. It all depends on how long I've been driving for and for how many miles.

Think I should take the truck out of overdrive on a few highway runs to eliminate or identify the torque convertor as the culprit?