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Discussion Starter #1
I just go my driveshaft back from NAPA (had it balanced and new heavy duty u joints put on) and after putting it back I still have the same problem. Near the center of the driveshaft by the front driveshaft loop it is rubbing the edge of the sheet metal that protects the gas tank. It only happens under 25 when i hit the gas hard but it's the worst if I try to take off from a dead stop fast - it's makes real bad vibration and scraping/grinding noise. I'm guessing it's not the driveshaft anymore since it was just balanced and all. The driveshaft feels firm at the transmission tailhouse - almost no play at all, and where the driveshaft bolts to the rear end, it feels firm as hell too. Is there anything I can adjust as far as the transmission alignment? It seemed to get a good bit worse when I changed to the poly tranmission crossmember bushings and solid tranny mount. I also have new poly IRS bushings and cover to IRS frame bushing/mount. Does anyone have pictures of changing the tailshaft bushing so i know what I'm doing and looking for if I have to go in there. I'm sick of changing stuff and it not being the problem...
 

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Discussion Starter #3
that might stop that noise but what about fixing the wobble in the driveshaft? are you saying it's normal for the driveshaft to move that much to hit it? I'm confused...how could it be that simple?
 

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that was an idea i threw out. dont take my word for it. im sorry i shouldve said that in the first place.
are you sure it's the driveshaft wobbling and not just the gas tank protector? can you feel vibration at certain/all speeds?
 

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Discussion Starter #5
i figured it was the u joints 'loosening up' under heavy torque loads like when i take off from a dead stop hard on the throttle. it feeling like something is dragging on the drivetrain when it makes the noise. it's fine once i get above 20, even at full throttle in any gear but 1st it's fine. it makes a subtle low tone grinding/rumble sound if i just give it enough gas to come close to the bad noise it makes when it hit's the protector. i'm stumped.
 

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Discussion Starter #6
I've drove around and tried to learn so more about the noise. Besides being real bad from a dead stop, it causes a hum/vibration through the car right between 1900 and 2200 RPM in any gear. Beyond that it is fine, even at full throttle in 2nd and 3rd. Full throttle from a dead stop is a mess, from off the line in 1st, all the way into the first half of second gear, it sounds like pulsing scraping noise (I'm assuming it's the driveshaft rubbing the protector) and a constant grind/hum/vibration until I let off the throttle. If I take it easy on the throttle from the line and then pick up speed after I hit 20 or 25 it feels like there's no problem except the hum/vibration in the RPM range above. Any ideas?
 

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Pedal Faster
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What about your IRS mount/bushing? Is it possible that the pumpkin itself is moving, changing the pinion angle, and allowing the shaft to move?
 

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94 Birdman said:
it causes a hum/vibration through the car right between 1900 and 2200 RPM in any gear. Beyond that it is fine
hmmm. that to me doesnt sound like the driveshaft (that sympton in particular i mean). the fact that it does it at a particular rpm in every gear. the driveshaft will be spinning at different speeds when the engine is at the same rpm, but in separate gears. it would make sense that at certain speeds there was a vibration.
 

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Discussion Starter #9
more research: i found that if i left from a dead stop and kept it in 1st but didn't give it a lot of throttle, it was fine but as soon as i give it any more throttle it makes that real bad noise in that 1900-2300rpm, in first above 2300, no noise. if i let off the gas during the noise and continue light on the throttle out until i get past 2300 i can hit it harder with no problem, if i don't let off when it starts making the scrapping noise it continues all the way through 1st if i'm on the gas hard enough...what does that sound like to you guys? i'm starting to think it isn't the driveshaft myself and that it might be the torque converter - could it be slipping or something? what normally happens when a tc starts failing and what makes them go bad prematurely? if it my tc, does that grinding noise mean i have metal chips going through my tranny? i think i'm getting closer to having this figured out, i appreciate the help so far, thanks.
 

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Here are some selected symptoms and problems:

Low pitch rumble at all speeds over 20 MPH; fluctuating noise when turning: Worn carrier bearings.

Cyclic vibration (unsteady in intensity), more pronounced over specific speed range. Worsens when decelerating: Pinion angle too low, needs to be parallel with front yoke.

Cyclic vibration (unsteady in intensity), more pronounced over specific speed range. Worsens when accelerating: Pinion angle is too high, needs to be parallel with front yoke.

Steady vibration that increases with speed: Worn u-joint or driveshaft is out of balance.

Whirling during decelerating/ accelerating above 10 mph, possible rumble: Worn pinion bearings.

Good luck.
 

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Discussion Starter #11
is it possible that a bad bearing would only act up in that rpm range i listed above? the car sounds fine except for when it that 1900-2300 range...i tried searching for torque converter failures and noises and they all seem to be a single clunk noise. my car has had a clunk in the drivetrain ever since I bought (happens when it shifts gears) and it tried to get rid of it by changing the u-joints, half shalfts, rear end, new carrier bearings in the used rear end i bought, wheel bearings, new rear upper control arm bushings, knuckle bushings, IRS bushings, and rear end case to frame mount...still a slight clunk when shifting gears - i'm starting to think i'll never get rid of it...

PS i covered the shiny ring on the driveshaft with duct tape to see if it was hitting and making the scrapping/grinding noise...nope. after a day of driving and making the noise intentionally a couple of times, the tape is still in tact, i might of been hitting before I just had the u-joint changed and had it balanced but it is fine now and the noise I though that it was causing is still present.
 

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Birdman,
Yes it is possible. From what I have read, I believe that your pinion angle may be high.

If you have a high mileage car chances are that you may have other problems with the rear end. For example multiple symptoms. It may be a good excuse to get a track lock and higher gears? :D

If you do not have much cash try having a specialist look at your pinion angle.
 

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Discussion Starter #13
after thinking about your post awhile, high pinion angle sounded the closest to my symptoms. how could I measure the pinion angle? changing the u-joint and having the driveshaft balance did help the noise go away a good bit...that was one of the reasons I wasn't to sure it was the torque converter or not, it didn't make any sense if the TC was at fault the new u-joints shouldn't have made a difference. so how do i adjust the pinion angle? maybe if I just make it lower it'll let me know if that's it just by how it sounds and reacts after. thanks...i'm ready to adjust that sucker...I just don't know how...
 

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Discussion Starter #15
I'm going to try shimming the cover-to-frame mount on the pumpkin with some washers tomorrow to see if that helps the problem. I'm thinking the driveshaft angles down from the transmission and angles up from the pinion, so shimming the back would give me less of an angle by the pinion, right? Also, reading the section at the end about what changes pinion angle made me think a little:

when I first swapped out my stock pumpkin for a trac-loc 3.27, i think the noise started then but at that point was very faint. at the same time i swapped the pumpkin i did some exhaust work that required the whole exhaust to be dropped. from bottoming out once or twice the c-shaped brace (behind the transmission, held in place by two bolts on each side) was curled over on one side covering the already bent bolts so I had to remove it with a sawzaw. the exhaust shop said it wasn't anything important and wasn't necessary to replace...but somewhere down the line someone mentioned to me that it was there to hold the tunnel in body (for the driveshaft) from seperating and spreading out over time. for some reason i never got around to replacing it. could that seperating have changed the pinion angle over the last six months making it as bad as it sounds today? i'm going to replace it just for the hell of it and was wondering if anyone knew how far apart the two bolts on the inside of the tunnel were from each other. i'll go under tomorrow after work and see if it's seperated any from not having that brace on if i can find out the correct distance they are supposed to be from each other. thanks. i'm still wondering how the pinion angle would act up in the 1900-2300 rpm range, that's got me confused. thanks for the help everyone.
 
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