Driveline vibration - Impala Tech
Transmission & Driveline Transmissions & Differentials

 
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post #1 of 14 (permalink) Old 05-28-2009, 05:35 PM Thread Starter
 
 
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Thumbs down Driveline vibration

Hey dudes.
I'm new to this forum, but no to Impalas or the auto industry. I have had my 1967 2dr hardtop for 25 years now.
I have a real problem that I can not track down:I installed a 700r4 years and it has served me faithfully despite neck snapping second gear!!
With my 4.11 gears, in 3rd at 3000 rpm..there is no driveline vibration. I swith it in 4th and boom!!Vibration.
I recently lowerd the car by cutting the coils(cheap).I have it on jack stands so the full weight is on the axle and correct body height is in play.
I have added a BowtieOverdrives.com crossmember to possibly correct a u-joint angle issue, and it seems a little better.
Why the vibration only in 4th?My motor is not tied to the frame;driveshaft is balanced and the tires too to my knowledge.

Thanks, Greg
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post #2 of 14 (permalink) Old 05-28-2009, 09:58 PM
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I'll guess it is the converter..when it locks up..just a guess.
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post #3 of 14 (permalink) Old 05-29-2009, 11:11 AM
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Originally Posted by dgwar View Post
I'll guess it is the converter..when it locks up..just a guess.
Converter locking up is a hydralic clutch that forces the mechanism inside the torque converter to stop slipping with a shark skin type clutch surface (only allows movement in one direction as the surface is covered with little triangular barbs that catch one way and feel smooth the other).

Third gear is one to one and has no gear, but forth gear is a gear and there could be problems with the drum or the over run clutch that could be causing a vibration. I am betting it is an oout of phase drive line as they only balance the drive line statically not dynamically (difference between a wheel and tire that is bubble balanced off the car versus a spin balance).

Big Dave
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post #4 of 14 (permalink) Old 05-30-2009, 10:57 AM Thread Starter
 
 
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driveline vibration

Thanks for the info, but all this is happening when the converter is not locked-up, as i have a manual switch to lock it up.
I realize that at 3000 rpm in 4th the driveshaft is doing like 4000 rpm. It's as smooth as silk @3000 in 1st, so I am to think that 4th is getting wonky.
Any hints
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post #5 of 14 (permalink) Old 05-30-2009, 10:19 PM
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Quote:
Originally Posted by geetee150 View Post
Thanks for the info, but all this is happening when the converter is not locked-up, as i have a manual switch to lock it up.
I realize that at 3000 rpm in 4th the driveshaft is doing like 4000 rpm. It's as smooth as silk @3000 in 1st, so I am to think that 4th is getting wonky.
Any hints
It's either the band or the 3-4 clutch slipping. The most likely culprit is the 3-4 clutch as it is what almost always goes, but there is an outside chance that the 4th servo isn't enough to hold the band. The stock teflon seals can allow alot of pressure to pass them. If you wanted to try something before pulling it out, installing a super servo from sonnax will offer 40% more holding power in 4th gear, and is fairly easy to install from the outside. If it gets the problem then you've extended your trans' life. If not then 4th gear will be that much stronger on rebuild!
http://cgi.ebay.com/ebaymotors/700r4...Q5fAccessories
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post #6 of 14 (permalink) Old 06-02-2009, 03:56 PM Thread Starter
 
 
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driveline vibration

Hey guys(and girls)
This vibration feels like its going loosen your fillings in your teeth.It is a high frequency vibration too..like the faster you go the more it vibrates.
As I have stated, 3000 rpm in 4th the dash is buzzing, but at 2500 in 4th its not(driveshaft is most likely at 3000),so when the motor is at 3000, the shaft is going....?3800 plus.
a 3-4 clutch would feel like a shudder, No?

Greg
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post #7 of 14 (permalink) Old 06-03-2009, 04:15 AM
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Originally Posted by geetee150 View Post
Hey guys(and girls)
This vibration feels like its going loosen your fillings in your teeth.It is a high frequency vibration too..like the faster you go the more it vibrates.
As I have stated, 3000 rpm in 4th the dash is buzzing, but at 2500 in 4th its not(driveshaft is most likely at 3000),so when the motor is at 3000, the shaft is going....?3800 plus.
a 3-4 clutch would feel like a shudder, No?

Greg
Greg, 4th gear slipping could feel like a shudder or like a vibration. If the band/clutch is barley holding on under light load, the more power you apply or faster you go could cause it to slip. And then it could very well be the driveshaft, without seeing it, this is where internet diagnostics reaches it's limit!

One thing to look for is the that the ujoints aren't loose along the trunion's axis. That is to say that if the C-clips that hold the caps are missing, the caps could walk out a little. The joint may check out and not have any torsional play, but could be moving side to side and you'd miss it except for a nasty little vibration. I had this happen to me with my 69' Impala. I kept checking the joints to see where this annoying vibration was coming from and just didn't find anything wrong. That is until I was winding it up on an acceleration ramp and then heard what sounded like forks and knives hitting the trans tunnel resulting in the worst vibration I have ever felt in a car!! Thank God I was able to limp it down the parkway to the next exit, then the driveshaft dropped down but was fortunately kept in place by the dual exhaust. The vibrations where so bad that even after I repaired the driveshaft and got it back into the car, I noticed that the trans(which had just been rebuilt) felt kind of funny. After a little while of driving it that same day, the trans started to slip!!! What I had found out later was that the vibrations loosened up the bellhousing bolts and allowed the trans and engine to come apart. Far enough that the convertor disengaged the trans pump gears, causing the trans to lose line pressure and causing the trans to burn up. That was NOT a very good couple of days.
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post #8 of 14 (permalink) Old 06-03-2009, 04:19 AM
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BTW, the 700R4 has a .70 overdrive. So that means the driveshaft is turning 30% faster than the engine when in overdrive.
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post #9 of 14 (permalink) Old 06-23-2009, 11:28 PM
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Has this vibration been present the whole time since the 700r4 was installed? Overdrives transmissions are prone to causing driveline vibrations. The factory tunes out the vibrations at highway speed, but that all goes out the window when the rear gears are changed. I had a 1988 Caprice with a 700r4 that was smooth in overdrive with 3.08 rear gears. When I swapped in 3.42s the car developed a vibration that started at about 60mph and got worse up to 70mph. I never did get it fixed, and I eventually swapped the driveline into an RX-7. The RX-7 had an IRS with a fixed differential and a 30 inch long driveshaft, and it didn't vibrate at any speed.
On your car I would double check the u-joint angles first, since your ride height was changed. If that doesn't work try and find a driveline shop that can balance the driveshaft at highway rpm. 'm not sure if such a place exists; the shop I worked at would balance driveshafts at around 400rpm or so.
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post #10 of 14 (permalink) Old 07-06-2009, 05:29 PM Thread Starter
 
 
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I actually have a shop such as yours looking at my driveshaft right now.I asked them to check for staightness too. Once i get it back I will check the angles.
I have read in Car Craft 2003 that ride height changes should not matter, as when lowering the car angles will change, but their relationship stays the same.That is to say, your slip yoke at the trans end may be 4 degrees positve or whatever, as long as your diff end maintains a 4 degree negative value.
I think off-roaders with lift kits have the craziest angles.Do they have problems?
And to finish, all the slammed cars in California would all have vibrations if lowering really mattered.
Any other theories?Are my thoughts sound?

Greg.
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post #11 of 14 (permalink) Old 07-07-2009, 01:22 AM
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Quote:
Originally Posted by geetee150 View Post
I actually have a shop such as yours looking at my driveshaft right now.I asked them to check for staightness too. Once i get it back I will check the angles.
I have read in Car Craft 2003 that ride height changes should not matter, as when lowering the car angles will change, but their relationship stays the same.That is to say, your slip yoke at the trans end may be 4 degrees positve or whatever, as long as your diff end maintains a 4 degree negative value.
I think off-roaders with lift kits have the craziest angles.Do they have problems?
And to finish, all the slammed cars in California would all have vibrations if lowering really mattered.
Any other theories?Are my thoughts sound?

Greg.
Pinion angle varies with ride height, because the upper and lower rear control arms are unequal length. But I don't think pinion angle is the real problem. From my own experience, vibration caused by too much u-joint angle is greatest at low speed and smooths out by the time you hit 20mph or so.
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post #12 of 14 (permalink) Old 08-20-2009, 12:30 PM
 
 
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driveline vibration

I'm a driveshaft engineer, and after reading through this, my suggestion would be to send your driveshaft to a reputable shop that can check your ujoint clearances, shaft runouts (out-of-roundness), and imbalance at near highway rpm. The force generated by an imbalance increases with the square of the speed, and 400 rpm won't generate squat for an imbalance signal, so it becomes hard to detect the proper amount and angle to locate the correction weight. At 3500 rpm, you've multiplied that force almost 77 times. Now it becomes easy to locate and correct. If you want a recommendation, Dynotech Engineering Services in Troy, Michigan offers this service. These guys build shafts for the OE's and all kinds of motorsports. I don't know what they will charge, but they provide a great value and EXCELLENT work. When you say that it gets worse as your speed increases, this is tyipcal of a balance-related issue. If it was in your trans, you would most probably feel it phase in and out - that is, get worse then better then worse as you maintain speed. This phasing is due to different things spinning at different speeds within the trans. Hope that helps, good luck!
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post #13 of 14 (permalink) Old 08-20-2009, 12:41 PM
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I'll agree with everything that Pete said, except his recommendation for a shop. Lots of guys that bought shafts from Dynotech on the SS forum have had problems with balance. I would suggest Denny's. Google them, and you will find lots of happy customers. The late model (94-96) SS guys (like me) that have swapped in the T56 deal with driveline vibes all the time. This is .5 6th gear OD combined with gears like 4.10s or 4.56s. For example, my engine is turning around 2200 RPM when doing 80 in 6th gear. That means my drive shaft is spinning at 4400! Doesn't take much more to get to a shaft's critical speed. The critical speed is a function of the diameter of the shaft (too skinny on OE applications), the length (loooonnggg on our cars), and the material (steel tubing which can flex). To raise the critical speed, you need to change one or more of the variables. Going with a slightly larger shaft is one quick way to accomplish that. Look under a recent GM van or pickup. You'll see a very nice, aluminum 4" driveshaft. If GM could have got away with 3" steel, they would have.

Denny's can do a steel shaft, or aluminum, and it will be high-speed balanced (something regular driveshaft shops just can't do).
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post #14 of 14 (permalink) Old 08-20-2009, 01:26 PM
 
 
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I'm really surprised by the negative input on Dynotech. They make more driveshafts for NASCAR than anybody else, their balance machines are the same $1M plus machines used by the Auto Mfrs and Tier 1's (because they are a division of Balance Engineering, which is the former balancing R&D arm of GM and supplies these machines to the automakers) and they have about 70 years of balancing expertise behind them. Maybe you want to contact both and make your own judgement based on comfort level, price, and timing.
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