So....where did they Driveshaft "myth" start?

J

J

OCCUPY LoD :)
Ever since I bought my Mark and began to learn about them, everytime someone mentions a vibration, they are told to by a one piece driveshaft. EVERY time.

Where did all this start, why do people just condone the two piece shaft without diagnosing it or actually trying to fix it?

I'm curious because depending on the amount of miles on ANY driveshaft, the u-joints will get dry and cause a vibration, expecially when they are "sealed" and not serviceable. Instead of slapping on some new joints, the inside of the shaft is blamed for the vibration.

Has there been proof of this, or do people just slap on a new one piece and call it good. When in all reality they are just swapping in a shaft with GOOD u-joints?

Awhile ago I took matters into my own hands and sent Max's old two piece shaft to the driveline shop where they balanced it (at 10K RPMs) and installed new u-joints. Bob (dbobo) was having vibration issues on his Mark at 70 MPH+ and wanted to buy a new one piece out of recommendations from the internet. I told Bob that it doesn't make sense to buy a new shaft when you're running the STOCK u-joints with 100k miles on them! So, after I got the shaft back from the shop (which they said was perfect), I slapped it into Bobs car and he said it was GREAT, no vibrations up to 95 MPH.

So, I know I only checked this theory on one shaft, but seriously, how many shafts were still good when they were tossed away with 65-165K miles on the stock u-joints?! Any thoughts or evidence?
 
Well I had vibrations pre and post shaft...

I think it has something to do with the mark VIII/T bird chassis.

My ex's 97 T bird also had a vibration... and so did our 93 Cougar.
 
None of my cars have this vibration, and they all have the original U joints as far as I know.
 
When I put gears on I tried new u joints before I bought a one piece and it still vibrated. Even after the shaft, there was still a small high frequency drive train vibration. You could hear it more than feel it, especially when you lean forward. I have a vibration analyzer and it sure a hell is the shaft. I even went as far as making my own custom tail stock bushing to take up some of the play (all the new ones I bought were horribly loose on the yoke). The custom bushing helped but it is still there. I went on to replace the motor mounts as well to stop things from moving around, that helped a little more. It is reasonable now, not going to pull my hair out!
 
J,
Having it work one time doesn't mean it's the solution every time.
Do you actually think you're the first person to try new U joints and a balance to fix the vibration problem? Don't you think that others have spent bad money to fix the situation?

It's not always the u joints and balance. Some of these shafts will flex under load at higher RPMs. The stock shaft in the 2nd gen marks are notorious for this especially with 4.10 gears.
Two shops that I went to for balancing would do it but not guarantee it. The third shop tried to balance to 6500 RPM and gave up because the shaft was flexing too much to continue. They said it's the luck of the draw and that the next one may balance just fine.

So.. it has alot to do with the shaft itself and it's qualities.
 
95blklsc said:
there was still a small high frequency drive train vibration. You could hear it more than feel it,
Click to expand...

This sounds more like the driveshaft "critical" speed as described in the link Lask Mrk posted.

FLM Fan said:
J,
Having it work one time doesn't mean it's the solution every time.
Do you actually think you're the first person to try new U joints and a balance to fix the vibration problem?
Click to expand...

Dang man, no need to jump down my throat. As I said above, I only tried this with one shaft, but that doesn't nix the FACT that as soon as someone posts a thread asking about a vibration people automatically say "Find a 93/one piece shaft". Whats to say they don't have a bad u-joint?

FLM Fan said:
It's not always the u joints and balance. Some of these shafts will flex under load at higher RPMs.
Click to expand...

I never said it was. EVERY driveshaft (or spinning object for that matter) will flex under load. My 88 Mustang had a stock shaft with 4.10's and at 100+ I could hear the vibration more then I could feel it. I did research and thats when I first found that TCOA tech article. I thought it was my gears whining after I just did them, turns out it was my shaft.

FLM Fan said:
Two shops that I went to for balancing would do it but not guarantee it. The third shop tried to balance to 6500 RPM and gave up because the shaft was flexing too much to continue. They said it's the luck of the draw and that the next one may balance just fine.
Click to expand...

I understand that it would be like the "luck of the draw" with the shafts, but its not that simple. Every shaft gets introduced to different environments, cold/warm/wet/etc, so it only makes sense that the internal rubber dampener breaks down more than others. With that being said, you would need a new shaft if they couldn't balance it.

The shop I took my to did an inspection on the internals (as far as I understood it, they flex the shaft to "open" the end section to view down inside, they don't take the shaft apart) and they said it looked good. They also said they would be able to rebuild the internals, modify them, or even BUILD a custom shaft to the same specs. Of topic, but their alluminum shafts were pretty inexpensive compared to an MMX.

FLM Fan said:
The stock shaft in the 2nd gen marks are notorious for this
Click to expand...

The Gen 2's are no different than the Gen 1's, they use the same two piece shaft. The only ones that are different are the 93's with the one piece shaft.

I think the issue is that the critical speed effects the shaft more because it isn't "connected" at the base of the shaft which kinda gives it that pendulum effect where it wobbles like a spinning top. This, ofcourse, will be greatly amplified by a bad u-joint, thus lowering the critical speed to a more logical speed of the vehicle that most people would reach on a daily basis, i.e. 90 MPH critical speed vs. 70 MPH.

Anyways......the purpose of this thread is to find out where the instant diagnosis of a bad shaft stems from, NOT whether or not I feel like there are bad diagnosis' going on.
 
J said:
.....whining after I just did them, turns out it was my shaft.
Click to expand...


icon10.gif
icon10.gif
icon10.gif
hahaha don't tell your wife!
 
i think that the biggest problem is the 2 peice shaft has more joints, which means more slop when they wear, which means more vibration. so the 1 peice has less joints, less slop when worn, less vibration.
 
bryantaylor said:
i think that the biggest problem is the 2 peice shaft has more joints, which means more slop when they wear, which means more vibration. so the 1 peice has less joints, less slop when worn, less vibration.
Click to expand...

It doesn't have any more joints than the 1 piece... it just refers to a tube in tube design.
 
maxmk8 said:
It doesn't have any more joints than the 1 piece... it just refers to a tube in tube design.
Click to expand...

i really need to look at one :D

but what i was saying still applies. more moving parts = more chance for slop.

but i wonder WHY they went to a 2 piece after only a year? is it cheaper and/or easier to make vs. the 1 piece?
 
It's more of a 'legend' than a myth.

J.W. wrote of this years ago as indicated by Last Mrk.

Fact is, the FN10 (and for that matter, the MN12) chassis is very sensitive to driveline and wheel/tire vibrations. The tendency is amplified when lower gears are installed for obvious reasons including harmonics from the flex of the driveshaft.

Every driveshaft will indeed have a natural resonance which will differ from vehicle to vehicle. My theory is when you have two such sources of resonance which coincide with each other, the resulting vibration is exponentially greater.

My own personal experience was to gamble with the one piece shaft on my '93 when I installed 4.10 gears. I lost the bet and bought an MMx driveshaft. Later I sold my 'vibrating shaft' to Bud who had a vibration issue with his Gen2 and it 'cured' his problem. Go figure.
 
Well said JP. After having owned 4 of these cars (and variations thereof) it is my main deterrant of not owning another. Every vibration is amplified... including brakes.

Back in the day 97/98s were notorious for "warping" rotors. I think sandy block went through 2-3 sets under dealer warranty before his car hit 20k miles.

The Crown Vic... the 200k BMW... the Jeep... my vette... my honda prelude. All didn't have driveline vibrations or warped brakes.
 
First I've heard of this vibration. Drove wifes Mark on the highway a few times and never felt even a hint of vibration. Guess I freigin' "RULE". :D
 
You must log in or register to reply here.
Back
Top