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Discussion Starter · #1 ·
Hi there,

I am currently having an issue with my 99 ZX2 (manual) 60,000mi. I think I have narrowed the problem down to either the differential or the CV Joints, though I am leaning towards differential.

Here are the symptoms:
When driving around 59-65MPHish and straight (62 is the worst), there is an incredible pulsating about 120bpm (fast) that I can feel through the whole car and especially through the steering wheel. The brake pedal does not pulsate (not warped rotors). When I am in a turn at 62ish, it dissappears (either direction). Also, seems almost like when I put the cutch in, the pulsating reduces in severity (slightly).

I put the car up an jackstands and removed the front wheels. I turned on the car and put it into 1st gear at idle -- no noise. Upped it to 2nd gear, a knocking sound came from the interior of the car (sounded like from the transaxle, though could be inner CV on both sides). As I climbed the gears, the knocking only sped up (not a problem with 2nd gear). I backed it down to 2nd again, and stopped one hub from rotating with my hands. The knocking increased in speed, but it did not sound as if any part of it cut out. The same happened with the other side. This led me to believe that it is a differential problem, since by stopping one side from rotating, I am stopping one of the inner CVs from rotating, and if that is contributing to the knocking, then I should notice at least some reduction in volume. Instead I got no reductionin volume, only an increased rate of knocking. I inspected the inner CV boots quickly and found no apparent leaks.

I removed the rotors and pads so it was just bare hubs spinning and tried the test again. This time no knocking in 2nd gear. The knocking would only appear when I put resistance on the drive axle (like the brakes were doing). It didn't take much resistance. I only took it up to 2nd, though I probably should have tested higher gears too.

I think it might be something with the differential. If anyone has any other ideas or tests I could run, I am open to suggestions. As much of a pain as it would be to have to pull my whole transaxle and take it to a shop instead of replacing CVs, I have been looking for an excuse to upgrade my clutch (which has about another 5,000mi or less left to it). The clutch couldn't be an issue, could it? The thing definatly engages fully--no slipping to speak of, just a hard grab when I engage it.

Thanks for any help.
 

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The fact that the knocking increased in rate when you had the car jacked up and grabbed one hub makes me believe that it is a diff problem too. Does the same knocking happen on either side of the transmission?

I assume of course that you have checked the tierods, control arms, and ball joints for integrity of bushings, etc.

It could be your bearings, but it's pretty unusual for bearings on both sides to die at the same time.

The reason why the knocking sound decreases in volume when you push in the clutch is probably because you're no longer feeding power through the tranny, so it's under less stress, but the wheels will still rotate the diff, so the knocking continues. Yeah I'd have to say it's most likely a transmission problem. If I were you, I'd use one of those mechanics stethoscopes and jack up the car and probe the tranny case.
 

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Discussion Starter · #3 ·
siragan said:
Does the same knocking happen on either side of the transmission?
I couldn't really pinpoint the location, since I did a brief test and had the car running. I didn't want to stick my head in there too far. It sounded to me like it was a singular noise emminating from the transaxle.

siragan said:
I assume of course that you have checked the tierods, control arms, and ball joints for integrity of bushings, etc.
Briefly, but yes, everything is in working order.

siragan said:
It could be your bearings, but it's pretty unusual for bearings on both sides to die at the same time.
I just replaced the driver's side bearings about 3 months ago. I find it hard to believe that that one is bad already. The sound is definatly not comming from the hub area, it is comming from the interior engine compartment more. Also, when driving down the highway, it sounds like the sound is slightly louder on the driver's side. This most likely is because the transaxle is on the driver's side.

siragan said:
The reason why the knocking sound decreases in volume when you push in the clutch is probably because you're no longer feeding power through the tranny, so it's under less stress, but the wheels will still rotate the diff, so the knocking continues.
I agree. Remember, when I took the brakes off the front, the noise stopped since there was no longer any stress on the drivetrain. I had to add resistance to get it to knock again.

One thing I forgot to point out before was that the knocking sound is always constant in rhythm with the speed of the car. If It was a CV or bearing, the rhythm would not be constant, because as one wheel slips, it rotates faster and one axle would be out of sync, producing a syncopated rhythm. Instead, if one wheel slips, the sound speeds up temporarily and then returns to normal, however, the noise never gets syncopated.

Thanks for your reply. I had a feeling that it was the transaxle, but I just wanted a second opinion.
 

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ecammit said:
If It was a CV or bearing, the rhythm would not be constant, because as one wheel slips, it rotates faster and one axle would be out of sync, producing a syncopated rhythm.
Good point. Usually for a CV to go bad, the joint will visually look like it's in bad condition (ripped boot, oil on the halfshafts, etc).

So yes, I think it's a tranny problem. I've never broken down a tranny before so I can't tell you exactly what part it is, but the guy I got my EGT from is a ford master technician and did work on my GT tranny, so if I can shoot the question to him I can see if I can get this figured out.
 

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Hate to say, but this is almost word for word what my 95 GT did. The differential had started wobbling, finally failed and needed replacement. For a 95GT, probably harder to locate than for a ZX2, the rebuilt tranny was $1200 minimum plus about $400 labor. I opted for a junkyard tranny plus the labor. Spent about $1200 total.

Before you spend the money changing CV joints, have it checked by a qualified transmission shop. I didn't, causing the old tranny to eat up my new driver's side shaft in short order, before realizing what was going on.
 

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Discussion Starter · #7 ·
I was quite certain it was the differential until I performed the backup test. The backup test told me there was more than likely a CV failure on the passenger side halfshaft.

A side note:
For those who don't know, the backup test is where you take your car to an empty parking lot and drive the car backwards in circles like a manic. If your problematic sound (a pulsating "shuckshuckshuck" noise in my case) only occurs when turning in one direction, you might have a failed CV joint.

The direction of your turning will determine which side the CV failure is on. When you are turning in the direction in which you hear the noise, the failure is on the side that is on the INSIDE of the turn. In my case backing up and to the right (steering wheel to the right) the pulsating noise occured and told me there was a CV failure on the passenger side. The reason that it is the INSIDE and not the outside is due to the fundamentals of why the test works.

Why reverse? Well, first I ask you, what causes a noise in a car? It is usually do to contact or friction that should not occur. Applying this knowledge, a CV joint noise is also the result of a contact of friction that should not occur. Given that this should not normally happen, there is mechanical damage to your CV. You also know that continuing to run something that is damaged will wear the part down improperly. You typically drive your car forward. What will happen is that the CV will actually wear itself down to facilitate traveling forward easier -- simple frictional wear. The result of this long babble: since your joints are worn to facilitate forward motion, traveling in reverse shifts the stress points to the opposite sides of the CV that aren't worn down. The result - the noise should be more pronounced as the problem is agrevated.

Why is the CV on the INSIDE of the turn the problem and not the outside? The answer is simple: Because of the way torque is applied, the wheel on the inside of the curve will complain the most.

I hope this helps someone.
 

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Discussion Starter · #8 ·
Final Problem(s):
Bent CV axle
Warped rotor
Bad Wheel Berring
Front end out of alignment

Gee, it is a wonder I was able to diagnose anything.
Everythiing I fixed cleared up the problem that much more.
 
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