I have a question regarding my 83 Z28. (see my signature for what all the car has installed...) What would signs of a stretched u-joint strap be? Would the car start shuddering hard around 60mph and fade mostly around 70-75? I'm wondering if it's a little stretched out but not sure. I will probably get my wheels balanced just in case too, and maybe an alignment, possibly driveshaft balanced too, but wanted to check with yall before really doing anything. A new strap is less than $10 so obviously that'd be the cheapest fix.

 

That is commonly found when driveline angles get changed on these cars.

You may want to inspect engine and transmission mounts first,

 

Never seen or heard of that happening.

Which is NOT the same as saying it can't or doesn't; only, that out of the hundreds of cars that I, my friends, family, co-workers, race buddies, etc. have ever had, I don't know of a single instance of it.

However, you can get new those in the Help! aisle at the store, or at the counter from the various U-joint mfrs such as Neapco and Dana. Cheeeeeeeeeep. If you think yours are bad, just change em out and see if it helps. My bet would be on, it won't make the slightest difference.

First step in troubleshooting a vibe is to determine if it's drive line (hmmmmmmmm) or wheels (wubbawubbawubbawubba). I.e. before the R&P or after. Start there. "Maybe it's U-joint straps, maybe it's wheels" makes no sense whatsoever.

 

Ok, I'll quick check the motor mounts, but the motor doesn't move, so I highly doubt those are the culprits. Trans mount is new, since the T5 is a new mod to the car.

Something I neglected to mention is that the vibration is not in the steering wheel... It's like the car vibrates up and down, not steering wobble. Maybe I'll check for bulges in the tires. I'm puzzled since I've never dealt with this kind of vibration. It's pretty violent too...

 

Is it speed related or RPM related? As in, can you duplicate the vibration in neutral or with the clutch pedal pushed in? (That would be with the engine RPM matching that at 60 MPH or wherever you feel the vibration is most intense when at speed.)

 

Speed related.

 

[QUOTE=Sgt_Nick383;6164942Trans mount is new, since the T5 is a new mod to the car.[/QUOTE]

Is the trans mount poly? If so, that well may be your issue.

JamesC

 

No, it's not poly

 

So, is it at DRIVE LINE speed, or WHEEL speed?

 

Wheel speed. I apologize for yet again failing to give 100% of the answer.

I'd tell you that I'm talking about the speed displayed on the speedo but I melted my cable and the speedometer don't work haha. I'm using a speedometer app currently.

It only happens when I hit 60 mph and up. Putzing around town, 0-60 runs, all fine. On the freeway, driving normally, 60mph comes around and it starts to shake like hell. Not in the steering. I'm going to check the straps when it dries up out there, because that was my first idea. The car makes boatloads of power... I'd guess 400-430 at the wheels.

 

OK cool.

Not a U-joint strap.

Put the car on jackstands under the axle tubes. NOT, a floor jack under the pumpkin; NOT, the OE jack somewhere; NOT, stacks of bricks under the "frame"; NOT NOT NOT NOT. JACK STANDS UNDER THE AXLE TUBES. Then have your assistant get in the car, put it in gear, and accelerate gently until it reaches whatever RPM in high gear it starts to do it at. Let's say, when you hit whatever speed, your tach reads 2000; have your assistant "drive" the car at 2000 RPM. While they're doing that, observe the vehicle and see if it's doing it. Yes = your issue is at the rear of the car; no = it's at the front. A great start.

We're going to help you figure out if it's an individual wheel(s), bent or out of balance, and if so, which one(s); separated tire(s); bent axle(s); and so forth.

Attack it with LOGIC and REASON, not a bunch of "maybe it's this maybe it's that" while making up the oddest and most fanciful possible "explanations" there are ... like, U-joint straps.

 

Thank you sir. I appreciate the time and thought put into your reply. I'll do that, and hopefully it gives me a little better of an explanation for you all. I'll keep you posted.

 

I'm watching this.

 

Are you having a similar issue?

 

No, I just want to see what the solution ends up being.
But my .02, you could have lost a wheel weight, or try
flipping your driveshaft 180 degrees.

 

Alright so got it on a lift to weld up split in the oil pan (don't ask) so was able to give everything a better look over. I see some questionable spots on the front tires. I'll put it on stands as you've advised to see if there's an additional issue in the back end though. If that's all it ends up being, I'll feel like an idiot. I'll keep y'all apprised.

 

Hey, you can feel like an idiot even if it doesn't, if you just really want to. I get to feel like one all the time.

Seriously, vibe problems can be hard to track down, if not approached systematically. Discriminating among triangular tires, bent wheels, bent axles, warped rotors, ... the list just GOES ON. Then when you have more than one defect at the same time, it gets even more fun.

 

I had a similar problem recently with a non third gen and did exactly as Sofa suggests. Vibration present so that narrowed it to the rear end. Pulled the wheels off and vibration still present. Pulled off the drums and vibration gone. It was unbalanced brake drums. One was 14oz out of balance, the other 10oz. Reproduction Mexican trash. I did some balancing work to them and vibration gone. Smooth as glass now.

GD