Shaking, back and forth motion at 1st and 2nd gear

[Patcon]

You need to know! It is hard to help someone from several thousand miles away. Even harder without all the facts.

[oranngetang]

Easiest thing to do so far was take out a spark plug, but you've already started replacing parts and have had it at the mechanics?

As for the clutch, if it's clutch chatter you're explaining, you'll only feel it when starting to move from a stop until it's fully released, not when you're shifting.

The description of your "car shakes side to side" when letting out the clutch is a symptom of a broken motor mount exaggerating normal clutch chatter, from running a performance clutch OR from hot spots on the surfaces.

Others will know better, but I find it hard to believe a vacuum leak on an SU powered engine causing an issue this pronounced, even if your vacuum advance is completely out of service. Assuming it's the brake booster for instance, just take the hose off the balance tube and cap the manifold for and moment. No change? Not the brake booster.

After reading through again, I think maybe your inclusion of the word "clutch" may have misled me and others. You pretty much perfectly defined clutch chatter, but if this is happening while accelerating once the clutch is totally engaged, it isn't clutch chatter.

What it does sound like is again fouled plug. Run the engine, pull wires, see if any of then don't cause an rpm drop. Pull the plug, if not all of them. It's likely fouled. A fouled plug may work better at higher rpm and cause a rough idle and hesitation at low rpm.

Do what you want, but replacing stuff without reason is counterproductive if you're left with the same problem. Especially if it's just a fouled plug from a rich mixture.

Doesn't hurt to replace these hoses anyway, but.... in the meantime....

Edited June 4, 2015 by oranngetang

[Patcon]

I suggested blocking off the booster several weeks ago. Don't know if that was ever done, as well as, eliminating other potential vacuum leak sources. More people on the forum will help you if you methodically answer individual questions and try what is suggested. If you don't help will dry up...

[Zed Head]

A methodical approach is the key.  As said, these same problems were described weeks, maybe even months ago.  But the solutions suggested weren't addressed, random work has been done, mechanics who don't seem to know what they're talking about are consulted, and the whole cycle is repeated.

 

Obviously, it's difficult to get good work done down there, but that's why it's even more important to keep track of what's done, and why.  And the descriptions of the problem are very important.  Clutch chatter and engine shaking due to misfire are two completely different problems.

[jalexquijano]

Easiest thing to do so far was take out a spark plug, but you've already started replacing parts and have had it at the mechanics?

As for the clutch, if it's clutch chatter you're explaining, you'll only feel it when starting to move from a stop until it's fully released, not when you're shifting.

The description of your "car shakes side to side" when letting out the clutch is a symptom of a broken motor mount exaggerating normal clutch chatter, from running a performance clutch OR from hot spots on the surfaces.

Others will know better, but I find it hard to believe a vacuum leak on an SU powered engine causing an issue this pronounced, even if your vacuum advance is completely out of service. Assuming it's the brake booster for instance, just take the hose off the balance tube and cap the manifold for and moment. No change? Not the brake booster.

After reading through again, I think maybe your inclusion of the word "clutch" may have misled me and others. You pretty much perfectly defined clutch chatter, but if this is happening while accelerating once the clutch is totally engaged, it isn't clutch chatter.

What it does sound like is again fouled plug. Run the engine, pull wires, see if any of then don't cause an rpm drop. Pull the plug, if not all of them. It's likely fouled. A fouled plug may work better at higher rpm and cause a rough idle and hesitation at low rpm.

Do what you want, but replacing stuff without reason is counterproductive if you're left with the same problem. Especially if it's just a fouled plug from a rich mixture.

Doesn't hurt to replace these hoses anyway, but.... in the meantime....

Okay.

 

I bought this 1972 240z last year and it came with a Center Force one clutch with stainless steel hose. I drove it for a year and its not until know that its starting to cause this back and forth shaking which is even present if i accelarate the car at 1st gear low rpm and reléase the pedal immediately. This should not happen. I will leave the purchase of an Airtex electric fuel pump on standby, so we can focus on the problem from another angle:

 

1. How do i test the brake booster? i disconect the hose from the balance tube and what should i notice if it is faulty?

 

2. How do i verify the clutch is chattering? My car has a 280z 5 gear transmission. Will i need to remove the clutch plate?

 

The idle mixture knob on both su carbs is set at 3 and 1/4 turns clockwise; RPM at 950 on idle

Edited June 4, 2015 by jalexquijano

[oranngetang]

Are you purposely avoiding the spark plugs for any specific reason?

1. If you suspect the booster is leaking, you may also notice it takes more effort to push the brake pedal. That said, we're diagnosing an acceleration issue, so all you would need to do for now is disconnect the brake booster and plug the port it's connected to at the engine. You're focusing on vaccum leak. If you plug the hole, it rules out a faulty booster or booster hose. It really is that simple, it doesn't matter if the booster leaks if it isn't connected. If the same problem exists, it isn't the booster.

2. If you foot isn't on the clutch pedal, the car is moving and still shaking, it isn't clutch chatter. If your foot is on the pedal and you're engaging the clutch and that motion causes the car to shake until it's fully engaged, its likely clutch chatter. I think it's been ruled out as you're saying it's happening while accelerating.

[jalexquijano]

Okay,

 

1. I am not avoiding the spark plugs for any specific reasons. I will pull them out and take a picture of all of them together. What color should they be? Coffee color or yellowish color?

 

2. Brake Booster leak check. I dont seem to notice that i need more effort to push the brake pedal. Anyway, i will disconnect the brake booster and will plug the port at the balance tube. SHould i use a rubber grommet to cap it or i need to get a screw?

 

3. when the back and forth shaking appear my foot is not in the clutch pedal. it also appear if i accelarate and reléase the pedal immediately. no foot on clutch when this shows up.

[HuD 91gt]

An easy way to block the brake booster, is to reverse the check valve on the firewall which is in the middle of the vacuum hose from the balance tube to the booster. It only flows one way (if working properly).

I've done this before and works great. You could also disconnect the hose at the check valve and shove a appropriate sized blocking device, and use a hose clamp. Your over thinking your issues. Think methodically, figure out what your actually trying to accomplish and go from there.

[HuD 91gt]

An easy way to block the brake booster, is to reverse the check valve on the firewall which is in the middle of the vacuum hose from the balance tube to the booster. It only flows one way (if working properly).

I've done this before and and if my memory serves me correctly it works great. You could also disconnect the hose at the check valve and shove a appropriate sized blocking device, and use a hose clamp. Your over thinking your issues. Think methodically, figure out what your actually trying to accomplish and go from there.

[jalexquijano]

I checked the brake booster by removing the hose from the balance tube running the car at idle. Result was an increase in the idle. Put it back and the idle came back to where it was.

 

I lowered the rear carb idle mixture knob to 3 turns clockwise and the front one was left in 3 and 1/4 turns clockwise. Did my test drive and the car continues to shake back and forth in the following scenarios:

 

1. If accelerate in 1st gear and suddenly remove my foot from the gas pedal

 

2. if passing through a broken or bumpy non uniform road at low speeds in example the parking of a mall or supermarket. Need to step either real soft or real hard to avoid shaking.

 

I was advised to check on the distributor, to clean the guts with wd40 or to get a remanufactured one.

[jalexquijano]

Please find attached a picture i took of the car after changing all the bushing kit! Which is the transmission mount that could be causing this problem?

 

 

[HuD 91gt]

The bumpy road thing makes me believe it's a motor mount messing with your throttle linkage. Go over your throttle linkage very well, insure everything is lubed, and free of any stiction. This started happening after your ztherapy install as well?

If you get a change in idle speed you may probably have a small leak in the booster. For future testing and troubleshooting keep it blocked off. Did you drive it at all with the booster blocked?

Edited June 5, 2015 by HuD 91gt