Shifter Rattle

[Roger G.]

I am trying to troubleshoot what is causing a rattle in the shifter. This occurs between 3000 and 3500 RPM. It goes away below and above this range. It is most noticeable when the shifter is in 3rd gear location. Today I got out on the highway, and got up to 3300 in 3rd. Rattle began. Then pushed in the clutch and RPM dropped - rattle went away. Then gave it enough gas with clutch pushed in to bring it back up to 3300 - rattle came back. Then I repeated this process with 4th gear position. Same results, although rattle was barely noticeable. It is more pronounced with the shifter in 3rd gear position.

Took it back up to 3300 in 3rd gear until the rattle started again. Put it in the clutch and maintained 3300 RPM, and coasted to the shoulder. With the car barely creeping, the rattle continued. So it doesn't appear to be related to speed.

Went home, backed in the driveway, and came to stop with car running. Put it in 3rd gear with clutch in and took it up to 3300 RPM. NO RATTLE!

When this occurs, a slight lateral pressure on the shifter will stop it. I should mention that the shifter was replaced about 3 months ago with an aftermarket, the linkages were also replaced. It is in short throw setting. It shifts great and goes into reverse great, whereas before it would hang up. The other thing I have noticed is that there is a slight play in the handle when in any gear, maybe 1/8 to 1/4". Not sure if this is normal or not.

Other observations...at 3300 RPM, when the rattle occurs, the engine seems to be smooth. There is no shake felt in the steering wheel or in the car. Actually, I don't feel a significant vibration in the shifter either.

I placed an O ring between the reverse lockout and the shaft, and place a piece of vinyl tubing over the lockout rod to see if it would help, but there was little effect. It seem to be coming from below.

The motor is a fresh rebuild with about 1800 miles. The transmission was also gone through at the time.

So not sure what is going on. The fact that I can't reproduce it in the driveway is odd. Any ideas?

[Domenic T.]

Re: Shifter Rattle

Roger,
I had that on my 65 SS and it is a harmonic imbalance that will happen at certain RPM's. Clutch out or in says the pressure plate or the combination of flywheel/ pressure plate. The imbalance is normal as the amount of combustion is calculated as weight against the crank throws. There is a percentage used on the rotating mass that is considered weight. So this is a normal condition in my opinion. Some are perfect and some rattle. I use a 70% weight factor on my motorcycles and don't know what it is on a V 8 configuration.
My 65 did it about the same RPM's and I put rubber in the vibration area which was in the reverse lock out and it muffled the noise.

DOM

[Domenic T.]

Re: Shifter Rattle

Roger,
I didn't really explain my post clearly. The 70% is 70% of what is needed to equal the crankshaft counter weight. The other 30% is combustion. So 70% of the weight is the (piston & rod assembly) and 30% is the weight of combustion which can vary. This can cause the imbalance that gives you the rattle.
The automatic trans has a torque converter that keeps the balance in check as when it swings to the heavy side the oil inside swings to the light side. The force of combustion wasbsaid to be about 1600 to 2000 lbs under normal conditions.

DOM

[Roger G.]

Re: Shifter Rattle

Roger,
I didn't really explain my post clearly. The 70% is 70% of what is needed to equal the crankshaft counter weight. The other 30% is combustion. So 70% of the weight is the (piston & rod assembly) and 30% is the weight of combustion which can vary. This can cause the imbalance that gives you the rattle.
The automatic trans has a torque converter that keeps the balance in check as when it swings to the heavy side the oil inside swings to the light side. The force of combustion wasbsaid to be about 1600 to 2000 lbs under normal conditions.

DOM

Dom

That probably explains why it is not reproducible. Was not sure since pushing the clutch in and out didn't make a difference, and it occurs when sitting still and moving. Then other times it doesn't happen at all.

I'm not sure if a new transmission mount was used when the motor was rebuilt, I do know new motor mounts were used, wonder if that might be responsible.

[Domenic T.]

Re: Shifter Rattle

Roger,
Although mounts are important I would vote more towards the harmonic imbalance. If the mount makes solid contact or the trans mount is broken and moves side to side I would not think it is the mount.
You said the engine was a fresh rebuild and if they replaced the pistons, did the rebalance the crank?
I found that GM pistons for a given engine weighed all the same, flat top to dome. Got many arguments on that but take the old GM pistons off the shelf and show proof.
It stands to reason that all the rods & pistons had to weigh the same as then all the crankshafts child be balanced using the same tooling.
What I have found is that the piston people are making the pistons in balanced sets and the weight can vary more than a oz. With the GM pistons all Inever needed to do was grab one off the shelf and put it on the scale just to make sure.
Not to alarm you but if the pistons were changed and the crank not matched (balanced) it would rattle your shifter, but I think it would be more consistent. Then again if the crank was not matched to the new piston weights it would only change that percentage of balance ratio I was talking about, like maybe 70% to 65%, which would move the rattle to another rpm. I have found most balance problems in the flywheel especially when they use the stone resurfacer. I use a lathe, then static balance them.

DOM

[Duke W.]

Re: Shifter Rattle

All engines produce torsional vibrations that vary in frequency and magnitude with speed and load, and V-8s can have very small residual first and second order shaking forces or rocking couples that also can also excite resonance in attached parts. One example is "shifter buzz", which is common on a lot of Corvettes, even after they moved the linkage from the transmission to the frame. That helped, but did not cure all problems.

You said it's an aftermarket shift linkage, so there's nothing specific I can offer as a cure without knowing the design. It could be a design issue or maybe something is loose or out of tolerance.

You'll just have to experiment using whatever means you can come up with to provide damping in the linkage or change any natural frequencies in the linkage that resonate with engine frequencies, but as long as it doesn't buzz in fourth gear at typical cruising speed, you're way ahead of some early OE designs.

Duke

[Mike T.]

Re: Shifter Rattle

This might not apply since Roger did say he has an aftermarket shift linkage, unless it's a repro of the original Muncie shifter, but on the subject of shifter bushings, does anyone make ones that actually fit the inner shaft? I've tried the available aftermarket bushings and they are too thick to use, even after trying to 'sand' them down on the inside with a sandpaper 'flapper' setup. On my '66 smallblock Coupe, I luckily still have 'one' original bushing in it but the repro's just don't work. I suppose there is probably only one actual manufacturer but anyone have a suggestion on this. Also, my shifters still have the original plating, they haven't been rechromed.

[Roger G.]

Re: Shifter Rattle

Roger,
Although mounts are important I would vote more towards the harmonic imbalance. If the mount makes solid contact or the trans mount is broken and moves side to side I would not think it is the mount.
You said the engine was a fresh rebuild and if they replaced the pistons, did the rebalance the crank?
I found that GM pistons for a given engine weighed all the same, flat top to dome. Got many arguments on that but take the old GM pistons off the shelf and show proof.
It stands to reason that all the rods & pistons had to weigh the same as then all the crankshafts child be balanced using the same tooling.
What I have found is that the piston people are making the pistons in balanced sets and the weight can vary more than a oz. With the GM pistons all Inever needed to do was grab one off the shelf and put it on the scale just to make sure.
Not to alarm you but if the pistons were changed and the crank not matched (balanced) it would rattle your shifter, but I think it would be more consistent. Then again if the crank was not matched to the new piston weights it would only change that percentage of balance ratio I was talking about, like maybe 70% to 65%, which would move the rattle to another rpm. I have found most balance problems in the flywheel especially when they use the stone resurfacer. I use a lathe, then static balance them.

DOM

Dom...no alarm ....The crank was ground and balanced, and the flywheel was also balanced, but not sure how

All engines produce torsional vibrations that vary in frequency and magnitude with speed and load, and V-8s can have very small residual first and second order shaking forces or rocking couples that also can also excite resonance in attached parts. One example is "shifter buzz", which is common on a lot of Corvettes, even after they moved the linkage from the transmission to the frame. That helped, but did not cure all problems.

You said it's an aftermarket shift linkage, so there's nothing specific I can offer as a cure without knowing the design. It could be a design issue or maybe something is loose or out of tolerance.

You'll just have to experiment using whatever means you can come up with to provide damping in the linkage or change any natural frequencies in the linkage that resonate with engine frequencies, but as long as it doesn't buzz in fourth gear at typical cruising speed, you're way ahead of some early OE designs.

Duke

Duke...the shifter and linkage are original design repops...next time I get it on the lift I will check the linkages, look for anything loose, maybe add a some weight to the rods and see what happens.

[Dick W.]

Re: Shifter Rattle

I am trying to troubleshoot what is causing a rattle in the shifter. This occurs between 3000 and 3500 RPM. It goes away below and above this range. It is most noticeable when the shifter is in 3rd gear location. Today I got out on the highway, and got up to 3300 in 3rd. Rattle began. Then pushed in the clutch and RPM dropped - rattle went away. Then gave it enough gas with clutch pushed in to bring it back up to 3300 - rattle came back. Then I repeated this process with 4th gear position. Same results, although rattle was barely noticeable. It is more pronounced with the shifter in 3rd gear position.

Took it back up to 3300 in 3rd gear until the rattle started again. Put it in the clutch and maintained 3300 RPM, and coasted to the shoulder. With the car barely creeping, the rattle continued. So it doesn't appear to be related to speed.

Went home, backed in the driveway, and came to stop with car running. Put it in 3rd gear with clutch in and took it up to 3300 RPM. NO RATTLE!

When this occurs, a slight lateral pressure on the shifter will stop it. I should mention that the shifter was replaced about 3 months ago with an aftermarket, the linkages were also replaced. It is in short throw setting. It shifts great and goes into reverse great, whereas before it would hang up. The other thing I have noticed is that there is a slight play in the handle when in any gear, maybe 1/8 to 1/4". Not sure if this is normal or not.

Other observations...at 3300 RPM, when the rattle occurs, the engine seems to be smooth. There is no shake felt in the steering wheel or in the car. Actually, I don't feel a significant vibration in the shifter either.

I placed an O ring between the reverse lockout and the shaft, and place a piece of vinyl tubing over the lockout rod to see if it would help, but there was little effect. It seem to be coming from below.

The motor is a fresh rebuild with about 1800 miles. The transmission was also gone through at the time.

So not sure what is going on. The fact that I can't reproduce it in the driveway is odd. Any ideas?

One thing that many miss that can cause shifter rattle/buzz is driveshaft and u joints. Check your joints and driveshaft run out

[Domenic T.]

Re: Shifter Rattle

Roger,
That as they say in the aviation manuals, " it is a normal & abnormal condition". Many aircraft engines have placards restricting continous use at certain RPM's. A solution is to drive with your hand on the gear shift.

DOM