Team,

I recently retrofitted my car with a Ram hydraulic clutch system. The clutch unit itself is working beautifully...smooth as it gets.

I do have the gear rattle associated with the ZF tranny and solid flywheels, despite the installation of the ZF Doc shim kit. It's there in neutral and goes away when I press the clutch.

I also have what I believe is the same gear rattle while driving...particularly under 2.5K RPMs in any gear. In addition, I can feel vibrations throughout the chassis, most prominent in 5th and 6th. Is this in line with everyone else who has converted to SMF? Are the vibrations caused by broken mounts? Although they are newish (2.5 years old / 10K miles), the engine was hanging from them at a steep angle without the support from the tranny/C-beam assembly.

All educated and experienced opinions are welcome.

Ric

 

Replaced the u joints and had the driveshaft balanced?

 

Not sure how much vibration there is, but the DMF is designed to dampen it a little bit for the Corvette crowd that wanted the smooth quiet ride... and they went to the helical gears for the later PN ZF6 to make it quiter (you should have those in a 96 also).

I did the SMF conversion with a Fidanza Aluminum flywheel, and also the ZFDOC shims carefully measured and selected to load the axial movement at near zero. Never noticed any vibration, but never had any to begin with.

If you tortured an old set of engine mounts, it may cause a problem. The LT mounts are really nice, you can get some excellent aftermarket ones.

When did the vibration start, was something replaced or serviced?

 

Yes to both

 

The harshness and vibration started only after the swap to SMF.

To be clear, this is not rotational contains. This is/are frequencies transmitted to the chassis. Engaging 6th gear at 45mph really gets the party going. High gear and low RPMs is the aggravating factor.

 

I've had my RAM conversion for many years and I never had vibration in 5th and 6th gear. The only time it may do that is if I lug it in the wrong gear.
Low speed, just off idle is where my setup seems like it has more vibration compared to the stock DMF setup.
Question, does it vibrate in 5th or 6th when you disengage the clutch? If it does stop vibrating then it may mean you need your flywheel balanced. I never had to balance my RAM flywheel but I have heard that some others have had to.

 

You will hear some gear rattle at low RPM and high loads with a SMF, but you should not feel any vibrations. The sound is endemic to the transmission. Plenty of other transmissions do the same thing. It's not a problem.

First thing first: if your 96 has the stock gearing, then I don't think you should be using 6th gear at 45mph. That's too slow. For a stock engine, I'd say 55mph is a bare minimum.

Second, did your kit come with a disc that has a sprung or solid hub? Looking at their site, 90-0810 or 90-0180N both come with a sprung-hub disc, and that's what you want. If you got a solid-hub disc, then it's not the right part and could cause all kinds of weirdness.

A couple diagnostic clarifications:

1. Just to make sure, the vibrations don't happen at low speed with the clutch disengaged, right? It's only when the clutch is engaged?
2. If you leave the clutch engaged but let off the gas (i.e. you start coasting) at the same speed and in the same gear where you feel the vibration, does the vibration persist? Or does it only happen (or happen worse) when you are applying power to the wheels?

I don't think this a balance issue for any of the rotating parts: that would get worse as RPM/speed increased, not better. I agree with AZSP33D that you should check your motor mounts. I'd also take a really good look at all six U-joints, even if they're all new. This is the kind of thing vibration that a bad U-joint can cause, especially if the vibration only happens with throttle applied.

 

I could be wrong, but I think the vibrations are related to lugging the engine. Once the RPMs get past 2500 or so, the whole thing smooths out.

An imbalanced flywheel should be felt by free-revving the engine, correct?

 

Yes, ergo the questions I asked you above.

 

You will hear some gear rattle at low RPM and high loads with a SMF, but you should not feel any vibrations. The sound is endemic to the transmission. Plenty of other transmissions do the same thing. It's not a problem. There is the rattle as you describe it. Then there is a very noticeable "vibration" if I lug the car. I want to be clear...lugging is the aggravating factor. If I spin it to 4, 5, 6K RPMs it isn't any worse (or better) than it was before smoothness wise.

First thing first: if your 96 has the stock gearing, then I don't think you should be using 6th gear at 45mph. That's too slow. For a stock engine, I'd say 55mph is a bare minimum. I agree. I guess the DMF soaks up a lot of the engine vibrations/resonances/etc an engine naturally makes. I could do 45 with the DMF and not feel anything.

Second, did your kit come with a disc that has a sprung or solid hub? Looking at their site, 90-0810 or 90-0180N both come with a sprung-hub disc, and that's what you want. If you got a solid-hub disc, then it's not the right part and could cause all kinds of weirdness. 90-0810S...so yes, it is the sprung hub. The "S" stands for single clutch.

A couple diagnostic clarifications:

1. Just to make sure, the vibrations don't happen at low speed with the clutch disengaged, right? It's only when the clutch is engaged? Low speed, in gear, lugging the engine.
2. If you leave the clutch engaged but let off the gas (i.e. you start coasting) at the same speed and in the same gear where you feel the vibration, does the vibration persist? Or does it only happen (or happen worse) when you are applying power to the wheels? Well, Prior to the clutch swap, I did have a vibration at high speed between 65 and 75 or so MPH. Whether I was increasing speed past 65, or let off the gas (while in gear), I had a vibration within this range of speed. Again, that was there before the clutch swap and it seems to have appeared on a trip from Panama City to Miami, FL.

I don't think this a balance issue for any of the rotating parts: that would get worse as RPM/speed increased, not better. I agree with AZSP33D that you should check your motor mounts. I'd also take a really good look at all six U-joints, even if they're all new. This is the kind of thing vibration that a bad U-joint can cause, especially if the vibration only happens with throttle applied. Copy all!

 

Okay, that vibration (dependent solely on road speed, regardless of gear selection and throttle status) was almost certainly one or more tires out of balance.

But for the vibration you feel now - the one at 45mph in 6th - does it go away if you let off the gas and coast, or is it there regardless of throttle position?

PS - I again want to emphasize that with stock tire diameter, going 45mph in 6th gear in your car has the engine turning only 1020 RPM, and that's a bad idea. It is certainly possible that the DMF soaked up pulses that the SMF just won't. My engine wasn't close to stock, so I could never have even tried this. Maybe others with a stock engine and SMF and the same gearing can chime in and verify if this is normal.

 

I think you and M Squared are on the right track.

Just as a general statement... Very important to check ALL of the u-joint cap retaining rings (all 6 u-joints), if the clips/rings are not opened up well into the recess, take a punch and gently tap it in there. If it's still questionable, remove the clips and clean the groove with a 90 degree pick really well.

A vibration is the first sign of imminent destructive failure if this isn't carefully done.

Another issue i see with replacing the u-joints is that sometimes they are a little bit stubborn to remove, so you have to be able to properly support the ears when pressing it out, they are aluminum and they will bend otherwise. If a shop performs the work, you would want to witness it. Slightly misaligned ears will of course alter the balance. If you had to really stress them to remove the u-joint, get a new drive shaft or half shaft, because if you've ever seen one fail, you know it can be deadly.

 

]Okay, that vibration (dependent solely on road speed, regardless of gear selection and throttle status) was almost certainly one or more tires out of balance. I am fairly convinced I do indeed have at least one tire out of balance, which is what I'm feeling past 65 MPH.

But for the vibration you feel now - the one at 45mph in 6th - does it go away if you let off the gas and coast, or is it there regardless of throttle position? If I left off the gas, it goes away. If I ease into the throttle it's less intense. If I lug it harder, then it becomes more intense.

PS - I again want to emphasize that with stock tire diameter, going 45mph in 6th gear in your car has the engine turning only 1020 RPM, and that's a bad idea. It is certainly possible that the DMF soaked up pulses that the SMF just won't. My engine wasn't close to stock, so I could never have even tried this. Maybe others with a stock engine and SMF and the same gearing can chime in and verify if this is normal. I fully understand what you are saying and I believe you are correct. I do feel that lugging the engine was a lot less noticeable with the DMF. The SMF seems to really transmit EVERYTHING.

Would a rough running engine transmit even more stuff through the tranny? According to Bill B., a smoother running engine will minimize gear rattle. So it happens, I have a P0300 I'm chasing down. I have a brand new Petris Opti waiting to be installed.

 

The problem with the word "vibration" is that it has many meanings or contexts. Think of this: Solid engine mounts. I think that better conveys what I'm trying to describe.

 

Okay, so the vibration is not just RPM/MPH-dependent, but it is also load dependent (throttle position). So that rules out any imbalance of any rotating mass. Still a possibility is a bad U-joint somewhere: when these go bad they sometimes feel worse with more load (torque) from the engine.

A misfire could possibly contribute to this. You definitely need to solve that. The 96 was the only C4 to have a crank position sensor, and therefore I think it's the only one that can even return a P0300. But unlike modern cars, I don't think it can return P0301-P0308 codes that isolate a misfire to a certain cylinder. So this could be a misfire in any or all cylinders, and it could be random or regular. I strongly doubt it's the optispark: those either tend to run well or not at all. Although it's possible the actual cap and/or rotor are failing (which could cause some kind of misfire), that seems unlikely too. I'd be more inclined to suspect the coil, plugs, or plug wires, especially since the vibration seems load-dependent: as you increase cylinder pressure, the spark encounters more resistance to jump across the gap the plug's electrode, so a failing coil tends to start running badly at high torque/pressure modes. Auguring against this, though, is that your full torque peak happens around 3000rpm at WOT, and a bad coil would typically cause a noticeable misfire in that condition as well.
I think Bill generally means an engine that has a lopey idle, which does increase the rattle from the transmission at idle. Once it's revving a bit, it shouldn't run rough at all. My C4 was a good example: it had a cam with a fair amount of overlap and therefore had some "chop" at idle. With its SMF, the ZF definitely rattled. But with any RPM at all the engine would smooth out and the rattle went away. So the lower you set your idle and the more roughly an engine idles, the more rattle you'll get. But this is only at idle.

 

MM,

Yeah, this car has been more than a handful lately. It seems to run well at WOT until I hit 52-5500 RPMs, then starts to miss. The miss manifests itself as peaks and valleys. At about 5200, the RPMs seem to plateau, there is mild "bucking", and the revs continue to climb slowly.

Previously the pump was losing pressure at higher RPMs and causing the car to fall on its face. I fixed that and I have full pressure the entire time. But it seems there was another issue that was masked by the weak fuel pump.

EDIT: I do have a new coil (Blue Streak) to replace the Denso unit I put in 3 years ago. I'm also replacing the FPR just because.

 

Okay, I'd replace that coil for sure. Denso has not been good for awhile (e.g. they are terrible for 02 sensors for our cars), and the symptoms you describe sound close enough to a slowly-failing coil to make it the first diagnostic check.

 

Copy!

Coincidentally, I am moving to Sumter, SC which should be within 1 hour of Ram Clutches. I may persuade Mike at Ram to take a look at my car.

 

Since it misfires at that high of rpm, I would also suspect cap and rotor.

I know you have a new fuel pump.

But I would still attach a fuel pressure gauge, and see what it does at that rpm, where it starts act up.