Please help troubleshoot origin of drivetrain noise!

[Gregxster]

I apologize in advance, this may get a bit wordy…

I have a 69 Triumph Spitfire that I swapped in a 4AGE and T50 trans. The engine has been built up with a massaged head from OST (OST-33). The engine runs great and just friggen rips from 5k to 8k!

The T50 was “rebuilt” by a local trans shop, with parts he sourced. It shifts great but was noisy in 2nd and 3rd, especially low speed cruising at part throttle. So… I had another T50 rebuilt with a complete rebuilt kit that I sourced ( http://www.ebay.com/itm/-/171935128152 )by another trans shop. This shop said that all the parts fit (I got back all used parts) but that the gears looked to have been overheated (no broke, chipped gears). I installed this trans and took it for a spin… Exactly the same noise was still there!

This “noise” can be felt as a vibration in the body. I had the owners of both trans shop ride with me and they both said that it sounds/feels like metal on metal contact. I have searched extensively and have not found any contact points! The alternator was close so I got a shorter belt and now it is more than 3/4” away from the shock tower. This noise can be “felt” very little in 1st and 4th gears, but 2nd and 3rd gears, it is very noisy and annoying and sound like a chattering or rumble of the gears back and forth. I have pulled the drive shaft thinking it may be too long and bottoming out against the trans (the diff is mounted to the frame with poly bushings). The driveline has only about ¼” end play (possible problem?). The engine and trans has new Megan Racing motor mounts.

Currently, I am thinking it may be the light flywheel (http://www.ebay.com/itm/EXEDY-PAZ-STAGE ... 1a082324c6 ). I did an extensive search and found this may be a cause. OST – I believe I read something about an issue you had with lightened flywheels?? I love this light flywheel, the engine revs up like a sport bike engine, but not if it causes this noise and potentially damaging the trans.

Any thoughts???

[totta crolla]

I'm chasing exactly the same issue right now, sort of a resonance in 3rd gear at about 3000rpm it feels just like the exhaust is touching the body somewhere but it is definitely not. My thoughts were a gearbox bearing so I'm really pleased that you posted this up, you may have saved me a lot of work.
I also have a lightened flywheel that has been balance checked and found to be good, new balanced clutch fitted.
Propshaft joints is where I'm going next.
Will keep you posted.

[jondee86]

Gear rattle (gear tooth rattle) is often associated with the installation of
a lightweight flywheel and engine modifications. Typically, it will be more
noticeable when the gear teeth are lightly loaded and at lower engine speeds.
Here is one commentary from a clutch manufacturer...
http://www.advancedclutch.com/blog/tag/gear-rattle/

And here is an explanation lifted from a BMW specialists web page...

A piston engine's power delivery is not seamless like an electric motor. A piston
engine makes pulses of power very rapidly. How often? In the M3, (3 X rpm) per
minute. Now realize that any drivetrain component (transmission or differential)
has a certain amount of looseness or slack in it - it must, or being too tight would
create a lot more friction. So when the power pulse engages the transmission,
it is causing the rotational power going through the unit to take up that slack.
This effectively causes components to touch that were not pressed together a
moment before. Between each power pulse, those components de-couple. Press
any two hard objects together, whether it be a tea cup and saucer or a hammer
and nail, and you notice that noise is made. Repeat the contact-release-contact
cycle quickly and it makes a staccato sound - a rattle.

At higher speeds and loads, the gear teeth either remain in contact, or the
amount of tooth separation becomes too small to create the rattle sound when
the teeth come back into contact (bang together). Changing to a higher viscosity
gear oil can reduce gear rattle, and the BMW specialist has had success using a
mix of Redline products as detailed in this data sheet...
http://www.uucmotorwerks.com/html_techt ... rattle.htm

It is also possible that using stiffer engine and transmission mountings can
contribute to gear rattle. Reducing the reaction of the engine and transmission
assembly to power stroke pulsations will intensify the pulsations tranmitted to
the driveline.

You could try some experiments in loading the gears by driving at a speed where
the noise is bad, and left foot braking while pressing the accelerator enough to
hold a constant speed. If the noise stops or is greatly reduced under load, then
you can be reasonably sure that it is gear rattle.

Cheers... jondee86

[totta crolla]

I will try that left foot braking idea Jondee although having just checked my bonnet it is showing witness marks from the throttle body. When the chap did the smallport inlet for me he welded the flange straight on rather than at an angle as per the original. Fingers crossed that is the problem.

[Gregxster]

jondee86... I think you nailed it! This is what I was thinking and dreaded. It looks like I will be re-installing the stock flywheel and will add some 75w-140NS Redline gear oil!

Thank you for the info and links!

[jondee86]

Fingers crossed that is the problem.

When the Devil rides in your car he can play all kinds of tricks
I had a noise/vibration that sounded like hail on a tin roof. It occurred
around 5000rpm and you could drive through it if you kept your foot down.
I would have sworn it was a bearing somewhere in the drive train... I even
felt it through the pedals.

Turned out to be the clutch hardline hitting resonance and vibrating so
bad that it was thrashing against the firewall Zip-tied a bit of foam
around the hard line and noise gone. Just goes to show how easy it is to
be fooled into focussing on one spot when the problem is somewhere else.

Cheers... jondee86

PS: Yes, the top of the intake manifold comes perilously close to the
underside of the bonnet, so the angle on the RWD manifold is there for
good reason.

[jondee86]

I love this light flywheel, the engine revs up like a sport bike engine, but
not if it causes this noise and potentially damaging the trans.

I'd suggest trying the Redline before you consider removing your light flywheel.
As you have observed, a light flywheel is one of the better improvements you can
make to your engine. Also, you say that you have installed Megan engine and trans
mounts. Are these stiffer than the OEM Toyota mounts ? If theye are, and you still
have the OEM mounts, it could be worth swapping the OEM mounts back in as an
experiment.

Hard rubber, urethane or solid mounting any part of the drivetrain will result in
increased noise and vibration being transmitted to the chassis. This can cause
all manner of strange rattles and buzzing noises. Plus, with the gearbox being
right under your elbow, you are bound to hear a lot of mechanical noise that you
would not notice in a FWD car.

So if I was in your place, I would see if I could eliminate (or at least minimise) the
problem by other means, before ripping the light flywheel out.

Cheers... jondee86

[jondee86]

Just remembered this post... viewtopic.php?f=9&t=16559

I filled more oil into the gearbox, and at the same time changed to
this oil... Amsoil Manual Synchromesh Transmission Fluid 5W-30. The
difference in noise emanating from the gearbox was considerable. Not
only was the box much quieter, but shifting in general was improved,
and in particular, the typical T50 "notchiness" when cold was reduced.

So I would definitely suggest filling at least 1.5 liters of oil in thru the
shifter to see if it helps. I used the Amsoil as it has been shown to
help shifting in several brands of manual gearboxes. But Redline is
also reported to work miracles, so perhaps use that to see if the
"shockproof" claim really does help quieten things down.

Cheers... jondee86

[Gregxster]

When I installed the second rebuilt trans is when I installed the new Megan Racing mounts. One of the original mounts (new, Anchor brand) was softer than the other and I thought the engine and trans were moving around. The sound is more of a vibration felt through your butt and feet. The car has no carpets and you can feel the vibration with your hand on the center tunnel.

At this point I believe it is gear chatter from the "HD Kevlar sprung" disc. I'm going to keep the light flywheel and replace the clutch disc with a stock Aisin unit and use Redline oil. I'll give an update next week after installing the new disc

Gregg

[Gregxster]

So... I pulled the motor and trans, replaced the clutch disc with a stock Aisin disc, filled the trans with Redline 75w-140NS oil and put it all back together in 6 hours! While apart, I checked the flywheel bolts torque, cleaned the flywheel and pressure plate surfaces. The disc that I took out has six HD springs, the Aisin unit has 4 rubber bumpers in place of the springs.

Took it out for a test drive... Same noise/vibration, maybe marginally better. The trans shifts much smoother and the gear whine is not as bad. The clutch takeup is much smoother, also. I may have to live with it for now. I will be upgrading my differential to a Subaru R160 unit soon. Maybe the noise/vibration is coming from the diff and/or the drive line is too long and bottoming out inside the trans?

Gregg

[jondee86]

Seeing as you have independent rear suspension, there should be very little relative
movement beteen differential housing and gearbox. So an easy check would be to
unbolt the companion flange at the diff and see if you can push the front of the drive
shaft any further into the gearbox. Around 10mm before you bottom out should be
sufficient to ensure there is no (longitudinal) metal to metal contact while driving.

While under there make sure that the front and rear universals are phased correctly.
Out of phase universals will generate vibration in the driveline. I looked through your
build record, but couldn't see a driveshaft anywhere, so ignore this point if your
driveshaft is one-piece with a yoke welded on each end.

Cheers... jondee86

[allencr]

...both said that it sounds/feels like metal on metal contact.

I'm more inclined to go with them and/or the poly diff mount, then throwing parts & WAGs at it.
Also, any suspension mounts that are hard plastic?