narianu

I've spent hours and several hundred dollars trying to diagnose a front end noise . I've gone to several mechanics with no luck.

I have a 2001 Civic HX with a manual trans, 194k miles.

When I release the clutch and give gas to accelerate from a full stop, I get a pop noise from the lower transmission casing. I've had someone do slow starts with the hood up while I felt various parts of the car, but I have not been able to feel exactly where the noise comes from. My best guess is the lower transmission or passenger-side axle region.

Nuances:
• The noise typically occurs as the clutch is 80-90% released and the engine's torque is almost completelytransferred to the wheels.
• The pop noise only happens once, when moving from a complete stop. It also occasionally occurs when I'm in 2nd/3rd gear, and I back off the gas pedal a bit and switch from accelerating to cruising. I.e. I accelerate to 25mph, then let off the gas and the engine is no longer providing acceleration torque, but rather maintaining 25mph. This doesn't happen when in 4th/5th gear.
• It happens more frequently on very hot days.
• After a long trip (when the whole engine/trans are fully warmed up) , the pop noise occurs on almost every acceleration from a complete stop.
• If I rev the engine more (say, 2000 rpm) and release the clutch quickly, the noise doesn't occur. It's more when I keep the engine around 800rpm while starting to move, and sync the clutch release and gas pedal depress better.
• When I was trying to isolate the noise with a friend, we were on a flat parking lot. She was alternating from reverse and forward, and that transition would create a loud pop once the car started moving.
• My feeling is that some pressure builds up somewhere as I start to accelerate, and once the body of the car has momentum, the pressure releases as a pop noise.

What I've done:

Difference mechanics have suggested different things and I've tried everything they mentioned.

• Replaced all four motor mounts. Front and Driver's side are Beck Arnley, transmission mount is NAPA Balkamp (Anchor?), and rear is genuine Honda.
• Replaced both axles - one mechanic said that vertical and horizontal play in the passenger axle was causing the pop. Another said that the driver's side inner CV joint was losing grease. Replacing both didn't solve the issue.
• Replaced both ball joints
• Replaced both front LCA bushings
• Replaced front struts with Monroe quickstruts
• Checked the sway bar links, but they are fine.
• Drained and replaced the manual transmission fluid


Any additional insights of clues would be appreciated!

narianu

Does anyone have an idea or is any more info needed?

ezone

I don't think you are gonna fix this over the internet. You have replaced a pile of stuff already. (All bolts tight?)

Someone, live and in person, needs to figure out where the noise originates and what to do about it.

That means you need to demonstrate the issue directly to the technician so everyone is on the same page about what issue you want addressed.
A five minute test drive with the tech can save hours of guesswork and headaches when the complaint isn't really obvious to anyone but the main driver.

Ripulez

While ezone said it best, i can still hazard some guesses.

what kind of clutch do you have, is it aftermarket? many aftermarket clutches make loud popping noises.

the noise could also be related to the gears in the transmission itself.

narianu

Thanks, all, for taking the time to respond.

I have had a couple mechanics identify the noise. One of them suggested the axle(s), which didn't solve the issue.


I'm not sure as I bought the car second hand, but I don't have any reason to believe that it's not the stock clutch. When you say that aftermarket clutches make popping noises, would that be audible when depressing the clutch when the engine is off?

I also had that thought about the gears making noise. If you had to posit a guess, what part(s) would be causing that? Worn helical gears? Maybe the synchros? If it were one of these parts, it would likely generate a constant noise rather than a one-time pop, no?

Ripulez

with that many miles on the car, it could very well be aftermarket. i put a aftermarket 5 puck clutch in my 05 civic lx 120k miles, it is only audible when you are changing gears, letting off the accelerator, or even during hard turns or bumps. is there any rattling, or just a popping noise? regardless i have never heard a noise while the engine is off and depressing the clutch. i doubt this is transmission related if this is happening, check your slave cylinder perhaps? The only way for you to know for sure is to visually inspect the clutch and slave cylinder.

honestly the only real way to identify what part it could be in the transmission, if any, is by disassembling it and visually inspecting the two gear shafts and the differential gear. in all reality if the performance of your car hasn't been affected, i wouldn't worry to much about it (unless it really annoys the crap out of you)

P.S
there is a rubber boot that covers the release fork, keeping dirt/water/ect. out and keeping the grease between the release fork and the slave cylinder. This can cause noise or squeaking. when i replaced my clutch i noticed this boot was torn, mucking up the inside of the casing with the input shaft and clutch. i cleaned all inside the casing, replaced the boot, then re applied grease on the release fork.

narianu

This weekend, I'll try to feel around the clutch/flywheel area as someone starts/stops to see if the popping noise originates from there. Thanks for the suggestion!

narianu

Finally figured it out. The bolt for the transmission mount was loose! I didn't even think of checking that since I paid a mechanic $150 to install it more than a year ago, but now that I think of it, it's been loose since it was installed. I remember checking the mount back then and noticing a gap between the edge of the bolt and the mounting bracket, and assumed it was by design. Coming to think of it, I had that noise ever since the mechanic did the installation!

I narrowed it down feeling different parts of the frame/engine while a friend started/stopped the car. At one point, I could feel the vibration, popping directly from the mount. But it was tricky to find because the pop would reverberate throughout the frame and made it difficult to isolate.

Well, after spending $400 in the past couple months on parts, and after getting advice from two different mechanics, I've lost my trust in their diagnostics ability. At least I installed the replacement parts (axles, ball joints, remaining motor mounts, etc.) myself or I'd be $1000+ in the hole. And it was just a loose bolt!!! Anyways, I'm happy I solved it, and thanks to everyone for the input.

Ripulez

Well glad you figured it out, nothing like an easy fix after hundreds spent on other parts