Mazda 3 2005 - Vibration issue

Maintenance/Repairs
1

Hi all,

My son is away any college and I have been taking his car out now and then around town to give it a little exercise. This past weekend however I took it out on the highway and found it has a pretty bad vibration. The vibration is coming from the body, not the steering wheel, so i initially suspected the real wheel balance. Next I varied my speed betwn 50-75 mph expecting to feel the vibration intensity vary, but it did not. While doing that however I realized that when I let off the throttle, the vibration stops. Given it some gas and it comes right back.

I got off the highway and pulled in to a parking lot. Driving at parking lot speeds, accelerating or not, there is no vibration. Come to a stop either in gear or neutral, and the engine is rock solid steady. Then got back on the local streets and the vibration returned but only while accelerating, even gently.

At this point I should mention that we replace a bad motor mount a yr and a half ago when we bought the car, the upper passenger side. The mount damage was easily so it was an easy diagnose. Replacing it eliminated the vibration the car had at the time. We had also planned to replace the lower rear mount at the same time but the one we bought was defective, and the one we removed from the car looked fine, so we put it back in.

So now I am wondering if the rear mount has failed, but it is not possible to see the rubber unless you removed it. What you you guys think, could it be an issue with the engine itself, or do all these symptoms point to the mount?

Thanks in advance for your help!

David

2

This might be a difficult one. Sounds might be a misfire under load; do you have a check engine light lit? I am not sure how many miles on the car and what has been done. It could still be the mount. I think the crude way of testing the mount is to rev the car in gear while holding the brake and with the hood up to see how much the engine rocks.

3
Next I varied my speed betwn 50-75 mph expecting to feel the vibration intensity vary, but it did not.

Did the vibration frequency vary with speed?

4

I went through this with my daughter’s 2005 Mazda 3. If you do a search on Mazda 3 “body vibration at cruise speed”, you will find that this is a common problem with this car. The problem is the engine mounts. You should probably change all three mounts like I did, but you may want to try just changing the mount on the passenger side of the engine. This particular mount fails first because it has a viscous fluid in it to dampen vibration. The fluid leaks out, causing the vibration. It is the easiest mount of the three to change, just make sure you support the engine when you replace it.

5

Here is the text portion of the service bulletin. It has detailed direction about how to install the mounts.

.Subject:
BODY VIBRATION AT CRUISE SPEED

BULLETIN NOTE This bulletin supersedes the previous bulletin 03-001/06 issued on 7/21/2006. The APPLICABLE MODEL(S)/VINs section has been revised.

APPLICABLE MODEL(S) / VINs
2004-2007 Mazda3
2006-2007 Mazda5

Some vehicles may experience a body vibration when driving approximately 55 mph. This symptom is due to the characteristics of the No.3 & No. 4 engine mounts.

Modified No. 3 & No. 4 engine mounts have been established for service only. Customers having this concern should have their vehicle repaired using the following repair procedure.

REPAIR PROCEDURE

IMPORTANT NOTE: ^ This repair should only be performed if all tires and rims are confirmed to be in balance and all suspension components are in proper working condition.

^ Notify customers that use of the modified mounts will reduce vibration at cruising speed but may increase vibration at idle.

NOTE: Because idle vibration may increase, it is highly recommended to continue using mass production mounts for all other service concerns.

  1. Verify concern.

  2. Replace the No. 3 & 4 engine mounts with service parts according to the appropriate Workshop Manual section 01-10 ENGINE REMOVAL/INSTALLATION.

  3. Center the new engine mounts as outlined in ENGINE MOUNT CENTERING PROCEDURE.

  4. Verify repair.

ENGINE MOUNT CENTERING PROCEDURE

No. 1, No. 3 and No.4 Engine Mount Adjustment

  1. Warm up the engine.

  2. Raise and support vehicle on a hoist.

  3. Remove engine under cover.

  4. Lower the vehicle until the front tires lightly touch the ground.

  5. Secure the engine and transaxle using an engine jack and attachment as instructed in No. 3 Engine Mount And No. 4 Engine Mount Rubber Installation Note in appropriate Workshop Manual, section 01-10 MECHANICAL.

  6. Remove two bolts from No.3 engine mount bracket.

  7. Lift engine using jack until No.3 engine mount is lifted slightly from vehicle body.

NOTE: Do not raise engine too much or A/C pipe damage may occur

  1. Move the engine mount rubber or engine until installation hole on the vehicle body aligns with hole in the engine mount bracket.

  2. Lower the jack and tighten bolts on No. 3 engine mount bracket.

Tightening torque: 55.0-77.3 ft-lbf (74.5-04.9 N.m)

NOTE: ^ Do not allow the engine mount bracket to be misaligned.

  1. With engine supported as described in STEP 5, remove four (4) nuts and two (2) bolts from No. 4 engine mount top plate. Remove top plate.

NOTE: ^ To access the mount, remove battery box.

  1. Lift engine again using jack until No. 4 engine mount is lifted slightly from vehicle body.

NOTE: ^ Do not raise engine too much or A/C pipe damage may occur.

  1. With top plate of No. 4 engine mount removed, move engine mount bottom plate or engine until all four (4) installation studs on the vehicle align with the engine mount holes.

  2. Place top plate back on and tighten No. 4 engine mount bracket nuts and bolts to torque indicated

  3. Lift engine again using jack and loosen the two bolts on the No. 1 engine mount rubber until slightly loose on the No. 1 engine mount rubber.

  4. Shake/rock the engine back and forth.

  5. Tighten bolts in order below.

A. Crossmember-side No. 1 engine mount rubber. Tightening Torque: 68.7-86.1 ft-lbf (93.1-116.6 N.m)

B. Engine-side No. 1 engine mount rubber. Tightening Torque: 68.7-86.1 ft-lbf (93.1-116.6 N.m)

6

The check engine light has not gone on, but a misfire under load does make some sense. Should I check the plugs? I’ll do the rev engine in gear test and see what happens…

7

Insightful:
Did the vibration frequency vary with speed?

Not that I noticed

markmast:

I replaced the upper passenger side last year and it looks fine as far as I can tell. I am aware of the lower rear mount and can get to that one to change it, but where is the third one?

8

David, the third mount is under the battery.

9

Ah, great place to hide it. I will pull the battery this weekend and have a look

10

My son came home from school for thanksgiving so we were able to get out there this morning and change the transmission mount (under the battery). The mount was in fact bad and with the new one installed about 80% of the vibration is gone. I am going to guess the rear lower mount is also bad and change that one when he is back again for X-mas break.

Thanks for all the advice guys!!

11

Thanks for letting us know the outcome. It’s great to hear that you have gotten it solved.