Q: Mild thud sound when starting or stopping.

Hello, everyone.

99 automatic 62,000 miles.

The car makes a very mild thud sound in the back when it's starting or
stopping. I thought maybe the wrench in the trunk was shifting around
when I'm stopping at the traffic signal, but the problem persisted
even if I cleaned up the trunk. It's not consistent either; it comes
and goes depending on what kind of mood the car is in.

My usual mechanic wasn't sure what the problem was, but he didn't
consider it anything major. I tried a different place yesterday, where
the mechanic there wasn't sure either, but he'd find out if I leave
the car to him for the rest of the day. His conclusion was a complete
overhaul of the transmission, which (I think) most likely would solve
the problem, although I'm not sure such a drastic measure is
necessary.

Should I try another place and get the 3rd opinion? Any suggestions
welcome.
__
sol

In article >,
solamour > wrote:

> The car makes a very mild thud sound in the back when it's starting or
> stopping. I thought maybe the wrench in the trunk was shifting around
> when I'm stopping at the traffic signal, but the problem persisted
> even if I cleaned up the trunk.

Are the jack and spare tire tied down tightly? Are the brake caliper
slider pins working freely? Are you missing any muffler hangers? Are all
the lugnuts tight?

--
Lanny Chambers
'94C, St. Louis
http://www.hummingbirds.net/alignment.html

"Lanny Chambers" > wrote in message
...
| In article >,
| solamour > wrote:
|
| > The car makes a very mild thud sound in the back when it's starting or
| > stopping. I thought maybe the wrench in the trunk was shifting around
| > when I'm stopping at the traffic signal, but the problem persisted
| > even if I cleaned up the trunk.
|
| Are the jack and spare tire tied down tightly? Are the brake caliper
| slider pins working freely? Are you missing any muffler hangers? Are all
| the lugnuts tight?
|
| --
| Lanny Chambers
| '94C, St. Louis
| http://www.hummingbirds.net/alignment.html


and have you checked uni joints?

On Wed, 15 Nov 2006 17:59:55 +1100, "Justin" <,> wrote:

>"Lanny Chambers" > wrote in message
...
>| In article >,
>| solamour > wrote:
>|
>| > The car makes a very mild thud sound in the back when it's starting or
>| > stopping. I thought maybe the wrench in the trunk was shifting around
>| > when I'm stopping at the traffic signal, but the problem persisted
>| > even if I cleaned up the trunk.
>|
>| Are the jack and spare tire tied down tightly? Are the brake caliper
>| slider pins working freely? Are you missing any muffler hangers? Are all
>| the lugnuts tight?
>|
>| --
>| Lanny Chambers
>| '94C, St. Louis
>| http://www.hummingbirds.net/alignment.html
>
>and have you checked uni joints?

This is the moment when I feel completely lost, because car
maintenance certianly isn't my field. I tried without the spare tire
and the tools, but it still made the sound, so I think they are off
the hook. As for the other stuff, I let my usual mechanic decide, and
he always says he can't find anything unusual.

The second mechanic said something about worn differential (not sure
what that means), and that was the reason he suggested a complete
overhaul of the transmission.

Anyhow, I think spending thousands of dollars on a new transmission
for this particular car is not worthwhile, so I'm going to keep
driving until it no longer runs. I just hope it doesn't breaks down in
the middle of nowhere.
__
sol

solamour wrote:

> This is the moment when I feel completely lost, because car
> maintenance certianly isn't my field. I tried without the spare tire
> and the tools, but it still made the sound, so I think they are off
> the hook. As for the other stuff, I let my usual mechanic decide, and
> he always says he can't find anything unusual.
>
> The second mechanic said something about worn differential (not sure
> what that means), and that was the reason he suggested a complete
> overhaul of the transmission.
>
> Anyhow, I think spending thousands of dollars on a new transmission
> for this particular car is not worthwhile, so I'm going to keep
> driving until it no longer runs. I just hope it doesn't breaks down in
> the middle of nowhere.
> __
> sol

Whoa!

The differential and transmission are connected by a driveshaft, but
they are completely separate units on a RWD car like the miata.
In other words, one can go bad while the other still functions perfectly.
If it is a bad differential, that in itself does not indicate a
transmission in need of overhaul, and vice-versa.

62,000 miles is very low mileage for either part to go bad unless they
are defective or have been abused.
I would check with the mechanic for clarification and/or take it
somewhere else for yet another opinion. Is the car shifting normally?

Also, if your differential is going out, I would expect it to start
making a progresssively worse noise at higher speeds rather than just a
bumping sound at starts and stops. How long has the noise been occuring?

I am guessing that the problem is one of the more simple things that
have already been suggested or something similar. It could even be a
loose sway bar bracket.

Is there a miata group in your area? If so, subscribing to their mailing
list and asking about a local shop they can recommend might be worth doing.

Good luck!

Pat

"solamour" > wrote
> The car makes a very mild thud sound in the back when it's starting or
> stopping

It was a (only slightly) loose battery in our '90 a few years ago that made
this type of noise. You would think the mechanic checked for that, but isn't
he the one who wants to rebuild your transmission because the differential
is going bad?

On Thu, 16 Nov 2006 08:05:44 GMT, pws > wrote:

>The differential and transmission are connected by a driveshaft, but
>they are completely separate units on a RWD car like the miata.
>In other words, one can go bad while the other still functions perfectly.
>If it is a bad differential, that in itself does not indicate a
>transmission in need of overhaul, and vice-versa.
>
>62,000 miles is very low mileage for either part to go bad unless they
>are defective or have been abused.
>I would check with the mechanic for clarification and/or take it
>somewhere else for yet another opinion. Is the car shifting normally?
>
>Also, if your differential is going out, I would expect it to start
>making a progresssively worse noise at higher speeds rather than just a
>bumping sound at starts and stops. How long has the noise been occuring?
>
>I am guessing that the problem is one of the more simple things that
>have already been suggested or something similar. It could even be a
>loose sway bar bracket.
>
>Is there a miata group in your area? If so, subscribing to their mailing
>list and asking about a local shop they can recommend might be worth doing.
>
>Good luck!
>
>Pat

The car runs fine. Shifting up and down is no problem. It just makes
this rather dull knocking sound when I'm about to make a stop at a
traffic signal or when I get a green light and about to go. It's like
the car is cracking its knuckle. Well, the car doesn't have a knuckle,
but you get the point.

Funny thing is, when I make a really, really smooth stop, like
stepping on the brake ever so gently, almost no brake at all, I can
often prevent the sound. However, I can't make the sound go away even
if I accelerate really, really slowly, most likely because it's not
slow enough.

The noise has been around for a while. But it's not quite consistent;
it comes and goes. However, for the last couple of weeks or so, it
became slightly regular with varying degree each day.

I did find a local group http://www.sandiegomiataclub.org/, which I
think is worth checking out. Again, thanks everyone for taking time to
respond.
__
sol

solamour wrote:

> The car runs fine. Shifting up and down is no problem. It just makes
> this rather dull knocking sound when I'm about to make a stop at a
> traffic signal or when I get a green light and about to go. It's like
> the car is cracking its knuckle. Well, the car doesn't have a knuckle,
> but you get the point.
>
> Funny thing is, when I make a really, really smooth stop, like
> stepping on the brake ever so gently, almost no brake at all, I can
> often prevent the sound. However, I can't make the sound go away even
> if I accelerate really, really slowly, most likely because it's not
> slow enough.
>
> The noise has been around for a while. But it's not quite consistent;
> it comes and goes. However, for the last couple of weeks or so, it
> became slightly regular with varying degree each day.
>
> I did find a local group http://www.sandiegomiataclub.org/, which I
> think is worth checking out. Again, thanks everyone for taking time to
> respond.
> __
> sol

At 62,000 miles, that miata should have a long way to go as long as it
has had decent maintenance and continues to receive it.
If you were in Austin, I could point you to a mechanic that would find
the problem, give you an honest answer, and charge a very fair price. I
assume that there are people in the San Diego club that know of such a
mechanic.

If it were my car, I would, in this basic order:

1. check that the battery is secure
2. Look for any possible loose item that may be bumping the sheet metal
in the trunk.
3. Shake the exhaust and see if it is loose enough to hit either the
bumper cover or anything underneath the car.
4. Check that all lug nuts are tight
5. Grab the rear sway bar,shake it hard and see if it is loose at any of
the four mounting points.
6. Check the driveshaft U-Joints for excesive play. This would be an
unusual problem at 62,000 miles

This can all be done without taking anything apart. After that:

7. Grease the brake slider pins. This is a very good idea to do once
every year or two anyway.
8. Check overall brake condition. Make sure that the pistons are not
sticking in place at all.
9. Scream at the car - this helps, mine often cooperates after I
threaten to strip it and sell the parts on Ebay.
10. Check the differential, he may be right about that, but it can be
fixed or replaced without ever touching the transmission.

I am sure that I left something out, I always do.

No matter what, I would find a new mechanic when this one wants to
overhaul a transmission that is shifting fine because of a noise that is
coming from the rear of the car.

Again, best of luck!

Pat