Changed the gearset and now I'm facing issues
 

I'll try to explain myself (not going to be easy to do so in English and being as I am Mechanically Challenged).

About 10 days ago I took my car to my mechanic to change the suspension for the Teins Keinayo was kind enough to sell me and while they were at it I also decided to ask them to change all the suspension bushings and the gearset to the 3.63 gears I had bought from Mazmart. I picked my car up from the shop last week and I was delighted with how the Teins behaved and with the bushings.

The new gearset on the other hand was a totally different matter :mad:.

I'm going to try to describe what's going on: as soon as my car picks up speed I hear a distinct whining coming from the differential and also a faint noise like a thump which speeds up or slows down at the same speed the differential rotates. This particular sound is quite faint and it only becomes very obvious when I close the windows and turn the A/C on.

I had to leave the city for a previously set commitment this past weekend so I decided to take the car back to the shop and asked them to please check it. When I got back on Monday afternoon I discovered that they hadn't touched my car and my mechanic told me that the thumping sound I was hearing was transmission related and not differential related.

So I find myself in a bind; I know for sure I won't get any help from the current shop and I have to start looking for another shop. While I do so, and before I decide to sell the car, I wanted to get some feedback from the gurus in this forum about what could be wrong and how to approach this problem.

Many thanks,

Rafa

DO NOT SELL RAFA...hang in there bud!

I just think that they didn't set the backlash properly, have someone experienced do this for you

The whine is the rear end. They either set it up too tight, or too loose. Either will make them whine. The thump, well, that's hard to diagnose, but I would guess is diff related as the noise cam with the diff work. Video's of the thumping would help. Also put the car on jackstands and check all the bolts. Driveshaft, diff housing, diff mounts, PPF, etc.

the thump can be associated with it being too loose, no big deal, but i'd still want them to fix it

Hey guys, thanks for the quick replies. I'll see about getting a video (I'll need to ask one of my sons).

One thing I forgot to mention is: they had to buy some kind of ball bearing locally to install the gearset.

I hate being mechanically challenged! :vash:

It's worse with the A/C on? Are you not hearing A/C compressor or belt noise?

This is very bad. Whine = wear. As in, you don't really want to be driving it. It means the diff wasn't set up properly.
Can't comment on the thump. Could be a number of things related or unrelated.

Rafa,
I had R.F. Engman read your post. You should feel honored; he's probably has set up more miata diffs than anyone else on the planet.
He believes they probably replaced the bearing under the pinion head. This bearing typically does not have to be replaced, unless the person who disassembled the diff was careless and damaged it.
It is *possible* that the whining and knocking noise are both a product of the same installation error. If the interior surfaces of the case are not thoroughly and properly cleaned out, then it's possible to install the ring gear off axis, such that as it rotated it would have a tight spot on one end and a loose spot on the other end. The loose spot could also bang during change of acceleration. If set up in this manner, it could appear installed correctly. However the installer should have checked the pattern, and if he had done so, would have found the error.

What does the whine sound like? Is it constant? Wooompp wooompp wommmmp, or wwwwwwwwwwwww (if that makes sense). Does it change pitch? Is it related to wheel speed, or is it related to drive shaft speed?

What I mean by worse is that the sound is really faint and it is much more noticeable when I drive with the windows up (nothing to do with the A/C; that's just because in our weather if one drives around with the windows up and the A/C off the car becomes a sauna very quickly).

I thought the same thing about the whine so I parked the car. I told Dan (zabac) on a pm that I was thinking of selling the car; that was the reason behind his comment. I had started buying parts to build the motor (already have a set of pistons and rods) but I'm going to sell those. There's no way I'm going to allow a local shop to build me a motor. :mad:

About the thump; it sounds like metal on metal and I get the distinct impression that it's one of the pinions hitting something else as the gears turn.

I'm not sure if it's my imagination (I was planning to take out the car and try it with another car running side by side) but I get the feeling that the speedometer is also not working properly; especially when I reach speeds over 40 to 50 miles per hour.

Would it be a good idea to try to go back to the original 4.1 gearset the car had?

Sorry guys.

Thanks for the support Dan; btw, what do you mean when you say "backlash"?

bad idea, they would simply install the 4.1 wrong as well then...

Ben, first of all: :bowdown::bowdown::bowdown::bowdown::bowdown: for asking Mr. Engman to read my post.

All he says makes sense. They did indeed replace the bearing under the pinion head with one they bought locally.

The whining sound is constant and can only be heard when the car is at somewhat high speed. The thumping sound on the other hand can be heard even at very low speeds. Let me try to describe it: it sounds like toc, toc, toc and it's related to shaft speed so it speeds up as one speeds the car up thus the time between one "toc" and the next one becomes shorter and shorter as I speed the car up. It's like I can hear the differential's revolutions as it turns.

Did you get the 3.63 speedo drive gear as well? If not, then yeah your speedo is going to be far, far off from actual.

Going to the 4.10 again won't solve any of your problems. As it's going to have to be set up correctly. Might as well set up the gears you actually want.

Worst case (though expensive), you can ship your carrier to us and have Rick set it up.

At least that would be an option. Many thanks!

I did buy the speedo from you guys also. The speeds shown seem to be fine at low speeds. Don't put too much stock on that; it may just be me imagining things :bang:

Many thanks Dan, great link, I'll print it and translate it.

here is the important stuff...
1.8 Specs
Ring gear backlash (0.0036-0.0043)
Bearing preload (7.3004-7.3031)
Bearing cap bolt torque (27-38 ft-lb)
Lock plates on bearing caps (13-19 ft-lb)
ring gear to the differential (51-61 ft-lb)

you may want to study that info, and go over to shop and give them a test, $50 says they have no idea how to do it nor what the specs were supposed to be

If the shop wont re-do the gears (pinion depth + backlash), find a 4WD shop that has mazda experience and see if they can help out. You need a few specialized tools to do it yourself.

When I read your post my first thought was that a bearing is bad somewhere. I just didn't want to be the first one to say it, because there are way too many smart asses here that would just make fun of it. The type of sound you are describing and how it goes up and down with speeds sounds exactly like a bad bearing. I agree with the bearing theory. Most likely that is what the problem is. I have worked on cars before since I use to work in an auto shop, but I don’t have much experience with Miata’s.

Thanks to all for your input.

You know Dan, when I read the link you posted and began to see the types of tools needed I knew the only one I saw at the shop was the hammer. I'm exaggerating but not by much and they didn't follow any torque procedures for sure.

I also like Matt's 4WD shop idea. I'm going to look into that. If I'm not mistaken there's even some new Mazda SUVs that are AWD.

Yea, you need to somehow find a good shop. This obviously should have never happened. It wasn't an error, or a mistake, it was pure negligence. Oh, FWIW they likely put way too much backlash so it's loose, and that's the whining your hearing. Hard to say though. Anyway, best to not drive it and get it fixed by someone that knows their stuff. I'm gonna say there's nothing mazda specific you need to know to setup our rear ends. All they'll need is the specs Dan posted, a magnetic base dial indicator, a 6-7 or 7-8 inch micrometer, and a torque wrench. Ok, maybe a few other odd things but that's the expensive stuff.