codrus

After breaking the 5-speed in my 99 at Laguna in April, I put in an MSM 6-speed and a 3.9. Well, the 3.9 sucks, so I bought the 3.636 gears and swapped it for the 4.3 gears that were in the original diff from the car.

When taking the diff off, I noticed the companion flange was broken:



Here's what it's supposed to look like:



The cross-shaped thingey (cast iron) is held to the flange with rubber -- presumably it's some kind of vibration damper? What kills them? It was fine a couple years ago when I put the new motor in the car, and it's only had about 6000 miles since then. I didn't notice any particular vibration in the car before I blew up the transmission.

--Ian

JasonC SBB

Because race car?

curly

iTrader: (25)

No idea but most people remove those anyways.

Savington

iTrader: (31)

Pretty much because race car. The rubber used to bond the thing just isn't designed for what we do. It's only there to dampen small drivetrain vibrations and improve NVH, so removing it isn't a problem.

When they actually come fully loose, the vibration at 140mph is amazing. The 3.63:1 hi-power OS Giken that's going into Theseus has the little dongus removed.

codrus

Interesting. Mine was fully loose (it spun easily by hand when I was taking the diff out, without the driveshaft turning), but I didn't notice major vibration from it. Of course, I'm a wuss on the straight and was lifting at 110 or so.

I guess I didn't need to buy a new one to put in, ah well. I got ~ 50 track days out of the first one, and at the rate I'm making it to the track these days if the second one goes the same distance then I've got a long time before I need to worry about it again.

--Ian

JasonC SBB

What kills vibe dampers are vibes much larger than they are designed for.

JasonC SBB

Hey wasn't there a story about some Mustang doofus who disabled his speed limiter and broke his prop shaft at 140 mph?

Laur3ns

Mine is loose, how do I remove it completely? Drill it?
Drive shaft is out anyway...

Savington

iTrader: (31)

You might be able to cut it off, but I just removed the pinion flange.

codrus

Per the tech at the rear end shop who put in my 3.636 gears, R&Ring the pinion flange requires remeasuring the bearing backlash and preload, but not the pinion depth.

I don't think you could fit a cutoff wheel in there without also hitting either the diff housing or the flange. Maybe if you drilled a hole and then used a dremel with a grinder to cut sideways.

--Ian

Laur3ns

What does this even mean?

hustler

iTrader: (6)

I'm guessing the guy who doesn't want to measure something is not someone I'm going to use. Its a measurement, check it.

codrus

As I understand it, "setting up the rear end" involves three measurements -- locating the pinion gear front-to-back (the pinion depth), locating the ring gear side-to-side (backlash) and how far apart the two bearing caps are (bearing preload). The latter two can be done with just a 7" micrometer, but the first needs a half dozen different SSTs, at least if you do it the way the FSM says.

Writeup on doing the backlash and bearing preload:
http://www.miata.net/garage/diff_rr.html

Doing these measurements is the secret voodoo stuff that everyone says you should pay a shop to do, and the guy at that shop was of the opinion that I shouldn't R&R the companion flange later without redoing most of those measurements. He wasn't making any money on the flange replacement either (I was supplying parts that I bought from Mazdacomp).

So, can you remove the flange to get rid of the loose cross-shaped weight without messing around with the guts of the diff? I dunno, but the guy at the shop who does this for a living told me no.

--Ian

KMiata

Yes I'm bumping a super old thread...

Andrew I talked to you about this at MRLS this weekend. I keep getting different info from different people. I have a really old 4.10 torsen from an NA in the car right now, and this piece is totally loose and wobbling around.

What exactly is involved in removing it? Some people say you need to disassemble the diff, and others say you can remove the driveshaft, take the big nut off, and remove it.

Any guidance from someone who has done this would be greatly appreciated. thanks guys.

bbundy

You can take the big nut off and remove it without taking the diff apart. done it multiple times and never had a problem. The crush sleeve sets the pinion bearing preload but its not that sensitive and can be re-used a few times if you torque it a tad lower when you put it back on. The torque spec range is really wide for that nut.

Savington

iTrader: (31)

The problem is that the "big nut" holds the pinion gear into the differential, and if you don't torque it back down exactly the same, you can alter the pinion depth and mess stuff up. If it were my race car, I would want to at least check the pinion depth and backlash after removing the pinion flange.

Having said that, when it came loose at WSIR a few years ago, I jacked up the car, undid the nut, removed the guibo/dongus/damper, put the nut back in, and cranked it down as tight as I could with the tools on hand.