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pdexta
08-13-2012, 09:14 PM
Last week I took a left hand turn pretty hard on my crappy stock wheels/tires and the back end stepped out a bit. I heard a pop/clunk sound from the rearend and backed off it.

Since then I've gotten a vibration in 1st and 2nd gear at low rpms (2000-4500) under moderate load, like accelerating from a traffic light. I can hear and feel the vibration, and it definitely seems to be coming from the back end of the car. It doesn't happen at wide open throttle and doesn't happen in higher gears. It's particularly bad accelerating through left turns (nothing crazy or spinning tires, just regular driving).

I've checked over the coilovers and diff, everything appears to be tightly bolted down, as is the driveshaft. I don't get any vibration or whine at cruise or acceleration in higher gears. Transmission shifts fine. I've swapped wheels and it still does the same thing. It doesn't feel like I have any slop in the wheels/wheel bearings.

Any thoughts on what it might be? Anything I should check or try to eliminate as an issue? I'd appreciate any help or suggestions you may have.

Jester~
08-13-2012, 09:32 PM
Check to see if your lug nuts are tight. ....oh yea, I said it :)

How about the rear diff mounts? Did you notice any cracks in them?

pdexta
08-13-2012, 09:40 PM
Funny you mention lug nuts. Driving to work several months ago I had a strange vibration when I let off the throttle. I couldn't figure it out, called out of work and had the car towed home. It took hours to figure out that a couple lug nuts had worked their way loose and the wheel was vibrating. Man, I'm an idiot, but the lug nuts are most definitely tight now.

I actually looked at the diff mounts, but nothing looked abnormal (although you can't see much), and the bolts are all tight. Can the mounts themselves cause this type of issue? When it first started I actually entertained the idea that I'd broken the diff carrier, but it looks fine. Maybe you're onto something.

minuteman048
08-14-2012, 06:43 AM
You've been putting 300 HP through the rear differantial components so maybe something is finally going to give. Check universal on drive shaft and axle shafts. I figure those are the weakest points of the drive train.

Agent☣Orange
08-14-2012, 07:01 AM
Prolly time for that Ford rear end?

pdexta
08-14-2012, 07:27 AM
You've been putting 300 HP through the rear differantial components so maybe something is finally going to give. Check universal on drive shaft and axle shafts. I figure those are the weakest points of the drive train.

I think you nailed it. I've never had that problem before, every axle I've had a problem with has come apart in pieces, so I didn't even think about it. Since I installed my Beatrush diff brace I've been able to hear a clunking sound (especially in the parking garage at work where everything echos). I just assumed it was a downside of the brace, but a U joint would make sense.

Thanks for the advise, I'll pull her apart when I get home today. I've considered buying an extra set of axles to take with me to the track anyway so that might just work out perfect.


Prolly time for that Ford rear end?

You know, I should probably look into it, as much as I hate to even think about it. I've been wanting to do a gear change forever, but they're so expensive I just can't justify it. Sure would be nice to have a rearend that comes with a million gearsets to choose from.

IhasMIATA?
08-14-2012, 12:24 PM
Unbolt the driveshaft and see if there's any movement on the pinion gear? Or maybe it's a CV joint going bad in the axles????

pdexta
08-14-2012, 06:08 PM
The verdict is in and drumroll please....


I cracked my PPF! There's a crack across it where it bolts to the diff. Now I've just gotta figure out how the hell you fix something like that. I assumed I'd just have to get a new one, but maybe it's possible to have it welded? Gonna have to do some searches, hopefully I'm not the first to pull this off.

Jester~
08-14-2012, 07:01 PM
Pretty sure I have an extra one if you want it, I'd have to go look for it, but could tell you tomorrow. Not sure if an NA one (from a 90) is the same as an NB one....but if it is, and you want it, its yours.

Btw, DAMN! Cracked a PPF!

Jester~
08-14-2012, 07:26 PM
Ppf is the big frame that goes from the transmission to the rear diff. It stand for Power Plant Frame.

minuteman048
08-14-2012, 07:34 PM
Parts Group has on for $30.00.

http://www.partsgroup.com/store.aspx?category= Miata-Suspension&Page=0

At that price forget fixing it. Replace it.

pdexta
08-14-2012, 07:38 PM
Jester, thanks for the offer. I think they changed the PPF from NA to NB, although I'm having a tough time confirming it. On the other hand, I'm pretty sure you can swap a diff and transmission from any year so maybe they didn't change it. If you happen to find it I'd definitely be interested. I'm sure it's going to set me back a pretty penny to get one shipped to me.

Jester~
08-14-2012, 07:41 PM
No problem, I'm going over to my dads warehouse tomorrow morning...so I'll see if I still have it (almost certain I do). If you find out it works for you, it's yours.

That parts group link minuteman posted shows it's a 99-05 part, so I'm guessing it may be different. But I think your right that I thought you could swap a tranny and rear end seemlessly between the two. You could always take it, and then compare it to yours.

pdexta
08-14-2012, 07:43 PM
Parts Group has on for $30.00.

http://www.partsgroup.com/store.aspx?category= Miata-Suspension&Page=0

At that price forget fixing it. Replace it.

Nice find, I actually looked at their site but didn't see a PPF so I emailed them. I LOVE parts group, they've saved me several times and have the best service and pricing around. I talked to a welder friend and as soon as he told me I'd have to take it off for him to weld I threw the idea out the window. It's going to be a pain to swap it, so if it has to come out a new (to me) one is definitely going in.

minuteman048
08-14-2012, 07:50 PM
I bought my interior door panels from them and I ask them to pack them extra well so they would not get damaged. Drivers side is almost impossible to get for a 99-00 in good condition. The doubled boxed them for me at no extra charge. Helped me out several times and always look to them first.

minuteman048
08-14-2012, 07:54 PM
Pretty sure I have an extra one if you want it, I'd have to go look for it, but could tell you tomorrow. Not sure if an NA one (from a 90) is the same as an NB one....but if it is, and you want it, its yours.

Btw, DAMN! Cracked a PPF!

Where did you get it? Did it come with that 93 engine you bought?

Jester~
08-14-2012, 08:03 PM
It came with the 92 engine that's in my car now. ...actually you may remember it because you helped me unload the engine! He gave me the ppf and computer along with the engine and tranny.

Agent☣Orange
08-14-2012, 08:07 PM
Wow, cracked PPF! Well I've heard of it, always in high HP applications. Could be that Beatrush brace contribute to it, maybe not. There is a PPF reinforcement brace out there and it sounds perfect for your application but not much benefit for a regular Miata.

Picts when you get a chance please.

Link: http://www.good-win-racing.com/Mazda-Performance-Part/15-1006.html

Any chance you could get an old Thunderbird rear end in there cheap?

minuteman048
08-14-2012, 08:37 PM
At Parts Group just found PPF for a 90-93 so they must be diifferent for the NB's. Under suspension used parts.

http://www.partsgroup.com/store.aspx?category= Miata-Suspension&Page=0

pdexta
08-15-2012, 06:12 AM
Here's a picture of the crack:

http://i272.photobucket.com/albums/jj186/pdexta/ppf1.jpg

The location of the crack definitely makes me think the diff brace contributed to it. I wish there was a good inexpensive way to reinforce the PPF before it goes in, but I just can't being myself to spend $250 on that piece yellow posted.

minuteman048
08-15-2012, 07:20 AM
On the replacement unit have some steel bar stock welded on to beef it up in that area. Cheap but effective way to strengthen it. The if you want some bling and to protect the bar stock have it powdercoated if it's in your budget.

Agent☣Orange
08-15-2012, 08:13 AM
The PPF is aluminum.

minuteman048
08-15-2012, 09:19 AM
Well theres the problem, but you could add aluminum barstock. Just a little tougher to weld.

pdexta
08-15-2012, 10:13 AM
Treasurecoast got back to me the fastest and said it would be in the mail today. Really hoping it gets here this weekend so I have some time to get it swapped over without having to rush.

Jester~
08-15-2012, 11:22 AM
Glad you got one coming already. I just got done looking for my old ppf, and I dont have it anymore. Can't believe I would have thrown it away, so I probably left it in the corner of my storage unit when I moved out of it.

Tristan75
08-16-2012, 06:52 AM
OMG! you cracked the PPF... woowww. I started reading this thread today! after the diagnosis made by our friends, I thought about the PPF, but never thought it could brake!.

I've following the item YellowYata posted, the guy is from Florida... I remember contacting him in the past, he was offering a good discount if you went via him... if interested, can send you his details.

With that power ... I think it's time to look after a RX7 transition (some mod required) & differential.

Glad to see you solved the problem.