Can anyone help me save my 929? Differential is bad - Mazda Forum

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Old 10-30-2008, 04:58 PM
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Well, as I posted awhile back, the 'cluck cluck' sound from the rear turned out to not be the driveshaft carrier bearing. I put a new one in, sound still there. I took the car to the garage and up on the hoist, wheels under power, they confirmed that the problem is inside the differential.
I'm OK with putting in a used diff, as there appears to be 4 bolts/nuts for each of the 2 axles and the driveshaft, plus a few more to attach it to the floor/frame. Problem is that the only junked 929 in my area was crushed months ago. ****, I wish I'd bought the whole thing and stripped it!
Has anyone actually opened up a 929 differential? I'd really like to know if replacing a gear or shaft or whatever is doable.
Does anyone know of a used differential for sale, hopefully near eastern Canada?
Any comments and helpful information would be greatly appreciated. I'm looking at buying another car right now for winter, but I'd still like to have the 929 on the road, especially after I just did 2 weeks of bodywork and parts changing, only to have the f*&%^ng rear end go out....which has never ever happened to any other car I've ever owned BTW.
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Old 10-30-2008, 09:06 PM
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I'll let you know if I find one. I'd be willing to ship it to you too.

Whats wrong with your diff? Is it the gears or the center? There are some LSD centers on eBay for less then $250
http://cgi.ebay.com/ebaymotors/RX-7-RX7-FC...1QQcmdZViewItem

Here is what I got when I searched "rx-7 LSD"
http://motors.search.ebay.com/search/searc...ntrypage=search

Search= rx-7 Differential:
http://motors.search.ebay.com/search/searc...ntrypage=search

Couldn't find anything for the HC 929.
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Old 10-30-2008, 09:39 PM
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HAVE A LOOK IN TECHNICAL GUIDES.

MIGHT AS WELL DROP A fd TORSEN IN THERE WHILE YOUR AT IT..
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Old 10-31-2008, 10:00 AM
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Quote:
I'll let you know if I find one. I'd be willing to ship it to you too.
Whats wrong with your diff? Is it the gears or the center?[/b]
Info. much appreciated. I posted an on-line parts (used) inquiry yesterday, so I'll see what turns up in the next few days. I'm not very hopefull though. Do you or any one know if this differential is used in any other Mazda, truck, car or whatever? I suspect that it's another 'special' piece unique to the '88 - '91 929.

What's wrong is not known, without pulling the differential out and disassembling on the bench. It works fine, no noises, when the car first starts moving, then very soon starts to go 'clunk clunk clunk' intermittently, then randomly like a rachet sound, as if something inside the diff casing is banging on the casing as the gears turn. There is no loss of power to either axle, and the clacking-clunking is the same on city streets as on the highway, it just varies with the speed the gears are turning. Of course, if I continue to drive it, something will undoubtedly let go and I'll then have a really dead beast in my driveway.

From the service manual chapter, I'm looking at that 'knock pin' that holds the pinion shaft in place. It's supposed to be staked in place. One theory is this pin has worked loose and the pinion shaft is moving back and forth, hitting the casing as it turns. I've got no experience with a differential whatsoever though.

I suppose I could take it out and see if the problem is obvious, without any real disassembly, especially the pinion gear itself, which from the manual description, is quite a deal to 'set' correctly to the ring gear. Simply put, I ain't gonna go there, period.

For what the car is worth, I'll say about $800.00 as a used winter-beater, I'm not going to spend much to fix this, time or money. I would change out the differential if I had a used one, and I might, maybe, pull the one in it just for giggles to see if the problem is easily fixed, like a wandering pinion shaft, but as the weather here gets colder by the day/week (we expect snow real soon), any work on this POS is gonna have to be done SOON.

At this point, I'm seriously looking at leaving it as-is just so it can be driven to the junkyard......but man, I really really hate to do that...you know what I mean, after fixing everything up and all...but it looks more and more like throwing good money after bad. ****, I'm torn over this.
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Old 10-31-2008, 11:57 AM
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You can't scrap it now. Its 20 years old. You got a collector car .

Rx7 diffs fit. thats been confirmed. I'm not sure about mpv diffs or miata diffs.
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Old 10-31-2008, 07:04 PM
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some Miata/Roadster/Mx-5 (Whichever one it is in your region ) diffs swap with FC diffs so there is a good chance a right one will swap into HC. MPV has live rear end (not independent as HC) but the diff might fit
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Old 11-05-2008, 09:54 AM
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Well, after some soul searching, the car is now up for sale. http://fredericton.kijiji.ca/c-cars-vehicl...QQAdIdZ85662372
I'd still appreciate a lead on a differential, just for the new owner. I checked and none of the diff's mentioned are a bolt-in to the 929, but maybe internally the same. I'm not up to tearing one apart. I'll give it about 2 weeks, and if no sale, she'll be going to the junkyard.

Edit: I took it to a local transmission shop, and the mechanic and I went for a test drive. With the service manual in hand, we discussed the issue and it seems like there might be a shaft or pin worked loose and it's randomly hitting the inside of the casing, as I suspected. The oil is grey, full of metal particles too, not golden brown like it should be. He was also very sure it isn't a gear problem. He did say that the front of the diff could be removed without taking out the main carrier casing, if the axle mounting flanges could be pulled out first. Well, about 4 more bolts and the whole thing would be out anyway. If it doesn't sell, I think I'll take it out and see what is wrong, fix it, then go for a higher sale price to cover my costs.
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1986 Mercedes 560SL
1940 Pontiac Street Rod My Streetrod
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