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#1
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Why do front diffs blow up?
I just pulled the tranny out of my '92 LS-L and the front diff is toast! The case has a huge crack across the bottom and up the left side. I was wondering what usually causes these to fail so catastrophically? Would a bad tranny cause the diff to fail also? I just got this car as a non-runner so I don't know the history, but I'm planning to put a new diff in it. The tranny itself appears to be a rebuild- it's got rebuild markings all over the case and the fluid was clean with no big chunks of anything in it. The car has just over 100k miles.
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#2
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From what I seen and heard, they go out b/c the seals around the axles go bad and they start leaking gear oil. Once enough gear oil is missing from the diff, the metal ring & pinion gears aren't properly lubricated which leads to failure.
-Chike
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"Wise men talk because they have something to say; fools, because they have to say something." - Plato 2013 Cosmic Blue 5spd Evo X GSR 2006 Galaxy Gray 6MT RX-8 (sold) 2006 Steel Gray WRX TR (sold) 1996 Brilliant Red SVX L (sold) |
#3
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This cross-sectional pic...
..of an SVX 4EAT trans from Mr. Pockets locker lets you see the front diff.
-Chike
__________________
"Wise men talk because they have something to say; fools, because they have to say something." - Plato 2013 Cosmic Blue 5spd Evo X GSR 2006 Galaxy Gray 6MT RX-8 (sold) 2006 Steel Gray WRX TR (sold) 1996 Brilliant Red SVX L (sold) |
#4
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Front diff failure.
We have seen a lot of front diff failures. These seem to happen mainly on US transfer AWD models. The US 2WD models don't seem to break them and the Euro models don't.
The way I see it is. Front wheel spin is the major cause. When the front wheels spin, the open differential allows the torque to move back and forth, from one wheel to the other, depending on which has the least grip. This sudden 'grip spin grip' places large shock loadings on the gears. Usually it is the teeth on the crown wheel or pinion that break off to become lodged between the gears, to force them apart, breaking the housing.( they reinforced the caseing on later models) Front wheel spin should not happen. In the US transfer model when the front wheels start to spin, the TCU applies the Transfer clutch, to move the torque to the rear wheels, so that the front stops spinning. If the Transfer clutch stops working, the TCU can't move torque to the rear, to prevent the front from spinning, so the 'tyres smoke and the diff broke'. The Euro can't lose the rear drive as it is gear driven, so the front diff won't get the same loadings. The 2WD models use torque reduction, if the front wheels accelerate quicker than the 'set rate' that is written in its look-up tables. So the thing to watch is, if you get front wheel spin, check to see if the Transfer clutch is driving the rear wheels, if it isn't, get the clutch fixed. Don't allow the front wheels to spin Some like to put the FWD fuse in to smoke the tyres, but you are diceing with 'diffstruction' Harvey.
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One Arm Bloke. Tell it like it is! 95 Lsi. Bordeaux Pearl, Aust. RHD.149,000Kls Subaru BBS wheels. 97 Liberty GX Auto sedan. 320,000Kls. 04 Liberty 30R Auto Premium. 92.000kls. |
#5
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So Harvey, what would be the next thing to check if the fronts are still spinning even after the AWD clutch and solenoid have been replaced?
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David B. SVXipedia @ SVX-IW.COM -- SVX Information Warehouse 2.0 coming...eventually! Ebony 1992 SVX LS-L 5 spd Koni/GC Stebro 187k miles RIP (Rust In Pieces) 1993 SVX 5 spd Koni/GC Stebro Polyurethane bushings still available! |
#6
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Quote:
There are many Dave. The pressure going to the Transfer clutch at the port on the transfer clutch housing would be the first to check. This will rule out all the componets like the TCU, 'C' solenoid, wiring, piping, ect. If it has pressure but still no go, it could be the transfer housing oil seal rings, that pass the oil from the casing port, to the main shaft and the clutch, are leaking. There is the case of the transfer clutch cage breaking off the Transfer gear. If there is no pressure at the port, you just have to trace back through the series of componets to find the faulty one. Do you have a particular case in mind? Harvey.
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One Arm Bloke. Tell it like it is! 95 Lsi. Bordeaux Pearl, Aust. RHD.149,000Kls Subaru BBS wheels. 97 Liberty GX Auto sedan. 320,000Kls. 04 Liberty 30R Auto Premium. 92.000kls. |
#7
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Correct me if I'm wrong. I think that the seals start to go and let ATF leak into the front diffy. This cuts the differential lube (thins it out) and causes some over pressure and heat which eventually leads to catstrofic failure.
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Larry III & The Beautiful Naviguesser '19 Tungsten Pearl Outback 3.6R Ltd...."AISHA" '08 Harvest Gold Outback 3.0L. L. L. Bean...."AIJOU" '07 Gray Diamond Pearl Outback XT Ltd..."AH SO" '05 White Pearl & Silver BAJA Turbo..."AH HA" '97 Bordeaux Pearl SVX LSi..."SUBYDOO" '94 White Pearl SVX LSi..."PEARLY" '92 White Pearl SVX LSL w/touring pkg..."SVXY" '92 Teal SVX LSL w/touring pkg..."ALCYONE" '96 Polo Green LSi ... "MIDORI" '00 Black Dodge VIPER RT-10... "VINNIE" Engineers do it with precision. English teachers are novel lovers. Home: larrysingeriii@comcast.net SVX FEVER, CATCH IT AT A MEET NEAR YOU !! |
#8
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Quote:
-Chike
__________________
"Wise men talk because they have something to say; fools, because they have to say something." - Plato 2013 Cosmic Blue 5spd Evo X GSR 2006 Galaxy Gray 6MT RX-8 (sold) 2006 Steel Gray WRX TR (sold) 1996 Brilliant Red SVX L (sold) |
#9
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Quote:
Harvey.
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One Arm Bloke. Tell it like it is! 95 Lsi. Bordeaux Pearl, Aust. RHD.149,000Kls Subaru BBS wheels. 97 Liberty GX Auto sedan. 320,000Kls. 04 Liberty 30R Auto Premium. 92.000kls. |
#10
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My front diff blew because of front wheel spin ...but it was the transmission that was allowing the wheels to spin.
My 4EAT always seemed like it was in nuetral when in drive. If you didn't baby the gas the car would screech the front tires a tad and take out like a bat outta hell. If you slammed the gas half way or so, the front wheels would spin excessively and then take off. Everything in the tranny seemed to check out. I think the delayed gear engagement was the fault. It was like you were nuetral dropping the trans every single time ...stupid 4EAT.
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Mike - Proud owner of a Pearl 92 SVX LS-L 5MT with 78k miles and climbing 5-Speed Status: DONE! Lambo Door Status: On hold but will be a success 04 WRX 5MT, STi Short Throw Shifter, Group N tranny mounts, AZA Z-2 18x7.5 Rims, slotted/cross drilled rotors, stainless steel lines, 35/20% window tint, ecu bead crush, power mode button; 7" In-dash touch screen LCD, mobile computer, voice recognition, alpine PXA-H701 DSP, 2 JBL amps, focal speakers all around, 5 farad cap, and fiberglassed subs in the trunk. The Mobile Computer Interface - featuring the SVX | My Locker | My Secret Stash |
#11
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I think the MAIN reason the the front diffs are bad to go out, is because so many people replace 2 tires instead of 4 at a time.....mismatched tires will retire a front diff quickly.....my thoughts on it anyway...for what it's worth
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Huck Subaru Ambassador 92 SVX LS-Tour Magnaflow Exhaust, 5-Spd-AWD 88 XT6 AWD 5-Speed "Bride of FrankenWedge" 15 Impreza Premium Sedan 15 Crosstrek XV 5-Speed My 5-Speed "How-To" Write-up 1976 Pontiac Firebird Formula Current Count of Subaru's Owned.... "70" |
#12
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Quote:
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"The things you own end up owning you. It's only after you lose everything that you're free to do anything." 92 Pearl White Ls-l (138k) Euro Headlights & Blinkers, 97 Grill, Euro Tail Lights, SS Brake Lines, Stebro Exhaust, Slotted Rotors, Classic Registration 96 Legacy Outback (206k) 5-speed 2.2 Lightweight Crank Pulley, Group N Trans & Motor Mounts SOLD Wanted: Steering Wheel |
#13
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Funny thing to hang one's hat on, many fwd cars share the same ATF in the A/T and diff.
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ASE Certified Master Automotive Technician w/L1. ASE Certified Master Medium/Heavy Truck Technician. Certified EVT (Emergency Vehicle Technician) |
#14
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On my SVX previous owner didn't know about front diff dip stick, so after 318000 kms,run out of fluid and differ broke, see my locker for pictures
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1992 Pearl White SVX LS-L 1991 "Red Baron" Grand Prix GTP 5spd 2002 Chevy TrailBlazer LT |
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