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  1. #1

    Default 8.8 rear end bottoming out on spare tire well

    Well, I'm pissed. Put in my brand new 8.8 rear end, got the car on ramps and saw that i couldn't even get a pinky between the $230! B&M diff cover and the spare tire well. I didn't think to question clearance on an item LMR sells as fitting foxes, so now, I'm probably out $350 between the cover, more more fluid, friction modifier, gasket, etc. Especially infuriating because now that i have reason to question it, it seems others have had the same problem. Why sell the damn thing and piss off your customers?

    I also wasted a few hours trying to grind down the cooling fins at the top, but i could still only fit a hand between the two now. Guessing that would only allow about 2" of travel before the diff hits the tire well. How much space is needed?

    Our era of fox didn't have less clearance back there did it? Technically, it was for an '86 and up Mustang, but I assume that's just because that's when the 8.8s came along.

    Curious what you all would do... I guess I could bang the tire well with a hammer, though it's a very hard angle without taking the rear end out again. I'm also not sure that would even allow enough room.

    I could put the super thin one that came stock. Guessing that still fits my bigger 3.55 gears I put in? I feel like LMR should compensate me for at least the cover, fluids and gasket for selling me a lost cause and HUGE waste of time.

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  2. #2
    FEP Power Member richpet's Avatar
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    You do not mention what car you are talking about. That might make a difference.
    Also, gears are the same size. It is just the number of teeth that are different for the ratio.
    83 5.0 GT. Quicker than it looks! 10:1 (or just over) 306, Motorsport a332 cam, 140A alt, t5 conv, 8.8 w/ 3.27's, Edel rpm, alum rad, very worked e7's, Holley SA carb, etc... SOLD IT!!!!

    Now an 1981 Granada! .040 over 302, Edel E-street heads... Currently building a 347 because, why not?

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  3. #3

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    Ah, go to know on the gears. It's an 82 GT.

  4. #4

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    Companies sell cast aluminum gear covers for Mustangs because people want bling. In a Fox/SN95 Mustang, virtually not one company manufactures a cast aluminum gear cover which will clear the spare tire well.
    Jack Hidley
    Maximum Motorsports Tech Support

  5. #5
    FEP Super Member erratic50's Avatar
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    A length of 4x4 and a BFH is probably the answer.

    Seeing this post I’m concerned about it on my 85 build now. Time will tell I guess
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    Last edited by erratic50; 08-25-2019 at 06:07 AM.

  6. #6
    FEP Super Member mmb617's Avatar
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    There's a way to fix that problem.


    408/T5/3.73's

    We're not fast racers, we're more what's known as half fast racers.

  7. #7
    FEP Senior Member droopie85gt's Avatar
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    Anytime you're buying aftermarket parts, you have to plan on modifications. Some parts don't need em, some parts do. Hell some factory replacement parts don't fit right sometimes.

    Wouldn't be much to disconnect the brake line, the shocks, let it droop, get a small torch, heat the tire well up and beat it into cooperation. Just another day in the garage. Luckily it's in a spot no one will ever see, unless you take your spare out, so you're good there.
    1985 GT, Sunroof, 5 Lug, Rear Discs, 01 Graphite Bullets, 88 forged piston shortblock, 2.02/1.60 Alum heads, Weiand Stealth, Holley C950 TBI, BBK Long tubes

  8. #8

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    Many of these aftermarket covers actually make the lubrication situation worse. There is a reason the factory cover is hemispherically shaped, more than for spare tire well clearance. It keeps oil on the gear but not drowning in it and limits cavitation.

  9. #9

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    Quote Originally Posted by Jack Hidley View Post
    Companies sell cast aluminum gear covers for Mustangs because people want bling. In a Fox/SN95 Mustang, virtually not one company manufactures a cast aluminum gear cover which will clear the spare tire well.
    It wasn't about bling for me. Rear valance completely hides. I wanted the drain/fill plugs and thought the fins would be good for cooling...now they're mostly gone.

    Im hoping hammering the spare tire well will clear. Otherwise, I'll have a dented well and $350 worth of junk.

  10. #10

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    Pull that one off. Clean it up. Sell it on Craigslist and reinstall the factory one. Recoup some of your losses and way less headache. Been there done it and I’m sure I will go there again before it’s all over.

  11. #11
    FEP Power Member Saturn V's Avatar
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    I don’t want to argue with Jack, but the GT500 cover fits with no issues that I’ve noticed on my 84 GT.




    Sent from my iPhone using Tapatalk
    Present: '84.5 Mustang GT T-top, '06 Mazdaspeed6
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  12. #12

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    Quote Originally Posted by Saturn V View Post
    I don’t want to argue with Jack, but the GT500 cover fits with no issues that I’ve noticed on my 84 GT.
    Sent from my iPhone using Tapatalk
    Thanks for the info!

    Nice!
    The fill plug on top of my differential is a massive PITA, and is very rusted.


    Also, you're not arguing or disagreeing with Jack.
    Jack qualified his statement. Many engineers and/or teachers learn to do that quickly. :-)

    Quote Originally Posted by Jack Hidley View Post
    Companies sell cast aluminum gear covers for Mustangs because people want bling. In a Fox/SN95 Mustang, virtually not one company manufactures a cast aluminum gear cover which will clear the spare tire well.
    https://www.merriam-webster.com/dictionary/virtually
    =====
    virtually
    adverb
    vir·​tu·​al·​ly | \ ˈvər-chə-wə-lē How to pronounce virtually (audio) , -chə-lē; ˈvərch-wə-lē\
    Definition of virtually

    1 : almost entirely : nearly
    2 : for all practical purposes virtually unknown
    =====



    https://dictionary.cambridge.org/us/...lish/virtually
    ===
    Meaning of virtually in English
    virtually
    adverb
    uk ​ /ˈvɜː.tʃu.ə.li/ us ​ /ˈvɝː.tʃu.ə.li/
    virtually adverb (ALMOST)


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    ===



    Btw, a seller on ebay is now selling them for $69.
    Sweet!
    https://www.ebay.com/itm/Ford-DR3Z-4...r/153068099898
    Ford DR3Z-4033-B, Differential Cover
    Quantity: 8 available 82 sold / See feedback
    Price: US $68.97

  13. #13

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    Big Moon Rocket,

    I've test fit the GT500 gear cover onto a 1999 Mustang and a 1987 Mustang.

    The photos below are of the cover installed on a 1999 Mustang with an 8.8" axle housing, MM RLCAs, TA and PHB. The MM TA does change the IC location some from stock, so it does affect the path that the axle housing takes in the side view as well as its rotation versus vertical position.

    The photos below are taken with the axle housing held at the same height as each other. The gear cover is hitting the spare tire cover, which was already beaten some by a previous cover. The top of the axle tube is 3.5" from the bottom of the frame rail. If you pull the springs and frame rail mounted bumpstops out of a Fox or SN95 Mustang, the shocks are bottomed out when the top of the rear axle tube is about 0.8" from the bottom of the frame rail. From that standpoint, the rear axle housing in this photo is slightly above normal ride height and is hitting. We applied two passes of milling to the gear cover at the top and did some hammering on the spare tire cover. Once we were done, the top of the axle tube could get only 2.25" from the bottom of the frame rail. As this was a drag car, we didn't need that much bump travel so we left it as is.

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    I've also installed this gear cover on a 1987 Mustang with 8.8" housing and stock 4-link suspension. There was a little bit more clearance for the cover as the stock 4-link has short UCAs, which really pulls the nose of the differential housing down under large amounts of bump travel. The cover still needed a lot of milling to fit.

    One of the problems with a cast aluminum cover is that they don't have much ductility, so if they do hit an immovable object, they are going to crack.

    Before assuming that your cover clears, I would pull the springs out of the car and remove the bumpstops. Cycle the rear suspension from droop to full bump slowly with a floor jack under it.
    Jack Hidley
    Maximum Motorsports Tech Support

  14. #14

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    Also, regarding my statement from above. The GT500 gear cover was never designed to fit on an 8.8" installed in a 1979-2004 Mustang. It is just an accident that it fits, sort of.
    Jack Hidley
    Maximum Motorsports Tech Support

  15. #15

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    Quote Originally Posted by Jack Hidley View Post
    One of the problems with a cast aluminum cover is that they don't have much ductility, so if they do hit an immovable object, they are going to crack.

    Before assuming that your cover clears, I would pull the springs out of the car and remove the bumpstops. Cycle the rear suspension from droop to full bump slowly with a floor jack under it.

    Thanks Jack!
    Great advice, as always!

  16. #16

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    Quote Originally Posted by boogiestang View Post
    Pull that one off. Clean it up. Sell it on Craigslist and reinstall the factory one. Recoup some of your losses and way less headache. Been there done it and I’m sure I will go there again before it’s all over.
    Yikes, I've ground half the cover off. Probably worth a buck now. And the 3 qts. of fluid/modifier at $80...You think changing out the cover yet again would be easier than pounding out the tire well? Do I dare try catching the fluid and refilling? What a pain...

  17. #17

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    Quote Originally Posted by Jack Hidley View Post
    Companies sell cast aluminum gear covers for Mustangs because people want bling. In a Fox/SN95 Mustang, virtually not one company manufactures a cast aluminum gear cover which will clear the spare tire well.
    Since you've had experience with these issues, curious if you think my best bet is trying to hammer the tire well to clear or dumping all the fluid and reverting back to the stock cover.

  18. #18
    FEP Super Member Ken P's Avatar
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    Quote Originally Posted by 4eyedblind View Post
    Many of these aftermarket covers actually make the lubrication situation worse. There is a reason the factory cover is hemispherically shaped, more than for spare tire well clearance. It keeps oil on the gear but not drowning in it and limits cavitation.
    There is a video somewhere on YouTube where a larger clear Lexan cover is used to show this problem.

    I've also always liked to remove the stock cover and mop out every bit of old fluid. It me gives a chance to look for any metal fragments / shavings / debris. But I'm just obsessive like that...

    Then again when the stock cover is off it wouldn't be too hard to drill it at the bottom and weld in a drain plug.
    86 LX Coupe 4E
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  19. #19

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    I would use the stock cover. The only problem with it is that its very difficult to install a fill plug in it. The installation of the plug is easy, however it is tricky to mount it because the nut that holds the fill plug in on the inside tends to interfere with the ring gear. This will depend a bit on the gear ratio installed in the housing.

    You can reuse the gear oil if you run it through a coarse filter. You want to make sure that absolutely none of the silicone ends up back in the differential.

    The B&M product page for the gear cover is linked below.

    https://www.holley.com/products/driv...rs/parts/41297

    On the page it says "1983-2014 Ford Mustang, F150, Ranger, Explorer, Bronco, Thunderbird, Capri. However each vehicle may have other interfering components and adequate clearance and fitment should be verified prior to purchase & installation. Refer to ID guide and measurement diagram for specifications."

    However if you look under the Applications tab at the bottom, it only lists 2011-14 Mustangs. The installation photos are from a S197 Mustang. B&M knows that this product doesn't fit any 1986-2004 Mustang. The way they have listed the year range certainly implies that it fits 1983-2004 Mustangs. I would try to get my money back from them. Until someone does that, they aren't going to update the product page.
    Jack Hidley
    Maximum Motorsports Tech Support

  20. #20

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    Quote Originally Posted by Jack Hidley View Post
    I would use the stock cover. The only problem with it is that its very difficult to install a fill plug in it. The installation of the plug is easy, however it is tricky to mount it because the nut that holds the fill plug in on the inside tends to interfere with the ring gear. This will depend a bit on the gear ratio installed in the housing.

    You can reuse the gear oil if you run it through a coarse filter. You want to make sure that absolutely none of the silicone ends up back in the differential.

    The B&M product page for the gear cover is linked below.

    https://www.holley.com/products/driv...rs/parts/41297

    On the page it says "1983-2014 Ford Mustang, F150, Ranger, Explorer, Bronco, Thunderbird, Capri. However each vehicle may have other interfering components and adequate clearance and fitment should be verified prior to purchase & installation. Refer to ID guide and measurement diagram for specifications."

    However if you look under the Applications tab at the bottom, it only lists 2011-14 Mustangs. The installation photos are from a S197 Mustang. B&M knows that this product doesn't fit any 1986-2004 Mustang. The way they have listed the year range certainly implies that it fits 1983-2004 Mustangs. I would try to get my money back from them. Until someone does that, they aren't going to update the product page.
    Wow, Holley's (B&M parent brand) customer service response was to send a screen shot of a vague disclaimer on the Holly page (not even where I purchased from) saying they fit our cars but measure first to make sure it fits. Also offered a hat and some t-shirts for my trouble. Efffffff that.

  21. #21

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    Give your business to a different company and make sure that you tell Holley this.
    Jack Hidley
    Maximum Motorsports Tech Support

  22. #22

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    Quote Originally Posted by Jack Hidley View Post
    Give your business to a different company and make sure that you tell Holley this.
    Most definitely.

  23. #23

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    Interesting followup, LMR customer service called me. They said that floor pans/measurements were actually different in our cars. He said that replacement spare tire pans are listed from 86-93. I assumed ALL fox floor pans were stamped exactly the same.
    If that is the case, then my bad for trying. LMR was cool about giving me a new gasket and fluids and said they would add a fitment note on that product page since an 8.8 rear into our foxes is very common.

  24. #24

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    During the Fox run, they may have switched from a full size spare to a compact spare...
    Brad

    '79 Mercury Zephyr ES 5.0L GT40 EFI, T-5
    '17 Ford Focus ST
    '14 Ford Fusion SE Manual

  25. #25

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    According to Ford data, from 1979-1993, the car always used a B78-14 tire on a 14" x 5" wheel for the spare. The only exception is for the SVO Mustang.

    Ford may have changed the size of the spare tire well during this time period, but almost all of these cast aluminum gear covers will not clear the spare tire well in ANY Fox/SN95 Mustang.
    Jack Hidley
    Maximum Motorsports Tech Support

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