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Broken Differential mounts

 
Old 10-29-2018, 03:01 PM
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Angry Broken Differential mounts

Hi,

I have abit of a problem, both of my main differential mounts going through the bushing is broken. They both snapped (the nut) when they got removed, (Please no comments saying you should have used heat and so on, it was done...)

What are my options here? Are they welded on stock? Can I cut it out, drill a whole and put a nut on the back?

Thanks,
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Old 10-29-2018, 03:04 PM
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I'm having trouble envisioning what you are describing. A photo perhaps?
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Old 10-29-2018, 03:06 PM
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He snapped the diff bushing studs.

GG. Time for a new subframe.
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Old 10-29-2018, 03:07 PM
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I'm having a hard time visualizing what you're describing. Are you saying the studs on the sub frame were destroyed? Post up a picture.
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Old 10-29-2018, 03:12 PM
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Originally Posted by concealer404 View Post
He snapped the diff bushing studs.

GG. Time for a new subframe.
That's kind of what I was thinking.

Fortunately, used subframe are cheap. $200-300 on Ebay.

I would imagine that you could probably drop the subframe, drill it out, and weld some new bolts.
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Old 10-29-2018, 03:16 PM
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You're swapping the subframe.
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Originally Posted by codrus View Post
Basically I've come over to the camp of "If something is a reliability problem on the track, just ask Andrew and do what he says".
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Old 10-29-2018, 03:19 PM
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Originally Posted by Joe Perez View Post
That's kind of what I was thinking.

Fortunately, used subframe are cheap. $200-300 on Ebay.

I would imagine that you could probably drop the subframe, drill it out, and weld some new bolts.
yup, you have to drop it anyways. welding in some good quality studs should be an easy task for a welder.
with the money saved, maybe sand blast and powder coat it while it's out, too.
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Old 10-29-2018, 03:41 PM
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Old 10-29-2018, 03:49 PM
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Yup, that subframe is coming out.

Be careful while unbolting it from the body, lots of PB Blaster and heat, or your next thread will be titled "I accidentally pulled a couple of the studs which the rear subframe attaches to out of the body," along with this photo:



Once you've done that, the next repair involves cutting the car in half and then welding it back together:

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Old 10-29-2018, 04:01 PM
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Haha joe!

Ah fock, Then I have no excuse to change all the bushings in the rear then :P

Is the nut on the back a really bad idea ?
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Old 10-29-2018, 04:16 PM
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Originally Posted by Svensk View Post
Haha joe!

Ah fock, Then I have no excuse to change all the bushings in the rear then :P

Is the nut on the back a really bad idea ?
A nut on the back is fine if you can get a wrench on it when it's in the car. I've actually never taken the rear subframe off a Miata (one of very parts that have never been removed from my car), but I'd be kind of surprised if there's enough room.

--Ian
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Old 10-29-2018, 04:52 PM
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Originally Posted by Svensk View Post
Is the nut on the back a really bad idea ?
The problem here is that high-strength bolts of this length are almost never fully-threaded.

Honestly, there's only one good solution here. Drop the subframe, drill out the old stud, and have a pair of new bolts welded in.

Take the opportunity to have the subframe sandblasted and then powder-coated while it's out. You'll (hopefully) never have another opportunity.
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Old 10-29-2018, 05:50 PM
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Welding in studs is a terrible idea. You have to drill the old stud out accurately enough to install a new bolt in EXACTLY the same place, twice, because if you mess up either one, it throws all the driveline angles off and the car will vibrate and rattle for all eternity.

Alternatively, while you have the old subframe out, you can throw it in the trash, get another one for $100 or so, and ensure that the studs are in the right place.

You would be a fool to attempt the former option when the latter is available.
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Originally Posted by codrus View Post
Basically I've come over to the camp of "If something is a reliability problem on the track, just ask Andrew and do what he says".
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Old 10-29-2018, 05:57 PM
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Originally Posted by Savington View Post
Welding in studs is a terrible idea. You have to drill the old stud out accurately enough to install a new bolt in EXACTLY the same place, twice, because if you mess up either one, it throws all the driveline angles off and the car will vibrate and rattle for all eternity.

Alternatively, while you have the old subframe out, you can throw it in the trash, get another one for $100 or so, and ensure that the studs are in the right place.
Hm, I hadn't considered that. Yeah, I agree.

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Old 10-30-2018, 04:41 PM
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It could be fixed, but given the prevalence of replacement subframes it is easier not to. I would think (and am probably wrong) that bolting in the diff housing would locate them properly. I looked at that part of the subframe once, on the top side there is a round, maybe 2" diameter piece that is welded from the top, that I assume the threaded portion is attached to, but once that is removed there's no telling how many other ways the stud is attached.

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Old 10-31-2018, 12:23 PM
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Lol @ Joe using my rear cutaway picture. Haven't thought about cutting that car up in years.
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Old 11-01-2018, 02:33 PM
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thank you all

i am looking for a New subframe to replace. Might as well sand blast, powder coat everything and New bushing while Im at it
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Old 11-02-2018, 02:40 PM
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And don't forget the anti-seize this time
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