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What is the deal with solid diff mounts?


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#1 DrEaM

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Posted 19 August 2007 - 09:10 AM

so i just ordered a new steering rack from msa and i was going to order a solid diff mount BUT the sales guy told me that it would transmit ALOT of harshness back into the car, and that the solid mount was mainly for race cars... now i want to know what personal experiences are with going with a solid mount.. i'm thinking about going with the arizona z car mount or the msa mount some advice would be appreciated

#2 Clifton

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Posted 19 August 2007 - 09:53 AM

Doesn't transmit harshness, just alot of noise. If you have obnoxiously loud exhaust you probably won't notice. If it is on the more quite side it will get old hearing the hum.

#3 Pop N Wood

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Posted 19 August 2007 - 12:03 PM

The noise will vary depending upon the condtion of your diff. Some have had worse experiences than others

The bigger problem is they will cause your front crossmember to crack and ultimately destroy itself.

http://forums.hybrid...ad.php?t=108276

There are other threads where people have posted pictures of the destruction caused to their rear suspensions when the cracked cross member fails.

Not pretty.

#4 bjhines

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Posted 19 August 2007 - 12:22 PM

This is what you need to go along with the solid front mount. A solid rear mount.
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The solid front mount was designed to be used with a solid rear mount. The factory mustach bar is a spring and it bends into an S-shape. This will fatigue the crossmember and the lower chassis mounting points.


This is not my picture but one for the record.
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The crossmember is not only the next weakest link but it will fatigue to the point that it will literally fall apart on it's own.



Here are some pics of a cracked but still holding together crossmember. This one was never subjected to more than stock power. The damn thing made all sorts of creaking and clanging noises before I gave everything a good look. This is what I found, cracks everwhere.
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Definitely on the Dark Side

#5 bjhines

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Posted 19 August 2007 - 12:37 PM

Another approach to this problem is the Ron Tyler mount.

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The R.T. mount was designed to lower the nose of the differential for the JTR V-8 swaps. You will need to adjust the dimensions to suit your engine tranny combo.

This picture shows that it lowers the differential right to the crossmember's top surface.
Posted Image
Definitely on the Dark Side

#6 Pop N Wood

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Posted 19 August 2007 - 01:57 PM

This post should be hyperlinked into the FAQ thread.

#7 ktm

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Posted 19 August 2007 - 04:53 PM

Wow. VERY nice photos demonstrating the problem. I know I switched BACK to urethane from a solid mount (did not drive with it, only mounted it), after doing hours and hours of reading. I agree with Pop.
-Bo

#8 smoorenc

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Posted 19 August 2007 - 05:44 PM

I had the Arizona Z Car solid one on mine, but not for too long. I even tried sandwiching in radiator hose rubber to help dampen the noise levels. It finally became unbearable and I removed it.

#9 johnc

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Posted 20 August 2007 - 08:36 AM

Stuck and linked.
----- John Coffey, Fabricator at Benton Performance, LLC

#10 DrEaM

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Posted 20 August 2007 - 10:15 AM

wow thanks for the feedback and the pictures!!! :-o i will def be trying to go with something a little softer like the stock rubber mounts or if i can find one a urethane one.... do you guys know where i can find one at?

#11 JMortensen

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Posted 20 August 2007 - 11:27 AM

Try a little searching. There is a sticky post in the drivetrain forum that has info on several different front diff mounts. You won't find a poly mount, and the stock system with the strap and mount underneath is REALLY crappy, so you might look hard at the alternatives instead, including the one that bjhines showed above.

Jon Mortensen, owner/operator www.petdoorstore.com


#12 dhp123166

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Posted 15 July 2008 - 10:58 AM

I just replaced my worn out stock diff. mount with...

A brand new stock diff mount.

I had ordered a solid steel mount but cancelled it when after doing
research and ascertaining that a solid steel one might be too noisy and as I have already lost the upper registers of my hearing range extra noise is
something I would like to avoid.

The weak point in the mount is the rubber which when it is new is not a problem, it is only after a long time of degradation that it fails, and really
after normal driving how often do these things fail due to that?

Every decade or so, if that?

I guess it depends what kind of driving one is doing, 'cause like they say;

"If you are not breaking anything you are not trying hard enough..."

______________________________________________________________

'76 280 Z-daily driver "Sometimes stock is good enough"

#13 Matt 78Z

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Posted 30 July 2008 - 07:33 AM

You can take a stock one and make it solid with a couple small welds. You weld 1/4" stock between the outer and inner shell on the bottom by the crossmember.

The stock mount has a much larger surface area and wraps around the crossmember. This helps to disperse the load. Those solid metal pieces make for such a pinpointed load they tear up the crossmember.

#14 drmiller100

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Posted 31 January 2009 - 06:35 PM

old school answer is to buy 8 feet of 1/8 or so plastic wrapped cable from local hardware store, and 2 clamps.

Wrap the cables under the front cross member, then up and over the top of the differential. Pull it tight with a claw hammer, and tighten it up.

You can use a shot front diff mount with this solution.

#15 coolbeans

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Posted 22 October 2009 - 05:35 PM

What are the symptoms of a broken or worn Diff mount? I ask because I recently discovered a movement in the rear of the car that occurs when I accelerate or decelerate. It is more noticable on deceleration but is there on acceleration as well. When I let off the gas the car seems to slide out in the rear to the right. I have a Quafie rearend and Wolf racing cv joints. I recently ran sticky tires on the car as well.

Any help would be great
Jeff

#16 HLS30-08077

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Posted 22 October 2009 - 10:45 PM

The picture below is an example of a bad diff mount. You can see that the rubber is seperating from the metal. The first time you really GET ON IT (floor it or drop the clutch) the rubber will completely seperate and the diff will smack the upper diff strap (located above the diff to "Arrest" the diff under diff mount breaking conditions.

You can tell if it's wearing out by dropping the four bolts that hold the crossmember and letting the diff hang by the mustache bar. While it's hanging, apply a trwisting motion to the crossmember while watching the rubber and metal area or the mount. (as shown in the picture)

Dave

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[SIGPIC][/SIGPIC]1970 240Z (8/70) HLS30-08077

A Z is like a woman. Once you're married to it, Half of your income belongs to it!

240Z Headlight Relay Upgrade harness's for sale.
http://www.classiczc...ead.php?t=20365

240Z 260Z & 280Z Parking light upgrade harness's
http://www.classiczc...ead.php?t=20151

#17 HLS30-08077

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Posted 28 October 2009 - 11:19 PM

OK, so here's my "Question of the Day" for any of you, Brad, BJHines, etc, etc. In the pictures on post #5, It shows 2 bolts holding the GM mount to the R/T mount. So why did my R/T mount only come with 1 hole? And which of the 3 holes on the GM poly mount should I use? Should I drill another hole? Wouldn't 2 bolts be better than one?

Some one? Anyone?
Dave
[SIGPIC][/SIGPIC]1970 240Z (8/70) HLS30-08077

A Z is like a woman. Once you're married to it, Half of your income belongs to it!

240Z Headlight Relay Upgrade harness's for sale.
http://www.classiczc...ead.php?t=20365

240Z 260Z & 280Z Parking light upgrade harness's
http://www.classiczc...ead.php?t=20151

#18 johnc

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Posted 29 October 2009 - 07:22 AM

You're mistaken. Two bolts hold the GM mount to the diff housing and one bolt attaches to the RT mount. You don't need to drill another hole and two bolts won't make anything better. The mount is in compression under load.
----- John Coffey, Fabricator at Benton Performance, LLC

#19 HLS30-08077

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Posted 29 October 2009 - 09:16 AM

I'm not mistaken, I'm misinformed and confused. There are 3 holes on top of the GM mount. Should I just use the middle one? I know the mount is in compression when the car is under load (forward motion) but what about if the car is in reverse and the only thing holding the diff up is 1 bolt?

Just trying to cover all the bases. For safety, clarity and peace of mind.
Dave

Posted Image
[SIGPIC][/SIGPIC]1970 240Z (8/70) HLS30-08077

A Z is like a woman. Once you're married to it, Half of your income belongs to it!

240Z Headlight Relay Upgrade harness's for sale.
http://www.classiczc...ead.php?t=20365

240Z 260Z & 280Z Parking light upgrade harness's
http://www.classiczc...ead.php?t=20151

#20 JMortensen

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Posted 29 October 2009 - 09:28 AM

I'm not mistaken, I'm misinformed and confused. There are 3 holes on top of the GM mount. Should I just use the middle one? I know the mount is in compression when the car is under load (forward motion) but what about if the car is in reverse and the only thing holding the diff up is 1 bolt?

You could drill another hole in the RT mount and use two holes if it makes you more comfortable, but here are a couple questions for you that may ease your mind. How much torque do you put to the pinion in reverse vs driving forward? Enough to cause that bolt to fail under tension? How many bolts hold the stock diff mount to the crossmember that's taking 100% of the torque under acceleration? What size is that bolt compared to the one on the GM mount?

Jon Mortensen, owner/operator www.petdoorstore.com





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