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Oaklandjester

Welding mustache bar to drop mounts and dog bone

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Rebuilding a endurance track car after we totaled last one at Laguna Seca. We are putting a r180 in a 280 shell. ( 220 ho to wheels w/ rear dif cooler) We have a solid mount drivetrain except for mustache bar. Don’t really want to drop $500 on billit ones. Is there any reason I couldn’t reinforce the mustache bar and tie it to the drop mounts and dog bone?  

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Unless I am mistaken, the mustache bar is spring steel and if welded will harden and be susceptible to cracking at the edge of any welds.  I would think you would be better off making one out of mild steel flat bar than welding to the stock one.  It might be more prone to bending (however, with a solid front mount I don't think this would be a concern) but you shouldn't have to worry about it cracking.  

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I would imagine with a solid front mount and urethane bushings you won't get much out of a billet bar (at that point you probably get more flex from the bar than the bushings)

or you could try and get some aluminum bushings turned up to solid mount the factory bar, but then again the bar itself might not be stiff enough at that point.

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The bar already hasn’t PU bushings the issue isn’t “firming it up” is the fact the spring bar is the last flexible structure in a solid mounted drivetrain ( solid motor mounts, trans mount and ft diff mont) thus it flexes.  I now know I can’t weld the springbsteel (thank you Namor! )!so I orders Technon Toy bar and will diagonally brace the drop mounts and dog bone.  No real access issue as rear diff fills from inside car (remote fill) and drains from oil cooler feed line coming from then drain hole.  And I don’t see any real disassembly issues as it will come out as a entire unit. 

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4 minutes ago, Oaklandjester said:

The bar already hasn’t PU bushings the issue isn’t “firming it up” is the fact the spring bar is the last flexible structure in a solid mounted drivetrain ( solid motor mounts, trans mount and ft diff mont) thus it flexes.  I now know I can’t weld the springbsteel (thank you Namor! )!so I orders Technon Toy bar and will diagonally brace the drop mounts and dog bone.  No real access issue as rear diff fills from inside car (remote fill) and drains from oil cooler feed line coming from then drain hole.  And I don’t see any real disassembly issues as it will come out as a entire unit. 

Hasn't?  Did you mean "has"? 

Is there a real problem, is the question.  The system is designed to move and flex and dance around a bit.  Is something breaking?  Many people have found that the solid front diff mount is  a mistake.  You might be over-solidifying.  Maybe go back to a more flexible front mount, like the RTZ style mount.  In an endurance racer, driver comfort is a factor and having the diff solidly tied to the body could be am auditory torture device.  Isolate the diff noise, let it move, let the u-joints get a little work-out (makes them last longer).  Even the AZC billet mount uses PU bushing ends.  If you fasten the the mustache bar to the dog bones you'll be at full metal jacket level.

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Never run a combination of solid and flexible mounts on the same component. A solid front diff mount with a poly bushing in a mustache bar is a mistake, either go poly/poly or all solid. If you run a combination the poly will flex slightly adding stress to the diff, and eventually something will fail. There are plenty of threads on here illustrating these failures. 

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I did mean had,  we actually like full metal jacket mode, the car dances beautifully  with the solid driveline and we get more power to the ground faster...  we have cv axles so no u-joints. The car is already loud , two fuel pumps, diff cooler pump and exhaust, but with ear plugs and a helmet it all gets lost...  driver comfort is ok we have a full containment seat and we want to be able to feel in the seat of the pants what the car is doing. We are running 275# springs so the car is soft enough. I have come to the conclusion the bar should not be tied to the drop bars. I believe the TT unit will take the play out.   

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No advice on solid rear, but that is awesome footage. :D Looks quick.  And by awesome, I mean utterly terrifying Mad Max stuff.  Have you considered Roo Bars on all quarters?!

Edited by Zipper

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Funny  you mention that we kept getting suspension and wheels knocked around  from minor contact so I made oversized 18 gage fender flares (double wall- one hoop around tire and one plane to the fender with several 1/4# square tube struts to the inner fender well — problem solved... 

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Rather than weld the mustache bar to the drop links you can make a new setup that's one piece and bolts in.  Here's some pics of what I'd do for the inner frame.  While this does use a mustache bar I'd replace that with tubing that connected to the uprights out to the mustache bar outer mounts.  Then some simple triangulation would make it very stiff.  Rather than use the H style control arm I'd move to one of the toe-link style arms that have been built by a number of people.  

In case you're curious these are the rear suspension pics from John Thomas' national championship winning FP car.

Hope you find them inspirational,

Cary

001_015.JPG

MVC_012F.JPG

Susp1a.jpg

MVC_007F.JPG

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Wow. Forgot about those pics. Amazing that something so utilitarian and basic was on a car that won so many national championships.

I agree that a cradle is the way to go. I think blueovalz's rear setup integrating the diff mount was a nice idea, but that sort of thing (ideally tubing and not a big AL plate) could be integrated with something like this, so that the cradle which mounts the diff and the LCA mounts is a separate bolt in assembly and attaches to the stock mounts for mustache bar and diff xmember/strap mounting points.

TSS Fabrication makes similar products for Subaru rally cars. I think he puts too many bends in his products where he could have straight tubing, but here's an example and a  link to some more inspiration.
https://www.facebook.com/pg/TSSFAB.US/

16708640_1361575803893511_90241491043977

Edited by JMortensen

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