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Malbaby

Reducing rear chassis flex & twist with tub on.

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Can't resist to help you with that....;)

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Some heavy engineering there Stef,

you do this yourself?

John.

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Hi Malbaby,

    if you reduce your picture size to apprx 100Kb then you will be able to get dozens of pics uploaded.

I use MSPaint as it is on the computer and easy to use.

 

Roger

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15 hours ago, John Morrison said:

Some heavy engineering there Stef,

you do this yourself?

John.

Yes John, with the assistance of a mate. I am fortunate to have a hoist in my shed.

Trying to fix some of the annoying inadequacies of the factory chassis. I welded in a 900mm length of 65mm x 8mm plate snug inside the chassis lips, as in the first pic. My main intention was to reduce the chassis flex that occurs just forward of the coil spring bridge.

Then went further than perhaps necessary to reduce chassis twist....:D

 

Edited by Malbaby

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The question is whether the bracing displaces loading to elsewhere which may produce premature failure?

 

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Not my chassis....this is where 90% of the rear load is applied, and the site of rear chassis flex on the factory chassis, and to a certain extent, chassis twist.

After modifications, the load is still applied to the same area of the chassis. {How much load is required to bend a 8mmx 65mm plate in its vertical plane.??} 

IMHO...the above is the best overall outcome that can be achieved with the tub on.

tr rear chassis_LI.jpg

Edited by Malbaby

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In my younger days, just graduated as a mechanical engineer, there was no easy-to-use finite element analysis (FEA) software. A friend had a home made aluminium chassis based Lancia Aprilla special, roughly based on a Lotus 7, and it’s chassis appeared to be weak.

It took me several days of hand calculations (no computer then, not even Excell) to calculate stiffness in 2 planes, and I had to make best guess assumptions for  dynamic loads, but I was able to see where and how the chassis was best strengthened to reduce deflections. Nowadays this is much easier, as we have seen in several examples on this forum of computerized design and engineering. 

I wonder if anyone has ever gone through the exersize with a TR chassis?

Waldi

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42 minutes ago, Waldi said:

I wonder if anyone has ever gone through the exersize with a TR chassis?

Waldi

Paul Anderson did it ;)

 

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Haha Stef,

Ian Dury, Sex and Drugs and Rock&Roll, is all my BODY needs....but what about the chassis?

Waldi

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When I started rebuilding my 4A, I took the body to Andy Ansell at Triumph Sportscars. I mentioned that I had a 3A in 1968 and that the scuttle shake was a major feature of the car. He told me that he would do some things to the body that would just about eliminate scuttle shake. He did not share the trade secrets, but the car is impressively rigid. I suspect some clever seam welding. 

I also got him to replace the fibreboard between the cabin and the fuel tank with a fixed aluminium bulkhead which also seems to help rigidity. I suspect that improving the body helps more than strengthening the chassis. The 3A later had a roll bar fitted which actually touched the factory metal hardtop. That eliminated scuttle shake. 

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On 6/17/2019 at 11:20 PM, Malbaby said:

Trying to fix some of the annoying inadequacies of the factory chassis. I welded in a 900mm length of 65mm x 8mm plate snug inside the chassis lips, as in the first pic. My main intention was to reduce the chassis flex that occurs just forward of the coil spring bridge.

Then went further than perhaps necessary to reduce chassis twist....

Clearly you have a really nice car there,  so I hope you'll post a road-test of how the car handles (re. bump steer, etc.)  and how it feels ..subsequent to these changes.  This would pre-empt my asking ;  what you experienced and so why the need to fix  "..the chassis flex that occurs just forward of the coil spring bridge. Then.., to reduce chassis twist."

Personally I respect a man who takes an issue by the balls and gets on and actually does something about it.  ;)   And the fact that your thinking and my own, posted just a couple of weeks ago < here >  are along the same lines is great :P   ..perhaps that just goes to show how two individuals on opposite sides of the world ..looking at the same issues, can come up with very much the same solution.!

I've also proposed a cross-brace under the gearbox and gusset boxing of the forward 'Y'  ..but perhaps these might be part of your " I still have to complete more minor bracing work.."   In any case - I look forward to seeing those additional details.    Although I'd recognised the weak section ..just rear of the T-shirt,  I  hadn't yet looked into a resolution.  IMO.,  your solution of vertically orientated plates welded along the inner rails is neat.   8mm is probably twice as thick as I might have used, but that's not the point.  Might I ask what thickness of underbelly plate did you use to stiffen across the chassis.?     I also like your fitting vertical plates midway along the trailing link rails.  I can see the benefit of those, with no detriment.    

I'm still waiting on my car (..yet to be shipped from the US)  but I propose to do very similar,  and so it's really useful to know what can be done without lifting the body off,  and similarly really useful to see what you've done when knowing how exactly your exhaust fits through this area -  THANKS.   

I do hope you'll post further photos once it's all back together again.   

Thanks, 

Pete

 

Edited by Bfg

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Pete...I was prompted by my experience with.... looking at how much the top of the door gap widens from when the car was on ground weight bearing, and then up on my 2 post hoist [with the rear of the chassis being unsupported].... and the annoying slight vibration of the surrey top at the front windscreen fixing whilst driving.

I also had a slight diff whine, so good time to fix both issues.

I used 3mm for the under belly plate, with 2 strips of 5mm plate as shown for added stiffening where the plate crosses the inner chassis rails.

I run a single SS exhaust pipe as I cannot see any benefit in running twin pipes on a 4 cyl engine.

 

Edited by Malbaby

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That's interesting.  When looking at the chassis stiffness I was primarily considering chassis twist (because it most effects steering control), whereas your feedback of gaps opening is one the bend (of the whole chassis) as a beam,  and then you "went further .. to reduce chassis twist".   Out of curiosity,  do you recall approximately by how much your car hogged when on the two poster (when the doors were opened) ?   I'd guess the car was being supported at the same place as shown (rear outside corner by the IRS mount and forward at the ' Y ' ?)   sorta like this  . .

623703795_1080z-plus(850x458).jpg.b62514ad7832fdf221d01115709308d5.jpg

^ yeah I know..  this is the live-axle version of the TR4A ..but these were the clearest series of photos I could find to Photoshop together as a single composite, when I looked at its design (failings),  but now it helps me visualize the cause of your car's hogging.   The (static) loads of  { diff., IRS rear axle and suspension parts, plus spare wheel, exhaust can(s) and mass of fuel } to the rear  .. and { engine, transmission and ancillaries,  plus battery, front suspension, steering and cooling system } forward,  are not so distant ..relative to the lift points.  And yet they result in noticeable hogging on your very good condition four cylinder car.    It makes one wonder just how bendy a rusted (..but still on the road) TR5 or TR6 might be !   :blink:

So.,  you've now added doubler-plates to the two rails either side of the rear drive-shaft UJ.  And the central section is already stiffer with four rails, which with your cross brace (the blue box section and vertical plate to mid-place of the trailing link rail) are now tied together  ..so logically the other place it's bending is the single rail either side of the bell-housing ..between the Y and the triangulation to the front suspension turrets.  

In my assessment,  I alluded to the retrograde step in the IRS chassis' design  " the TR4 chassis has its central cruciform structure ie. from a further forward position, close to the forward turrets diagonal bracing (compare the foot well bolt holes in the illustration below) ".   So  I think on my own car  I'll be adding doubler-plates  (similar to what you've done at the back) to those forward rails.  

Thanks again.

Oh and just to confirm.. you did support both the front and the rear of the chassis, re. " [with the rear of the chassis being unsupported] " ..so the door gaps were correct before  you welded those doubler-plate reinforcements in ?? :ph34r:

 

"I used 3mm for the under belly plate, with 2 strips of 5mm plate as shown for added stiffening where the plate crosses the inner chassis rails."   I guessed you had used 3mm and 6mm, so I wasn't far off..   I'm presuming the 3mm plate replaced the original underside T-shirt plate,  so in effect you've thickened this and extended it (as Waldi  suggested in my CAD thread) to the outside rails.  I concur with the cross-bracing and your upright plates to mid-point on the trailing-arm rails, and then to gusset those,  so although at first glance your solution seemed a little "heavy engineering'  ..it actually makes more sense than half-a-dozen smaller gusset plates.  Of course the difference in weight down-under the chassis  is negligible relative to the overall weight and c. of g.    Nice One Malbaby.! 

"I run a single SS exhaust pipe as I cannot see any benefit in running twin pipes on a 4 cyl engine."    I had come to the same conclusion when approaching from ; saving the cost, weight and hassle of running a twin exhaust ..of negligible performance benefit.   Again we are of like minds.   My 4A  is coming with a 4 into 2 into 1 extractor manifold in mild steel,  thereafter I'm planning on running a single S/S pipe and (transverse) silencer.   

We look forward to your updates. 

 

Edited by Bfg
reason ..always grammar !

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