105 Panhard Rod Conversion

[Colin Byrne]

hi guys,  competing in Targa again this year and we discovered the rules of our class has changed and we're able to add a pan hard rod now.  So here are a couple of photos of the mount on the axle.  I'm still waiting for some laser cutting for the body mount and will add more photo's as more gets done.  Aim to have it all done for Winton next month

[Scott Farquharson]

Nice work as usual Colin.

[Nick Shardey]

Hi Colin, I'm fairly new to all this, can you please explain the benefits/purpose of a panhard rod.

Thanks

Nick

[Colin Byrne]

Thanks Scott

Hi Nick
The T-piece that provides the lateral location of the rear axle on 105 has a few drawbacks.  One of them is the rear roll center is determined by the point at which the t-piece connects to the diff.  As this is at the top of the diff 105's have a very high rear roll center, coupling this with the low front roll center (particularly if you lower the car) you end up with a very steep roll axes.  This is one of the main reasons for the "twitchiness" of 105's and the need to run very stiff front springs and very soft rear ones, which can introduce problems of its own.  So the main reason for the addition of the pan hard rod is to lower the rear roll center. 
The second job performed by the t-piece is to act as a top trialing arm to limit the rocking forward and backwards of the axle under acceleration and braking.  While it does a pretty good job of this because there is effectively only 1 arm there can still be some movement of the diff, particularly under heavy breaking.  So I'll be adding 2 additional top trailing arms further outwards near the original lower trailing arms

[Nick Shardey]

Thanks Colin, well that makes perfect sense. As I have bought just about everything I can off Vin to improve the handling of mine; I look forward to seeing your future pics so I can at least plan to appease my unreasonable desire to spend more money on these cars that we love.

Nick

[k76]

Just out of interest, what's the functional difference between a panhard rod and watts linkage?

[Colin Byrne]

both are methods of laterally supporting an axle, the pan hard rod is more simply however it has the drawback of the pan hard rod moving in an arc which translates to the axle shifting side to side as it moves through its suspension movement.  With a panhard rod the coll center is dermined by the height of the point on the pan hard rod that the center line of the car passes through, the roll center of a watts link is determined by the pivot point of the actual watts link.  Watts links are better in nearly all aspects, unfortunately not allowed under the rules i have to comply to.

[Scott Farquharson]

Following on from Colin - any tranaxle car has a watts link - many have converted the link to the back of the di dion to be adjustable ie so you can move the locating point up and down therefore allowing adjustment of the roll centre. 

[Colin Byrne]

any tranaxle car has a watts link

Is this entirely true scott? as you can have IRS in a transaxle car so no need for a watts link

[Scott Farquharson]

I meant all "transaxle" alfa's ran a watts link - ie alfetta, 75, 90, giulietta etc - not "any" transaxle cars.....

[Colin Byrne]

sorry, misunderstood

adjustable ie so you can move the locating point up and down therefore allowing adjustment of the roll centre. 

absolutely that can be a very useful tuning aid indeed, similarly by moveing the pan hard mounts up and down the roll center can be modified, which is what all those holes in the mount are for (actually there a few more holes since that photo as I decided I needed to add some "lightness" )

[Colin Byrne]

Finished the body mount this afternoon, the heat has slowed me down a bit, to hot to be welding!, just need to machine up a few spacers, make up the control arms and order some new rear springs should have it all done by Winton (I hope!)

[Colin Byrne]

some more

[Colin Byrne]

Well it's finally all finished.  Haven't driven it yet, still got to put the gearbox back together and fit it in, next weekends job.  Went together OK should be an interesting day at Winton as we've changed a lot of things at once- roll centers, spring rates, ARB settings and shock settings!

[Sheldon McIntosh]

Excellent work Colin, as always.

For those that don't know Colin, he does all this with one hacksaw blade and the ruler on the back of his cigarette papers.  Amazing.