Birkin rear suspension joints

[Guest Silverspur]

Drove my Birkin S3 for the first time today and the handling was scary to say the least . I am thinking i need some compliance in the rear and looking at the trailing arms it seems they are trapped/ pinched where they mount so rod ends seem like a good idea . Does anyone know where i can find something like the ones in the picture .

 

Thanks Dave

[slomove]

I am wondering if something else may be wrong with your setup. While the rod end/ball end links are a certain improvement (I have them on my car) I noticed only a moderate change in handling. I suspect your spring rates and/or shock settings may not be optimal or if some other problem if it is pinching (which it should not do as designed). At some point you could buy such ball joint radius arms from MSI/Vacaville but they are out of that business for along time. Maybe somebody else picked that up.

 

FWIW, I fabricated my ball joint radius arms myself from 5/8" alloy tubing, cut-off 1/2" bolts and QA1 XF series ball joints. Was not difficult, even with my modest welding skills. Has been holding up since 2003, see pics below.

 

 

 

 

[slomove]

Few more pics....maybe I should mention the rod ends in the picture are cheap McMasterCarr parts. After they wore out I replaced them with the above mentioned QA1 rod ends and installed protective rubber washers as well.

 

 

 

Edited May 31, 2015 by slomove

[Guest Silverspur]

There well may be other issues but the rear does seem very stiff .

i dont know what the spring rates are but the Gaz shocks are one klick from full soft , front camber is 1 deg neg with 1/8 in toe in and tires at 22/24 psi .

any comments or advise will be appreciated.

thanks

[xcarguy]

Silverspur,

 

 

Welcome to the forum. Former Birkin owner here. FWIW, when I drove my Birkin for the first time, it was very squirrely during hard braking. Turns out it was an alignment issue (front end-to-rear end relation). In other words, the wheel base on one side of the car was slightly different than the other. May want to visit this on your car.

 

And congrats on the purchase of Jackel's S3! :cheers:

[Automoda]

Your problem isn't the joints. I've had both types and the only real change I noticed is that the urethane joints tended to throw the car slightly to the side after a huge bump, and the heim joints are less so.

 

I'd say either the springs are too hard or the alignment is wacky. If you want to do a quick test, take the springs off of the shocks and move the suspension around to check for problems. Birkin's have amazing handling and you should never be described as 'scary'. Something's up. When I was changing springs to be a little stiffer to work better with the heim joints, I almost ordered springs that were 2x the correct weight. I guess someone told me what rate to get but they meant for the whole back end, not each spring. I'd have had the same experience you sound like you've had.

[rzempel]

One more thing that will give you scary handling is having your steering tie rods mounted on top of the steering arm rather than beneath them where they're supposed to be. Easy mistake, but easy to fix, too,

[Davemk1]

Does your car have a live rear axle or IRS?

 

dave

[Guest Silverspur]

Dave ,My car has a live rear axle .

Rzempel , tie rods are located on top , no suprize as everything else on the car is installed incorrectly, i can see how that will affect things ,thanks .

also i notice i have no preload on the rear springs so i will adjust that too .

still would like some spherical rod ends on the suspension links , i will have to make some if i cant find a kit .

swmbo has me working in the yard today so the car is on hold .

Thanks Dave

[Guest Silverspur]

Rzempel , you nailed it ! Swapped the track rods to below the steering arms and its a different car altogether .

jacked the rear springs to 20mm preload as per the Birkin instructions but now the rear shocks are topping out , wonder if the spring rate is too high ?

Now i can get on with dialing in the Haltec then an anoying oil leak that will mean the engine out ,bugger,

thanks for the help guys .

.

[Davemk1]

With the live axle car you can improve things in a HUGE way by getting rid of the stock control arms and putting in arms with rose joints on the end. They benefit the car it two significant ways.

 

First is that you get ride of a large amount of stiction so that the axle can move up and down with ease and not have all those rubber joints adding resistance. This will help keep the rear wheels stuck to the floor which of course is a challenge in a live axle car due to the unsprung weight of the set up.

 

Next is harder to explain......the rubber bushed ends in the stock arms rotate in a barely acceptable way but they do not allow the car to lean to one side very well. This is due to the ends not wanting to let the axle come out of plane with the chassis. Off the cuff this would seem to be a good thing as it helps keep the car from leaning as much.......but it's really not a good thing as it acts like a very stuff anti-roll bar (sway bar) and it does a vey good job of over-weighting the outside tire and nearly lifting the inside tire. This means one tire (inside) is doing very little work and the other tire (outside) is trying to do too much and can't handle the load.

 

The combination of the two is a car with a rough and bouncy ride that does not feel connected to the road and when pushed at all in a corner it tends to snap oversteer and wants to go backward into the shrubs.

 

I owned a live axle Birkin years ago and it was tough to drive anywhere near the limit and then I replaced the crap control arms and the car came alive and felt like it should. A much smoother ride and a higher limit if traction .......and......and easier time approaching the limit. A win-win-win. I bought mine from a guy who made Birkin parts named Woody and his business was in Vacaville CA. I don't recall the name of the biz.

 

Good luck and have fun.

 

dave

[Guest Silverspur]

Davemk1

i ran across woodys name but i think he is out of buisiness now . I am hating the binding in the current set up to rose joints it must be , i will source some decent ends then fab up the links .

thanks for the advise .

[Automoda]

You don't need to fabricate anything except perhaps some tapered spacers to center the heim joints. Speedway, Summit, Jeggs-- They all carry aluminum and steel rods of the correct length. I might be able to look up the stuff I bought if you're interested.

[Guest Silverspur]

Thanks , if you you can let me know what you used it would be helpfull

[rzempel]

Here's what Woody's kit consisted of:

 

BIRKIN S-3 RADIUS ROD UPGRADE PARTS & PRICE LIST

DESCRIPTION LOCATION PART # QUANT

Aluminum Radius Rod RR5105 4

Rod end, right hand AU-MM-8TY 4

Rod end, left hand AU-MB-8TY 4

Jam nut, right hand SJNL08 4

Jam nut, left hand SJNR08 4

Tapered spacer, 1/4" forward inner rr pick-up BNA119-0001 4

Tapered retainer spacer forward outer rr pick-up BNA119-0003 4

Tapered spacer, 3/8" rear rr pick-up BNA119-0004 8

Road spring, rear by application 2

Rod end ID bushing BNA119-0006 8

 

You can easily duplicate this with parts from Pegasus. Just measure the rod length (12 inches, IIRC) and order to match. If you buy metric, you can avoid the cheesy "Rod end ID bushing" spacers Woody used to convert Imperial bearings to metric mounting bolts.

 

This mod *will* bring a noticeable improvement in handling.

 

Randall

[Guest Silverspur]

Thanks Randal , i will get on the interweb and do some shopping .

regards Dave