Modern trailing arms for the 914?, 986 carriers/calipers/e-brake, more adjustability, more tire? Options

[Chris914n6]

Cut down Boxster rear hub assm and just weld aluminum sheetmetal and tubing to copy the 914 arm mounting points/shock. Easy peasy and cheap.

Or maybe bolt the Box Assm to the AL trailing arm which would allow for toe and camber at the hub via spacers.

I'd also use a mass produced sleeved rubber bushing from another car/truck that presses in, example the Nissan Hardbody ft upper susp arm.

Whoever makes them can send me a set as payment (IMG:style_emoticons/default/smile.gif)

[andys]

Having gone down the path of custom trailing arms (still mounted on my car), the more I studied the stock design the more sense it made. I also took a stab at aluminum, but only got as far as machining the bearing carriers. See post #32 at: http://www.914world.com/bbs2/index.php?sho...tive&st=20#

Andys

[live free & drive]

As a point of reference this thread on the weight difference between steel and aluminum 911 trailing arms is instructive:

http://forums.pelicanparts.com/porsche-911...arm-weight.html

[914werke]

Im sure its been documented somewhere on here before but as a point of reference using my bathroom scale: a OE 914 BARE (no bearings no shaft nothing) trailing arm is 15 lbs.

[rick 918-S]

Anyone have a 914 arm they can post laying the same way this 911 arm is oriented?

Lets see what the two look like.

[horizontally-opposed]

Cut down Boxster rear hub assm and just weld aluminum sheetmetal and tubing to copy the 914 arm mounting points/shock…

Or maybe bolt the Box Assm to the AL trailing arm which would allow for toe and camber at the hub via spacers.

Anyone have a 914 arm they can post laying the same way this 911 arm is oriented?

^ Now we're cooking with some gas.

Why replicate/redo/machine the trickiest part—the wheel/bearing carrier—when an arm can be made to accept a 911 or 986 wheel carrier? 986 is appealing as they're plentiful used or new, and engineered to deal with loads from 255/17 summer tires up to MY2000~, and 265/18 summer tires from MY2000~ on, when mounted on a 2900-3200lb mid-engined car. Wheel bearings availability is probably just fine and will be for a long time, and they're ready for 986 rear calipers and incorporate an internal drum e-brake. For the truly nutty 914 builds, there's provision for a lateral link (to the transmission?) and even a wheel-speed sensor for traction control.

Aluminum 911 trailing arms Rick just posted are out there new and used as well, but are probably in greater demand for obvious reasons. Might be sliced and diced to work, however, and also mounts 911 calipers/e-brake.

That would leave design of the blade/arm and front end. I suspect the outside cost on a pair of new arms has to be $5,000-7,500 before even a small group would consider them, and there will have to be advantages besides weight in order to make them compelling. Could it be done?

[horizontally-opposed]

986 wheel carriers, Porsche-engineered, made in Italy by Brembo. Looks like a high-quality part. Available for $120-200 used, thanks to two per 996 junked and four per 986 junked.

I almost forgot about Porsche's cost-saving move to design these to work at the front or back of the car (LF/RR or RF/LR), which allowed them to use just two castings for all four corners of the 986. Wheel bearing, 986 caliper mounts, and integrated e-brake are all very nice—and I suspect this piece will be hard to beat for weight vs strength. Not sure what to do about that shock mount—could it be put to use via machining or custom shocks, or does it need to be removed?

[horizontally-opposed]

A couple more images.

The 986S and 986.2 went to a larger wheel bearing, I believe in conjunction with the 18-inch wheel approval (or near it), but the early setup was engineered and approved for a 255/40ZR17 tire at the back of a 3,000~ pound Boxster, and a 225/40R18 summer tire at the front of 996s. I remember a Porsche engineer saying this design was also an answer to problems with the front wheel bearings used on the front of 964 and 993 race cars—which had reached their limits with 18-inch slicks.

[rick 918-S]

My thought was to see if a 911 arm could be sourced and used as is with an adapter to the suspension ear and mount on the 914 chassis without cutting the car or the arm. My concern is the triangle the 911 arm forms when adding the flat bar may interfere with something. The 914 part does not form a triangle. Likely for a reason.

That 986 hub looks inviting...

[horizontally-opposed]

My thought was to see if a 911 arm could be sourced and used as is with an adapter to the suspension ear and mount on the 914 chassis without cutting the car or the arm. My concern is the triangle the 911 arm forms when adding the flat bar may interfere with something. The 914 part does not form a triangle. Likely for a reason.

That 986 hub looks inviting...

(IMG:style_emoticons/default/agree.gif)

Suspect the far wider triangle of the two-piece 911 trailing arms is afforded by the narrow transmission ahead of the axle line in a 911—the only way to do that in a 914 would be to reverse the trailing arms in a 914…an idea Porsche thankfully abandoned with its very first mid-engined sports cars in the early 1950s.

914 arm is triangulated, though to a much lesser extent…but that still needs to be considered and replicated.

Agree about 911 arm + modded 986 wheel carrier + some form of triangulation (that maybe doubles as a toe-adjust). Not sure it will be lighter if it's going to be cost effective, but it might be stronger, newer, and integrate a 986 e-brake, 986 caliper mounts, and wheel bearings in the bargain. I've never liked the idea of slicing the 914 trailing arm to add the 911 e-brake and caliper mounts. I know a lot of people have done it, and successfully, but I have also seen those conversions go wrong. 986 front calipers, meanwhile, are easy to adapt, and probably the best technical solution for a 914 (modern, light, stiff, cheap, plentiful, available for more and less power thanks to 986S, and set up for a mid-engined car rather than a rear-engined one). Only count against them is they don't look as period or as cool as 930 brakes…but the latter are big $.

I can't draw to save my life, but the Rennline outer 911 arms are only $250 a pair, while it seems like a nice pair of 986 carriers with e-brakes run $200-300 a pair. So the challenges will be figuring out mating the 986 carrier to an (existing? 911 outer?) trailing arm, the forward pivot/mount, hub placement, body clearance, and triangulation. Oh, and the stub axle, too. See? "Easy." Had an offline conversation yesterday, and a good engineer to speak with this about was named.

I wonder if the 986's "pinch" strut mount can be removed so a trailing arm can be made to attach the carrier and also locate the 914's lower coil-over mount.

[horizontally-opposed]

There are a lot of interesting starting points, from mild to wild, and perhaps one of these vendors could modify something they've got to suit and also provide integration for triangulation to the 914's inner mounting ear.

[horizontally-opposed]

Elephant offers a surprising number of choices—but I guess it makes sense as there's a lot going on at the back of a 911…

Was expecting these 959s of 911 spring plates to be $4-5k. They're priced at $2500. So the range from Rennline to 959 appears to be ~250 to ~2500. The wilder Elephant arm also makes a possible point (or two) for triangulation evident. Might have to be flipped side to side and/or modified to fit on a 914 to avoid the curved arm from interfering with the body.

Would I pay $2500-4000 for an arm like this, in a 914, vs $3500-5000 for rebuilt arms with all the tricks? Yes.

[horizontally-opposed]

And yet another option from Elephant…

Not sure I see the need for ride-height adjust with all of the kits available to do the same with 914 rear dampers, but then again, I still haven't bought one of those sets. Might be nice to fine-tune the ride height and even corner balance the car with my less than exotic Bilstein HD/Weltmeister setup—particularly if it's part of the bargain in a trailing arm upgrade. No need to replace springs I like with threaded sleeves and new springs of the same rate.

[stownsen914]

A while back I looked into redesigning the 914 rear suspension for my racecar. The options are a bit limited due to the relatively wide flat 4 or 6 engine being in the way. A 911 trailing arm would be a great option, if you could get it to fit. But there isn't room for the inner mount.

Dual wishbone type suspension is an option, but of course would mean a lot of modifications to to the chassis. I've seen it done on a few tube frame 914 racecars. I've also seen stouter trailing arms like the ones on Sheridan's 914.

The challenge is twofold for the 914 - the trailing arms flex, and the chassis in the rear suspension area needs reinforcement too.

In my case I added a lot of tubing to the car when I built it to strengthen the chassis. The trailing arms are just stock one with the welded reinforcement kit. Someday when I re-do the rear suspension, I'm planning a custom trailing arm with the adjustments at the hub, similar to what Sheridan did.

[rgalla9146]

My GT conversion.
Is this lighter and stronger ?
If the trailing arm were re-shaped (narrow + taller ) could it accomodate the narrow
body wheel / tire requirement ?

[914werke]

Gawd that's Purtty! (IMG:style_emoticons/default/biggrin.gif)

[mepstein]

Rory also has some suspension console reinforcement that you can see in the pic.

[horizontally-opposed]

My GT conversion.
Is this lighter and stronger ?
If the trailing arm were re-shaped (narrow + taller ) could it accomodate the narrow
body wheel / tire requirement ?

Whoa! Never saw these. Very cool, and I'd be curious re: your questions.

I have no doubt that Porsche engineered (and overbuilt) the 914's steel trailing arms down to a price. I doubt it did so with a 50- to 100-year service life in mind, but there's no doubt they're long-life parts. I cannot remember hearing of a failure, but they were reinforced for racing by Porsche and others.

I do wonder what goes on inside of the boxed sections, as it's "unlikely" they were treated for condensation/rust any better than the 914's longs and center tunnel were. What did yours look like inside when they were sliced up, Rory?

Rory also has some suspension console reinforcement that you can see in the pic.

Some very nice work indeed on Rory's car. That car keeps impressing me, visually and technically—how has it not been nominated for COTM yet? (IMG:style_emoticons/default/blink.gif) (Makes mental note.)

I've been considering the reinforcements below next time my engine comes out. The inner mount reinforcements are from Tangerine Racing, while the outer is from Patrick Racing. Like the idea of reinforcing the outer mount with the long, but wonder what an engineer with relevant experience might say—and don't love having to remove the rocker panel to adjust if that's what would be necessary. The factory did some interesting things with rocker panels on some of its rally cars, including leather straps to allow the back of the rocker to be peeled open for field service. Looks cool on a Monte Carlo works GT, but zero interest in that for a road car.

[rick 918-S]

Some of that 911 gear looks like a Rube Goldberg devise. I having a hard time imagining those parts not flexing (twisting) under a torsional load.

[rgalla9146]

Rory also has some suspension console reinforcement that you can see in the pic.

Simple triangulation of inner ear and in the case of the rear trunk increased
cross section of transmission crossmember.