Blue 90 RS

I'm going to be rebuilding/replacing my suspension this summer. I've pretty much decided on a full set-up from Spohn:

399R Tubular Adjustable Torque Arm - Transmission Mounted

D-7-1604 Poly Transmission Mount

995R Tubular Steering Brace (Wonder Bar)

990 Front K-Member Braces

202R Rear Lower Control Arms - Boxed with Polyurethane Bushings

210-S Rear Lower Control Arm Relocation Brackets - Stock Rear End

104R Panhard Bar - Tubular Adjustable with Polyurethane Bushings

732R Tubular Front Lower A-Arms - Bushings - Spring Boxes

D-7-1604 Polyurethane Transmission Mount

D-7-506 Polyurethane Motor Mounts - Small Block Chevy

923R Front & Rear Sway Bars Set - Solid 4140 Chrome Moly

Cost is a factor. All of these parts are the "mild steel" construction instead of the "chrome moly" except for the sway bars, so I'm not going "full tilt" with this. I'll also be adding subframe connectors and a strut tower brace at some point. The car is lowered 1" on Eibach Pro Kit springs, and has new Monroe struts & shocks all-around. It rides great and gets good fuel mileage. Doesn't look too bad, either (in my opinion).



My question is this:

Will it be worth my time & money to also swap to the Spohn tubular K-member on a car that is only driven on the street?

This car will never be a big-power, "numbers" car, nor even a daily driver. It's destined to be a cruiser, meant for sunny days and back-road romps. No racing of any kind. It's a 305 V8, bone stock (for now) and will never see more than a heads/cam/intake swap at most. Probably never break 300 hp at the crank. I'll also be doing a brake upgrade at some point in 2014 or 2015, both front and rear. My interest is mainly in updating the car to be reliable and responsive for street use, whether running down the interstate, buzzing around town, or having fun on some curvy mountain roads. I want it to feel "tight", not loose or rattly. Again, reliability is the main objective.

Swapping out the K-member will be a $500+ affair, and pretty labor intensive. I don't have a garage or carport to do the work in; only a gravel drive in the sunshine. I think the tubular k-members look really cool, but if it's not going to give me any real benefits for my application, then I don't want to invest the time or money in it. Is it "that good" of a piece and I should swap it? Is it more of a "track piece" that I would not be able to fully appreciate for my application?

What are your thoughts? Would you spend your money?

paul_huryk

You should skip the k-member as it is expensive and also will take a fair amount of time to put in.

You should change these if budget allows:

TQ arm

Trans mount (optional, but if worn, replace)

Steering brace

Rear lower control arms

Panhard Rod

Motor mounts - if needed.

You could do the front control arms without the k-member - they are much stronger than stock and have new ball joints and bushings.

You can swap larger sway bars from an IROC or WS6 car along with new bushings and end links - no reason to drop $400 on new bars.

I would also swap out the Monroes for Bilsteins or Konis too - if money permits (if it were my car).

Blue 90 RS

Thanks for the input. That's kinda what I was thinking.

Anyone else care to weigh in?

TEDSgrad

iTrader: (4)

Struts/shocks & tires - get the best! If what you have is fairly new, then "planned obsolescence." Without these, the other parts are wasted money.
Since you're already 1" lowered, consider the "jegster" - axle side lowering of the panhard mount will help "tighten" the car (you can do this when you do the LCA mounts).
Good bushings are next - delshpere/roto-joint. On the rear LCA's and panhard, you can get away with poly on the body side (to reduce vibration), BUT NOT ON THE AXLE SIDE. Buy LCA's and panhard where you can swap out the connection ends so you can experiment or replace those ends as the market always improves.

Lurbie

iTrader: (3)

Great question. I had looked at a K-member swap too, seeing people's response to your question has me wondering the same thing now. I'll be doing a 383, but plan on the same driving habits, so I guess I'll save my money for other things.

Reid Fleming

iTrader: (2)

K-member? Absolutely not. They are expensive, less strong than stock, and of no particular benefit other than weight. Unless I had taken out my back seats, removed carpeting, gotten rid of the passenger seat, taken out the A/C etc, I wouldn't bother with the K-member unless you were racing and needed every weight savings possible. Even then I'd probably keep the stock K-member.

The good news is that the Prothane poly transmission mount vibrates less than the Energy Suspension one. The bad news is that for many (me included) it still vibrates too much. You can try it if you want. It's a cheap mod. And if you don't like it, go back to rubber. I tried it. Kept it for about 5 months and went back to rubber. Smooth sailing after that. It's a weird thing though. Some people report no vibration. Some report a mild livable vibration. Others say it's terrible. Mine was great at anything less than 2500 RPM. At 2500, it would vibrate and hum and rattle. And when I went wide open throttle, it would sound like a chain clanking around down there.

LCA relocation brackets.....Sure.

Poly engine mounts? I'm just not a fan of poly with the exception of in the sway bar bushings.

I'm not sure which sway bars you have right now. But something a touch bigger probably isn't a bad idea.

Do the torque arm last. If traction isn't an issue and you're not going hard on the throttle in the corners (which you won't with Munroe shocks), I don't think the torque arm would make much difference.

I'd recommend the Del-Sphere ended LCA and PHB.....No squeaking, no greasing, no problems.

I like Spohn stuff. But I wouldn't buy his Wonderbar. Get the one that TDS sells. The TDS bar fits everybody's car with ease. And it has a better mounting setup.

Reid Fleming

iTrader: (2)

I know you mentioned SFC, definitely get those. The mild steel vs chrome moly parts aren't as big of a weight savings as you'd think. My hunch is that the reason vendors never list the weight of steel vs chrome moly is that if they did, nobody would buy the more expensive version.

A pair of LCA weigh 10 lbs total. A pair of chrome moly LCA weigh about 8.9 lbs. Consider that the weight savings of doing a 12 or 14 point roll cage in chrome moly is about 15-20 lbs weight savings. That's a lot of material. On the race track, 20 lbs can win a race. On the street, it's a bag of groceries.

Blue 90 RS

Reid Fleming - good input. Thanks for your advice!

87350IROC

iTrader: (2)

Less strong than stock? Do you have any information to back that up?

Sorry, if you have done the calculations, then I apologize and would love to see your assumptions. I just can't stand when people repeat what they have heard with no thought as to whether it is correct or not. Have you seen anyone provide an intelligent explanation for this "fact"? I have not.

The OEM k-member was almost certainly not sized for static strength. I think it is silly to consider only one aspect of the design requirements when comparing these parts.

John

Blue 90 RS

Just a curiosity on my part, but do you have any info to show that it's equal to or better than stock? Right now it just looks like two differing opinions to me. Can either of you clarify why you think it's better or not? Just by appearance, it doesn't look as "beefy" as the stock piece, but many replacement parts can be slimmer/lighter if engineered correctly. Where could we find specs on either part to compare?

87350IROC

iTrader: (2)

Devin,

I have not attempted an analysis for either piece. Which is why I did not provide an opinion on the strength. I am not arguing against any opinion because I do not have one of my own. But I do demand more proof than "somebody on the internet said it" for me to trust an opinion. I am just trying to help you by pointing out that in my opinion there is little basis for the opinions I have seen over the years on this subject.

Either way, static strength is not what I would be comparing here. Who cares what the strength is as long as it is enough to do the job, with margin? Zillions of miles driven on both stock and aftermarket have proven both the stock and aftermarket k-members to be strong enough for normal and track driving. I would be much more concerned about the stiffness of the two parts as the k-member is linking several points across your front subframe. More stiffness will not do any harm. But less stiffness would provide a less desirable driving experience along with increasing the stress on the surrounding parts.

In addition to stiffness, I would be concerned about the consistency of manufacturing and the fatigue properties of the design. Obviously there is no issue with the stock k-member in either regard. GM uses very conservative design requirements and has competent engineers. As for the aftermarket companies, well your guess is as good as mine. GM would not put welds where many aftermarket companies do. This goes for all suspension components. There is just a higher risk of failure on a welded joint, the joint cannot reliably be inspected without cutting the weld.

John

Blue 90 RS

87350IROC (John), Thanks for your input. Much appreciated!

Alice89

iTrader: (6)

I'm guessing that its just an assumption people make combined with half-facts. What I mean is I have seen many welded suspension pieces (both square and tubular) get wiped out on the street by hitting a curb or running over something at high speeds. I've seen this both in person and on various internet forums. Either the welds give-way or the tubular/square pieces get bent badly.

Knowing the above damage described; it's easy to assume that a tubular K member could get bent easily in a head on collision; or by smacking a curb.

On the other hand I've seen many wrecked f-body's but never a bent factory K-member.
I have no actual evidence other than speculation; but I would assume the factory K-member is stronger than aftermarket welded pieces. Just like I would assume the factory spindles are stronger than aftermarket welded spindles.

Blue 90 RS;

The Suggestions already made to spend $ elsewhere on your suspension are all much wiser than putting that $ into a tubular K-member. Unless you need a lot more space or your constantly changing motor mounts; then the K-member can wait.

BTW, Your car looks great. Are those SLP's? Whatever they are they look good with blue.

87350IROC

iTrader: (2)

Yup, as I pointed out, manufacturing is a big potential problem. But a poor weld does not mean the part was not designed strong enough, instead its a manufacturing error.

Regardless of the validity of this statement, the last thing I am thinking about in a collision is if my poor k-member made it. If the worst I have to do is replace a k-member, I am lucky. People talk a lot about hitting road debris. In my entire driving career I have never struck something that would be even close to damaging a structural part of the car. So that is of little concern to me. If somebody is constantly hitting large road debris I suggest rethinking your choice of vehicles.

Your assumptions are fine and at least you have stated your reasons for thinking that. This is all about making an informed decision instead of just saying "x is the best". Remember, ever race car has a welded roll cage. The general concept of welded tubes is not dangerous or inferior in every instance. It is all about execution of the design and manufacturing.

Agreed. The benefits of the k-member are reduced weight and more access to the bottom of your engine. Money is better spent elsewhere like on top quality tires, then shocks and struts.

John

Alice89

iTrader: (6)

That part made me laugh! Your right about manufacturing differences and the quality of welds from company to company. I have a few Spohn parts and the welds on the Panhard bar are excellent. I've never actually seen Spohns k-members in person; but if their built like the LCA's I have then they will probably stand-up to major abuse.

BTW In terms of road debris you would have to hit something major to casue damage; I ran over a damn ladder going 40 in my old formula once! Luckily it didn't do any major damage other than scrap the exhaust.

Pocket

iTrader: (24)

I have a spohn k-member and will not recommend it to anyone. So many design flaws it's not funny. Do a search for my gripe list with pics

To the op, for a cruiser I'd stuck to shocks, struts, bushings, SFCs, and fresh mounts

The founders rear suspension package is only a few bucks over bushings for the rear and not having to press them in will save a lot of trouble. Add springs if yours are saggy. Moog replacements are inexpensive

Go with a set of sway bars from a ws6 or Iroc. 34 or 36mm front will be a huge improvement. Rear bar upgrade is optional, the front will be the biggest improvement

Do NOT run tubular a-arms on the street

The kyb f/r shock/strut package is an excellent bang for buck set that's a good median of performance without an excessively harsh ride

Any 3rd gen will benefit from SFCs. Any brand will do. I prefer the outer style that can be welded to the punch rail for that extra little something. They also make good jack/stand locations

Blue 90 RS

Why not? I would assume the stronger tubular pieces that are also lighter than stock would improve both ride and handling. Less unsprung weight is always good, and stronger is better too, no?

I have brand new tires & wheels - 17x9.5 ZR1 replicas with 275/40R17 BF Goodrich Sport Comp II's at all four corners. I have brand new shocks & struts as well, although they're just the best-available from Monroe. I'll upgrade those when it's time to replace them again. I put new springs in just a few thousand miles back - Eibach ProKit 1" drop. I'm considering replacing the steering box as well, since mine is original to the car and has over 206,000 miles on it. I'd like the quicker-ratio box that was available on the IROC/Z28 cars.

hellz_wings

iTrader: (2)

I run tubular a-arms on the street. Had them on since 2009, what's the issue with them pocket? I have UMI's first design, which were lacking a few features, but the new ones look phenomenal.. And I've hit my fair share of potholes in the past 5 years I'm surprised my engine didn't just fall out underneath my car lol. The only thing I don't like is the poly bushings, I would rather have the adjustable ones (for adjustability) or the del-alum ones.

91ls1t56

DO NOT BUY SPOHN ANYTHING ! It is all junk. I have the tubular K member for a ls swap the T56 crossmember and adjustable TQ arm ALL JUNK ! I wont sell the stuff because I would feel so bad for stealing somebody elses money. Complete garbage . For example the K member is two sides connected with one bar. Then they notch halfway through that one bar for tie rod clearance. The tie rods still rub at various stages of suspention travel. I also had to shim an engine mount 1/4 inch to level out the engine and it is still a little low. The crossmember is huge bulky and a horrible design. The Torque arm worked on the stock rear end but, it is huge so that it will work on a 9 inch rear. I now have a 9 inch rear and the huge bracket that holds it to the housing hits the top of the transmission tunnel way before the axel tubes hit the bumpstops. Now that we know it dose not work as advertised we know that it is extra big and bulky for no good reason whatsoever. I will say that when I first pulled these pieces out of the packaging and looked them over I was impressed with the welds, finish, quality fasteners. Trying to use these items is another story. I would not recomend this manufacturer to my worst enemy.

Alice89

iTrader: (6)

I've been using Spohn's parts for years on both 3rd & 4th gens and I've also helped install a few Spohn parts on Mustangs at the shop. So far I haven't had any issues let alone considered there parts to be junk.

Do you have a thread or pictures that I can look at? I wouldn't mind seeing the k-member.

midnightfirews6

iTrader: (1)

I thought this was considered a bad idea for most since the balance of the car changes drastically?

Seems like a lot of people have similar experiences. There are pages on pages of peoples' gripe lists with the Spohn K-member, so I'd be leery.

And I, too, am interested in why you wouldn't run tubular a-arms. I don't think my stock ones will allow for a good press fit if I change ball joints again so I was planning on picking up the new UMI pieces when funds allow.

Spohn subframe connectors are really good, and their strut mounts are said to be the safest design out there. Can't speak for anything else, but it seems like quite a few people have had quality issues with some of their other stuff.
I can't complain about anything I've bought from UMI thus far though.



Anyway to the OP, a tight quick ratio steering box will be a great addition, as well as:
-SFC's/ wonder bar/ k-member braces/ STB
-Konis
-Spohn strut mounts
-tubular rear LCA's and panhard bar with poly bushings on the body side and roto-joints(also called del-sphere) on the axle side
-delrin bushings in either stock or aftermarket a-arms.
-lower control arm relocation brackets

I'd also go with fresh poly bushings on front and rear sway bars, which you may consider switching out to fine tune your setup. You can get a million different sizes off of stock third gens, so just go to the junkyard and bring a digital caliper to find the ones to suit your needs, and order the corresponding bushings if necessary. With the Pro-Kit I'd run a 36mm in the front and then whatever size rear necessary to keep the car from being too tail-happy... probably 21 or 23mm.

Unless you're really putting power down or need the adjustability, a torque arm is one of the last things I'd have on the list. Nice piece to have, but it's expensive and won't be as noticable as the other pieces. I wouldn't bother with a tubular K-member on anything other than an engine swap where space is needed or an all out drag car where every single ounce counts. The weight is down low near the roll center, so it really doesn't do much for handling. A lightweight hood or aluminum heads (or both!) would be of much bigger benefit for that purpose.

91ls1t56

What exactly do you want to see ? The tie rods hit and the engine sits crooked. Other manufacturers were able to fit TWO bars connecting both sides and maintain the ability to use stock A arms.

Alice89

iTrader: (6)

Never mind, I already did a search and found pics of the problem. It's weird that some fit perfect with no rubbing while others have major issues. Maybe a faulty jig?

Alice89

iTrader: (6)

It seems there are a lot of complaints on their steering kit. Their LCA's & Panhard bar on the other hand are awesome; I've run them in both my iroc & my old formula.

From what I've read many members here have had good results with them. However you have to have it set properly; and use appropriate spring rates. I have the jegs piece but I have not installed it yet; I'll make a thread on how it feels once I take it to the track. You have to raise and lower depending on what your doing (street/track).

midnightfirews6

iTrader: (1)

Glad to hear they worked out well! Seems like all of the part vendors are kind of hit and miss from product to product as far as whose is best.

And I've read that too... But like you said, they set it up properly with proper spring rates and are driving their cars competitively. Being that the OP has the Pro Kit and just wants a nice handling street car, I feel that jumping into suspension geometry may be overkill.

Alice89

iTrader: (6)

That's a good point, I forgot he was only an inch lower. I'm going to be at about a 26in rear fender height so I'm thinking I'm going to need all the adjustment I can get. The OP is probably at around 27-27.5in rear fender height by the look of his pictures; he probably wont need this for street use unless he goes lower. Even then his spring rates would have to come up in the rear.

TEDSgrad

iTrader: (4)

RC axis front to back is pretty dramatic. I would only suggest lowering just one hole position. It really does "tighten" the car. No need for both sides (that is overkill, IMO), just one hole lower on the axle side.

Blue 90 RS

I appreciate everyone's input here. Lots of good information, and some good opinions, too. I'll definitely be re-hashing all of this before I order my upgrades. You can't have too much knowledge, can ya?

Thanks again!

Pocket

iTrader: (24)

Do a search for redraif. Any design that fulcrums the spring perch across a tube is a terrible design. Search long enough and see a couple scary stress analysis of tubular a-arms. Hard to beat the thick gauge stamped steel a-arms for strength and longevity

articwhiteZ

iTrader: (56)

iv spent the last 2 hrs going back over old post.. anyone have a link to the rash of pics showing all the bad stuff on the K members not working.

would like to see them.

Blue 90 RS

Ditto here....

Alice89

iTrader: (6)

Here you go:
https://www.thirdgen.org/forums/ltx-...-k-member.html

I did a lot of searching last night and I must say that all the aftermarket K-members have had issues. (PA-racing, spohn, BMR, UMI & another one I cant think of off the top my head) They are all finicky; One can be installed on a car and everything fits but on a different car there are major clearance issues. It must be a faulty jig. With that said the definition of aftermarket parts is "It doesn't fit." I'm sure you all have heard that one before.

articwhiteZ

iTrader: (56)

i know all my spohn parts (front end) bolted up in 20 min. but i have not driven the car with it. (front end is off)

starting to think spohn made his k member for a stock front ride height...
and the jig with only one car.. not checking 5 or 6 others..

my car has never seen a dirt road. or rain..just car shows and the 1/4 mile.
and it sits at OEM specs. (50.000 miles)1992 Z28

i also know the OEM tie rods are smaller then any after market.
my oem rods are about half the diameter of the replacements.
i looked at 3 diff makes..

this is starting to add up now.
have to do a full update when it all gets put together...

Pocket

iTrader: (24)

After I cut the front brace mounts off, the k-member installed without a hitch. So many issues didn't change how it bolted up

Still think it's stupid a spohn LSx swap k-member has to have a front brace cut off to clear the ls1 fbody alt and low mount Ac compressor. Silly since the stock k-member with the brace clears the alt. Ac won't fit either way, but knowing that, why put the mount on there?

The main hoop being 3" lower than the oil pan is a QC problem. Notching the main hoop for the tie rods a major weakness to fix a design flaw from the start. Main hoop angle, QC problem. Motor mount pads being at an angle, QC problem. A-arm mounts off f/r QC again

All those issues stem from a poor design and crappy jig

People can post all day how their stuff fits great, but several having repeated issues means the fabrication going in/out of specs frequently. If the company cared anything for their products they'd build a repeatable part. Having someone do a stress test before pushing it out the door wouldn't hurt either

articwhiteZ

iTrader: (56)

well i can say that if it's going to bolt up and fit a stock spec 3rd gen.it's going to fit mine.. if i even get one rub or bump. ill will post it. and full sets of Pics... and if it fits without any probs. ill do the same.

just like the AFR 220 Eliminator heads not taking any other stud girdle but the ones AFR makes..

91ls1t56

Put your front suspention and steering together without the coil springs. Now you can fully compress and extend your suspention through out its entire travel. Do this with the wheels straight, half turn and full turn. You may luck out with the smaller stock tie rods.

articwhiteZ

iTrader: (56)

thats the plan. the front is all coil over all spohn.
all my parts are new on the front. using spohns bump steer kit.
have all new tie rods. had them yellow zink plated. so if any of there parts dont fit there parts.or together then i will let every one know.

Pocket

iTrader: (24)

Measure your k-member to oil pan clearance before and after. That was my biggest gripe. The 3" drop makes any speed bump a scrape zone. It's the lowest point on my car, and I kept it as close to stock ride height as possible. I have 4" over the axle exhaust and even that is higher than the k-member

articwhiteZ

iTrader: (56)

ill have to see if its lower then my ladder bars under the car.
and my front tires are 26" tall. and my back ones are 29" tall