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Don't box your L body subframe, here's why.
I had a two inch sheet metal welded to my GLH's body rear subframe's U channel. At first, the rear suspension was really stiff, it would lift the rear wheel when there is a slight incline on the parking lot I drive into. Then, I felt the rear suspension get softer and softer as it no longer lift the rear wheel as much anymore. Maybe a year later since I welded the subframe, I noticed the cracks.
I now uses a n/a omni subframe with a polybushing sway bar.
http://polybushings.com/pages/swaybarLrr.html
My advise don't box up the U channel or you'll be needing to replace it soon.
http://www.thelostartof.net/tryingbe...rame/pic65.jpg
http://www.thelostartof.net/tryingbe...rame/pic67.jpg
http://www.thelostartof.net/tryingbe...rame/pic69.jpg
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http://www.thelostartof.net/tryingbe...rame/pic76.jpg
http://www.thelostartof.net/tryingbe...rame/pic78.jpg
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Re: Don't box your L body subframe, here's why.
LOL. What size PB rear sway bar did you end up with? I put the 1 1/8" on my GLHT and cut the stock bar off. Under 30mph stuff was a lot of fun. Over 30 MPH was dangerous oversteer. It snapped around on my entering a freeway off-ramp when I had to nail the brakes to not hit the car in front who decided to take it 20MPH slower than needed. Thankfully I had the skills to catch it and keep from hitting the light pole.
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
GLHNSLHT2
LOL. What size PB rear sway bar did you end up with? I put the 1 1/8" on my GLHT and cut the stock bar off. Under 30mph stuff was a lot of fun. Over 30 MPH was dangerous oversteer. It snapped around on my entering a freeway off-ramp when I had to nail the brakes to not hit the car in front who decided to take it 20MPH slower than needed. Thankfully I had the skills to catch it and keep from hitting the light pole.
Brake bias issue?
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Re: Don't box your L body subframe, here's why.
It has to bend somewhere.
I used a 7/8 inch ADDCO bar mounted over the stock welded on bar. It made for a very neutral handling car, but when compared to driving my other GLH with only the stock bar, I didn't notice much difference. Both handled similarly and produced identical autocross times. Both cars cornered on three wheels.
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Re: Don't box your L body subframe, here's why.
I haven't noticed any breakage on the k-car axles I've welded, other than the actual welds I added cracking. :p
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
Vigo
I haven't noticed any breakage on the k-car axles I've welded, other than the actual welds I added cracking. :p
Yeah, but the K-based rear axle is an entirely different animal than the L-body. The L-body was listed as a semi-independent rear suspension. You don't want to box the connecting member for exactly this reason. It HAS to flex. Box it in, and it will flex at the next weakest area, which is most likely where the cracks occured...
It's a very good lesson, and I am glad tryingbe posted it as a good "this is what not to do" lesson for others...
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Re: Don't box your L body subframe, here's why.
Well, they're both torsion beams and 'semi' independent. I guess the k-car part was built with the benefit of L-body hindsight as it's simpler and more compact and apparently holds up better to the same basic modification. It looks like strengthening (or doubling up?!) the actual torsion bar going all the way across there would be safer as it puts its forces into the strongest-looking part of the whole thing.
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Re: Don't box your L body subframe, here's why.
Years ago, I stitch welded a simple piece of strap onto the bottom of that U channel on the GLHT; within a short time that strap was banging and slapping as the twisting cracked several of those stich welds. After that, I installed Johnny's rear sway bar (without cutting out the stock torsion bar) which stiffened the car up a lot. I recently went back to stock for daily driving.
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
DevoBuzz
Brake bias issue?
not in a straight line, but with the inner rear wheel up off the ground and the outer rear riding the shoulder on 1" square contact patch probably. It had stock rear brakes and a SLH1 package on the front. Like I said, tons of fun at low speed as you could rotate the car way to easily. At high speed at neutral or negative throttle it was way worse than any 911 I've driven.
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
GLHNSLHT2
What size PB rear sway bar did you end up with?
1 inch. I have not experience any oversteer issue, not even when I drove it hard at autocross. I don't drive aggressively in the wet.
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Re: Don't box your L body subframe, here's why.
That U channel was obviously meant to flex, def do Not want to be welding that up!
When I hole drilled the Charger rear member (some may remember certain people having heart attacks over this LMAO!!!) I Knew all I was doing, along with removing weight, was making for an Easier flexing rear suspension. Since I also knew I was adding the 1" PB rear sway bar, this was of no concern to me.
Now, was it shear Luck that I ended up with the most well balanced rear suspension I could have ever hoped for................
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Re: Don't box your L body subframe, here's why.
Now I'm curious how to approach my GLHS. The front bar is a shortened 1.25" Daytona unit with heim joint end links. This has been done and sitting on the shelf for years waiting for the car to be done. My rear axle is sitting with a pile of other parts waiting for powdercoating, but I need to decide on the rear bar before doing so. Stock bar by itself? Stock bar with the PB rear bar added? Cut off the stock bar and just run the PB bar? FWIW, the rest of the suspension will be rebuilt factory Konis with the LRE lowering springs and stock brakes.
Brakes may be upgraded in the future, but no plans for that yet.
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Re: Don't box your L body subframe, here's why.
On a side note, one of the first things I noticed about the new Fiesta ST is that their "twist beam" rear axle design is incredibly similar to our L-bodies, as was the GM J-body design from the '80s to early '90s. So there has to be some benefit to the design.
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
supercrackerbox
Now I'm curious how to approach my GLHS.
1-1/8 inch poly bar with no stock sway bar.
http://polybushings.com/pages/swaybarLrr.html
Quote:
Originally Posted by
supercrackerbox
So there has to be some benefit to the design.
It's CHEAPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP!!!
Look at the high cost FWD cars and see who uses this design.
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
tryingbe
It's CHEAPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP!!!
Look at the high cost FWD cars and see who uses this design.
Fair point. But it seems to be an effective alternative to a true independent rear suspension.
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
supercrackerbox
Fair point. But it seems to be an effective alternative to a true independent rear suspension.
I would argue it's just cheaper to make and assemble.
Neon.
http://i66.photobucket.com/albums/h2...spension-1.jpg
Saturn S series.
http://www.saturnfans.com/photos/dat...-stockpipe.jpg
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Re: Don't box your L body subframe, here's why.
My Insights and Prius use a very similar design to the l-body piece. Ground clearance is definitely better with that vs the K-car type.
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Re: Don't box your L body subframe, here's why.
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Re: Don't box your L body subframe, here's why.
So, is there a consensus as to the best design for the rear suspension on a front wheel drive car?
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Re: Don't box your L body subframe, here's why.
Fully independent suspension would be my guess.
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
tryingbe
Fully independent suspension would be my guess.
Bingo
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Re: Don't box your L body subframe, here's why.
that neon rear suspension looks very cost effective - at least from a manufacturer's point of view
even if it does look like it's made outta some twigs (or because)
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Re: Don't box your L body subframe, here's why.
Fully independent yes, but some kind of anti-roll mechanism has to be a part of it too, right?
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Re: Don't box your L body subframe, here's why.
The only advantages to a fully independent suspension on a FWD are slightly better ride, NVH, weight (to a point), better dynamic chassis control, and bragging rights...maybe more room to route exhaust, etc. In some instances it can help performance, but from an autocross or road course perspective the twist beam and semi-trailing arm suspension set-ups have proven to be just as effective and can perform just as well or better than a full IRS. Remember, once you jack the inside wheel off the ground, no matter what type of suspension, you have 100% weight transfer. This will happen to ANY FWD car with a high degree of rear anti-roll stiffness...which most high performance type FWD cars do to help front traction and turn-in.
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
tryingbe
Be careful, that was my exact setup.
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Re: Don't box your L body subframe, here's why.
stone cold stock the shelby charger suspension worked great when still only 3-4 years old
really good rear shocks were a must
many were already dead by then
I didn't have issues with it wanting to rotate at anything under 50 mph going around a decient curve in an on ramp
but turn left or right at speed onto any side street on 3 wheels - yeah no problem
.. unless your sitting in the back and not wearing a seat belt
lolololol
my buddy ... the thump he made as he hit the driver's side rear interior panel ...
though I did learn to keep the tires with the most tread on the back as the worn ones will let the rear rotate really badly in the rain or wet as there's simply not enough weight to keep the car in place without the extra tread to grip with
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
Dr. Johny Dodge
though I did learn to keep the tires with the most tread on the back as the worn ones will let the rear rotate really badly in the rain or wet as there's simply not enough weight to keep the car in place without the extra tread to grip with
This is what happened to my GLHS...
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
johnl
Fully independent yes, but some kind of anti-roll mechanism has to be a part of it too, right?
Correct. More important on the rear then the front ;)
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
Shadow
Correct. More important on the rear then the front ;)
That really depends on spring rates, where the weight on the car is and what the cars intended use is.
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Re: Don't box your L body subframe, here's why.
Harry, From a knowledge point I'm glad you welded your suspension, proved it would crack and you didn't crash!!!
As the L body is semi independent, the U channel is the part that must be able to twist.
Welding solid prevents it from twisting, and that left the ends vulnerable to cracking as they weren't designed to twist.
Some folks U bolt flat steel to the U channel to allow some twist, especially if the U bolts are strategically placed.
EG: Fewer U bolts, spaced farther apart, more twist, many U bolts close together, less/no twist.
The rear anti roll characteristics can be fine tuned by adding/removing U bolts.
Same thing might be accomplished with welding the flat stock, many close welds= cracking, fewer welds, further apart, ...
Due to the design, there are very strong forces acting on the channel that joins the semi independent trailing arms during driving and cornering. The channel needs to be able to twist somewhat, but as mentioned, the twisting can be tuned.
SHADOW!!!!!
A while back Rob decided to lighten his rear trailing arm assembly. I cautioned him about these very strong forces acting on the channel, but he assured me his calculations that came from an Engineering background were valid.
Everyone knows the L body assembly was overbuilt and could be lightened extensively and that's what he did. He might post some pics, but from memory its full of holes!!.
He later bragged about transporting a few engine blocks and a bunch of other things in his Charger with no ill effects.
So, in the end, Harry has proven Shadow to be correct, lighten everything up concerning the assembly, allow it to twist, no problem.
Remove the ability to twist and even the overbuilt stock assembly will crack on each side of the now nontwistable assembly.
Thanks
Randy
PS:
Anyone know the interchangeability of L body rear suspensions? A guy on another forum has a damaged 1988 Horizon wants to know if a 1983 Horizon rear suspension assembly will fit. He posted it looks similar but not the exact same, and I cant find any info or pics.
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
Pat
That really depends on spring rates, where the weight on the car is and what the cars intended use is.
Yeah yeah, I posted that way too fast with Not enough info;
My post was in reference to my own experience with the Charger. The missing info is the Charger has Slowes tubular cross member and DJ's tubular heim joint A-arms. I'm running 350"/lb springs up front and stock shortened springs/ shocks rear. With that combo and my modded rear trailing axle and the addition of the PB 1" rear anti sway bar, the Charger Destroys the handling characteristics of its former self.
Add to this the fact that I am comparing the Charger With front anti sway bar vs it now Without! ;)
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
GLHS60
SHADOW!!!!!
A while back Rob decided to lighten his rear trailing arm assembly. I cautioned him about these very strong forces acting on the channel, but he assured me his calculations that came from an Engineering background were valid.
Everyone knows the L body assembly was overbuilt and could be lightened extensively and that's what he did. He might post some pics, but from memory its full of holes!!.
He later bragged about transporting a few engine blocks and a bunch of other things in his Charger with no ill effects.
So, in the end, Harry has proven Shadow to be correct, lighten everything up concerning the assembly, allow it to twist, no problem.
Remove the ability to twist and even the overbuilt stock assembly will crack on each side of the now nontwistable assembly.
Thanks
Randy
Bro, ixnay on the ics pay. Otherwise Someone is bound to have a hit Say it Fay!
Know what I say!?
Oh, and by the way;
That was 4 engine blocks and 3 cranks and a bunch of odds and ends like TQ plate couple of heads ect ect + my wife and myself with luggage for the wknd. + Don't forget the spare/jack and I even think I squeezed and air tank in there. ;)
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Re: Don't box your L body subframe, here's why.
This evolved into a great thread.
Not saying anything new, but on the track with stock GLHS spring rates and anti-sway bars but with Koni coil overs, I found that rear induced oversteer, the rate of rear rotation, was critical to be able to get the front wheels pointed straight, straight down the next straight, as early as possible, so that they were pulling the car and NOT steering it. Rear ride height and tire pressures were key puzzle parts in getting the car to rotate at the right rate, not so fast as to force me to slow the car down on the entries and not so slow as to delay going WOT. Credit to Craig St Pierre who taught me "get the wheels straight before you mat it."
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
GLHNSLHT2
Be careful, that was my exact setup.
Would you care to elaborate?
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Re: Don't box your L body subframe, here's why.
I know this is a slightly older thread but tons of fwd cars used and still use semi-independent rear suspension.
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
thedon809
I know this is a slightly older thread but tons of fwd cars used and still use semi-independent rear suspension.
Exactly. They are a twist beam semi-independent design. They are designed to flex. It isn't like someone here discovered it by accident....lol.
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Re: Don't box your L body subframe, here's why.
On my GLHS Omni autocross car, I used 1" rear bar, 1-1/8" front bar....
the mopar autocross springs with a coil cut off all round. With stock Koni's.
I adjusted handling with tire pressures and shock adjustment.
Won a lot of autocrosses!
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
Johnny
On my GLHS Omni autocross car, I used 1" rear bar, 1-1/8" front bar....
the mopar autocross springs with a coil cut off all round. With stock Koni's.
I adjusted handling with tire pressures and shock adjustment.
Won a lot of autocrosses!
Well I've got that rear bar that I just bought from you, and I'm taking my rear axle in to be powdered this week. I just want to make sure I'm doing the right thing when I cut the stock bar off.
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Re: Don't box your L body subframe, here's why.
OR leave it on and see if you like it that way first. You can always take the stock one off if you think the over steer is too much.
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Re: Don't box your L body subframe, here's why.
Quote:
Originally Posted by
GLHNSLHT2
LOL. What size PB rear sway bar did you end up with? I put the 1 1/8" on my GLHT and cut the stock bar off. Under 30mph stuff was a lot of fun. Over 30 MPH was dangerous oversteer. It snapped around on my entering a freeway off-ramp when I had to nail the brakes to not hit the car in front who decided to take it 20MPH slower than needed. Thankfully I had the skills to catch it and keep from hitting the light pole.
I ran into a similar situation with my Reliant-
Installed the rear control arm from my old '86 Daytona into the car which had been boxed in. Problem being the Reliant is far lighter in the back than a Daytona! On a twisty back road the car would grip... grip... grip..and then.. ROTATE!
Did a complete 180 degree spin with utter lack of control, car gave no warning at all. Once one tire breaks loose its party over!
Taught me a good lesson and by the grace of God did not cost me a car or the life of someone coming the other direction.
Gary