Ouch. The results of a tired chromoly frame...

[K-fab]

My old Tazcar is getting tired. *It's almost six years old, it's seen a bunch of races and thousands of miles across the desert floor. *The desert's not nice to equipment either.

When I did the RX1 engine transplant, I found a crack all the way through the main rear cross tube right by the inside mount of the left trailing arm. *I looked for similar cracks on the other side but didn't find any.

Today I finally get a chance to take the old Dez out into the desert and throw some roost. *It's been almost four months since I've had the chance to play in it.

The Dez has new rear sneakers - ungrooved BF Goodrich A/T's. *They are great when grooved, but they don't last worth a squat. *I took some advice from this board and tried them ungrooved. *They SUCK!!! *I was having major issues keeping the back end of the Dez behind me. *Especially under braking. *Turn into a corner and just start to lay into the brakes and I'd find the back end sliding. *Fortunately, and interestingly enough, they never got out of hand - they'd just let go and start sliding, but they'd never spin me out. *The more time I put on them, the more I realized that they were very predictable, but no traction was to be found.

I think I may try the BFG's up front and go back to the Goodyear Wrangler A/T's in the back. - if this still give me too much front end, I guess I'll go back to the Goodyears all the way around. *Those things wear like steel while the BFG's wear like, as Rorty said, pink erasers.

So about 15 minutes into my raid on the desert, I come across what looks like it's a small pond when it rains out here. *It was sort of egg shaped and the banks were fairly steep - it made a great little oval course. *A dozen laps each way was fun. *When I left the area, I did sort of a left hand slide/jump out of the bank. *At the top of the bank was a small rut. *I dropped the rear right wheel into the rut and it slammed the car pretty hard - made the chassis try to roll over a bit. *It wasn't a really hard feeling hit, but it was solid enough.

Nothing felt tweaked or broken and the rear wheel still looked good in the mirror.

I went on away from the pit area and was having a blast. *I follow a horse shoe shaped trail that leads me away from the Carefree Highway out towards the mountains and then it doubles back on the other side of a wash and comes back to the highway.

As I got to the highway I turned around to run back down the train and I suddenly found that I had one wheel drive. *The car was pulling right, so I knew I'd lost the right side drive shaft or CV or something. *I never felt anything let go, it just suddenly had one wheel drive. *WTF now???

I hopped out and checked - the right axle had pulled out of the outer CV, the trailing arm was sitting at a funky angle. *Closer inspection showed that the frame had broken at the trailing arm inner mount and, at the time,the only thing holding the piece of the frame to the car was one tube.

I was lucky enough to be able to just cut across the wash and go straight back to my truck - probably 2 - 3 miles instead of 10. *I just drove really slow.

By the time I got back to the truck, the only thing holding the trailing arm on the car was the nerf bar.

Driving the car up into the truck was about the only sketchy thing. *One wheel drive up a set of ramps into fourty inch high box van is not fun. *Get the speed going, launch into the truck, nail the brakes. *Got it on my first try. WHEW!!

Anyhow, here are pix of the damage. *I'll have to pull the car completely down to the frame and Neil said we could just throw it on the jig table again and weld new stuff on. *I think he has a two stroke (old style) Tazcar chassis upstairs - it may be easier to just transfer all the stuff into a new old chassis and modify the chassis into a desert car. *I know what to do now. *I'll have to redo the engine mounting again, though. *Arrrgh. *It won't be easy either way.

I believe that the reason for my cracked and torn frame is just what you hear about chromoly - the stuff is great until it's been worked hard for a while. *Then it becomes brittle. *None of the tubes tore like mile will - they all ripped/snapped cleanly. *Check out the one engine mount - it pulled a hole out of the tube. *I guess I got good penetration on that weld, eh?

[hero_saku39]

Ouch........my pressureized frame idea would have come in handy there...sorry your ride was cut short.

[masterfabr]

I assume you made yourslf some extra work going out playing instead of working,huh? That'll teach ya!But in a way you have sparked the controversy of 4130 or mild *into a fire again.First let me say that rorty and others have me convinced that for these small to mid size cars mild is plenty strong enough with proper triangulation.Ok most of us agree on that point I think.But for me I don't buy into the cromo gets brittle *or fatigues easily thinking.As far as I'm concerned the problem is due to just one of 2 causes.Either poor welding practices or the builder used thinner wall cromo because the thinner cromo has the same or equal strength as the thicker mild.For drag cars that is fine but for offroad I feel you should use same wall thickness cromo or mild.WHY?!?!?!?First IMO you need the mass of the thicker tube to resist the flex(cromo is a spring steel afterall) that causes the work hardening that occurs with the thinner wall tube.You don't save that much weight and you sacrafice a lot of durability.Second,welding the thinner tube will affect the thinner tube to a much greater degree metallurgically than the thicker tube.I've got litterally hundreds of miles on the dragster,All .058 wall 4130,215" wheelbase that weighs 1450#.I have never cracked a tube EVER and that with datalogged VERTICAL *G's of 5 even 6 at top end.This car has been 1 1/2-2 foot off the ground at 180 mph on the bumpy strips we have here in Kan/Ok/Mo/Ark MANY times. That wall thickness is approx equal to .095 mild but there is NO WAY I'd use that for offroad.See what I'm getting at?Fabr

[bdkw1]

Cool!

At least it doesn't look like you bent the shock shafts.

[K-fab]

Master - you may be on to a good point.

The tubing is all .065. *It's too thin for it's application. *Plain and simple. *Jay and I discussed this just a while ago.

I'm thinking I may talk to Neil about one of the old mild frames he has and rebuild the old gal. *It would make a wonderful pre-runner.

[Philabuster]

Damn. *

At least you got to put a few desert miles (with video!) on it after the four-stroke heart transplant.

I'm looking forward to the ressurection.

[renegadespec1]

K fab,
sorry to hear bout taz,
Chro-mo does work harden, I'm surprised you got as many years/milage you did out of the chassis! I stayed out of the chr-mo debate just for the plain fact that quite some time ago I built a couple of OVAL track buggies out of some chr-mo I scored for cheap...tig welded them up...Yes they were lighter, and seemed more rigid than they're mild steel counterparts...neither one finished a second season..no one got hurt but they both suffered catastrophic failures...(control arms tearing out going into the turn) the resulting endo's were cool to see...I guess...wasn't so cool in the cockpit! The cages started to tear apart in the ensueing crash... Those were the 1st and last built out of chro-mo...That's just my experience with the stuff...Chro-mo has it's place in buggy construction, the main chassis isn't one of them...

[masterfabr]

Your experience only highlights my opinion precisely.Those frames used thinner tube to save weight.That IMO is wrong for any offroad car.You shouldn.t use thinner cromo to save weight.You should use the same wall as mild requires when using cromo to gain strength not thinner to save weight.Therein lies the problem.IMO, cromo is not the problem,it's the builders poor choice of using too thin a wall to start with.fabr.

[renegadespec1]

The breakage looks exactly what mine looked like only mine was on the right front

[Bullnerd]

Heres the real problem," Turn into a corner and just start to lay into the brakes".

You've got your cornering sequence all confused.

Its brake, then turn, then mat-it!