BANG! goes the C6

Toivo · #1 (**permalink**) 11-16-2001, 07:07 PM

Testing and tuning the engine.
This involved getting the engine under load and at high RPM's.
So, putting the C6 in 2nd and accelerating the car, suddenly all forward gears are loss.
Reverse still works.
After loading the car on a trailer, and bringing it back, it seems some forward gear returns, sort of. Jerky, seems to be locked BETWEEN gears, like two bands engaged or something (and I don't really know that much about transmissions...it just felt like it was hunting back and forth between gears).
I'm for just getting a whole new valvebody and replacing it.
Does this even sound like it MIGHT work/solve the problem?
What could cause this?
The trans is basically a 1968 original, it does have a new front pump, converter and pan, and the fluild looked good.

Any ideas?

Thanks

poorboy · #2 (**permalink**) 11-17-2001, 10:55 AM

Toivo;
From your discripson I would pull it out and have it built. Sounds like it has overheated and damaged the clutch packs and drums.

Poorboy

427sharpe · #3 (**permalink**) 11-17-2001, 11:12 AM

You've lost the main band and/or the low governor servo. Means a total rebuild (sorry....) because those damned itty-bitty metal parts are now spread out throughout your gearbox. Maybe God intended Cobra's to be manuals. There is a story in Brock's book about an employee testing one of the first slushbox Cobras "at speed" on a hwy in So Cal and having this happen--car went into low and locked the rear wheels and sent the poor sob spinning down the highway. No hits, no damage (other than stained seats I presume). Guy refused to drive another. Today, they make a reinforced hi-performance clutch pack, servo and sun gear--B&M I think. Not too expensive. Good luck, and be careful!

Toivo · #4 (**permalink**) 11-17-2001, 08:23 PM

we're still not sure what happenned.

maybe I didn't describe things as best as possible.

The trans didn't lock up. It just lost all forward gears. Reverse still works. After the pan was pulled this morning and the contents examined, no major metal was found. Did seem to have a few shavings and or moly lube mixed in the fluid.

Can someone explain how a line lock would work in a C6?
It's almost like that's what's going on except the trans isn't locked up.

Again, could some permutation of blocked passages / locked plungers or whatever in the valvebody account for this?

427sharpe · #5 (**permalink**) 11-19-2001, 04:59 PM

When you lose the band or governors, the trans doesnt 'lock up', it loses whatever gear the band engages. In your case, I think you lost the low band because you lost all forward gears. May have lost a sun or planetary gear too. Only a teardown will tell. You can run a pressure diagnostic on the trans in the car if you have a 300 psi pressure gage with HEAVY DUTY 1/8" line with an 1/8" NPT fitting. The diagnostic pressure port on a C6 is just brhind the linkage that retains the backup light switch. It's a small hex plug. NOTE: DO NOT EXCEED 20 SECONDS TEST TIME IN EACH GEAR OR 2 MINUTES TOTAL TIME---YOU WILL BURN UP THE TRANS!!!!! Hook the gage up to the port, and measure your pressure readings at idle with the brake applied, than compare to the normal:
Neutral---50 to 80 psi
Drive 1 and 2--50-95 psi
Reverse--60-150 psi
If you do this and post the results, I will post the correct diagnostic flow chart to help you find the problem.

Toivo · #6 (**permalink**) 11-19-2001, 05:16 PM

Thanks for the offer.
I'm getting a 'new' (rebuilt) C6 to be delivered next week.
Built by someone who knows what they're doing (full roller, Kevlar, reworked valvebody).

The trans that blew was basically original and probably shouldn't have been behind the new engine (built for torque).

Further study/examination of the remains suggests the forward gear clutch went (fine abrasives mixed in the fluid...)

Anyway, the trans had a long and honorable life. Hope the next one lasts as long.