Transmission

jczar · #1 (**permalink**) 05-02-2005, 10:12 AM

Yesterday, I just took my Cobra (unfinished) out on the road for the first time. Just down the road and back. Had the neighbors out on their porches on the return trip. What a thrill. I experienced some difficulties that perhaps someone could enlighten me. The C6 automatic transmission slips when trying to accelerate. If I go slowly it seems the transmission can keep up with the RPM's. It also makes a screeching sound. One other item is when I let off the accelerator the car wants to steer to the left. Possible alignment problem?

Thanks
John

blykins · #2 (**permalink**) 05-02-2005, 10:59 AM

Do you have a stall converter? Checked tranny fluid?

Have you had the car aligned?

jczar · #3 (**permalink**) 05-02-2005, 12:19 PM

I just have the standard power converter. I did check the fluid before and after the run and the fluid level is fine. I did not yet get the alignment which probably explains the car pulling to the left. Thanks for your imput.

John

blykins · #4 (**permalink**) 05-02-2005, 03:57 PM

New tranny or used? When you pull the tranny dipstick, does the fluid smell or look burnt?

jczar · #5 (**permalink**) 05-03-2005, 07:00 AM

It is a used C6 tranny. I had the transmission cleaned and checked by a professional before installing. I did replace the fluid with a synthetic transmission lubricant.

mickmate · #6 (**permalink**) 05-03-2005, 07:11 AM

Is the vacuum modulator hooked up and the kickdown cable properly adjusted?

jczar · #7 (**permalink**) 05-03-2005, 07:23 AM

Nickmate,

I'm using the Lokar kick down cable. I have it adjusted on the carburetor to where I really need to stomp down on the accelerator before it kicks in. I have a vacuum hose running from the intake manifold to the modulator. There is a screw inside the hose fitting of the modulator. Could this screw need adjustment?

HighPlainsDrifter · #8 (**permalink**) 05-03-2005, 03:21 PM

Hi,
The trans NEEDS full time vacuum at idle[under carb throttle plates or in intake manifold]

Make sure you have not used ported vacuum.

Good Luck,
Perry.

mickmate · #9 (**permalink**) 05-04-2005, 11:27 AM

Perry makes a good point make sure it is full manifold vacuum. I would get a good inch pound torque wrench and the specs for the bands and check them before I drove it any more. Check that before touching any other adjustment screws.

jczar · #10 (**permalink**) 05-16-2005, 07:55 AM

Thanks for the input guys. I finally made it back to the garage this weekend and tried your ideas. It didn't make any difference but now I know why. I don't think my problem was the transmission. I tried to drive the car up a ramp and it could not make it to the top. I had my wife try driving it up the ramp while I looked under the car and realized the drive shaft was turning but not the wheels. I believe my problem is the differential slipping. It is a posi differential. Any ideas what to do?

Tim Brewer · #11 (**permalink**) 05-16-2005, 09:28 AM

Let us know what rear end you have, 8.8 or 9? A posi rear requires an additive to make it not slip. Some newer fluids will already have it mixed in , but not all. Either way you must have it.
Also, you do have about a 80-90 wt gear oil, right? The stuff that stinks.
Tim

jczar · #12 (**permalink**) 05-16-2005, 10:21 AM

Tim,

I have a Ford 9 inch rear. I'm using a synthetic 75W90 lubricant that already has the additive. Is the function of the additive for the clutch plates to operate or is it just for anti-rattle?

John

blykins · #13 (**permalink**) 05-16-2005, 10:38 AM

It's a friction modifier. It increases the friction in the oil so that the clutches will stick better.

Is it a new differential or used? It could be shot.

mickmate · #14 (**permalink**) 05-16-2005, 10:49 AM

Hey John, be real careful with the missus driving and you doing the undercar stuff, that's the stuff domestic disputes or worse, injuries are made of. The type of slipping the posi will stop is from one side to the other. If the drive shaft is turning and the wheels aren't then the differential is toast. Remember the driveshaft will turn about 3 1/2 turns for 1 axle turn so it may be a little deceptive to look at.
Be careful!

jczar · #15 (**permalink**) 05-16-2005, 11:28 AM

This is a rebuilt posi. It has new clutch plates and seals. I have a 4 ounce bottle of the modifier. I could add this to the unit to see if it will solve the problem.

RallySnake · #16 (**permalink**) 05-16-2005, 12:55 PM

JCzar,

The positraction part of the differential only comes into effect when the tires are slipping on the pavement. If there is loss of motion within the differential, there must be some seriously broken parts. Could be an axle shaft or spider, if it were a ring or pinion gear, you would hear some bad grinding sounds.

At least rear end parts are a lot cheaper than transmission parts, good luck!

Paul

jczar · #17 (**permalink**) 06-20-2005, 01:10 PM

Just an update...I pulled the posi-traction out and had it checked. The gears weren't set correctly. The posi is now back in and it runs great. Thanks to all that gave me suggestions. You guys and gals are the best.

John