Alright, I think I'm having an issue with my transmission but I'm hearing a few different possibilities of what it can be. One thing that I definitely know nothing about is transmissions.

A little background on my car first. It is a 78 Z28 and has a 468 bbc making around 650 hp and 640 ft lbs of torque with an M22 4 speed rockcrusher with a 9" rear end that is tubbed and narrowed with 4.88's.

My problem - I think something is either wrong with 4th gear or my clutch. I am being told it's the clutch but I just don't see how. When in 4th gear and 4th gear only if I nail the gas the car begins to pull but then it seems as if the R's are going higher than and the car isn't pulling as hard as it should be. (Almost like it's slipping a little bit and pulling at the same time). In 1st, 2nd, or 3rd gear there is absolutely no problems at all and the car pulls hard as all hell as it always did. If I don't floor the pedal in 4th then there is no problem or slip. The car accelerates smoothly. It only appears to be when I nail the gas in 4th gear. Reverse is fine also, there is are no problems with reverse. There are no problems shifting into any gears, the clutch doesn't feel soft or hard (the pedal feels normal), I don't smell the clutch burning at all, and I have no grinding noises. I'm a little bit confused by this but maybe someone that knows transmissions better than me can help. Thanks

John

 

Sure sounds like the clutch, and more likely a pressure plate that's not strong enough for your torque.
Why in 4th gear? I'm sure you notice that if you were to leave it in 4th and slow the car way down, then accelerate from there, the engine will bog down more than if you downshift. Being in a higher gear at slow speeds puts more force upon the clutch as it tries to get the weight of the car moving. Another thing is that some pressure plates have small weights that are allowed to slide outward and push against the back of the plate as the engine speeds up. That applies more clamping force on the pressure plate as the rpm's climb, something it wouldn't be doing as much in the lower rpm band. You probably just need to be downshifting out of 4th sooner than you have been.