gears grind???
 

When i put it up past 4 thousand RPMS only in first the gears grind unless i double clutch it. What do you think the problem is and how much would the fix be.

Synchro
 

Your synchro's are toast. Depending on which stang you drive (and which tranny it is, T-5, 3650, etc) and its age, the repair may be available under warranty or by TSB (technical service bulletin). There's a TSB out for this problem - search www.allfordmustangs.com - they have a tsb listing.

If you're out of warranty and out of luck, the repair will likely cost over $700 at a dealer, or a little less at a transmission shop. They have to remove the transmission, crack the case open, and replace parts - never a cheap road.

If you have it done, I recommend you replace the bearings (esp. the throw-out bearing) at the same time. If you've got a lot of miles on the car, consider an upgraded clutch - little additional labor (though the parts will cost you about $200 or so - replace the flywheel too - oe is a cheap item at $29, less than resurfacing the original).

Finally, be sure they check out ALL the wear surfaces in the tranny - 1st is usually the first to go, but the 2-3 synchros are often not far behind...

If the whole tranny is essentially gone, probably cheaper to replace with rebuilt aftermarket unit - if you've got lots of money, you could even upgrade to a 6 speed...

luck

tripleblack