on my 1970 mustang coupe automatic which i suspect has a c4 trans or whatever it came with stock. when i put it in reverse u hear a loud drop and bump like a gear drops into place it reverses fine but is that normal? it doesnt do it in any other gears

 

When was the last time you changed the fluid in that tranny? It sounds like the reverse bands aren't getting enough good lubrication. To do it right, it takes about 16-20 quarts of Type F fluid to change the entire system. If you need to know how to do it, get back.

 

Ya may want to also jack up the rear, set the emergency brake, then get under the car and turn the driveshaft to see how much play there is.

You should also use it as an opportunity to check the U-joints & grease in the diff. From what I have seen, this is the most neglected fluid level to get checked. I'm not saying the level should be low enough to cause the problem, just a preventative check.

Always check the Free & Easy things first!

 

yea i think it may be the differential or the u joints because the transmission is fresh full n red so do u know any where where i can get a diagram of how to greese the differential and add fluid and how much play should their be in the driveshaft?

 

There will be a plug that you remove from the diff housing. You will fill it so the grease comes up to the bottom of the hole where you removed the plug. Do not over fill this cause it will cause grease to leak out the axle & pinion seals. More isn't always better!!!

It is very important you use the correct grease for your diff type. If it's a limited slip, you need special lube for it. If you put regular grease in that type of unit it will distroy the disks in it. Just write all the info down exactly as it is on the tag and we can figure out what type it here or you can check with a local parts store or Ford dealership.

How many miles are on the car? To be honest with you, unless it has other issues, I would check the grease and not worry about it unless it gets noticibly worse.

To get an exact check of the clearance on the ring/pinion, I think it would have to be taken out to be checked with a dial indicator. I can't remember how many 1000's of an inch it has to be within to be considered normal.

You may also want to check your curb idle to make sure it's isn't too high. That will magnify any problems further back.

 

Might it have a shift kit?
When a u-joint breaks, bad things can happen...