It sounds like your clutch is not fully releasing.   When a transmission is "breaking in" it will feel a little notchy in shifts but it should never grind in any gear.  You mention that it is and this indicates that you could damage the transmission if you don't resolve the problem.  When a clutch does not fully release it can be due to usually two things - bellhousing alignment or an improperly adjusted clutch.  You didn't mention what bellhousing you are running.  if it is a Ford factory unit, it should be good but should doesn't mean always.  If it is aftermarket, it should be checked to make sure it is square and true to the crank.

The first test I would suggest is easy.  Find a gradual slope and stop the car nose pointing up.  You want the slope to be gradual so that gravity doesn't affect the test too much.  Turn the engine off.  Hold the brake, pop it in neutral, and release the brake.  It should easily roll backwards.  I guess you could do it rolling forward if you really had to.  Next, hold the brake, put the trans in 4th gear.  Do not press the clutch yet.  Release the brake and the car should not roll.  Slowly - and the key is slowly - push the clutch pedal down and note when the car starts to roll.  This is the point where the clutch just starts to release.  If the pedal is just and inch from the firewall when it starts to release, it will not shift properly because it is out of adjustment or you do not have adequate travel if you are using hydraulics, for example.  If you have several inches of travel left when it starts to release, this would potentially show an alignment problem, or a mechanical or installation issue with the clutch.  Report your findings on this test.

Their first test is essentially the same thing.  Lift and support the back of the car.  Put the trans in 4th and get a second person.  Have the person fully depress the clutch pedal .  Crawl under the car and rotate the driveshaft by hand.  If you have limited slip and rotate the tires the mechanical advantage from the large tire diameter won't show drag very well.  You should be able to freely rotate the driveshaft and the only drag you might feel would be from brakes if you have drums,  Have your helper pop it into neutral and repeat.  The effort should be slightly easier because you are not rotating the clutch disk or the rest of the transmission.  If it is difficult to rotate in 4th gear, this can also point to an adjustment or alignment problem.  You can repeat the first test.  Have the person put it in 4th and put load on the driveshaft.  Have them slowly depress the clutch until you can turn the driveshaft and have them note the pedal position.

Test 2 from them shows the same thing.  If the tires spin when you are in first gear the clutch is not releasing fully.  In fact, you may find that it will be difficult to even get it in gear with the wheels in the air.  You might have to start it in gear to avoid a clash.

You do not need to break in your transmission.  You need to sort our your clutch or you will break your transmission.

BTW - If the transmisson/bellhousing is misaligned with respect to the crank centerline the input shaft of the transmission will be cocked at a slight angle.  When the clutch is depressed the edges of the clutch disk will still be making contact with the flywheel and pressure plate essentially opposite one another and the clutch will effectively still be engaged.  One symptom of this condition may be a clutch that chatters a bit when it is engaged.  The input bearing to the transmission does not like misalignment so not only could it make it difficult to engage but you will prematurely wear that bearing.

Last edited by GPatrick (10/30/2019 10:58 AM)

i follow this interesting post because i can learn something about T5 . I realized some difficult to engage gears ,  up and down . It grinds a little only at low rpm . Sometimes happen to drive hard , but quick gearing seems iimpossible at high rpm .  When i was young dad explain me how to change gears in old cars , making a double press twice on gas pedal during the change of gear . We refers at this move . as " the double " . This was on cars without the sincro on gear . 
I am little wonder about grinding with this new t5 and also when referring to misalignment . 
The block holes for bellousing are fixed , the bell has no slot to move to center it . 
The transmission has no slot to move to center it , so how can be that someting is not aligned ? there is also one pin to be sure that bell goes exactly there . 
When i bolt up the clutch i used the tool came with to aligne clutch and flexplate, then trans slide in very easy . 
What is an improper adjusted clutch  '?  refers to linkage not adjusted , or something to do with clutch and pressplate ''? 
Mine is new , open correctly , but not sharp on gearing and as sayd need to operate at low rpm . 
Thanks ! 
 

Last edited by Alessandro (10/31/2019 8:48 AM)

GPatrick wrote:

There are offset dowel pins that allow you to re-position the bellhousing.   A dial indicator is affixed to the flywheel or crank and the bore and face of the bellhousing is checked for excessive runout.   The typical specs are that misalignment of the bore should not exceed 0.005" or 0.010" TIR.  If the runout is greater than 0.005" you would install offset dowels and position them to move the bellhousing accordingly.  If you have a factory bellhousing, they are usually quite good.  Aftermarket bellhousings can be off by quite a bit in some cases.  Most manufacturers of the aftermarket bellhousings will state in their instructions that you must measure, and if necessary, correct any misalignment.  Grinding is most often caused by an incorrectly adjusted clutch linkage.  Try some of the checks in my first post as a quick way to see if you have issues.  If it is always difficult to get it into first while sitting, press the clutch and drop it into 4th gear first and then move over to first.  But ultimately you need to correct the clutch issue.

With lucky my bellhousing comes from toploader swap and is ford + adapterplate for t5 , 
About clutch i don't know if there are clutches deeper than other or dimension of  10 inch with pressure plate are all the same ?  i mean there are clutch that desengage more than others ?  
Before i did the swap i found as accessory one block to put under fork fulcrum   . This give less travel to do same job, correct ?  this block is necessary only with some bellhousing . is this useless or helpful ? 
Thanls again 
 

A T5 should never grind if everything is right.  Gear engagement should be very smooth as well.  The synchro design pioneered on the T5 was later used in the T56.  The T56 was smooth enough to be used by GM in the Corvette, Dodge in the Viper, and Aston Martin in the DB series.

So, if you're getting grinding something is off.  If you aren't using stock parts (e.g. not a Fox T5 bellhousing) I would be concerned that you have an alignment issue.  Adapter plates on bellhousings made for other applications seems like a place where the alignment could easily go awry. 

Alessandro, we used to call that a "double clutch" in vehicles that had no synchronizers.  Clutch in shift to neutral, clutch out, clutch in shift into the next gear, clutch out.  Interesting that racing transmissions are often converted to dog ring shifting which eliminates the synchronizers.  Those can actually be shifted without the clutch.  On an upshift anyway.  Downshifts are a bit tougher, but for drag racing they rule.