S-10 5 speed

Have Flathead motor backed up by a WC , S-10, 5 speed trans. While driving the trans shifts fine but once it warms up it's very difficult to put into gear. I have to shut the motor so as I can get it into a gear. I thought the fluid may be bad, so I drained it and filled it with DEX III. Any idea what I'M dealing with

 

Sounds like the clutch isn't releasing completely.
It was working fine?

 

. initially when I was first driving then as it warmed up it started to act up

 

What did it have for transmission oil in it before? ATF or Gear oil If it had gear oil you may be in for a transmisson rebuild or worse.
Do the gears grind or just not move after it warms up?

 

How long has the problem been there, has the gearbox swap just been done and just started, or slowly getting worse over time?
Is it hydraulic, cable or linkage release?
I know all of these suggestions are'nt relevent to your problem, but here's a few suggestions.
Others will probably chime in as well with more.
Worn, damaged, bent, cracked linkage?
Is the spigot bush/bearing binding up, not allowing the input shaft to freewheel with clutch in, at operating temp.. (lack of clearance/lubrication).
G/box input shaft bottoming out, against the spigot bush/ bearing when hot, or inside rear of crankshaft.
Dry clutch plate/input shaft splines.

 

Does it have a slave cylinder or Hydraulic throwout bearing.
Or cable ?
If hydraulic
Heat sinking ?
Do you know how to shift up or down with out the clutch while driving
wants hot ,
if you do that will more likely
Tell you if internal problem with transmission
Or clutch releasing issue
Throw out bearing ,slave cylinder, cable

 

Is a clutch related problem, probably just warn out or linkage problem. Also, if it's a hydraulic set up and the flywheel has been surface, it needs a shim between the flywheel and crank. Being its behind a flat head and there is some adapting going on, there is a good chance the clutch is not disengageing all the way. But it is in the clutch

 

Need to know if hydraulic or mechanical linkage.

 

try matching engine speed and road speed and see if the gears will engage easily that way....if it does, it would point to the clutch not fully disengaging

spigot=pilot

 

If its hard to shift with engine on, usually that's a clutch clearance issue. Clutch not fully releasing keeps pressure on the sync/blocker keeping them locked together.

Verify clutch clearance when cold and then again when hot.

Worn shift pads will have you punching the dash or elbowing the back seat. Unless the shift forks are bent, worn pads usually just increase shifter throw and sloppiness.

If it really is a WC the Dex II/ATF is correct for fluid.
But if it was rebuilt with br*** synchronizers gear oil is what will be needed. Fiber use Dexron.

 

Pilot bearing bad ?
Keeps the input spinning when clutch released.

 

If you decide to slide it back apart check the following.
1. Use a dial caliper on the OD input shaft of the transmission and the ID of the pilot bushing (mine has a bearing).
2. Visually check the back of the crank for a witness mark that may indicate the input shaft being a bit too long.

I took my transmission out last year after similar issues. I ended up t******* the input shaft about 3/8" and chamfering the end. I also turned down the input shaft with fine sandpaper that I lubricated with machine oil until I had a looser fit in the bearing. That took an hour or two but it was totally worth it. My flathead and T-5 have never been happier together.

What fits together cold may not be in their happy place once they reach operating temperature.

 

A little time consuming but maybe check the alignment/indexing of your bellhousing. What brand bellhousing-adapter are you using? Pretty good procedure here.

https://www.moderndriveline.com/proper-bellhousing-alignment-indexing/