T5 Blocked Downshift

Hey Guys

I am trying to determine what may be causing some blocked downshifting issues I have been recently experiencing

The set up:

Volvo 240 - B230FT
Master Cylinder - Centric PN 136.39000 (1 YO)
Slave Cylinder - Centric PN 136.39002 (new and fully bled)
Clutch Fork - Standard Fork from a 740 hydro setup Shimmed
Flywheel / Clutch Yoshifab Billet Flat Flywheel FX250 Clutch
Trans - Tremec T5 newish
Adapter -DeeWorks
Fluid -Tremec HP-MTF

The issue:

Occasionally when trying to downshift from 4th to 3rd I am unable to make the shift. It almost feels like something is blocking it. I have to re-engage into 4th then try again.

This seems to only occur when it is hot out (+30?C / 85?F) and I have been driving for a while. It also only seems to happen at lower engine speeds. Mostly prevalent when downshifting as you would when coming to a stop. High speed downshifts do not seem to be a problem.

Once I had this condition when downshifting from 5th to 4th. I have never experienced it in any other order (3rd -2nd, 2nd - 1st) Upshifts are all smooth and complete without issue.

I do not have any grinding when upshifting into any gears. Nor is there any grinding when shifting into reverse.

The issue is not easy to replicate and sometimes it occurs repeatedly where other times it is completely fine.

I have about 0.8" of slave cylinder travel and the pivot ball on the clutch fork is shimmed out quite a bit (don't know the exact measurement) but the fork isn't perpendicular to the slave, it is angled slightly forward.

When the system is at rest I can push the slave in about another 1/4" so it isn't bottomed out.

My thoughts are I am not fully disengaging the clutch and I need to shim the pivot ball forward a bit more (mil or two) but I don't want to overtravel the release bearing to the pressure plate.

I was curious if anyone else has experienced something similar.

Kinds of sounds like a small issue with the syncro catching? Not the clutch dragging.

My T5 would balk on 1-2 and 2-3 shifts when driven hard. It just wouldn't go past the blocker into gear, once you'd hit that issue you had to back off, pause, then try again. Not an issue with the clutch, and not an issue when driving normally.

Ya, sounds like bad syncros, you might have to double clutch it. My T5 won't up shift to 4th without double clutching since the syncros are bad. I knew this when I bought it but only paid either $75 or $100 can't remember if I haggle or not.

What fluid in the trans? That can make a pretty big difference. They were designed to run Dexron III, but the current run of the mill Dexron VI that is 'backwards compatible' is actually quite a bit thinner so it can help meet CAFE standards. Going back to something just a little thicker may help the syncro's out a little.

I had some kinda notchy shifting in mine with Castrol Dex VI, moved over to Redline High Temp ATF which is a Dex III compatible, higher viscosity (much closer to Dex III standards) and it did help out a bit.

gsellstr said:

What fluid in the trans? That can make a pretty big difference. They were designed to run Dexron III, but the current run of the mill Dexron VI that is 'backwards compatible' is actually quite a bit thinner so it can help meet CAFE standards. Going back to something just a little thicker may help the syncro's out a little.

I had some kinda notchy shifting in mine with Castrol Dex VI, moved over to Redline High Temp ATF which is a Dex III compatible, higher viscosity (much closer to Dex III standards) and it did help out a bit.

Click to expand...

I have been running Tremec HP-MTF since new. I did flush it once after my initial break in.

The box has about 3k miles since I installed it and I would be pretty shocked if the synchro's are toast.

I took a short video of my cycling through the gear and releasing the clutch in neutral then cycling to another gear

What strikes me as odd is when I shift it into gear you can see the driveshaft move slightly.

See the video here

https://www.youtube.com/watch?v=caNhMRZwbLU

That's just the last bit of momentum from the spinning clutch disc/input shaft as it is linked to the output shaft.

I wonder if maybe you've got a pilot bearing that's not handling heat well? It could be slightly binding, so the input shaft is still retaining speed, won't slow down as much as it needs to?

Have you tried getting it to the problem temp, get the car on stands, have someone in the car put it in each gear while you turn the driveline underneath? That would be an easy way to see if there's something binding on the input side when it's hot.

Or just try putting it in reverse when it's hot. That's a good indication of any slight clutch drags.

gsellstr said:

I wonder if maybe you've got a pilot bearing that's not handling heat well? It could be slightly binding, so the input shaft is still retaining speed, won't slow down as much as it needs to?

Have you tried getting it to the problem temp, get the car on stands, have someone in the car put it in each gear while you turn the driveline underneath? That would be an easy way to see if there's something binding on the input side when it's hot.

Click to expand...

I have not but the pilot bearing I used I got from a Ford dealer so I would assume its similar to the Timken FC65174 Pilot Bearing (If not the same)

JohnMc said:

Or just try putting it in reverse when it's hot. That's a good indication of any slight clutch drags.

Click to expand...

I actually tried this today and it lightly ground going into reverse each time.

The method I used wash clutch in ->1st gear -> neutral -> pause -> reverse

I recall from my Mustang days that this can happen if there is play on the main shaft instead the required pre-load.

So last week I pulled the trans to shim the pivot ball fork a little. I initially tried two washers (~3mm) but it put the fork to far forward to where I think the release bearing was in constant contact with the pressure plate fingers. I was unable to wiggle the fork at all when installed this way so I pulled the trans again and removed one washer.

I installed everything and the fork was slightly loose which led me to believe the release bearing wasn’t in contact with the pressure plate.

I re installed everything and have since been on a few hard runs with the car. I am pleased to say I get no more blocked shifts once the drivetrain is warmed up. I also no longer have the slight grind going into reverse if I allow a few seconds pause for the main shaft to slow down.

Another side note and real bonus.

The T5 is silky smooth. I mean it wasn’t bad after all the tweaking I did but there was still a narrow coast down drone at 3k RPM. No idea what I did to get rid of that but it is smooth like a a trans should be. I took my buddy for a ride the other other day and he couldn’t believe it had the same trans in it from the last time he went for a ride.

Thanks for everyone’s help and I’ll update this thread if anything changes but for now this thing is awesome.