6MT Clutch Frustrations: Diagnosis?

I have a 2014 4.0/6MT access cab with just under 70k miles. My frustrations with the clutch in the Tacoma have been building to the point where I need to find the cause of the problems. The symptoms are:

• Clutch pedal is numb. I am having a hard time finding the engagement point while driving. I also feel like the engagement point changes while driving (but that could be driver error). Like effort below, the feel is inconsistent. Sometimes I have good pedal feel, other times none.
  
• Clutch pedal effort is inconsistent. The temperature is starting to drop and effort when cold is higher. However, I have driven the truck a couple of miles with pedal effort being very high, made a 5-minute stop and come back to a light and smooth pedal. Also, a long highway drive will yield a light, smooth pedal for a period of time.
  
• Clutch pedal effort seems to be related to temperature. When ambient temps are 80-90F and above, the pedal effort is higher and pedal feel is worse. When temps are below 40F, pedal effort is high, but feel is OK. The sweet spot for temp in regards to pedal effort and feel seems to be 50-70F.
• Possible clutch drag/gear engagement issues. When pedal effort is high, gear selection can be difficult. Second and third gears are the worst offenders. Second can require a double-clutch on the upshift, especially when the transmission is cold. Third has required a double-clutch to get smooth engagement.
• I was starting to hear the release bearing chirp in extreme cold last winter. I have not heard the bearing in moderate temperatures this year.

What I have tried:

• Clutch pedal bushings and pedal shaft replaced with Toyota parts. The bushings were lubricated with Super Lube and the pedal ball socket for the master cylinder pushrod was lubed with Toyota body grease “W”. This helped some.
  
• Transmission oil changed to Amsoil Manual Transmission
  $30 75W-90 Synthetic Gear Lube - 1 Quart (Pack of 2)
  75W-90 at about 61k.
• The clutch and brake fluid was flushed at the dealer about 25k and 2 1/2 years ago.

I have become frustrated enough that I would like to resolve the clutch issues, but I am not sure where to start. I have been reading what I can find here on the forum and am getting more confused as to what the problem may be.

Do the symptoms above sound like they could be in the hydraulics? Would it be worth replacing the master and slave cylinders? Is there any failure mode for the accumulator?

I will admit with the difficulty finding the engagement point, I haven’t been the easiest on the clutch. Are the issues more likely to be in the hard parts (pressure plate, disc and throw-out bearing), I.E. burnt clutch?

Could I be running into the infamous trans input quill wear?

Thanks in advance for the help,
Nick

 

OP, are you the original owner? If not when did you acquire? You mention that there was a fluid flush at 25k. Was that done, in part, to issues about the clutch? Not clear to me if you inherited the problem from a previous owner or yours from the beginning.

FWIW, I have the same truck, also a '14. I love the clutch in mine and it is the OEM Aisin. I have tried the Amsoil stuff and was not impressed at all. Made shifting awful so I got it out. However, at this point I am not thinking that new bushings, link adjustments or gear oil swaps are going to do much for you.

Not knowing the full history it almost sounds like it had some rough treatment early in its life, but IDK. If this were mine I would be pulling the trans and taking a real close look at the clutch itself, including the flywheel, PP, disk, and T/O bearing, but that is just me.

 

This is unusual so..
What are you using as hydraulic clutch fluid? It seems that there is an issue with your viscosity.

 

https://www.tacomaworld.com/threads/what-does-a-clutch-fluid-accumulator-do.180006/

 

I agree with @gearcruncher
Do a search on clutch accumulator. Remove it! It fixed all the clutch inconsistencies for me!!

 

i agree, the solution is almost certainly to remove the accumulator.

 

And then flush the fluid again. Bet there is plenty of water in it.

 

The way the pressure plate behaves can be temperature affected. Sounds like it's not fully releasing the disc at times. Might need a new clutch assembly

 

Have you tried simply bleeding it? Kind of sounds like air in the system and it’s the easiest thing to try.

 

In response to all the responses:

• I am the second owner. I picked it up used in Spring of 2018 with just a little over 40k miles. The clutch seemed OK at time of purchase, but started feeling “off” shortly after. I can’t tell if I caused any damage by slipping the clutch or if I bought someone else’s problem.
• The clutch fluid was changed in the Spring of 2019 or about 20-25k miles ago at the dealer. Apologies - the fluid was not changed at 25k miles on the odometer.
• The clutch fluid is was whatever the dealer used. I am assuming it is the correct fluid. The brake and clutch were all bled/flushed at the same time as the truck was 5 years old. The fluid looked OK before the flush, but I tend to be proactive on maintenance.
• I have been reading up on the clutch accumulator. I am tempted to remove it and use the NAPA brake line connector. However, I thought I would try to remedy whatever problem I am having before deviating from stock.
• I will try to find someone to help bleed the system again to see if it changes anything.

in regards to the clutch hard parts (pressure plate or throw-out bearing) can any estimation be made of their condition through the inspection cover?

Thanks again,
Nick

 

Get under the truck and watch the slave cylinder movement while a helper pushes on the clutch pedal. Measure the throw or make a good mental note of what it looks like. The next time it gets hard to select gears or the pedal starts to feel funny, crawl back under there and look again. Is the slave push-rod still moving the same distance?

If yes then the hydraulics are fine and the problem is in the clutch unit.

 

Bold highlight in your quote is mine.
I got a strong feeling that you got someone else's problem since, as you say, it showed up shortly after purchase.

I'm doing this entirely from memory but yes, you can remove the inspection plate and partially observe a few limited things. Some dental mirrors or homemade mirror may also help.

IIRC you should be able to see portions of the fingers of the pressure plate where they contact the throwout bearing, and possibly some of the attachment bolts of the PP but may need to rotate the engine.

Check for strong burnt smell, unusually large accumulations of clutch dust, broken pieces, and if there are any signs of any bent diaphragm fingers on the PP. You might also be able to see if there is any deep wear on the fingers from contact with the release bearing. You might also be able to fab a wrench to check for loose mounting bolts around the perimeter of the PP.

Also check the quill (input shaft of the transmission) where it enters the trans to see if any obvious cracks.

 

I finally had a chance to pull the inspection cover this weekend. I forgot to get an inspection mirror, but I did take a good look at what was visible of the TOB and pressure plate spring fingers.

The first observation was a all the pressure plate fingers had a reddish-brown appearance around the contact point with the throw out bearing. The contact point inward was clean and the outer perimeter of the pressure plate were both clean, but the middle 1/3 of the pressure plate fingers had the odd-colored deposits. I did not see any step, groove or excessive wear in the pressure plate fingers. Could these reddish-brown deposits be rust? Or is it friction material?

I did not observe any chunks of disc material. I did see a couple of hair-like strands around the back side of the throw out bearing collar. I am assuming this is clutch material?

Finally, I did not have a helper, but I was able to wedge the clutch pedal down with a shovel handle to see the input quill. I did not see any cracks on the quill, but the area of TOB travel has definitely polished the quill. I did not see and pronounced step between the polished portion and the unworn portion through the inspection hole. However, I could not see the passenger side of the quill.

In the process of inspection and wedging the pedal, I accidentally pushed the clutch slave cylinder the wrong way (forcing fluid backwards through the system). I want to say the first couple pedal applications after the inspection were light and had good feeling. However it quickly reverted to a heavy pedal. The only thing I changed in that area was pushing the slave cylinder pushrod backwards. Does this mean there could be debris in the clutch slave cylinder or I have a partially-failed clutch slave?

Thanks again for the help!

 

In my SCCA car (another marquee) the symptoms you describe were a failing slave or failing master. you could go through 2-3 slaves before ever having a master problem.

2nd problem was the system needed a bleed, often due to a hose connection weeping.

Does your fluid level stay up to snuff? If so, there could still be 'internal bypass' problems, somewhat indicated by your temp change after messing with the slave.

 

Thanks for the feedback.

I have not seen any drop in the fluid level or leaks on the ground. I had suspected a bypassing issue on the master or slave, but wanted feedback from others. I would still like to hear if anything else in the inspection raises any red flags. The reddish-brown deposits seemed odd.

Thanks!

 

Again, if the slave/clutch fork is moving its normal distance when the problem is happening then it's not a hydralic problem. the problem is inside the clutch unit.

Pull the trans, replace the clutch assembly and flywheel, repair the quill as needed

 

OP, this ^^^^^^. Its time to get serious.

 

I understand about measuring the fork throw to verify the hydraulics. However, I don’t have a frame of reference. Does anyone have a measurement for me to compare against?

 

You say it was "flushed at the dealer 2.5yr ago"

As in they gave it to a 16yo luber goober who ran a bottle of DOT4 through the right rear brake?

some German cars in a certain year switched from DOT4 to DOT4LV (Low Viscosity) claiming their ABS units have thinner passageways. I have not heard of such a thing present on the old 2nd gen Tacoma

What do you mean by internal bypass/temp change?

Does the 2g Taco have a clutch master cyl?
I thought it was just brake master cyl under the reservoir, and maybe clutch master cyl as the pedal connected to clutch slave at the trans. I'll have to look.
I wonder if there are any test procedures to diagnose if they are leaking/failed seal internally. IF there is a clutch master cyl at the pedal I don't know if it has a bleeder (probably not) or should just be bled at the slave.
I guess if in doubt, it may not hurt to chuck a new part on it, because it still may not be too expensive and give the peace of mind that at least it was replaced.

especially if the master is plastic I would replace it just on that fact alone...

If you are doing this DIY it is not that expensive. FW resurface $50. Clutch kit $200-300.
At that point if every other component in the system is replaced (FW, TOB, clutch, PP, fluid, slave, etc.) I would not want to compromise that by not replacing a $130 master cyl especially meaning doing an 8hr job over again.
So now that I think about it I may replace my master cyl.
I don't imagine a malfunction in this system will be healthy for the trans inside to prevent wear/tear on gears and synchros, so I'd probably try to get it sorted before looking at a trans teardown/rebuild to renew those.

Think about it. If you address TOB, FW, PP, clutch, slave, fluid, and so on, then the only thing left to rule out that HASN'T been replaced (if you still end up having problems) would be the master. I don't think there is much else in the system. Besides maybe lines and hoses that hopefully aren't leaking or kinked. Rocks don't really fly up there so I don't see what could pinch them. So then why not replace the last piece of the 90% complete puzzle. Just my 2 cents.
Usually with major problems you start with whats easiest and cheapest to try and fix it first. Obviously a master cyl (~$130) is easier and cheaper than putting new synchros in a trans.

Many people also delete their accumulator.

I'm not sure the best amount of fluid for a full bleed. I've heard everything from
-10, 15, 20, 25, or 30psi
-cracking lines, gravity bleed, operate pedal or don't
-pressure bleed, no vacuum, 1, 2, 3, or 4L
I'd probably take the more>less approach regarding this, without going too far...(crazy PSI can rupture a plastic reservoir)

supposedly clutch master cyl failure = pedal won't return upward