Black Magic of the Clutch Release System

There are two issues at play here, but they're both related to the force applied to the release bearing. To confirm what has been said, the release bearing is absolutely intended to be touching the pressure plate fingers all the time, and should be spinning at all times.

Specifically looking at the 1GR/RA6x setup, the first issue is that Toyota used two different manufacturers for the clutch in the 2005-2008 Tacoma, Aisin and LuK. The Aisin and LuK pressure plates do not have the same height when installed, however the same release bearing was used on both from the factory.

The force applied to the release bearing by the clutch fork (when the clutch pedal is not depressed) is solely provided by the spring in the slave cylinder. This spring also ensures that the clutch does not require adjustment as it wears. The force the spring is applying to the release bearing is of course a function of how far the spring is compressed, and so the taller pressure plate will have more force on the release bearing than the shorter pressure plate.

The bigger issue then became that for a period of time, Toyota USA/Canada only sold the LuK clutch as a replacement for the Tacoma, Tundra, and FJ Cruiser, the latter two only having originally come with the Aisin clutch. So now what you have are three models that, due to what was installed at the factory or at the dealer, have different height clutches. This also happened for the release bearing.

The second issue is related to how much force the spring in the slave cylinder applies, and that is something that is a bit delicate - and something Toyota has updated on a few vehicles over the years. You want to apply the minimum amount of force that will prevent squealing.

So Toyota's answer was to: first, pull the transmission, check what type of pressure plate was installed, and change the release bearing to the appropriate part that matches the installed pressure plate; second, to replace the slave cylinder with one that has a stronger spring force; third, to replace the release fork ball to a slightly taller/stronger one. Toyota also switched to only selling the Aisin clutch setup for the 1GR.

The issue that I've seen come up over the years since then, is that many people (Toyota and aftermarket dealers included) don't know which thing is which. Does that aftermarket pressure plate have the same height as the original LuK clutch, or is it the same as the Aisin one? Is the release bearing the short one or the tall one? Did that aftermarket slave cylinder have a light spring or heavy spring installed?

Here are some Toyota part numbers for those interested:

31230-60231 - Short Release Bearing (for LuK Clutch)
31230-60241 - Tall Release Bearing (for Aisin Clutch)
31236-35050 - Improved Fork Ball
04313-34011 - Slave Cylinder Overhaul Kit with Heavier Spring (for Tacoma/Tundra)
04313-60182 - Slave Cylinder Overhaul Kit with Heavier Spring (for FJ Cruiser)
31470-35181 - Complete Slave Cylinder with Heavier Spring (for Tacoma/Tundra)
31470-60361 - Complete Slave Cylinder with Heavier Spring (for FJ Cruiser)
31210-60280 - Aisin Pressure Plate
31250-35452 - Aisin Clutch Disc

If you want to err on the cautious side with a new clutch go with the tall release bearing 31230-60241.

Jeff

 

I'd have guessed Jeff was a historian because he smokes a pipe and has written a nice long essay. I'm an engineer so 8 years ago when I bought my Tacoma I just fixed the problem by changing the slave cylinder spring. I've sold my Tacoma now having spent about $10 over 8 years fixing this problem. My guess is this problem will never die because no one bothers to understand what it is so guys just keep pouring the money into URD and Toyota parts. Good-bye all.

 

Former Toyota parts guy, currently almost an engineer (3 months to go!), I do have a decent pipe as well though, haha.

Agree, it’s a good fix.

People should be aware of the differences in height on the release bearings though, if they’re ever in there.

Jeff

 

Thought I would share my experience with the Throw Out Bearing squeal on this forum.

I have a 2007 4.0 6 Speed Tacoma.

I got a shop to replace my OEM clutch with a LUK clutch, after a couple days of driving I noticed a metallic chirp sound any time I engaged or disengaged the clutch. Shortly after I noticed a squealing sound coming from around the bell housing area.

When I went back to the shop who replaced the clutch, they said it could just be a faulty throw out bearing that was put in, so they once again put in a brand new thowout bearing. This only got rid of the noise temporarily, the squeal and chirp came back. I decided to look online and found many threads about this seemingly common issue with these 6 Speed transmissions.

While I spent months reading online, trying to find a solution to this problem, the noise continued to get worse and worse. The options I found to try and solve the issue were either:

- Clutch Masters Hydraulic Release Bearing
- URD Throw Out Bearing Sleeve Kit
- Toyota TSB "Fix"

After reading about people's experiences with the CM Hydraulic Release Bearing (Loss of fluid, inconsistent pedal feel)

I decided against that option because of the mentioned unreliability of the product.

I finally decided to go with a combination of the URD Throw Out Bearing Sleeve Kit and the Toyota TSB.

I had a shop install the URD Kit, while also replacing the original Slave Cylinder and Fork Support that came with my truck with the updated TSB parts.

So far (drive from the shop to my house), there has been no squeal or chirp. I will periodically post updates on whether or not my truck remains squeal and chirp free.

 

Is this the part you had the shop put in?
https://urdusa.com/throwout-bearing-upgraderepair-kit-2005-tacoma-v6-6-speed/

 

Yes. I also had them install the updated Slave Cylinder and Fork Support that is listed in the TSB from Toyota.

 

The historic solution was an external spring and adjustable rod on the slave cylinder. This always ensured the bearing was pulled away from the pressure plate but required periodic adjustment. Remove spring, move shift fork back and forth, giving about 6mm (1/4" of play). As the clutch disc lining wears thinner, you have LESS-free play and need to adjust every 6000 miles. PITA, so every manufacture went to "self-adjusting" clutch release. Yep, the bearing is lightly rubbing the fingers of the pressure plate (clutch cover system). Hence noise.

Trivia question for Jeff Lange. When did the accumulator appear, and why? Congrats on getting your degree (what school? What degree? Cal Poly SLO 1980's for myself, EE, ended up in the world of automotive electronics. Fuel Injection, ECU, ABS, worked for the company in Germany when we came up with this crazy idea called CAN. Hybrids later worked on something call USB. Damn it, back into the car world). Traveled the world, still having fun. NDA, so can not talk about most stuff. Just don't get stuck in taillights. Buddy went to work for GM, designed tail lights for 30 years. Then again, he was home every night, maybe not a bad deal after all.

 

Toyota started adding accumulators or similar to their hydraulic clutch setups more commonly in the late 90's. They typically exist to smooth out clutch operation and to reduce vibration transmitted while operating the clutch to the pedal. Not all Toyotas use them, but many do. I usually prefer the more direct feel, even if it means it's a bit less refined.

University of Alberta, Mechanical Engineering

Most of my job search revolves around doing things that I find interesting, hopefully getting paid relatively well to do so, haha. I could see an appeal in designing tail lights for a bit, but yeah, probably not a great long-term option, haha.

Sounds like you've had your hands in some interesting stuff as well. I do appreciate a good CAN network.

Jeff

 

Still no chirp?

 

700km later and no chirp.

 

Jeff - is there a way to research your truck and clutch-kits used for original assembly to properly marry new parts?

 

According to the parts catalog,

Sept. 2004 to May 2005 will be LuK Clutch
June 2005 to May 2008 with either be LuK or Aisin Clutch
June 2008 to Aug. 2015 will be Aisin Clutch

Sept. 2004 to Sept. 2010 will have the release bearing for LuK clutch.
Sept. 2010 to Aug. 2015 will have the release bearing for Aisin clutch.

That's probably quite accurate for how it came from the factory. For what trucks have in them now, anyone's guess.

Jeff