No more throw out bearing chirp!!!

[NurseGuy]

Tech Background: Ford Master Tech: Fwd Communications from: Sheppard, Eugene Re: TOB question
Ford equipped most Fox and all SN95 Mustangs with a self-adjusting mechanism designed to maintain proper clutch cable tension at all times. As the clutch disc wears, the mechanism automatically adjusts the cable tension so the clutch continues to operate correctly through its entire life.
A properly adjusted clutch cable has some tension on it. This keeps the throwout bearing in constant contact with the fingers on the clutch pressure plate diaphragm. That contact is essential for the self-adjusting mechanism to work. Contrary to popular belief, this is a design feature and does not prematurely wear out the Mustang throwout bearing.
The stock self-adjuster consists of a plastic quadrant/pawl gear assembly. The plastic wears out over time, but aftermarket pressure plates with higher clamp loads speed up that process. Even in a stock setup, age degrades the plastic and breakage becomes more likely with each passing year. The solution is to replace the plastic mechanism with long-lasting metal parts.
The typical replacement is a non-adjustable, aluminum quadrant. Be aware that once you remove the stock self-adjusting mechanism, clutch cable adjustment is no longer automatic! You must replace it with some method of adjusting cable tension. Maximum Motorsports does this with an assembly called a firewall adjuster, which lets you easily adjust cable tension from under the hood of your Mustang. To compensate for normal clutch disc wear, you'll need to adjust the cable tension periodically.
As the clutch friction disc wears and gets thinner, the end of the diaphragm fingers touching the throwout bearing push on the bearing, applying more and more load to the cable and increasing its tension. This starts to disengage the clutch, leading to clutch slippage. Keep up with adjusting your Mustang's clutch cable to maintain good performance and avoid premature clutch disc wear. Note that this adjustment process is not for changing the pedal position at the point of engagement/disengagement. Please see our Clutch-Pedal Height Adjuster that's designed to make that change correctly.)

 

[NurseGuy]

i just don't know what to believe anymore

 

[NurseGuy]

Adjusting Clutch Cable Tension
The goal of adjusting the clutch cable is to put enough tension on it to keep the throwout bearing in light contact with the clutch diaphragm fingers, ensuring both proper clutch operation and long clutch life. Do not use the firewall adjuster to customize the pedal height or adjust where in the pedal travel the clutch engages or disengages. (Maximum Motorsports makes Clutch-Pedal Height Adjustersspecifically designed to do that job correctly.)

 

[General karthief]

The 'chirp' you are hearing could be one of several things, note that the tob slides on the cone of the trans and spins at the same time. If the cone is dry, or the tob has excessive play on the cone when you engage the clutch it contacts the cone and makes the 'chirping' sound.
if there is no 'preload' on the tob to clutch fingers the tob can stop spinning or slow down and when you push on the peddle it 'chirps' as it contacts the fingers because it is not spinning at the same rate,
it also could be the pilot bearing, if it is dry or worn can make this sound too, it was more problematic with the old style bushings than with the new style bearing types. We chased such a problem when a customer brought in a stang with a 'chirping ' sound and found the he had installed a bushing (dry at that) and not the bearing that is supposed to be there.
Let me say my car has 50k on the cobra clutch setup with no issues with the required tension on the stock cable, everything was installed new including the wct5 but the same stock cable it left the assembly plant with. I drive this thing like I stole it, I cut it no slack in first and second gears and the only 'chirp' I've heard is from the tires when I do happen to hit third gear successfully.

 

[NurseGuy]

New pilot bearing, TOB, retainer sleeve, and he also mentioned some bearing ("cone shaped") but didn't tell me which one. The chirp is mostly intermittent and most notable at higher RPM. EVERYONE I've spoken to says that this is a somewhat common issue with the SN95's. My ex and I had SEVERAL mustangs (1969 Mach 1, 2002 Mach 1 which is what I usually drove, 2 Cobra's, 2 foxbody's, and 2 SN95 GT's). NONE of them chirped. Granted..... he was a Ford Guru and owned a shop....so he knew his way around a Stang. As a matter of fact, he named his dirt road leading to his house Mustang Drive. Anyway.... back to my car..... I'm not thrilled that mine is being so problematic. Then again, it is 20+ years old!

 

[jozsefsz]

Definitely agree that additional preload is bad for the crank thrust bearings, and also bad for the longevity of the TOB. This is where the air-gap comes into play. The chirp however does not indicate the TOB is bad, however, so that's not the end of the story, as they will do this when it's a quality part and brand new. Especially when it's brand new as it doesn't have a convenient amount of dirt on the input shaft where it rides to keep it steady. It's bouncing around because there's nothing to actually maintain the air-gap and it feels free to bounce back & forth along with the clutch fork. Leave the air gap, remove your dust-cover, and push the fork back & forth - you'll hear it clack up against the pressure plate as you move it around.

The short version is, comparing the stock self-adjusting setup with any Ford of prior generations, Ford half-assed it and left out a return-spring mechanism, opting instead to make the TOB constantly ride the pressure plate. "New improved TOB's can handle it" was the rationale. The reality was that you were lucky to get 40k miles out of one before it rattled itself to death, long before the clutch actually wore out.

Here's that engineering exercise @NurseGuy. If your TOB is in constant contact with the pressure plate, even when you're cruising, it's at a constant let's say 2000rpm theoretically (assuming little slippage and whatever gear / speed you're going). That's the equivalent of a 17" tire (P245/45R17) with an external circumference of 80.6", which rotates about 800 times per mile, traveling at about 2.5 miles per minute, or 150mph.

Considering the TOB is internally-lubricated, and it's a tiny little piece of crap compared to a wheel-bearing, how long do you think it should last spinning at the equivalent of your wheels traveling 150mph at all times, whether you're idling or cruising down the highway? TOB's are intended to be in contact with the pressure plate only when your foot is on the clutch - if you want your TOB and crank to last at all that is. In every other car but these Fords.

As I mention, the real solution is to maintain the air gap. But to maintain the air-gap without chirping, you need a return spring. This is what I'm talking about. Run air gap, no chirping, TOB and crank last much longer, no longer sold but you can make your own from the hardware store for about $10.

LDC Chicago Clutch Freeplay Correction Kit

Product number two from LDC Chicago Superior Automotive Products Inc. is now available. Dana designed this freeplay correction kit for his car and it...

www.svtperformance.com

 

[Potomus Pete]

Are we speaking of aftermarket. I have a BBK it seems to me that its not a self- adjust. I adjust it under the car correct ???

 

[FastDriver]

If you need it for clarity's sake, I can post an image out of Ford's '93 service manual showing that it is engineered to have some preload. However, I think what @josefsz is saying is fascinating, and that spring is a pretty cool idea. It will actually maintain the air-gap to ensure complete separation of the T/O bearing and the pressure plate. I'll bet that works a treat!

I'm in a different boat. Even with a quick release quadrant, my twin discs engage just off of the floor and still don't get to any air gap with the pedal fully out. So, there's no way around maintaining preload for me.

 

[NurseGuy]

Is it "okay" to drive with the TOB riding on the fingers??? Mine is touching just ever so slightly. I am supposed to be driving it on a 3 hour trip this weekend and need to know if it is okay to do so. I'm also going to do the spring mod and if it prematurely wears the bearing then so be it. I cannot keep driving around sounding like a cricket!

 

[FastDriver]

Preload implies that it rides on the fingers, and yes, absolutely ok. I don't refute what josesjz said, it may be/probably is an improvement to use a spring and an air-gap, but the initial design was meant with preload in mind.

The exact pressure is unclear, but I think your "ever so slightly" is surely not too much.

 

[NurseGuy]

I consulted with Maxim Motorsports who specializes in mustang modifications and engineering/repair. They said that these TOB's are MOST DEFINITELY designed to ride the fingers. Chirp is very common and they said that using the spring modification will only speed up the wear of said bearing. It makes sense to me.... if that bearing is sitting there not moving.... and you engage the clutch, it pushes the bearing into contact with the PP fingers sending it from ZERO to RPM speed nearly instantaneously which creates excess loads and demand on the bearing. Let's say your RPM is at 4500..... you push the clutch and the bearing goes from ZERO to 4500 RPM nearly immediately. It makes sense that this would speed up deterioration of said bearing. The bearing, from what they say, is designed to be in constant motion and ride lightly against the fingers so that it spins with the clutch. I think I trust them more than some of the responses that I've seen in these forums.... not saying that you guys don't know your stuff as I'm sure you do. BUT..... when a Maxim guy tells me something..... I tend to believe them.


Side note..... how does one know if the clutch is completely disengaging????

 

[NurseGuy]

here is a copy of the email from Maxim....

Mr. Peacock,

There is absolutely no uncertainty here. The throwout bearing on all 1979-2004 Mustangs, is designed to be in constant contact with the pressure plate fingers on the clutch. The spring which is located on the pawl gear as part of the clutch adjusting mechanism is designed to create a small amount of cable tension to do this. Below is a write up that I've done on this subject. It helps explain why some people think that the throwout bearing on a Mustang should not touch the pressure plate fingers when the clutch pedal is in the upwards position.

Proper adjustment of the clutch cable tension in a Mustang is important to give proper clutch feel, and to avoid premature failure of the throw-out bearing, clutch disk, or crankshaft thrust bearing in the engine. Contrary to popular opinion, the clutch cable in a 79-04 Mustang, when properly adjusted, is designed to have some tension on it, keeping the throw out bearing in constant contact with the fingers on the clutch pressure plate. This slight preload is designed to keep the throw out bearing centered with the pressure plate, minimize noise, and improve the clutch pedal feel.

One common myth is that constant throw out bearing contact will lead to throw out bearing failure. This is true of older mechanical linkage clutch activation systems or any other type of non self adjusting system that is not periodically adjusted, especially ones that don't use an angular contact throw out bearing. The Mustang angular contact throw out bearing was designed to be in constant contact with the clutch cover's diaphragm fingers. As the clutch friction disc wears, the outer end of the pressure plate diaphragm fingers move towards the engine. Since the pressure plate diaphragm fingers are small levers, the opposite end of them, the end at the throw out bearing, moves in the opposite direction as the clutch wears. This direction is towards the throw out bearing. If the clutch is adjusted so that when new, the throw out bearing is just touching the clutch pressure plate fingers, as it wears the throw out bearing will push on the clutch fingers more and more. This causes an increasing load on the throw out bearing and the crankshaft thrust bearing, and causes the clutch to be partially disengaged all the time. This also reduces the clutch's torque capacity and can lead to slipping. If periodic adjustment is not made to the preload on the clutch fingers, early failure of the clutch will occur.

Older non self adjusting mechanical clutch release mechanisms, used by auto manufacturers, are typically adjusted to have a large gap between the throw out bearing and pressure plate fingers, so that disengagement never occurs as the clutch friction disc wears. Even if the mechanical linkage does have some user adjustability, the auto manufacturer is going to assume that it will never be adjusted over the life of the clutch, so they set the gap between the throw out bearing and pressure plate fingers to never require adjustment. The major disadvantage to this is that much more travel at the throw out bearing is required to disengage the clutch. This causes the clutch pedal travel to be much longer, the force much higher or both. This is why with some non self adjusting linkages, the clutch is adjusted to have a gap between the throwout bearing and the clutch fingers when new.

Hydraulic throw out bearings are a special case of a self adjusting system. After installation, they self adjust to have zero clearance between the throw out bearing and the clutch fingers. This happens exactly the same as brake pads self adjusting their clearance to the brake rotors in a hydraulic brake system. However, with the hydraulic throw out bearing, there is an absolute mechanical limit to how far the bearing can move rearwards towards the transmission. When the bearing is first installed, it is pushed rearwards on the bearing stand and then the height of the bearing stand is adjusted with shims so that there is some gap between the face of the throw out bearing and the clutch fingers. This is to allow the fingers to move rearwards as the clutch wears. The very first time the clutch pedal is pressed, the throw out bearing will be pushed forward by the hydraulic fluid until the fingers are pressed down. When the clutch pedal is released, the throw out bearing will move rearwards until the clutch fingers have stopped pushing it, leave these two parts in light contact.

As delivered from Ford, the Mustang has a plastic quadrant and pawl gear assembly designed to self adjust the clutch cable tension over the life of the clutch. After you've upgraded your clutch quadrant to a stronger, aluminum design, it is necessary to manually adjust the tension on the clutch cable yourself. Before doing this, there are a couple of things that need to be checked. You need to make sure that your firewall adjuster is properly screwed to the firewall. The clip that holds the transmission end of the clutch cable housing to the bellhousing, must be installed. This clip is located underneath the clutch fork cover. The mounting bracket that supports the middle of the clutch cable housing to the driver's side frame rail must also be attached, or some other bracket should be used to support the weight of the clutch cable near the large U-bend, unless the MM Universal clutch cable is used. The goal here is to hold the clutch cable housing at right angles to both surfaces that it is mounted to at each end. This is to minimize slop in the system. If you watch the cable housing at the firewall end, while someone else presses down on the clutch pedal the first ½", you can see the cable housing straighten itself to be at right angles to the firewall. Before the housing has straightened itself, the clutch cable will not have moved the clutch fork at all.

Once the clutch cable housing has been properly aligned, you can move on to adjusting the cable tension. Loosen the firewall adjuster so that there is a small amount of play in clutch cable at the clutch fork. Put your hand on the clutch pedal pad and press down lightly and release. You will hear a slight clink when the pedal is released. This is the sound of the clutch quadrant contacting its upwards stop. Turn the firewall adjuster to increase the tension on the clutch cable some. Press down on the clutch pedal pad with 3-5lbs of force. You should still hear a slight clink and feel the quadrant come on and off the stop. If the pedal didn't come off of the stop with 3-5lbs of force, decrease the cable tension some with the firewall adjuster. Repeat this process until the clutch pedal just comes off of the stop with 3-5lbs of force. Remember to periodically readjust the clutch cable tension as the clutch wears.

If you have installed a clutch pedal height adjuster (MMCL-7 or MMCL-10), you need to pay extra attention to the adjustment of your clutch cable tension. The clutch pedal height adjusters only allow the height of the clutch pedal to be lowered. When the clutch pedal height is reduced, the total amount of clutch pedal travel is reduced because the lower limit of the clutch pedal travel is the firewall. In a stock SN95 Mustang, there is about 7" of total travel at the clutch pedal pad. If you lower the clutch pedal as far as the height adjuster will allow, you will only have 5" of travel at the clutch pedal pad. This is a travel reduction of 29%. This means that the throw-out bearing will also experience a 29% reduction in its travel. This is important to keep in mind.

The chirping that you hear, is the sound of the pressure plate fingers rubbing on the face of the throwout bearing and speeding it up to the engine rpm. This means that there is not enough tension on the clutch cable pushing the throwout bearing against the pressure plate fingers. There are cases with damaged or aftermarket clutches, where the installed finger height of the pressure plate varies too much. This causes only a couple (highest) fingers to touch the front of the throwout bearing. There may be chirping from this as there isn't enough friction to keep the bearing turning. By the time you have added enough cable tension to create enough friction to stop the chirping, the clutch may have a considerable load on it, which can result in premature throwout bearing failure and/or clutch slippage on a high power car.

Sincerely,
Jack Hidley
Maximum Motorsports Tech Support
www.maximummotorsports.com

 

[FastDriver]

Maybe so, maybe not. This is the first time I've heard of the spring mod on a fox clutch, but not the first time I've heard of an air gap, which incidentally is easily measured at the firewall if you pull back on the cable lightly with one hand and measure the "air-gap" between it and the adjuster with the other. This also is what Wally at promotion performance recommends, and he's one of the most respected drivetrain guys in the country. I would defer to his wisdom here, as well.

Regarding the additional wear between the bearing and the PP fingers, you're not wearing through the bearing surface... just ain't happening. The fingers? You have a point there. However, the important question is not whether you increase wear at all (intuitively, you do), but whether or not that wear is going to lead to replacement before the disc & PP wear requires replacement first.

One thing is for certain: replacing a clutch is a hell of a lot easier and cheaper than replacing a crank. A motor might go 300k+ miles. Whereas, you're going to replace quite a few clutches if your driving is proportional to the passion you have for the hobby.

There's not always 1 right answer. And even though I happened to be on the side of the MM guy this time, it doesn't always fall to a "he's right, and you're all wrong" sort of thing. I admit to being intrigued by jose's approach.

 

[NurseGuy]

As am I! I second your response. Are you saying that there should or should NOT be constant contact on the fingers? Keeping in mind that my stang is NOT a fox! It's an SN95. I wish it were a fox though! They seem to be less problematic!

 

[FastDriver]

... Ford's '93 service manual showing that it is engineered to have some preload.

Preload implies that it rides on the fingers, and yes, absolutely ok...

Right. Sorry about that. We have the same mechanical cable system in our cars, fox/SN95/New-edge. So, it applies to both you and me.

I'm saying that, as designed, the T/O bearing is meant to ride in contact with the PP fingers. It says so, as I stated earlier, directly in Ford's service manual from '93. I would not tell jose that his "should not" be in contact, however. If done right, I'll bet that's a perfectly good approach.

Clear as mud?

 

[NurseGuy]

THICK MUD! HAHAHAHA. What about this f*cking cricket chirp! Argh it annoys the out of me. It sounds like I have a freaking super charger I guess that's the only "cool" thing about it.

 

[NurseGuy]

My baby! Side note...... who wants to buy a Cadillac DeVille????? I need to get it out from under my carport so I can put BlancaStang in there. South Georgia hail storms are BAD NEWS for paint and body!

 

[jozsefsz]

Great thread, great discussion. My read of the MM message is that a stock quadrant setup (automatically adjusting) which is in constant contact by-design is preferable to an out-of-adjustment manual-adjuster, and I can't argue with that. The issue that a lot of folks get into with our cars at they age is that the stock quadrant is actually plastic, and after years in the heat they tend to become brittle. Mine had a few teeth missing so I went for an aftermarket replacement - and those are pretty much universally manually-adjusted (so you need a firewall adjuster or adjustable cable). The two best options imho are to put it in light contact with the pressure plate like stock, or to leave an air-gap with the return spring. I think most folks do the air-gap with no return spring, and there are lots of old threads complaining of chirping, which I believe is because we're missing that critical design component that all the older Fords with manual adjustment had - the simple return spring.

If you have the stock self-adjuster, you're going to be in contact, no choice in the matter. If it's manually adjusted, keep it adjusted for best results, whichever your approach. I like the air-gap because of the mentioned thrust-bearing wear, and because my first 2 TOB's lasted around 40k while the clutch had plenty of material remaining - despite Ford (and MM's) assurances that the bearings were designed for that abuse in-mind. Remember, Ford's interest is in selling cars, and the aftermarket's interest is in selling parts. My interest is in getting things to run as long as possible as cheaply as possible. And I don't put much faith in stuff manufactured these days - no matter the name-brand it's likely made-in-China and of lesser quality than what would be required to spin at 1-5000 rpm indefinitely for tens of thousands of miles. It's getting hard to even find wheel bearings in the aftermarket that'll last 50k - even Timken isn't what it used to be.

The return spring is also kind of nice because it got rid of the slack at the top of the pedal movement that happens when you leave the air-gap (normally not noticeable but can get noisy over bumps with the pedal bouncing up & down). It's how Ford did it for decaded prior, and very successfully, when most everything was manual. Those old pressure plates had all kind of irregularities and sloppy tolerances, but chirping was not a problem and the TOB's usually outlasted the friction material. To old timers like me who like to work on old cars, it was an obvious solution to the problem and lets us have our cake (long TOB life, less engine wear) and eat it (no noise and reliable operation) too.

No matter what you choose, and I think we've laid out all the options pretty nicely, I wish you the best.

 

[fredfifty]

is this similar to the chirp?


View: https://www.youtube.com/watch?v=jx7xWNHhPFU

 

[NurseGuy]

is this similar to the chirp?


View: https://www.youtube.com/watch?v=jx7xWNHhPFU

YES! VERY SIMILAR!