cmonSTART |
Mon Oct 24, 2016 12:59 pm |
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Hi Folks!
What's the general life span of a throw out bearing? I have about 30K on mine (changed when I rebuilt the engine) and I'm highly suspicious of an impending bearing failure. There's a nasty squeal coming from back there through certain RPMs, changes with the clutch. Sure sounds like it's going bad!
My current bearing came with my Sachs clutch kit.
http://www.busdepot.com/kf25101
Any better parts out there? I was planning on pulling the engine for some maintenance soon anyway, so now's the time to replace it!
78FI Bus - stock. |
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airschooled |
Mon Oct 24, 2016 1:15 pm |
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Mine came used with my bus and has about 60k on it. No ill effects yet. I think Colin had more than 500k on his original from his '73 bus.
The throw-out bearing isn't in use when the clutch pedal is released, as long as you have some free play in the pedal.
Robbie |
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jtauxe |
Mon Oct 24, 2016 1:18 pm |
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The Sachs bearing is as good as any -- probably better than most. I have never had a throwout bearing fail, as I always replace it when I am in that part of the vehicle, replacing a clutch or something.
But premature failure could be attributed to driving style. I don't know what yours is, but some folks like to ride the clutch pedal a bit too much, like at a traffic light or other times when it should just be happily idling. I try to use that bearing as little as necessary. |
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SGKent |
Mon Oct 24, 2016 1:31 pm |
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the general industry rule was replace when noisy or when you are replacing the clutch disk. That said, older bearings were probably better made so I'd spin it in my hand to see if it felt notchy or gritty before replacing it. |
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Wildthings |
Mon Oct 24, 2016 4:25 pm |
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IIRC, there is a service bulletin out there that tells how to lubricate the face of the throwout bearing by drilling a hole in the bellhousing.
Throwout bearings last a long time, I have had them go hundreds of thousands of miles on a rig in highway service. |
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cmonSTART |
Mon Oct 24, 2016 5:42 pm |
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Hmm... I think that since I'm planning on doing an engine pull soon I'll just swap in a new bearing to be on the safe side.
I need to find a way to accurately record the sound I'm chasing. The issue is it really only happens enough to home in on while I'm driving, so I can't be in two places at once. I might try to set up my GoPro in the engine bay.. hmm. |
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wcfvw69 |
Mon Oct 24, 2016 8:20 pm |
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cmonSTART wrote: Hmm... I think that since I'm planning on doing an engine pull soon I'll just swap in a new bearing to be on the safe side.
I need to find a way to accurately record the sound I'm chasing. The issue is it really only happens enough to home in on while I'm driving, so I can't be in two places at once. I might try to set up my GoPro in the engine bay.. hmm.
As someone already mentioned, the "new" bearing might not be as good as the one you're replacing. It's kind of sad but true. You really can spin the throw out bearing in your hand and tell if it's rough or pitted. I've used the same throw out bearing for decades as well. They were REALLY made well back in the day. |
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SGKent |
Mon Oct 24, 2016 8:41 pm |
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Wildthings wrote: IIRC, there is a service bulletin out there that tells how to lubricate the face of the throwout bearing by drilling a hole in the bellhousing.
Throwout bearings last a long time, I have had them go hundreds of thousands of miles on a rig in highway service.
new ones are sealed bearings and the race has plastic on the face to quiet it. Not much to grease unless it is original in which case I doubt if many are with the mileage on these vehicles. |
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busdaddy |
Mon Oct 24, 2016 8:44 pm |
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cmonSTART wrote: The issue is it really only happens enough to home in on while I'm driving, so I can't be in two places at once.
So let's get more specific about exactly when it occurs.
Firts of all is your clutch cable adjusted so there's at least 1" of freeplay before the bearing touches the pressure plate? , can you easily push the pedal down with 1 finger a ways before it becomes too stiff to move?
Does this sound happen while driving at random times?, or only while the clutch pedal is depressed?, any other factors like only when in gear or only while coasting in neutral? |
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skills@eurocarsplus |
Mon Oct 24, 2016 9:08 pm |
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so, I want to say this about free play as it makes me want to smash my monitor every time it comes up...
this is how I adjust the clutch:
hold arm till it pushes the t/o bearing against the p/p.
wind in wing nut till it stays there.
feel clutch pedal
if its all mushy I have put the t/o bearing against the pressure plate. you need to overcome the elasticity in the cable somewhat. bottom line is you need to adjust it so the transmission is ez to get into reverse.
I have had the 3/4 to 1" free play as the book suggests only to have a poor shifting bus. in 20 years doing this, I have never had a problem..
every modern car or anything with a hydraulic clutch has the t/o bearing ride the p/p anyway. |
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old DKP driver |
Mon Oct 24, 2016 11:47 pm |
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I will tell you all how this all came about in 1971 along with what 'Wildthings'
has said.
I was a VW tech then and there was a time back then when there was a run of
release bearing noise when contact between the bearing and pressure plate
was noisy do to the grease used in the bearing.
We were instructed to drill 2 holes in the bell housing and lube the bearing
surface with "graphite spray grease'" it did Not work ib cold weather since
the ball bearings on the opposite side of the thrust surface were really the
problem.
The grease used was similar to 'Bosch grease and would clump up in cold climates and not fully lubricate the bearing being pressed against the pressure
plate and could be felt and heard through the transmission until fully warm.
Ball bearings rotating in thick grease when cold do not have a long life and require time to reach ambient temperature, and this was the problem. |
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Hoody |
Tue Oct 25, 2016 1:45 am |
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So Skils and DKB, are you referring to the earlier tranny? I am guessing if it came out in 71 that you are. Skills....does that method work for an 091? The OP shows a late Bay. |
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cmonSTART |
Tue Oct 25, 2016 3:42 am |
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Let's save our monitors folks...
Clutch tightness is not an issue - if anything I have a bit too much right now.
I'll try to record the sound this week while I'm driving and see if that helps shed new light on it.. |
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Wildthings |
Tue Oct 25, 2016 4:22 am |
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skills@eurocarsplus wrote:
every modern car or anything with a hydraulic clutch has the t/o bearing ride the p/p anyway.
Hydraulic clutches are natural self adjusting while the cable operated clutchs on these vehicles are not. Since most people tend to ignore doing maintenance as long as they can, if you set the adjustment with little or no free play then they will let the clutch go to the point of having slippage before they get around to adjusting it. Bad policy in my opinion to recommend people adjust their clutch to anything near zero free play. |
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skills@eurocarsplus |
Tue Oct 25, 2016 5:26 am |
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Wildthings wrote:
Hydraulic clutches are natural self adjusting while the cable operated clutchs on these vehicles are not. Since most people tend to ignore doing maintenance as long as they can, if you set the adjustment with little or no free play then they will let the clutch go to the point of having slippage before they get around to adjusting it. Bad policy in my opinion to recommend people adjust their clutch to anything near zero free play.
WHAT? as the cable stretches, the arm on the transmission moves FURTHER away from the pressure plate. it sure as hell doesn't tighten up. there is no way it's going to make the clutch slip
would you like an illustration? I think people have no idea how to visualize how this system works. |
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Wildthings |
Tue Oct 25, 2016 5:57 am |
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skills@eurocarsplus wrote: Wildthings wrote:
Hydraulic clutches are natural self adjusting while the cable operated clutchs on these vehicles are not. Since most people tend to ignore doing maintenance as long as they can, if you set the adjustment with little or no free play then they will let the clutch go to the point of having slippage before they get around to adjusting it. Bad policy in my opinion to recommend people adjust their clutch to anything near zero free play.
WHAT? as the cable stretches, the arm on the transmission moves FURTHER away from the pressure plate. it sure as hell doesn't tighten up. there is no way it's going to make the clutch slip
would you like an illustration? I think people have no idea how to visualize how this system works.
Don't think I said a thing about the cables stretching, so where did you get that from?
Maybe you should study up on what happens as a clutch wears causing the adjustment to tighten up and the eventual slippage that will occur once the freeplay is gone. Seems like you are the one that can't visualize how the system works. |
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skills@eurocarsplus |
Tue Oct 25, 2016 6:20 am |
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Wildthings wrote:
Maybe you should study up on what happens as a clutch wears causing the adjustment to tighten up and the eventual slippage that will occur once the freeplay is gone. Seems like you are the one that can't visualize how the system works.
the p/p doesn't "grow" when the clutch material disappears...were that the case, every car with a hydraulic clutch would be in deep crap. |
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cmonSTART |
Tue Oct 25, 2016 7:00 am |
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My clutch freeplay issues are likely due to the cable stretching - I carry a spare, just haven't gotten around to installing it yet. I've been too busy with general body work. Either way, I have too much freeplay as opposed to not enough at the moment.
Regrding the noise, it's sort of an weird squeel when the engine decelerates, such as when I shift or coast in gear, and it only seems to happen higher up in the RPM band, like 3 to 3500K. It will happen a small amount at a steady cruise up there, but if I take my foot off the gas and coast it gets more pronounced. Likewise if I take my foot off to shift I hear it too.
Still working out a camera mount... |
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lil-jinx |
Tue Oct 25, 2016 7:42 am |
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The clutch disc is sandwiched between the fly wheel and the pressure plate,when the clutch pedal is out [clutch engaged]the springs in the pressure place squeeze the clutch disc locking the engine and transmission together.
The throw out bearing rides on the transmission input shaft between the clutch fork and the pressure plate diaphragm spring,when you push the clutch in the throw out bearing pushes against the diaphragm spring taking the force off the pressure plate,releasing the clutch,
as the clutch wears the pressure plate moves closer to the flywheel which moves the diaphragm spring closer to the throw out bearing which takes away the freeplay between the bearing and the diaphragm spring,if wear continues the diaphragm spring stops at the throw out bearing and can't go farther preventing the pressure plate from applying max pressure to the clutch disc,allowing the clutch to slip.
With no free play there would be pressure on the throw out bearing all the time causing bearing wear, and also you would not know if your clutch was wearing,free play or lack of it indicate clutch wear.
On a hydraulic clutch there is a clearance between the throw out bearing and the diaphragm spring it is a small but constant gap,[not really a gap but a lack of pressure] much like the clearance between the brake rotor the brake pad. |
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SGKent |
Tue Oct 25, 2016 8:29 am |
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skills - what Wildthings is speaking of is correct. As the disc wears thinner the plate moves towards the flywheel pushing the fingers farther out. That reduces freeplay. When it is gone the clutch slips. If the cable stretches that is a different kind of problem.
As to hydraulic - they are not totally self adjusting. If the initial internal adjustment on the slave is not set right the clutch will slip after it wears a little. A good friend went thru SIX clutches on his Nissan because the factory mechanics overlooked that little spec. I adjusted it for him on the 7th clutch which I put in and the issue went away. There is a rod like what is between the brake master and power booster that needs an initial clearance checked whenever the clutch slave is replaced. |
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