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Author Topic: Clutch Brake Adjustment  (Read 8211 times)
lyndon
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« on: January 19, 2008, 07:46:41 PM »

Quoting from another thread:

They say there are no stupid questions but I think there is ONE.  That question is "why didn't I ask BEFORE I tried that".  LOL

This comment encouraged me to ask about adjusting my clutch brake. It's pretty much useless right now, even with the clutch right to the mat. Otherwise, the clutch adjustment is great, with about 1.5" of free play.

Adjustment sounds simple enough, from what I read in the manual, but I've never tried it. Is this as simple as it sounds, or should I be very afraid?

Don
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Don
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« Reply #1 on: January 19, 2008, 07:57:04 PM »

Hi Don.  Not sure what bus you have, but the adjustment should be pretty straight forward on any clutch. 

Consider that the clutch brake my have become worn.  They now make two piece clutch brakes that can be installed without removing the transmission.  If yours is warn (not sure how to tell you to check - your manual might give you some guidance), you will have to find a way to remove yours (will have to cut it out if it is a one piece unit) and then installing a two piece unit will seem like taking candy for a kid Smiley.

Jim
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Jim Shepherd
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lyndon
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« Reply #2 on: January 19, 2008, 08:25:02 PM »

Thanks, Jim. After rechecking the manual (MC-9, BTW), I could not find any guidance on determining whether the clutch brake is worn out. Would it be fair to assume that the inability to adjust it without losing all the free play would be the best indicator?

The manual says to adjust the clutch brake by adjusting "the free travel with adjustment bolt on activating lever." I'm thinking this is the external lever. Or do I have to find something inside by removing the inspection plate?

Don
« Last Edit: January 19, 2008, 08:59:47 PM by lyndon » Logged

Don
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« Reply #3 on: January 19, 2008, 09:15:36 PM »

Don, I am close to being in over my head on this one.

I would remove the plate and look at the clutch brake material.  It might be obvious that it is worn.

With the cover removed, you can have someone push in the clutch and see if it is pressing on the brake in full pedal position.  That might help you see if you can make the clutch adjustment push on the brake after it is adjusted according to the manual. 

I am getting tired tonight, so my reply might not be as good as it should be.

Perhaps you might want to take a look at this site (about the best I could find) and see if it helps:  http://www.heavydutytrucking.com/2004/12/040a0412.asp

Then I would crawl under the bus (after proper blocking!!!!) and play with the adjustment and watch the brake squeeze. 

I will be glad to pick away at it tomorrow, but I hope some of the more experienced folks in this area pick up the slack - pun intended Grin.

Jim
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Jim Shepherd
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85 Eagle 10/Series 60/Eaton AutoShift 10 speed transmission
Somewhere between a tin tent and a finished product
Bus Project details: http://beltguy.com/Bus_Project/busproject.htm
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lyndon
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« Reply #4 on: January 19, 2008, 09:37:17 PM »


I will be glad to pick away at it tomorrow, but I hope some of the more experienced folks in this area pick up the slack - pun intended Grin.

Jim

I'm about to call it a day, too, so let's give it a "brake."

Many Thanks!

Don
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Don
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« Reply #5 on: January 21, 2008, 01:44:15 AM »

Are you certain the clutch has a clutch brake?
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buswarrior
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« Reply #6 on: January 21, 2008, 08:15:47 AM »

As Tony asked: Are you sure you have a clutch brake?

There are few older coaches that have a manual transmission with clutch brake capability.

If you do have one, if the proper procedures are followed for adjusting the clutch, the clutch brake will be in adjustment by default.

Unless the wearing surface has been worn away, in which case, you'll know because when you push the pedal to the floor, you can't get the transmission internals to stop spinning to get it into gear smoothly.

The complete and single reason that clutch brakes are ruined is by pushing the clutch too close, or to, the floor while the vehicle is moving. and I mean moving so much as an inch. Forwards or backwards.

In other words: If you have a clutch brake, NEVER put the clutch to the floor unless you are stationary.

When changing gears, coming to a stop, etc, the clutch only needs to be pushed beyond the friction point, not to the floor. Clutch use is another of those myths of history, full of outdated or wrong direction.

The clutch brake is intended to stop the spinning of the internal gear sets so that a starting gear may be engaged smoothly when stopped. It is not for any other purpose, and does not do anything positive, if you push the clutch down too far while moving.

One of the clutch brake's mating surfaces is connected to the driveline in a way that it will be ground down quite rapidly by the movement of the vehicle, in a way that it was not designed to withstand.

Old GM owners all wish that the clutch brake feature had been available on their coaches, and most MCI's too....

happy coaching!
buswarrior
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gus
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« Reply #7 on: January 21, 2008, 02:31:36 PM »

I question also if you have a clutch brake, very rare on a bus?

If you do you probably have a Spicer clutch which is adjusted either with a wrench or with a large flat screwdriver or an auto brake adjuster.

Very few people know how to adjust these Spicer clutches. I had to do this by default on my antique Dodge semi because I couldn't find anyone who knew how to do it.

I recommend you find an old timer at a truck repair shop to show you how to do it. I have an instruction book somewhere and will try to find it if you need it.

If your clutch brake plates are worn out they must be replaced before adjusting the clutch. There is a way do do this without removing the trans which involves cutting sections out of the plates.
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lyndon
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« Reply #8 on: January 21, 2008, 05:08:41 PM »

Are you certain the clutch has a clutch brake?

Hmmm, fair question, since the brake has not worked since I picked up the bus.

But I have a 1988 MC-9 -- one of the newer of this model -- and my service manual is dated 1-1-89. It makes several references to the clutch brake, none in the context of this being an optional feature. The specifications section says it should be a Dana "Dry 2-Plate, Pull Type", 15.5 inch 2-10 spline, 2800 lbs plate load. (The transmission is a 5-speed Fuller 11605, BTW).

When I pull the inspection plate, I guess I'll know for sure, but it has always felt like the thing is just starting to grab when I stand on the clutch. If I rush, I have to grind it a bit to get into first from a standstill, but with a bit of patience, I think there's some braking going on.

Hopefully, next weekend will provide an opportunity for the visual check.

Thanks,

Don
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Don
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« Reply #9 on: January 21, 2008, 05:53:51 PM »

Don, if you have 1 1/2 in of free play, the only way you can turn in more clutch brake is to reduce the free play. Clutch brakes are very sensitive to over use, if you just touch the clutch brake momentarily to stop the gears from rolling they last a long time with one driver. If you change drivers and someone holds the clutch down at a stop sign it will eat the clutch brake, especially the cheap one piece type that usually comes with a rebuilt clutch. The 2 piece replacements are a little better but still will not take alot of abuse. If you have a good clutch brake you will have 3 clutch positions,(1) all the way out,(2) on the floor (against the clutch brake), and(3) above the clutch brake for after entering 1st or reverse and regular shifting. You cannot hold pressure on the C/B for more than a few seconds and it is not used for shifting, only entering first or reverse.

Go to a truck shop and look at a 2 piece, the standard input shaft sizes are 1 3/4 in and 2 in and you will need to get the right one, maybe your book states size or maybe you will have to measure it somewhere inside the bellhousing with a caliper or other tool.

If you look inside the bell all the way to the front (engine) you can see the C/B. Have a helper push the clutch pedal all the way in and observe if the C/B is being compressed. It should be in one piece and is splined to rotate on the shaft, so it cannot turn on the input shaft even when released and be good.

I have changed many and always have used a torch to blow the old one off the input shaft, so keep in mind the fire hazard! Unless you are comfortable with a torch under your bus and have a good idea what you are doing I would pay a shop an hour to change it out for me.

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lyndon
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« Reply #10 on: January 21, 2008, 06:23:48 PM »

Thanks, Larry ( I hope it's Larry Smiley ) for the tips. I was hoping to hear some input from a few members that have had their fingers dirty with clutch brake dust. From a driving standpoint, I have plenty of heavy truck experience, but did not know clutch brakes were so rare in coaches.

(On a side note, the rare exception where we would use the clutch brake in motion was to "quick-shift" out of 1st or 2nd when pointed uphill -- not highly recommended, of course, but doable if timed just right. The idea is to be able to sync up when the grade causes the truck to slow faster than the transmission can. Miss it and start all over again, which is not so great for the clutch on a grade).

In any event, I will be taking your advice about going to a shop if the brake is toast. Me-with-torch is dangerous under the best of circumstances. I'm still hoping to get something out of an adjustment, though, but I can't get to the bus until the weekend to verify the pedal height, free play, etc.

Don
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Don
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buswarrior
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« Reply #11 on: January 22, 2008, 08:06:27 AM »

Those are clutch specs, not clutch brake specs.

I'm suspecting there is no clutch brake. If you get the internals in those 5 speeds spinning when out of gear and clutch engaged when stopped, they slow down fairly well on their own in a few seconds with the clutch pushed in.

Bus drivers are historically notoriously hard on manual transmissions, clutches being changed out with a frequency that would make a truck owner cringe. A clutch brake wouldn't make it past the second stop sign before it was burned right out of there by coasting into the stop with the clutch pushed all the way in.

And that "tip" about dipping into the clutch brake on a steep hill to aid in gear shifting, is one of those destructive myths I was referring to. If you are paying for the upkeep, you do not want to be doing that.

Uphill causes a panic, when the right strategy needs to be clam and slower than normal. And the anticipation, coupled with the fear of losing momentum often leads to the throttle being still open as the clutch is disengaged, giving the driveline a little goose, further speeding up the gear sets.

Abusing the clutch brake seemed to work because it takes longer to put the clutch deeper, giving the gear sets more time to slow down to match the next gear. If you had waited the same split second longer without going as deep, it would have gone in too.

What mechanic will tell someone to stop wrecking stuff and slit his own throat?

happy coaching!
buswarrior
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gus
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« Reply #12 on: January 22, 2008, 02:56:28 PM »

As I remember Dana bought Spicer a number of years ago.

Be sure to tell us what you find, especially if it does or does not have a clutch brake.
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lyndon
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« Reply #13 on: January 22, 2008, 09:39:57 PM »

And that "tip" about dipping into the clutch brake on a steep hill to aid in gear shifting, is one of those destructive myths I was referring to. If you are paying for the upkeep, you do not want to be doing that.

Buswarrior, I can assure you that the little aside in my previous posting is no myth, not only because I have seen it done by a very few of the most experienced truckers I have known -- all of whom understand the abuse it can cause to the clutch brake, BTW -- but because I have done it myself. Destructive? Perhaps. A myth? Absolutely not. But I did qualify the remark with a "not recommended" disclaimer.

Let me be clear. I was not referring to a situation where simply being patient could possibly work, because I was referring to a situation where simply being patient means you a standing still. In other words, say, you are loaded to 80,000 lbs on a 5% grade and start out in bull low. You cannot gain enough momentum to shift into second by simply waiting, unless you are willing to simply wait until you reach the summit.

So there's your first choice: wait until you reach the summit. Your second choice is to start out in a higher gear in order to gain enough momentum to shift. Obviously -- assuming you engine has enough power -- this will murder the clutch. The third choice is to "panic" shift and grind that puppy into second gear whether it wants to go in or not. Which brings us to the fourth choice, the little "tip" as you called it. Clearly, option choice #1 is the correct one, in terms of wear & tear, never mind the risk of major drivetrain failure.

The problem with the clutch brake trick is that you are trying to brake the spinning transmission main drive gear from 2000+ RPM, rather than from the 600 RPM idle speed it was designed for. That is not to say, however, that it will not work. With perfect timing, a clean upshift is possible, not imaginary or a myth. Extra wear on the clutch brake is the price, of course. (Note that the transmission is in neutral at this point; otherwise, the clutch brake is trying to stop the whole bus, which is why you do not want to stand on the clutch while moving in gear! This is probably the source of confusion about never using the clutch brake when the vehicle is in motion.)

After the first million miles, or so (and maybe a mountain pass or two), uphill does not "cause a panic". And yes, I have used this technique on my own truck (seldom, of course), for which I was paying the bills. And no, I have never lost a drivetrain component -- clutch and clutch brake included -- prematurely or catastrophically, so I guess a lot of mechanics were "slitting their throats" a few years back.

And no, I did not stay at a Holiday Inn last night.

I guess my "aside" led this thread a bit off topic. Gus, I will be happy to let you know what I find.

Don
« Last Edit: January 23, 2008, 12:25:08 AM by lyndon » Logged

Don
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lyndon
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« Reply #14 on: January 27, 2008, 01:33:57 PM »

As I remember Dana bought Spicer a number of years ago.

Be sure to tell us what you find, especially if it does or does not have a clutch brake.

Gus, I had a chance to get at the bus yesterday, and pulled the inspection plate. A couple of shots give a fairly clear view of the clutch brake, so I guess there's no doubt it's there. In the second shot, I slid it back for a better look.

It doesn't look too healthy to me, so I think I'll have to live with it for now (as I said, cutting it out of there is not a job I'd want to tackle). A measurement of the the adjustment showed an exact 1/2 inch gap between the brake and release bearing, to I'm hesitant to even try getting any more out of it; a slipping clutch would be a larger problem. (Any thoughts?)

The excess grease from the bearing probably isn't helping much, but with a clamping type of brake, I'm not sure how much of a difference that would make. The manual requires high temperature grease; I'd guess that regular chassis grease has been used, which flowed out like water.

I wiped out what I could and gave the bearing a few shots of high temperature synthetic grease. I'm going to check the service records to see it the clutch is likely due for replacement anytime soon.

Don


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Don
1988 MC-9
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