Manual transmission poll

[charby]

Old John Deere with the lever clutch?

Nope IH and Case before they were CaseIH

[Poper]

I'm having a hard time visualizing this. I'm quite sure that disengaging car clutches puts thrust load directly on the flywheel, from the throwout bearing by way of the pressure plate springs, which flywheel is connected directly to the crankshaft.

The only "solid" connection of the clutch assembly to the flywheel is at the perimeter where the pressure plate is bolted in place.  The mechanical lock up of the clutch is the pinching of the clutch plate between the pressure plate and the flywheel by the pressure plate springs.  The force applied by the throw-out bearing to the pressure plate release levers is leveraged to retract the pressure plate surface off the clutch disc so that the clutch disc can spin free of the pinching action of the pressure plate and flywheel.  In other words, all of the force to release the clutch is consumed by the pressure plate springs.  None (theoretically) of the force necessary to disengage the clutch is transmitted through the flywheel to the crankshaft and to the thrust bearing.  Mechanical clutch mechanisms apply the force of your foot through the pedal, linkage and a lever directly to the throw-out bearing.  Hydraulic systems apply force directly to the throw-out bearing with a slave cylinder.

I wasn't talking about the throw-out bearing; but the crankshaft thrust bearings. Throwout bearings are cheap.

I think you may be confusing a thrust bearing with a pilot bearing.  But no, throw-out bearing replacement is not cheap - unless of course, you are pulling the transmission (and transfer case in a 4x4) yourself.  An neither is a pilot bearing or air cooled VW gland nut.

Why would accelerating cause any thrust load on the crankshaft? Unless it's an airplane, I don't see where any thrust loads come from.

Thrust loads are applied to the crankshaft any time the engine work load varies.  Throttle advancement increases thrust onto the crankshaft because the thrust from the piston is greater.  Whenever you increase the work load on the engine, whether via a propeller (aviation or watercraft) or a transmitted load through a transmission, drive shaft, final drive combination or any other means of doing work with the engine, a thrust load/axial load/asymmetrical load, is applied to the crankshaft.  The engine designer can run you through the calculations as to why he places his thrust bearing in the particular location he does, but just take my word for it, its location is not chosen at random.  Under starting conditions, the greatest load applied to the thrust bearing will be when the engine fires and catches.  The load applied by your foot to the clutch is an almost infinitesimal amount, as far as a thrust bearing is concerned.  I doubt it is even taken into account as a design load on an engine's thrust bearing.

I pulled a lot of vehicle engines apart for Uncle Sam's Air Force.  Quite honestly, I could not tell the difference in wear of the crankshaft thrust bearing between one with an automatic transmission and one with a manual transmission.  And we had a lot of both in vehicles large and small.  The usual wear issue was age and lots and lots of miles.  The greatest factor on the pace of wear was that any particular vehicle might have several dozen to several thousand different operators over its serviceable life time.  Therefore, it was constantly trying to "wear into" an operating "groove" that (likely) never happened.

I hope this is helpful.

Poper

[RoadKingLarry]

My M715 had the parking brake partially disabled so I park it in gear and chock at least 1 wheel if on a hill. My new tractor has a clutch interlock, it isn't an issue to me. My '52 Allis Chalmers does not have a clutch interlock. If you are standing on the ground and start it in low gear it will take off even at the lowest throttle setting, bonus points for hitting the kill switch before it runs over you and drives through the back wall of the shop.
My daughter's truck has a clutch interlock. All well and good till the clutch locks up and you can't push in the pedal. Put in neutral, jump across the selelnoid to start, get a push down an incline to start rolling and speed shift the 10 miles to the shop that was going to fix the clutch. The fun part was getting across the highway.

[Tallpine]

I almost never use the parking brake on a manual transmission, unless I am letting it sit and idle and then I either park it where it can't roll or chock it.  We lost a fire truck because the parking brake released by itself and then it jumped over the chock too!     (we always leave them running on scenes because you never know when you will have to move right now and you don't want to have a dead battery)

With an automatic, I use the parking brake on hills just to keep the park pawl from jamming up.  Better to just not park on hills - park sideways with the wheels turned uphill.

The clutch safety switch is mostly for idiots.  I unplugged and jumpered it with a short piece of bare wire on our old Suburban (2wd 4speed).  Don't remember why now except probably the switch was flaky.  It came in handy when the clutch went out and we limped it to the shop.  The switch on my 76 GMC sometimes comes unplugged, usually on a rainy night 

I may disable the clutch switch on my 1989, just because it is so hard to get it down far enough to start without having the seat too close to the steering wheel    I'm not fat at all but I hate having my arms bent that much all the time when driving.  The gorram engineers must have just assumed that everybody was going to order an automatic.

I was driving pickups and trucks long before they invented the clutch safety switch 

[K Frame]

I always use the parking brake, except in winter. Had the brake freeze on once.

Years ago the neighbors kid across the street parked their pickup, didn't use the parking brake, didn't turn the wheels, and left it in gear on the inclined.

It ended up in my Mother's van.

She was sorely pissed, but they took care of it.

A few months later, guess what happened again, only this time the damage was a LOT worse because of where it hit.

That time the police got involved, the kid lost his driving privileges for quite some time, and had to drive his Mom's little foo-foo Chevette (probably the worst punishment of all).

[coppertales]

If your parking brake doesn't hold the vehicle, have you ever given any thought of fixing it?  From all the so called theroy you guys are posting, have any of you ever given a thought of reading the owner's manual that comes with the vehicle?  I have been a mechanic for 50 years and never have heard of what alot of you are saying.....on topic, I put my motorcycle in neutral except when parking on a hill.  My F150 has to have the clutch pushed in or the truck will not start.  Yes, I park it in gear and  my parking brake works just fine.....chris3

[Tallpine]

If your parking brake doesn't hold the vehicle, have you ever given any thought of fixing it?  From all the so called theroy you guys are posting, have any of you ever given a thought of reading the owner's manual that comes with the vehicle?  I have been a mechanic for 50 years and never have heard of what alot of you are saying.....on topic, I put my motorcycle in neutral except when parking on a hill.  My F150 has to have the clutch pushed in or the truck will not start.  Yes, I park it in gear and  my parking brake works just fine.....chris3

On the fire truck that we lost, the entire parking brake mechanism had just been replaced by one of our volunteers 

Of course, it was a Dodge, too 

[zahc]

Thrust loads are applied to the crankshaft any time the engine work load varies.  Throttle advancement increases thrust onto the crankshaft because the thrust from the piston is greater.

I don't think we are using the term "thrust" the same way. When I say "thrust force" I mean a force directed along the axis of the crankshaft. In a car engine which is bolted to a transmission, there shouldn't be any thrust load on the crankshaft unless something weird is going on, no matter what the engine load. It's all torque.

Mechanical clutch mechanisms apply the force of your foot through the pedal, linkage and a lever directly to the throw-out bearing.  Hydraulic systems apply force directly to the throw-out bearing with a slave cylinder.

Yes. If the throw-out-bearing is pushing on the pressure plate levers, to disengage the clutch, then there must be a thrust bearing somewhere that keeps the flywheel/pressure plate assembly/crankshaft from simply moving forward and pushing the crankshaft through the radiator. Else, the clutch would never disengage. Where do you suppose this thrust bearing is located? In all the cars I have seen, there is no extra or special thrust bearing. The axial load from the throwout bearing is simply applied to the flywheel where it is transmitted to the main crankshaft bearings (at least one of which has a thrust bearing incorporated). This is how I was taught to measure crankshaft end-play...you lever against the front crankshaft pulley to force it one way and then you press on the clutch to force it the other way.

What is the logic behind parking with the front wheels turned? I suppose it's so the car will turn into the curb instead of rolling straight back, but it seems like turning the wheel either way will accomplish that, assuming you park fairly close to the curb.

[Tallpine]

What is the logic behind parking with the front wheels turned? I suppose it's so the car will turn into the curb instead of rolling straight back, but it seems like turning the wheel either way will accomplish that, assuming you park fairly close to the curb. 
 

If you park on a sidehill and turn the front wheels uphill, then either way the vehicle tries to roll (forward or backward) is uphill.

At a curb:
* turn wheels into curb when facing downhill; the other way the car would roll out into the street
* turn wheels away from curb when facing uphill; either way it would eventually hit the curb on the same side of the street, but sooner if the front wheels catch instead of the back.  Get enough momentum and it will roll right over (wheels being round and all  )

[Jamisjockey]

If you park on a sidehill and turn the front wheels uphill, then either way the vehicle tries to roll (forward or backward) is uphill.

At a curb:
* turn wheels into curb when facing downhill; the other way the car would roll out into the street
* turn wheels away from curb when facing uphill; either way it would eventually hit the curb on the same side of the street, but sooner if the front wheels catch instead of the back.  Get enough momentum and it will roll right over (wheels being round and all  )

This.  Stops the vehicle from rolling into traffic or the vehicle behind or in front of it.

[drewtam]

The miata BP4 thrust bearing is incorporated into main bearing #4. One can barely make it out in the first picture.





This was just an excuse to post engine rebuild pics. :)

[zahc]

Cool, the '99 miata I just bought is leaking from the front of the motor but not enough to warrant an immediate teardown. I will probably do a timing belt/crank seal/cam seals/water pump/radiator flush mega-maintenance eventually.

[Hawkmoon]

I wasn't talking about the throw-out bearing; but the crankshaft thrust bearings. Throwout bearings are cheap.

The throwout bearing in my Jeep Cherokee also incorporates the clutch slave cylinder, and it is NOT cheap. Neither is the labor to replace the slave cylinder/bearing unit in a 4WD Jeep.

[Hawkmoon]

I don't think we are using the term "thrust" the same way. When I say "thrust force" I mean a force directed along the axis of the crankshaft. In a car engine which is bolted to a transmission, there shouldn't be any thrust load on the crankshaft unless something weird is going on, no matter what the engine load. It's all torque.

Then why do the engines have thrust bearings?

[Tallpine]

The throwout bearing in my Jeep Cherokee also incorporates the clutch slave cylinder, and it is NOT cheap. Neither is the labor to replace the slave cylinder/bearing unit in a 4WD Jeep.

Yeah, Fords are the same way     Plus once that you have the transmission and transfer case out, you might as well put in a whole new clutch.

My old GMC truck had a hydraulic clutch, but the slave cylinder was outside the bell housing and it just pushed the outboard end of the fork just like a regular clutch linkage, but without the linkage.  It had a dual master cylinder: one side was the brakes and the other side was the clutch 

When the TO bearing did go out, I used a slice of a big log and some 2x lumber to support the transmission while I unbolted and just slid it straight back to clear the clutch.  The bell housing had the dust cover you could take off and reach right up into the housing.  All I need was enough clearance to slip the TO bearing off the end of the input shaft.  I never mucked with the pressure plate so everything was still lined up to go back into the pilot bearing.  The transmission alone in that truck weighed more than most car engines today.  Of course it helps that once you crawl under the frame rail, you could sit up on the ground under the cab 

And I discovered that the TO bearing had a grease zerk 

[zahc]

Then why do the engines have thrust bearings?

They have to have something to keep the crankshaft lined up underneath the pistons/rods and keep the crank journals from hitting against the block. The normal main bearings can't support any thrust load so at least one of them has thrust bearings incorporated. There is a spec for crankshaft end-play (typically .005-.010") and often you can get different thrust bearing thicknesses to adjust it. But the thrust bearing is not something that takes any load except, well, the throwout bearing.

[Poper]

They have to have something to keep the crankshaft lined up underneath the pistons/rods and keep the crank journals from hitting against the block. The normal main bearings can't support any thrust load so at least one of them has thrust bearings incorporated. There is a spec for crankshaft end-play (typically .005-.010") and often you can get different thrust bearing thicknesses to adjust it. But the thrust bearing is not something that takes any load except, well, the throwout bearing.

That's not entirely accurate.
The load transmitted to the thrust bearing is a load, though I can find nowhere that it has ever been measured.  Because the force applied to the throw-out bearing is for the purpose of compressing the pressure plate springs, the springs must absorb most of that force.
Torque converters also put a thrust load on the crankshaft.  Imperfect alignment of drive belt/pulley systems put a thrust load on the crankshaft, too.
From an article written on the analysis of thrust bearing failure:  http://www.4secondsflat.com/Thrust_bearing_failures.html

Although thrust bearings run on a thin film of oil, just like radial journal (connecting rod and main) bearings, they cannot support nearly as much load. While radial bearings can carry loads measured in thousands of pounds per square inch of projected bearing area, thrust bearings can only support loads of a few hundred pounds per square inch. Radial journal bearings develop their higher load capacity from the way the curved surfaces of the bearing and journal meet to form a wedge. Shaft rotation pulls oil into this wedge shaped area of the clearance space to create an oil film which actually supports the shaft. Thrust bearings typically consist of two flat mating surfaces with no natural wedge shape in the clearance space to promote the formation of an oil film to support the load.

The crankshaft turns on a film of oil under pressure from oil pump.  It literally "floats" on a film of pressurized oil rather than run on the bearing surface, which is why they can run such a long time under quite heavy loads.  With this in mind, the need for a little end play is obvious - the thrust bearing cannot take a constant friction contact with the crankshaft. 
As to causes of thrust bearing failure, the article states:

Loading:
A number of factors may contribute to wear and overloading of a thrust bearing, such as:
1. Poor crankshaft surface finish.
2. Poor crankshaft surface geometry.
3. External overloading due to.
    a) Excessive Torque converter pressure.
    b)    Improper throw out bearing adjustment.
    c)    Riding the clutch pedal.
    d)    Excessive rearward crankshaft load pressure due to a malfunctioning front mounted accessory drive.

"Starting the engine with the clutch pedal depressed" is not stated as overloading the thrust bearing.

With all the above, it appears the load applied to the thrust bearing when depressing the clutch pedal while starting the engine is an insignificant factor contributing to thrust bearing wear.  Just another "old wives' tale", so to speak. 

I saw a lot of torn down vehicle engines in Uncle Sam's Air Force, and before and after, too.  I can honestly say I know of no report of a single one having failed due to the failure of the thrust bearing.  But then, my specialty was a General Purpose Vehicle Mechanic and I only worked on the vehicles that were painted blue.  I can't speak for the ones painted yellow.

If one is most concerned with wear in an engine, a recommendation is to use Exxon Elite 20W50.  This is an ashless oil approved for use in piston aircraft engines.  This study (http://www.utexas.edu/research/ctr/pdf_reports/0_5532_P3.pdf) concluded: "it was not surprising
that this oil had the lowest rate of change of wear metals of all of the oils tested."

JMHO, of course.

Poper

[Triphammer]

Never had a standard with a clutch safety swith. How would you push start such an animal?

[280plus]

Never had a standard with a clutch safety swith. How would you push start such an animal?

By yourself I assume? Neutral then jump in quick, push in the clutch, put it in first, release clutch.

Next dealie. I had an old ford F-100 with well over 200,000 miles on it. I parked it on a hill in front on my house in first gear with no brake and the wheels straight. Got up in the morning and the truck was gone. The engine was so worn it didn't have enough compression to hold it on the hill. It had rolled down the hill, across the "tee" intersection and off into a field on the other side of the cross road. One of those "Thankfully no one was hurt" moments. Insult to injury, the cops had it towed. 

ALWAYS set the handbrake and turn the wheels into the curb on a hill!!

Another thing. How do you get going up a hill without drifting backwards first? Release the clutch just to the point where it will hold the car on the hill before releasing the brake. The car SHOULD be able to hold itself on a hill while idling. A little practice goes a long way. You can feel the engine pick up the load when you get to the right spot in the clutch release. This is a momentary thing until you can move your right foot from brake to gas and release the clutch all the way. NEVER hold the car on a hill using the clutch for any length of time, it'll overheat and at least glaze if not fry. It's a good way to reduce clutch life and glazing leads to chatter in the clutch.

[280plus]

Now,,,let's discuss "chirping" second... 

[Tallpine]

Never had a standard with a clutch safety swith. How would you push start such an animal?

Doesn't make any difference because you aren't using the starter anyway.  The safety switch only breaks the power to the starter relay.

I had an old ford F-100 with well over 200,000 miles on it. I parked it on a hill in front on my house in first gear with no brake and the wheels straight. Got up in the morning and the truck was gone. The engine was so worn it didn't have enough compression to hold it on the hill. It had rolled down the hill, across the "tee" intersection and off into a field on the other side of the cross road. One of those "Thankfully no one was hurt" moments. Insult to injury, the cops had it towed.

Don't worry!  It'll come back 

(also, see one of my previous posts: my daughter's pickup started lurching down the drive one day.  The six cylinder would not hold it.  One of the dogs started barking at it and I chased it down and put it in low range before it hit anything)

Another thing. How do you get going up a hill without drifting backwards first? Release the clutch just to the point where it will hold the car on the hill before releasing the brake. The car SHOULD be able to hold itself on a hill while idling. A little practice goes a long way. You can feel the engine pick up the load when you get to the right spot in the clutch release. This is a momentary thing until you can move your right foot from brake to gas and release the clutch all the way.

Is this a question? 

I've had to use heel and toe of my right foot to handle both brake and gas pedal at the same time.

Generally, trucks have at least one lower gear than the normal starting gear, for using when starting on a hill, etc.  The trick is getting across the intersection before the light turns red again 

The newer pickups with five speeds can be a pain to get started on a hill with a load.  I guess you're not supposed to pull a load with them 

[Hawkmoon]

But the thrust bearing is not something that takes any load except, well, the throwout bearing.

And it takes that load EVERY time you step on the clutch to shift gears, which for most people driving a standard transmission probably amounts to hundreds of cycles a day. What difference does one more, to start the engine, make?

My '88 Cherokee's original clutch lasted over 200,000 miles. It was finally replaced be cause the slave cylinder pooped out and, as long as the transmission and transfer case had to be removed to replace the slave cylinder, it would have been foolish not to replace the entire clutch while it was exposed.

The engine now has 287,000 miles on it. I always depress the clutch when starting the engine. There's nothing wrong with the engine bearings -- they're all original, including the thrust bearing.

[41magsnub]

Anybody use a hill brake like my new Subbie has?  My understanding is it engages the electric parking brake (that is still screwing with my head a bit) then lets off as soon as I start slipping the clutch a bit.  All I've been able to do is kill the engine when trying to use it so far.

[Tallpine]

Anybody use a hill brake like my new Subbie has?  My understanding is it engages the electric parking brake (that is still screwing with my head a bit) then lets off as soon as I start slipping the clutch a bit.  All I've been able to do is kill the engine when trying to use it so far.

It used to be standard practice to use the parking/handbrake like that, since most people have two hands but very few have three feet.

But that was back in the days when you were expected to know how to drive without a bunch of automatic and computer controlled stuff. 

[Cliffh]

Another thing. How do you get going up a hill without drifting backwards first? Release the clutch just to the point where it will hold the car on the hill before releasing the brake. The car SHOULD be able to hold itself on a hill while idling. A little practice goes a long way. You can feel the engine pick up the load when you get to the right spot in the clutch release. This is a momentary thing until you can move your right foot from brake to gas and release the clutch all the way. NEVER hold the car on a hill using the clutch for any length of time, it'll overheat and at least glaze if not fry. It's a good way to reduce clutch life and glazing leads to chatter in the clutch.

I've used the emergency brake on occasion.  Slip the clutch until it starts catching, then release the brake.  Easier with a hand-operated e-brake.