clutch slipping...again

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Petros
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My tercel:: '84 Tercel4wd w/extensive mods
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clutch slipping...again

Post by Petros » Fri Jan 11, 2019 1:04 am

my clutch had started to slip about two years ago, figured it was about time to replace it after about 100k of very hard miles, many in 4wd.

I recall many on this forum having fitment problems, so I tried to buy an ASISIN brand clutch assembly (factory clutch), found one on Rockauto at a good price and purchased it. Oddly, the private lable box had the Asisin brand pressure plate (made in Japan), and a "LUK" brand pressure plate (made south Africa). the TO and pilot bearing were japanese brand, so I had no reason to mistrust them. I installed them all without incident, but after only a year it would occationally and noticabley slip when I lug the engine. It got progessively worse, I figured it was that off brand friction disk, or perhaps it was contaminated.

So I ordered another friction disk, they are cheap and if the pressure plate was still good (should be, it only had about 20 k miles on it), I thought I can get away with a quick disk change. When I had it out, the flywheel was scorched with some minor surface cracks. I did not want to take the time to have it resurface, I usually do not have trouble with the flywheel after just sanding it to break the old glaze. and except for some minor glaze, the disk looked okay. It was well within specs for thickness, it did not seem like it would slip. I installed the new disk.

After I got it back on the road, on hard acceleration I had a small amount of clutch chatter when I shift. with proper clutch technique, or on normal shifting, it would stay silent, but wondered if I should have taken the trouble and extra time (and cost) to have it resurfaced. But no noticeable slippage. Too late now, I made a mental note to make sure I resurface my flywheel next time it is out. I usually end up removing the trans or engine for other reasons eventually (leaky seal or gasket, etc). I would get to it eventually.

when my center two pistons on the engine blew out, damaging the rings, last year I rebuilt the engine. since it was out and apart, i had the flywheel resurfaced (came out very nice, took a few oz off of it too). When I installed the flywheel I cleaned it very well with soap and water, and than brake parts cleaner, same with the pressure plate assy. it all went together normal, same stiff bolt up as normal. Nothing felt amiss on assembly.

Now that I finally got it back on the road, within about 30 miles, I notice the clutch is slipping again when I was lugging the engine on uphill runs (highest torque load on the clutch happens at lower rpm, high throttle setting...lugging it). No more slip after the next 130 miles, including some hills on the hwy, but I tried to avoid lugging it.

I can not tell you how frustrating that is. I am getting tired of pulling this car apart. Now I wonder if my good quality Japanese Pressure plate assy may have been weak. It does not have that many miles on it, it looked fine. I did a detailed inspection of it when I cleaned it, all parts, pivots, spring, etc looked like new.

My questions for you all is this:

1. is there a bench test (when it is out of the car) to determine if the pressure plate assembly is good?

2. does a resurface flywheel have a "wear in" period before it grips well?

3. Any other reason the slippage might go away, or what else could cause it?

4. anyone have a new clutch slip a bit at first, and than settle down and grip good?

I am hopping to avoid having to pull it apart if possible, if I do, I will get all new parts (all Asisin brand).

I have a lot of old pressure plate assemblies kicking around my garage, I have been meaning to scrap them all, though I know some are not too old and worth keeping as a spare (they came out of parts cars with good low wear friction disks with them). Perhaps, for the amount of work it is to replace the clutch, none are worth keeping..unless there is a reliable way to tell if they are good without putting them in the car.

I will also double check the clutch linkage and cable to make sure it is not too tight. The auto adjuster had the correct amount of free play when I connected up the spring on the cam so the cable will tighten, it seems unlikely but it is worth a check. Odd thing was, I found an extra spring (the type with a hook at both ends) in the foot well on the carpet when I got everything back together. I doubled checked the auto-adjuster but all three springs are present and it appears to be working properly. I had my whole heating system apart to replace the heater core, so it may go on one of the heat system flap doors, I have yet to completely replace all of the ducts, and finish putting all the ducts and panels back under the dash. So that coil spring with the hooks on it may go somewhere not shown in the diagram in the FSM. but it does no appear so.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

teranfirbt
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Re: clutch slipping...again

Post by teranfirbt » Fri Jan 11, 2019 5:10 am

In my experience, clutches are a lot like brakes, they need a little bit of a bed in before they work correctly. Every new clutch I've had I've done a small break in when fresh by slipping it just a little excessively (like, 2-3 seconds more than one would expect) and then driving it super casual/gentle to cool everything back down. I've had good experience with this method, the clutches will have a little bit more slip than normal out of the box and then get nice and grippy after breaking them in this way. As long as you don't get things too hot and glaze over the clutch, you should be good to go for awhile.
What RPM do you generally slip the clutch at to get going? I've been running an Exedy clutch on my 4AFE for ~30k miles without issue, but I also tend to be very gentle on clutches. I generally don't take off at more than around 1500 RPM, and I'll slip it as little as possible.
To answer your questions:
1 - There might be a way to check that's outlined in the FSM. I imagine it'd be a combination of measuring the bolting surface to friction surface and then measuring force vs. displacement of the diaphragm. The first test is pretty easy, straight edge and a pair of calipers, but the second would take some pretty neat equipment to get right.
2 - Generally yes, as I outlined above. Scorch marks and surface cracks are a sure sign that the clutch was being abused and overheating, which will ruin the friction disk pretty quick. All flywheels should be surfaced before a new clutch goes in, it would definitely explain your chatter and slipping.
3 - If the flywheel surface was scorched and cracked it's a sure bet that you'll want to pull it out. If the friction disk still has plenty of material you might be able to get away with only surfacing the flywheel, but it's probably worth doing the whole job.
4 - Every new clutch I've dealt with has slipped a bit after install, but once I bed it in once or twice (making sure to allow everything to cool a bit between floggings....) they've settled down and gripped well.

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splatterdog
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Re: clutch slipping...again

Post by splatterdog » Fri Jan 11, 2019 10:29 am

Can't remember, is the flywheel stepped requiring 2 cuts(pressure plate mating surface lower than clutch disc)? If so did they keep dimensions the same?

Is the throwout bearing pilot on the trans grooved in any way?

Lastly is a frayed or sticky cable not allowing full return?

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Petros
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Re: clutch slipping...again

Post by Petros » Sat Jan 12, 2019 12:44 am

Yes, the face of the flywheel is stepped and when they resurfaced it they kept the correct step in the face.

The disk is new, the flywheel is newly resurface, and I used the pressure plate that is two years old and appears in great shape.

FYI I had no further slipping today at all, it feels solid and grabs normally from a dead stop. It only slipped once on an up hill run at hwy speeds at about 2000 rpm. It only had about 12 to 15 miles on it from install and first start up.

It appears to have needed some wear-in, but i will keep an eye on it in the coming months, especially on the steep hills.

Funny thing is, I have to drive up a quarter mile of steep gravel road at 20 percent grade to get home. And there was no hint of slip on that hill the two times I have driven it with the new clutch.

Maybe it is all good, and just needed some breakin.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

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splatterdog
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Re: clutch slipping...again

Post by splatterdog » Sat Jan 12, 2019 6:49 am

Could be. New surfaces are actually pretty rough on brakes too. Only hitting on the peaks initially. I've seen brake shoes take a year or two before full drum contact was made.

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Petros
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Re: clutch slipping...again

Post by Petros » Sun Jan 13, 2019 3:52 pm

last night I had to drive up a steep, 20 percent grade street that was perhaps a mile long. not a hint of slip. odd it was so easy to make it slip in the first few miles of driving, but now seems okay.

I am going to give it another week, and than try the clutch test (stall out the engine using the clutch). if it stalls the engine, than I would consider this a non-issue.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

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Petros
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Re: clutch slipping...again

Post by Petros » Fri Feb 15, 2019 6:11 pm

all the recent snow, and getting stuck in it several times, has caused the clutch to slip and over heat several times. This normally would not happen if the clutch was up to snuff. I ordered another clutch, I have to assume the pressure plate is weak (not enough clamping force) because I replaced the disk recently. but I have been also looking around at ways to bench test the pressure plate assembly for clamping pressure, just to verify the pressure plate is weak.

I think I have devised a simple way to bench test the pressure plate. I have like 4 or 5 used pressure plates in my garage, I was going to scrap them, but I might use this test to see if they are any good, and test the one I remove from my car this weekend. I will also test the two new clutches (different brands/sources) I have ordered and should be coming in this weekend.

two ways, simplest would be to put the pressure plate face down on a table or work bench, and devise a lever that will push down on the pressure plate fingers (using a throw out bearing), and than measure how much force is on the lever when the pressure plate lifts off the table top. if i use weights on the lever end, I can calculate the force require to compress the spring. This would only get me a comparison, and it would not measure the spring force as when a friction disk was installed under the cover.

the other way may be better, but a bit more work: put a flywheel on the table first, than install a disk and the pressure plate on the flywheel (fully bolted down with the six bolts), than use a lever to press down on the fingers of the spring (again using a throw-out bearing). To tell when the pressure plate releases the disk, either put a strip of thin fabric, or using a tool like a screw driver tip, to see when the disk is free. I can either see when I can rotate the disk in place, or tug on the fabric strip until it slips free when the pressure is released.

in either case I would have to come up with a way to fix the end of the lever fulcrum to the work bench, and I would need a lever long enough so a reasonable amount of weight would compress the clutch spring. Either a scale, or just weights, used at the end of the lever, increasing the weight or force on it until the pressure plate lifts off the disk.

there is even a way to determine the clamping force from this information, by multiplying the applied force to the throw out bearing by the spring lever ratio. But that is not important in a comparison between different pressure plates. It would be nice to know what the clamping force specication is for a tercel clutch assembly.

For example, if I put 50 lbs on the end of the lever to get the pressure plate to release, and it was at an 7 to 1 lever ratio, it means it took 350 lbs on the pressure plate to release it. if the clutch spring lever ratio was say three to 1, that means the clamping force on the disk would be 1050 lbs.

Any thoughts? does anyone know where to find the clamping force specification for the tercel clutch?
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

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NWMO
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Re: clutch slipping...again

Post by NWMO » Fri Feb 15, 2019 8:44 pm

Petros,

Since you’re nerding out on this test anyhow, you should be able to caculate the needed pressure based off of the clutch plate area, coefficient of friction between the clutch plate and flywheel and max torque w/ the typical engineers factor of safety.

Of course, it would be best to find a toyota spec, but not nearly as much fun :).
Psalm 37:4 "Delight yourself in the Lord and he will give you the desires of your heart"

Live each day to make a positive difference in someone else's life AND on your bad days, just keep it to yourself :)

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Petros
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Re: clutch slipping...again

Post by Petros » Sun Feb 17, 2019 11:14 am

First test indicates there is 20 percent difference in 4 different brands of clutch pressure plate assy. One of the lowest was actually a used ASiN brand.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

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Petros
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Re: clutch slipping...again

Post by Petros » Tue Feb 19, 2019 10:21 pm

I set up a simple lever rig, with a handly weight on the end of the lever. I weighed the load I had at the end of the lever when the plate released, and multiplied the lever ratio to get the force required to release the pressure plate (force required to lift the plate off the disk).

I had 4 used clutches in my scrap pile, an ASIN of a different style, that I realized must be a honda clutch since it was a different dia. The used Asin listed below was what came out of my Tercel (that was slipping under heavy laods). I also had an ASCO (made in Japan), a "DK" brand (unknown to me, it has a logo that is like the Minicooper wing logo with the "DK" in the center, anyone know?), an unbranded one with "made in Great Britain" on it but no brand (could be made in India, Hong Kong, who knows). These all looked similar in design.

I ended up buying two new clutches, one from Rockauto, one from Amazon. I had order the Beck Arnely from RA, but later realized I can get the one from Amazon faster at no extra charge, it was a Luk brand (according to their website all parts are US made, but the name sounds Chinese). The Beck Arnely was actually a ASCO brand (the box said made in Japan), and the Amazon clutch was actually an ASIN (Japan), with a LUK disk (made in South Africa), and with Japanese pilot bearing, and an unmarked/unknown throw out bearing. I installed a Koyo (Japanese) new throw out bearing I had since mine was wearing out (after about 200k miles), and threw out the unknown brand.

The release force is directly measured by weighing the weight required, and multiplying the lever arm ratio. the clamping force of the pressure plate assembly should be about the same ratio in each brand, but is dependent on the diaphragm spring lever ratio, it was about 3 to 1 but varied slightly from one brand to the next (the length of spring "lever" to the fulcrum, and the distance from the fulcrum to where spring bears on the pressure plate). It was difficult to measure accurately without cutting open the pressure plate assembly since these lengths are internal to the clutch cover.

USED PRESSURE PLATES (release force in LBS)

Made in UK 355 lb
ASIN 364
ASCO 419
"DK" 426

NEW Pressure plates (Release force in LbS)
ASCO 515
ASIN 532

this would correspond to a clamping pressure that would range from about 1065 to a high of 1596 lb. it appears it is not worth reusing pressure plates, Springs do not wear out normally if the loads are within their normal elastic limit, but they do get microscopic fatigue cracks that serve to weaken the force that is transmitted. it is such a big job to change a clutch, it is not worth saving $40 to reuse the old pressure plate. The only way to know if it is still good is to rig the test jig and compare the spring strength.

An interesting piece of data, the different brands of pressure plates ranged in weight from 7 lbs (low) to 13lbs high. it hardly seems worth the expense of shaving 4 or 5 lbs off the flywheel if you buy a clutch that weighed 6 lbs more than other brands. the Asin brand was at 8 lbs, right at the low end of the range. All of the different brand of disks were about the same weight, and same dimensions.
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'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

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xirdneh
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Re: clutch slipping...again

Post by xirdneh » Mon Mar 04, 2019 1:33 am

You might as well measure the clearance too. When depressed it should be about .050" . I had that bad one a while back that was .005" . I kinda figured out that the travel distance of the throw-out bearing was about .375" .
Love those Tercell 4x4 wagons but they sure suffer from road noise.

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