Videlicet

So I'm having an issue with my 1991 240sx, when I give it full throttle it starts revving higher without actually speeding up. I figured it was the clutch slipping, but when I finally finished putting a new clutch in and it's still doing it. Any ideas what the problem is?

ultimateirving

did you see any oil back there? Rear main seal leaky?

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NukeKS14

Did you pull the flywheel and have it resurfaced? If you just tossed a new friction disk on a glazed flywheel that wont help things either. What you describe does sound like a slipping clutch.

NashT

This could be a few different problems. Can you provide more details about what steps you took when replacing the clutch?

What kind of exhaust are you running? Still have the cat?

Videlicet

To be honest, I tried recreating the issue yesterday, but it ran fine. Is it possible it has to do with breaking in the clutch? Because I have hardly put any miles on it. I wasn't aware until recently you're supposed to break in the clutch. And yes I did resurface the flywheel, I still have the cat, and I'm running some cheap catback exhaust I got off amazon

NukeKS14

Possible. We have no idea what powertrain you're running. Is the engine stock? Swapped? Turbo'd ka? Turbocharged ka24de's overrun the oem clutch relatively easily on mild boost. I powered through mine on a t3t4 setup with oem exhaust and cat at 8psi on an enthalpy tune.

Videlicet

it's stock, only thing my car has got is an intake and an exhaust

NukeKS14

Did the rear main seal seem intact? Ultimate was asking about oil. Yeah if your rear main seal is leaky or otherwise getting stuff on the clutch like leaky shaft seal on the transmission, thatd cause it to slip. Was your flywheel dry when you removed it? How did it look? Have you bled or replaced your clutch master or slave cylinder? How is your pedal pressure? If the shaft on your master cylinder is misadjusted at the pedal, could be trapping pressure and not allowing your clutch to fully disengage. You can adjust the shaft with i believe a 12 or 14mm combination wrench to loosen the retaining nut at the pedal. If its overly tight youd want to shorten it. Anything you did with the car when this problem began?

Videlicet

I dont think its leaking. Flywheel was dry I believe. The clutch pedal is now really easy to push down since I changed the clutch. I think I released the pressure from the master cylinder a few months ago which didn't really change much

NukeKS14

What do you mean by 'released the pressure from the master cylinder' ?

Videlicet

Sorry i think I confused the master cylinder for the slave cylinder. I remember now I didn't actually release pressure, I just tested if it was trapping pressure. It was not.

Videlicet

I tested it again today, if I push the gas past a certain threshold it will rev up faster than it should, after a second or two in the higher rev, the actual speed will start to catch up to where it should be. Is it possible this is actually the engine not the transmission? Is full gas possibly causing it to over rev?

NukeKS14

You are having an issue with your brakes.

Hear me out.

Did you do anything with your brakes recently? How is your brake pedal feel? Does it do this going up a hill more than on a flat road?

I believe you have brake pressure trapped causing drag. A stock ka24de should NOT overpower the clutch.... unless your brakes are dragging. Check rotors. Smell burning? Are they hot and look glazed?

jedi03

also with question above you do need to be easy on the clutch to allow it to bed just like brakes...putting power down before it can do so will be just like worn clutch...unless you have heavy duty clutch eg racing clutch

TheRealSy90

The only way the engine can physically rev up without the car accelerating in relation to the engine rpm is when the clutch is slipping. There is no other possibility aside from spinning the tires.

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mgbsr20det

Agreed


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Videlicet

I drove my car yesterday 3 separate times. It had the issue the first time I drove it but for some reason the second time I drove it the problem was completely gone and it drove perfect. Later that night I drove it and once again it had the issue. Now that I have felt how it should be driving I realize its not just slipping in the higher RPM, its slipping the whole time, just not that much.

it's very strange that it temporarily, for no reason that I could tell, drove fine. My brakes seem fine, so is it that the clutch is not being fully engaged somehow?

s13 @ fullboost

You more than likely need to adjust the master and get it dialed in. What can happen is the fluid can heat up & if you have it adjusted past the vent the hotter it gets its going to put more pressure on the slave as the fluid expands.

I could be totally wrong I am sitting here guessing on the internet, but I wouldn't be quick to disregard this info.

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NashT

What fullboost is talking about is what happens when the plunger shaft that goes into the master cylinder has been adjusted too far out, which in turn causes constant pressure on the brakes and becomes stronger as the brake fluid heats and the brakes are used, which traps fluid that cant be released, which causes brake lockup. This is very uncommon unless you replaced the brake booster and the plunger shaft was not set correctly from the parts manufacturer.

Anyways...

When you replaced the clutch, did you just do the disc, or did you also replace the pressure plate.

Also, can you try describing the problem your having in a different way? Im thinking maybe you are just describing the issue your having incorrectly or not using the correct terms possibly.

The reason I asked about your exhaust is because, Ive seen cats be clogged up, but depending on the drive cycle the packing can either be clear allowing exhaust to flow and then stop up the flow intermittently. This would cause more of a power loss or engine bogging down than a slipping feeling. If this is the probem your experiencing, just unbolt your cat and see what the guts/ packing looks like.

Also how is your engine idle rpms? Is it constant or changing? Literally meaning at idle, once engine is at operating temp.

NashT

Also are you still running the clutch proportion valve/ block?
If you are, they can be a pain to get bled without a vacuum bleeder.

If you want to delete it I can look and tell you the exact size brake union to buy so you can delete that shit. Its an M10 something, cant remember off the top of my head but you can buy one at any parts store for less than 5 bucks.
By deleting it, the clutch pedal feels more natural and like how a hyd clutch should feel.

When you did your clutch how did you bleed the hyd system?

Im wondering if your pressure plate is on its way out, and if you also have air in the clutch hyds. (Why I asked if you only replaced the clutch disc by itself)

Videlicet

NashT

I did replace the pressure plate along with the clutch, and I also resurfaced the flywheel.

As for describing it in a different way: Essentially it feels like the engine is working without the power properly reaching the wheels. When I press the gas, the engine revs faster than it should be able to in the given gear.
Basically I can rev the car as easily as if it we're in neutral. The more I press on the gas the more it "slips" (or whatever it's doing). In higher rpms it "slips" very easily. When I'm around 3K if I nail the gas, it will not accelerate at all but instead just rev up higher, (which to me feels like it is slipping somehow). I can only bring it up to speed if I gradually increase the gas.

my car idles fine from what I can tell, it's always been slightly inconsistent.
As for the clutch proportion valve/ block and hyd system, I'm not entirely sure what those are to be honest.

I would be very happy if it turns out to be something as simple as the cat, since I can just straight pipe it for 50 bucks and be done with it. But I have my doubts its something like that.

I've had power loss before from an air leak in the EGR which caused it to rev about 1000rpm higher than necessary in every gear, but it never felt like the transmission wasn't gripping. Pretty much just felt as if the car was slower.

NashT

Okay cool, thanks for the details.

Like others have stated it sounds like the clutch, but more so in my opinion the pressure plate is shit. Very well may just be a manufacturers defect.

What kind of clutch kit did you purchase?

And when you say you resurfaced the fly wheel, did you take it so.ewhere and they put it on a lathe, or you just used a die grinder and sanding discs to "resurface" it?

If you have the money buy an ACT kit or a white bunny clutch kit. Either of those are by far the very best kits even with mild turbo builds that can stand the abuse of track days and daily driving for years.

If your car was one that was swapped to be manual you wont have the hyd block for the clutch. Next time your under the car, look at the slave cylinder on the trans, and trace the hardline. It it goes to the frame on the right side to a block that has two 10mm bolts, and a larger hardline that just makes a loop (thats the proportion valve) its more of a hyd dampner in my opinion, but deleting it really does change the pedal feel in a positive way

NashT

Also in my replys "hyd" is just short for hydraulic.

Ex: how did you bleed the hydraulic clutch system?

NashT

Only other small detail i can think of did you torque the pressure plate to spec, or just wing it.

But with the problem your having, shit would have to be pretty loose.

Feel free to PM and ill send you my cell #, then I can send you pictures of the shit im talking about. I can never get pics to freaking upload on zilvia

Videlicet

The clutch kit I purchased was made by south east clutch according to OEM specs. I got the flywheel resurfaced at Advance Auto.
I did not torque the pressure plate to spec.

Something I'd like to note, is that this issue started before I changed the clutch, and replacing it doesn't seem to have changed that. This makes me think the issue stems from something related to the clutch, but also something I did not change with the clutch install. Whatever is keeping the clutch from gripping, I don't think it's directly caused by the pressure plate.

NashT

The only thing I can think of, especially with you continuing to be vague.

Is maybe there is air trapped in the fluid for the clutch hyd lines. And your slave cylinder is keeping pressure on it thus not fully retracting when the clutch pedal is not depressed.

Ive asked you several times about bleeding your clutch.

Videlicet

I did not bleed the clutch

TheRealSy90

It's the clutch man.

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NukeKS14

https://www.youtube.com/watch?v=pHrdfBYo_BQ

video tutorial to show you how to bleed the clutch master/slave cylinders and delete the damper box if you so desire.

Videlicet

Sorry guys I know I haven't responded to the thread in a while. I have been pretty busy. I think the issue might just be that it needs more transmission fluid. I don't know how long the current fluid has been in there, but I don't want to run the risk of changing it. Does anyone know how I can figure out how much fluid to add? Or how I can tell if it needs it at all?