Acceleration issue

[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?

[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.

[mgbsr20det]

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.


Agreed


Sent from my iPhone using Tapatalk

[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.

[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.

[TheRealSy90]

It's the clutch man.

[Videlicet]

I did not bleed the clutch

[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?

[NukeKS14]

Gears do not 'slip'.

To check the fluid level on the mt you have to jack the car up front and rear so it's level and remove the fill plug (upper one) on the transmission. If fluid trickles out it is full. The procedure for filling is to add mt fluid until it begins trickling out of the fill plug and cap it off.

What is it you are afraid of risking? Aside from wasting money?

[mechanicalmoron]

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?

You have a manual transmission, which means if it slips internally, it's totally destroyed.

See if you can pull the release fork a bit by hand. If the master is releasing pressure properly, when the pedal's up you should be able to push the slave in a little bit with a few pounds of force, one hand.

Otherwise, it sounds like you haven't worn your new clutch in - new clutches often don't fully engage or disengage until you've let it slip some, but don't overheat it - this is why they talk about a "gentle" break in period - don't just sit and smoke it, but let it slip plenty when you take off, in between plenty of cool-down time.

Do you smell it?

You did a clutch but never changed the tranny fluid?

[zombiewolf513]

Maybe your clutch pedal isnt adjusted properly. Too tight and the clutch will slip. You could also have poor throwout bearing tolerances.

[Videlicet]

Sorry for the late reply. I've been pretty busy.

I got around to adding new gear oil. It took quite a bit too fill so it probably was low. But it didn't do anything to help the problem.
Eventually I ended up replacing the transmission. This was mostly due to the car no longer shifting into reverse, and having trouble shifting into other gears. While it fixed the shifting problem it only partially fixed the slipping. But at least it seems to have helped some. It still slips a little but not nearly as much. It might just need a new clutch now, I'm not sure.

I should have replaced the clutch while I was changing transmissions but I got impatient since I would have to wait a while to resurface the flywheel. I figured it would be fine with its current one since it was relatively new. Unfortunately I have to put this problem on hold for the time being since now the car is having other issues with overheating.

I just wanted to thank everyone who gave me advice on this. If your interested in helping me figure out my latest issue, here is a link to my new thread

https://zilvia.net/f/showthread.php?p=6390462#post6390462

[SrRaycer]

Coming from someone who has had tons of clutch issues....

It's definitely a clutch problem.. not brakes... not transmission fluid

First, the clutch needs to be bled, you said that you didn't do that, Idk if you've done it since.

Second, where is your pedal engagement/disengagement point? Is it high? If it's too high then your clutch is not completely engaging. I'd bet money that this is the problem.

[Videlicet]

I did bleed the clutch. Did not help unfortunately. And my engagement point isn't very high, it got lower when I changed the clutch.

[zombiewolf513]

You need to readjust the pedal every time you change the clutch. I have a feeling youve been setting it too agressively. There should be a tiny bit of slop where youre just pushing against the return spring on the pedal before you feel pressure from the clutch. If theres no slop that means the clutch bearing is disengaging the clutch by preloading the springs and weakening the friction between clutch and flywheel, eventually making it slip. Too much slop and the clutch wont disengage and itll be hard to pop out of gear