Clutch Slip Issues

[WCKD350]

Hey Guys, wanted to see if anyone has had any similar issues or has any insight on this clutch problem.

This started about a year ago with my OEM clutch. Anytime i would do a hard pull from 3rd-4th-5th my clutch would begin to slip and give itself anywhere from 1-400 RPM. I’ve noticed it only happens once i let off and shift slowly into either 5th or 6th gear. it’s so bad that the car will buck when going into 6th gear. I figured my OEM clutch was toast and bought my first Vengeance stage 2 clutch (rated for 850 ft of tq) and an OEM slave cylinder. After doing the proper 1,000 mile break in period. I got with my tuner and began to data log for a new E85 file. The car felt amazing as i was only doing pulls in lower gears 1st-2nd-3rd. As soon as i got on the freeway home i did a pull in the higher gears 3rd - 4th -5th and had the same exact issue. I contacted Vengeance and they sent me a replacement stage 2 clutch and unfortunately i had the same exact problem. I decided to try another new clutch from them and just finished the break in and even installed another new slave cylinder & a braided clutch line only to have the same exact issue arise. Is this a problem with my transmission?

To summarize the car has no issues entering any gear, has never grinded gears, works as intended in lower gear pulls only gives me issues with higher gear pulls. I have tried three brand new stage 2 clutches and still no luck.

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[robvas]

I don't see what could be wrong with the transmission that would be causing the same thing that you would see as clutch slip

 

[WCKD350]

I don't see what could be wrong with the transmission that would be causing the same thing that you would see as clutch slip

I agree, my next plan is to replace my master cylinder. If that doesn’t work i guess i will try a Mccloud brand clutch instead of the Vengeance. Even though i had this same issue with the OEM as i do with the Vengeance clutch.

 

[Inthehighdesert]

Question. Assuming you changed the fly wheel with the new install. Also, the torque on the pressure plate bolts was good. Don‘t have experience with vengeance but do mcleod on the 350. With 800ish in front of the mcleod it felt like oem with the exception the engagement point was more to the top of the peddle. My car at the time was low mileage, but when I swapped the clutch I kept the oem cylinder.

 

[WCKD350]

Question. Assuming you changed the fly wheel with the new install. Also, the torque on the pressure plate bolts was good. Don‘t have experience with vengeance but do mcleod on the 350. With 800ish in front of the mcleod it felt like oem with the exception the engagement point was more to the top of the peddle. My car at the time was low mileage, but when I swapped the clutch I kept the oem cylinder.

Yes, all torque specs were met. Also the Vengeance kits come with a new flywheel and they recommend and OEM cylinder so that’s what i went with. Is it possible my master cylinder is the issue? That is literally the one part i have not replaced.

 

[DaveJP]

Could it possibly be relates to the tone ring issue? Bucking/surging in higher gears are symptoms of that problem.

 

[WCKD350]

Could it possibly be relates to the tone ring issue? Bucking/surging in higher gears are symptoms of that problem.

i’m not sure we have taken the trans off 4 times now i’ll do it again and check

 

[Talliuz]

I have the same issue in my 19' 350. After pulls, the stock clutch pushed on my foot back up a lot harder than normal after pressing it. Then sometimes when upshifting right after pulls, the revs would go up by themselves briefly before upshifting. And when staying in gear and cruising right after pulls, it would slip and the car would physically feel like it was stuttering. This would all go away as it cooled down however.

I went in and replaced with a McLeod RXT 1200. After the 1000 mile break in, it did the same thing lol. I had the clutch changed, aluminum flywheel, braided lines, and replaced the stock slave/throw out bearing. But now, the only issue is that after 3 or 4 pulls, the clutch slips while e cruising right after pulls and the revs go up by themselves when upshifting after pulls. This all goes away with a little bit of time and cooling.

I spoke to other mustang guys around my area and they say it sounds normal and they experience it too, some to a smaller degree than others.

 

[WCKD350]

I have the same issue in my 19' 350. After pulls, the stock clutch pushed on my foot back up a lot harder than normal after pressing it. Then sometimes when upshifting right after pulls, the revs would go up by themselves briefly before upshifting. And when staying in gear and cruising right after pulls, it would slip and the car would physically feel like it was stuttering. This would all go away as it cooled down however.

I went in and replaced with a McLeod RXT 1200. After the 1000 mile break in, it did the same thing lol. I had the clutch changed, aluminum flywheel, braided lines, and replaced the stock slave/throw out bearing. But now, the only issue is that after 3 or 4 pulls, the clutch slips while e cruising right after pulls and the revs go up by themselves when upshifting after pulls. This all goes away with a little bit of time and cooling.

I spoke to other mustang guys around my area and they say it sounds normal and they experience it too, some to a smaller degree than others.

So it’s just normal? there is no way to fix it? Because mine is the exact same it will go away after letting it cool off. But unfortunately mine is pretty much after every hard pull in the higher gears.

 

[Talliuz]

So it’s just normal? there is no way to fix it? Because mine is the exact same it will go away after letting it cool off. But unfortunately mine is pretty much after every hard pull in the higher gears.

Yes, it is normal from what I have seen. A lot of other mustang guys have it. Never spoken to another 350 owner that has it until you though.

I could try to replace the master cylinder that houses the fluid, and see if that works. But I do not think its an issue for me as I do not see leaks in mine. I think it is literally just due to expanding clutch fluid as it gets hot that causes slipping.

 

[Champale]

This is a long shot but is your clutch pedal returning to the top of its travel after these long pulls? On some cars like the Boss 302s the clutch pedal would not return all the way, resulting in slippage. I don't recall what the fix was 10 years ago, though.

 

[WCKD350]

This is a long shot but is your clutch pedal returning to the top of its travel after these long pulls? On some cars like the Boss 302s the clutch pedal would not return all the way, resulting in slippage. I don't recall what the fix was 10 years ago, though.

Yes, clutch pedal is acting as intended. Never fails to return to the top

 

[Champale]

Ok well just a thought. On the OE Boss clutch, it seemed like it was all the way up but you could put your foot underneath it and pull it up another half inch or so. I ended up with a Spec clutch that didn't help the issue and then an RST that cured it.

 

[WCKD350]

Yes, it is normal from what I have seen. A lot of other mustang guys have it. Never spoken to another 350 owner that has it until you though.

I could try to replace the master cylinder that houses the fluid, and see if that works. But I do not think its an issue for me as I do not see leaks in mine. I think it is literally just due to expanding clutch fluid as it gets hot that causes slipping.

Yes that’s my next move i’m going to replace both my master cylinder and tone ring. I’m on the same boat as you have never seen a leak from my master but i figured its the only piece of the puzzle i have not touched yet.

 

[sk47]

I think it is literally just due to expanding clutch fluid as it gets hot that causes slipping.

Hello; Just read thru this thread and must say your take makes sense. Back in the days of mechanical clutch mechanisms a slipping clutch was always due to some fault. I can see hot fluid trying to expand slightly in a restricted space with the effect of the slave cylinder pushing out a bit. What i do not get is how this potential "hot fluid issue" has not been a known thing for so long.

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