Ford Power Stroke Nation banner

Tuning and tranny Gods only !!!!!!!

2K views 20 replies 8 participants last post by  superf350 
#1 ·
Here is something for you tuning and tranny guys to ponder.

Couple months ago, I was screwing around with a 12sec truck(Imelmo)......before someone de-rails,...I know I had no chance, it was just something fun to do.

We were on an old air strip, racing.....here's the dilema...

I have a Manual transmission, with a South Bend clutch....


When I dropped the hammer, my rpms went through the roof, yet I barely moved, I shifted into 3rd, same results.....I thought I smoked the clutch.

Well.....after that,...no problems when I would get on it,....it's like it fixed itself...

Ok,...fast forward to the Bash on the Bayou,...I pulled a trailer,...I beat the hell out of the truck the whole way,....no problems.

I decide to race the truck on the track,...I line up,...light turns,...and I stand on it,...it moves,...but not reall hard,...I slam it in 2nd,....lots of reving,...but not going anywhere.

Screw it,...I slamm it into 3rd,...more reving,...but the truck is slowing down...

I coast to the end of the track at a whopping 35mph......it seems like I really smoked the SB clutch this time.


I hook up to the trailer, hoping to limp home,.....but damn it all to hell,....no problems.....now I'm really confused.

I pulled the trailer all the way home (2hrs), not taking it easy,...and it hasn't acted up again.


Now for the crazy question-----I heard, I can't remember where, ....but.....here it goes.....

...A guy said the the manual transmission have a saftey,...that when you are REAL HARD on it,...it will release something to save the tranny,.....do you tuners guys know anything about this?.....do you tranny guys know anything about this?

I don't know if it is true,...but sounds plausible,...because normal driving(beating on it),...I don't have a problem at all.......but if I am EXTREMELY hard on it,.....it slips like it's blown.

Any ideas?
 
See less See more
#2 ·
I am in no way a tranny guru, but I had this problem with my Y2K F350. I had a ceramic disk clutch and it would slip while trying to sled pull. I drove the truck from the pull which was about a 4 hour drive with no problems. I went to my buddies shop and told him what went down and he said lets hook your truck up and see what happens. Sure enough we hooked my truck up to this huge poll, I let the clutch out and the engine rpms would go up but no wheel spin. You need to use an organic clutch instead of the ceramic, if that's what you got. There's probably still a video on diesel-central of the attempt. That was a few years ago so I can't remember all the gory details other than being glad I've got an automagic tranny now!
 
#3 ·
...A guy said the the manual transmission have a saftey,...that when you are REAL HARD on it,...it will release something to save the tranny
It's called the clutch. Seriously.
Short explanation: clutch can't handle the higher RPM slipping.

Longer explanation:
Clutches really don't care too much about absolute RPMs (other than exploding speed), they care about RPM differences and torque.
At low RPM differences (normal driving) you are not transmitting a lot of torque, so the truck accelerates fairly well.
At high RPM (high torque) differences the friction of the clutch on the flywheel is not high enough to propel the truck forward in a reasonable amount of time, so the clutch get hot and sits there slipping, further reducing the friction until the whole thing melts and locks together in a friction weld.
The reason that it holds once moving is that the static friction is greater than the dynamic friction.

There are a few ways to fix this:
1. Don't race/pull/compete. (You La guys are nuts anyway, so that ain't a gonna happen)
2. Use a much stiffer clutch spring (bandaid fix).
3. Replace the clutch.
 
#5 ·
Guys,...I have a South Bend clutch,...so I already have an aftermarket setup.

I have maybe 450hp,...dunno anymore.....but that is still short of the 550hp clutch that I have.



I'm kinda seeing the other thing you are saying though,...maybe I glazed it,...and it can no longer hold the power.

I have only had it in for about 2 1/2 years,....I'm pretty hard on my truck,...but I thought that when I bought the 550+hp clutch that it would be able to take a little more abuse than it has.


I bought another 2 months ago(when it slipped the first time).....much stronger SB clutch,...it's still still in my garage,...I haven't had time to install it.....now I guess I'm gonna have to find time.
 
#8 ·
true,...very true,...

Peter at South Bend told me that I'd never have to worry,...and that the clutch I bought was actually rated around 750hp,...but they label them "550+hp",...just to be on the safe side.

That all sounds good,....but 2 1/2 years,...well under the rating of the clutch,...
......and it is slipping under a heavy load,...that has me worried.

.
 
#17 ·
Try driving 4 hours to a sled pull, hookin to the sled with your brand new clutch and the truck don't move. I called the guy I bought the clutch from and told him what happened and he sent me another one. A couple months later I ripped the center section out of that clutch and I called him back told him about what happened and guess what, he sent me another clutch free of charge, didn't charge shipping or anything. That's service, btw it was Tom at Carolina clutch that hooked me up.
 
#14 ·
my brother had a deal like this with his truck. it made 430 on the dyno and had a 550 sb clutch in it,lasted maybe a month of hard street use. long story short,we put a dd sb in it and never had a problem with it again. i like the way the dd feels alot more than the single. just my .02s
 
#15 ·
Disclaimer: I know nothing specific about SB clutches.
I do know that most things like clutches are rated for the power they can hold once fully engaged. The power rating during engagement (slipping) is very dependent upon the apply force (springs in this case I believe), the ability of the clutch material and the flywheel to carry away heat, and the surrounding medium (in this case air).
At work we have some clutches in machines that run in a hydraulic bath very similar to an automatic transmission. I would not want to run them without the bath as the oil carries away a lot of the heat during engagement, they just simply wouldn't survive. Those same clutches slip madly while trying to engage if you tie off the output shaft, put will transmit probably close to 3X that amount of torque once they are engaged.

The issue of clutch slippage is one of several reasons that OTR trucks use a lot more gears than a pickup.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top