4R70W advice (or just advice in general)
 

Hi, I've had to replace the intermediate shaft in my mustang gt 3 times now (on my third one now). The first two I broke were stock and the third was a performance hardened shaft. I don't want this to happen again and am trying to see if my habit of shifting at high rpm's (I know that's bad) caused this last break. I shift at about 6k but I think when it broke I was at about 6.5k rpms. Is it possible to do damage to a tranny from over revving? The other two times it broke (they were both stock) were accidents on me from bumping my shifter in to lower gears at high speeds (like 80 mph in to 1st gear) so no mystery there. I will however put a 6k rev limiter from now on so don't bother telling me about that.

It sounds more like a performance transmission is better off now than just replacing shafts constantly. Did this just happen driving the streets or at the strip?

wait you have a 2800 stall and a shift kit and you are ramming your automatic into 1st gear at 80? Anyways how do you like your stall and stage 3 shift kit?

If you are breaking your intermediate stub shaft repeatedly, there is something wrong with your setup. Guys are in the 9s on the stock '01+ shaft. Call Darrin @ BC Auto and he'll help you narrow down your problem. My car shifts at like 6500 on the stock shaft with no problems. BTW, if you are shifting at 6,000+ you need to look into spiral retainers. Your stock snap rings are going to give eventually.

lol, it wasn't purposely done. When I floor my car the whip lash sometimes throws your body in the seat and if your hand is lazily resting on the shifter then you instinctively pull back on it (shifting into 1st). It's a B&M hammer shifter, not the stock one. Oh and btw I love the shift kit. I run times that cars with higher hp can't even run (about a 12 flat 1/4) and I can attribute that to the transmission.

It is a performance transmission. I rebuilt the transmission with alto clutches, high energy band, and a lot of other stuff including a performance valve body change and going full manual (no electronics). This happened on the street luckily 2 minutes from my house.

The first two breaks might be from driver error. The fact that you broke an aftermarket hardened one means something is not right. The shaft is designed to break first instead of destroying other more expensive components in your trans. You definitely should not have broken the aftermarket one if everything was working right in your trans. I don't know if it has something to do with your shift kit or anything else that might have been done to your trans. It is definitely not your level of power.

I'll check it out thanks, but there is variation in your statistic that doesn't apply to me. Most people that run their car at the track also don't put 10k miles a year on their car. Maybe 500-1000 tops. If guys who run 9's drove their car 10k miles a year, they might be breaking a lot more than intermediate shafts. I really shouldn't be shifting at 6k+ anyway. My setup isn't made for it. My supercharger screws max at 6k rpms (w the current pulley) and my cams are made for 6k rpms. A very reputable (for my area) tranny shop that builds performance stuff engines, trannys, etc. built my 4R70W so I don't think its setup wrong. He was surprised the hardened shaft broke. He said I'll find a way to break anything...

You know I think it might be the shift kit myself. Though it's awesome that it holds the torque but something doesn't seem right because it shifts so hard even at low rpms. I can't change the shift pressure via the programmer anymore since I put the shift kit (no electronic shifting) in but somehow it seems like the shift pressure is ultra high. I did a lot of mods at once so I can't pinpoint one mod to cause the problem but I used to snap the stock aluminum belt tensioner in two when I shifted from 1-2 at WOT. I found the ford steel tensioner and it bent that one so I bought a Thumprrr racing "unbreakable" billet tensioner and haven't had anymore problems (also used to shred gator back belts under WOT I use whatever brand O'riely stocks now with no problem).

Who does your tuning? The shift kit may be part of the problem. Most shift kits including the transgo kits accomplish a nice hard shift by jacking up the line pressure instead of widening the feed holes in the valve body to fill the clutches faster. I know my transgo kit shifs hard, but it takes a long time to complete the shifts. There are also parameters that can be modified in a computer controlled transmission such as torque reduction during shifts to help extent the life of your trans. That shift kit might be doing more harm than good.