codynutt

Hey guys. This is my first post here...and to any mustang forum for that matter. I am a total newbie. I have a 2005 Mustang GT with a KB supercharger. The car has been tuned by Ken at Kenny Bell and as far as the engine is concerned, it runs fantastic and makes boat loads of power. The only problem I am having is when I am at or neat WOT with the transmission. The car never fails to shift, but it does sometimes sound like the RPM's jump between gears and or right as it shifts to the next gear...sometimes a few hundred RPM...possibly even up to 1k more. It usually seems to happen between 3rd-4th gear, or at least that is when it is most noticeable. I have a data log and have made a graph showing the comparison or engine rpm, trans input speed, and trans turbine speed if that would help anyone. I am not sure what exactly I am looking at to be honest. I have asked a local mechanic and he didn't seem to have any answers...Any help would be greatly appreciated! I am attaching a link to download the data log and graph if anyone can tell me anything from that. Thanks in advance!

https://drive.google.com/open?id=0B7...VQ2anZCWW9NV3M

https://drive.google.com/open?id=0B7...VQ2anZCWW9NV3M

07 Boss

I didn't look at the logs but from experience it sounds like you need to rebuild and beef up your tranny. How much boost and power are you making? These transmissions are not made to handle much more than 450 rwhp. That is why Whipple offers two kits for our cars. The one for the automatics comes with a bigger pulley and does not produce the same power as the regular 550 HO kit. The reason why is that these kits were developed with Ford and they felt that the 550 kit was too much for these delicate trannies. In fact, Shelby Motorsports would not tune my car with the 550 HO kit and the stock tranny. I had to swap trannies before they would put her on their dyno.

You can try and increase line pressure to help the clutch bands grab quicker but you are just covering up the symptoms of the problem. I would start looking at swapping out or building your tranny because it is slipping between shifts.

I'm a big proponent of building a car from the ground up. I put my transmission, drive train and suspension in before I installed my blower. Why? To avoid the scenario you are in now. When you add boost to these 5R55s transmissions it's not a matter of if, but a matter of when they will go out. Trust me, I'm on my 3rd one.

codynutt

Thanks for the reply 07 Boss! I appreciate it! I bought the car this way, so unfortunately I didn't have the option of making changes in the order I would myself or even know exactly what has been done for that matter. I do know that the transmission is not stock. It has been upgraded but I frankly do not know exactly what was done to it...and really no way to know without pulling it out. I do know that it never slips at all on a WOT downshift...this car will easily spin the tires and wash the rear out at 35 mph if you are not careful when it downshifts...so it definitely isn't like it is totally slipping all the time. I just didn't know if the data / graphs I provided would be an easy indicator or obvious issues to someone experienced with that kind of data...or if there is even a mechanical issue at all.