Centennial GT

I have a 2003 Mustang GT that can't hardly even do a burnout in 1st gear. It seems to be bogging down in only first gear. My car is an automatic and has 4.30 gears. It also has a itsx tuner and brand new stage 2 4r70w with a 3200-3500 stall converter, as well as a o/r h pipe with welded on magnaflow cats and flowmaster 40 mufflers. Whenever my car bogs in first gear my 0-60 changes from around a 5.0-5.3 to 7.6 second. There are no check engine codes and at idle there does not seem to be a misfire. I would really like to "experience" the 4.30's working with the higher stall but first gear struggles. I can send videos of it happening and when it doesn't happen. Now the bogging always happens in first gear at anywhere over 1/2 throttle.

Buck Sergeant

Hay Buddy, this is a good one. Are you carbureted or fuel injected???

Buck Sergeant

What your problem sounds like is a slipping set of clutches. There are more then one set in an automatic transmission. The 'clutch pack' that control first gear in your transmission are the ones that are at fault. Now, here is a simple way to test what I am saying: put the car in Reverse and hold the brakes while applying throttle. Look for excessive RPM's on the tach. Most (of the older) transmissions operate similarly where the 1st clutch pack and what was the highest clutch pack (3rd or 4th) would both be applied in order to obtain reverse. The important thing is, since it's ALSO used in reverse, any slippage in the first clutch pack will show up in both places (first and reverse gears). Now, please realize that the front pump output pressure is increased dramatically in reverse (250PSI instead of 100PSI, IIRC) so a slipping clutch wouldn't necessarily slip as much in reverse as in first gear. That is why I suggested you 'power brake' it a little bit. If your engine revs much higher then normal in reverse then it usually would (similar, but not exactly the same as it acts in first gear) then your problem is verified to be in the first clutch pack (or in its circuit: solenoid, piston seal, valve body, etc...).

Derf00

I don't have any experience with the suggested test method but, I agree that it sounds like your clutch discs/packs are worn/wearing out.

Centennial GT

The only issue with it being the 1st gear clutches is that it was doing it with the old transmission and I tore apart the old transmission and the 1st gear clutches were worn. However, I just replaced the transmission with a brand new one this week with all the upgraded parts and stall converter so it shouldn't be the clutches. I am fuel injected with the stock injectors and stock fuel system on a remanufactured 4.6 2v motor. I think it may have something to do with the cats being clogged or maybe bad plugs even though the spark plugs were changed not 10,000 miles ago. So, I don't think it is my clutches and may have something to do with the tune or fuel delivery. Thanks guys for all the responses. Ive just put in a ton of money for first gear to still be laggy.

Buck Sergeant

Just a thought. My 2014 GT automatic was acting in the same way. The tranny checked out. So on a hunch, I pulled the rear differential and found worn clutches. I installed the "carbon fiber" clutch pact and the problem was gone. Just food for thought. Keep me updated, I'm checking with my pit crew to see if they have any suggestions.

Centennial GT

Thanks Buck Sergeant. I may look into that as that was my next thought, but I don't know why that loss of power wouldn't then apply to all gears. Could anyone fill me in on how that works? Thanks guys

Buck Sergeant

I'm still with you on this issue. You mention a new 4R70W tranny. but what is the history/information about the torque convertor? I'm still looking at tranny/convertor issues. If everything checks out, then possibly rear end clutches. Off the wall possibility. Could this possibly be a 4R70E tranny? If so, the "internal Electronics" must be changed.

Buck Sergeant

Also, Here is why I am looking at the torque convertor. As the output pressure from the torque converter drops, the transmission will be starved and start to slip. This may manifest itself as a general loss of power when driving, especially when accelerating. Address this as soon as possible to prevent prematurely wearing out the friction material in the transmission. Slippage can also occur if the converter clutch fails to engage fully, leaving only the fluid-coupling effect, which is inherently inefficient.

Centennial GT

My transmission should not be a 4R70E as I just ordered it not a month ago. Everything in the transmission is brand new, ie. 3200-3500 stall converter, clutches, valve body, shift kit, bands and should be a 4r70w. The company that I ordered the transmission from sent a faulty transmission (the pump seal wasn't holding up and it fell out of overdrive when I got to about 1/3 pedal), but everything else worked as promised from what I can tell. I used to be a little stupid with my car and before the new transmission and I would launch the car in 1st but at 3000 rpms from a roll, and it would feel like a ton of bricks. So, I think I may have worn out the clutches in the rear. At first when the problem arose I thought it was the torque converter but I don't feel it really "slip" is the issue. It just feels like it is starved somehow, and then when it hits second gear it spins the tires and takes off. Again, thanks for all the help. I really appreciate it!