Back to topic..........3.90's are a great gear ratio for street/strip use. I had a 96 Cobra and went with 3.73's and then 4.10's. I started using the car for commuter duty and the 4.10's were a little to steep.
3.90 Gears!!!
- Thread starter SVTdubs
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Silver 03 Cobra
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Thanks to a dumb ass dealer I guess I'll try a set of 3.90's. I have FRPP 4.10's in my 03 now. I am taching 7k in third in the 1/8 when I cross the line and 7k in fourth in the 1/4. I installed my 4.10's soon after I got my 03 in June. I detailed the underneath of the car before I took it to the dealer for the broken TOB retainer problem. I noticed a small film of oil on the differential. No drops or streams. I was hoping it was the grease I lubed the pinion seal with when I installed the 4.10's breaking down.
The dealer I am taking my car to now is very willing to replace anything on your car under warranty and even looks for things to replace. When I went in to get it after the warranty repair, the manager told me my differential was leaking. I said it may be leaking. He said they found my pinion nut was loose. They knew I had 4.10 gears because the manager is an 03 nut and is about to buy one. He wanted to know all about my mods. This dealer is not an SVT dealer. He asked me who did the gears and I said I did. He went on to tell me about the crush sleve. I know how to change gears and have done several. I actually over tightened the pinion nut slightly. If you install new bearings the free running torque is 16-20 inch-lbs. I was at 22. I think the loose nut was BS and an excuse to put on the warranty repair for the oil leak. The seal leak was repaired under warranty. After two days I noticed oil on my exhaust. I don't have a film anymore, I have a full blown Old Faithfull. Man I am pissed. I didn't ask them to touch my rear end. It also should not have been done under warranty because I installed 4.10's. I would take it back but they would do the same thing again. I really think if the pinion seal is leaking, the differential should be disassembled and a new seal installed. I was always told not to reuse a crush sleeve. The dealer just pulled the pinion flange and popped in a new seal. You can't get the crush sleeve out from the front. I also do not know how they can torque the nut properly this way either. I doubt they put RTV around the outside of the seal and that is why it's leaking.
So rather than take it back to have them do the same stupid thing again I thought I would try 3.90's. I am worried I will lose time on the track with the new gear. Right now my best 60 ft is 1.609 and I usually pull 1.62's all day. I know I won't pull as good off the line but maybe I can pick up some trap speed, spin less and stay in the power band pulling through the line. I am getting better at driving and ran my best pass a couple of Sundays ago at [email protected] mph. I only got to run one pass because my car started cutting out under throttle. It turned out a piece of rubber from my filter stuck to my MAF screwing up my A/F. I usually run two tenths better after I make three passes. I was running a new exhaust, a set of single chamber Flows with turn downs. I really think I could have gotten in the low 7.2's that day if I could have run two more passes. If 3.90's are "supposed" to be better than 4.10's, then I'm looking at 7.0's. I'll believe it when I see it. But, I'm willing to give it a try.
Pro 5.0 (shifter company) also sells 3.90 gears as well as Moser. I am trying to find out if Precision gear also sells a set. As soon as I get them I'll post the time slips with the 3.90's and 4.10's.
The dealer I am taking my car to now is very willing to replace anything on your car under warranty and even looks for things to replace. When I went in to get it after the warranty repair, the manager told me my differential was leaking. I said it may be leaking. He said they found my pinion nut was loose. They knew I had 4.10 gears because the manager is an 03 nut and is about to buy one. He wanted to know all about my mods. This dealer is not an SVT dealer. He asked me who did the gears and I said I did. He went on to tell me about the crush sleve. I know how to change gears and have done several. I actually over tightened the pinion nut slightly. If you install new bearings the free running torque is 16-20 inch-lbs. I was at 22. I think the loose nut was BS and an excuse to put on the warranty repair for the oil leak. The seal leak was repaired under warranty. After two days I noticed oil on my exhaust. I don't have a film anymore, I have a full blown Old Faithfull. Man I am pissed. I didn't ask them to touch my rear end. It also should not have been done under warranty because I installed 4.10's. I would take it back but they would do the same thing again. I really think if the pinion seal is leaking, the differential should be disassembled and a new seal installed. I was always told not to reuse a crush sleeve. The dealer just pulled the pinion flange and popped in a new seal. You can't get the crush sleeve out from the front. I also do not know how they can torque the nut properly this way either. I doubt they put RTV around the outside of the seal and that is why it's leaking.
So rather than take it back to have them do the same stupid thing again I thought I would try 3.90's. I am worried I will lose time on the track with the new gear. Right now my best 60 ft is 1.609 and I usually pull 1.62's all day. I know I won't pull as good off the line but maybe I can pick up some trap speed, spin less and stay in the power band pulling through the line. I am getting better at driving and ran my best pass a couple of Sundays ago at [email protected] mph. I only got to run one pass because my car started cutting out under throttle. It turned out a piece of rubber from my filter stuck to my MAF screwing up my A/F. I usually run two tenths better after I make three passes. I was running a new exhaust, a set of single chamber Flows with turn downs. I really think I could have gotten in the low 7.2's that day if I could have run two more passes. If 3.90's are "supposed" to be better than 4.10's, then I'm looking at 7.0's. I'll believe it when I see it. But, I'm willing to give it a try.
Pro 5.0 (shifter company) also sells 3.90 gears as well as Moser. I am trying to find out if Precision gear also sells a set. As soon as I get them I'll post the time slips with the 3.90's and 4.10's.
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Does anyone know who actually manufactures the FRPP gear sets? Maybe the 3.90's are already out there under another name? Is there a way to find out?
Dana
Dana
I've posted several times the reasons, so I won't repeat it here, but IMHO adding a higher ratio gear to an '03 is a waste of time and money. At best, you'll run the same.
Power is what makes a car quicker, not gear. On N/A and centrifugal supercharched Cobra's that don't have a lot of low end torque, higher numerical gears get you into the powerband faster which will improve ET when you have traction.
'03's are pretty much always in the powerband.
A good webpage about the effect of gears is here:
http://mclements.net/mrc-PowerTorque.html
JT
Power is what makes a car quicker, not gear. On N/A and centrifugal supercharched Cobra's that don't have a lot of low end torque, higher numerical gears get you into the powerband faster which will improve ET when you have traction.
'03's are pretty much always in the powerband.
A good webpage about the effect of gears is here:
http://mclements.net/mrc-PowerTorque.html
JT
Silver 03 Cobra
New Member
- Joined
- Mar 8, 2002
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- 2,054
National Drivetrain lists 3.90's in their ad in this month's 5.0 mag. They don't show them on their website.
I may have been wrong about Moser. I think it was Motive Gear. I just wonder what is the best brand. As far as FRPP the preferred gear is due mostly to shimming. Shimming is trial and error without a lot of measuring instruments they use in shops. You can almost be dead on 100% of the time a .03 pinion shim will be dead on every FRPP install. I'm sure with other brands they may be too tight to even pull the caps or loose as hell when you first start out so you will end up breaking it down a few times getting the backlash correct. I plan on installing a set of 3.90's in the next 2-3 weeks. I run consistent 7.40's at a local track so I'll know how they work compare to 4.10's.
I may have been wrong about Moser. I think it was Motive Gear. I just wonder what is the best brand. As far as FRPP the preferred gear is due mostly to shimming. Shimming is trial and error without a lot of measuring instruments they use in shops. You can almost be dead on 100% of the time a .03 pinion shim will be dead on every FRPP install. I'm sure with other brands they may be too tight to even pull the caps or loose as hell when you first start out so you will end up breaking it down a few times getting the backlash correct. I plan on installing a set of 3.90's in the next 2-3 weeks. I run consistent 7.40's at a local track so I'll know how they work compare to 4.10's.
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Ill wait to see how u like them so check back with us!
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