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Offline bbobcat75

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rear end gears!!
« on: July 24, 2013, 07:11:58 AM »
have a 3.18 rear gear in my 78 wagon with a 2.3, soon to be a 2.3t out of a 79 mustang.
question is if i install a rear end with 3.40 gears would i be gaining or losing anything?!?!  im thinking it should be a little better on the take off, but not sure how much i will lose on the top end / highway car does 85 easy now on the highway!!
 
thanks
 
 
1975 mercury bobcat 2.8 auto
1978 mercury bobcat wagon 2.3l - soon to have a 88 tc drive line
1975 ford pinto - drag car - 2.3l w/t5 trans - project car

Offline Pinto5.0

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Re: rear end gears!!
« Reply #1 on: July 25, 2013, 01:19:28 AM »
It will probably add about 300 rpm in drive & throw the speedometer off a few mph
'73 Sedan (I'll get to it)
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Offline 74 PintoWagon

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Re: rear end gears!!
« Reply #2 on: July 25, 2013, 09:05:05 AM »
I believe around 200 or so, here's some handy calculators.

http://www.4lo.com/4LoCalc.htm
Art
65 Falcon 2DR 200 IL6 with C4.

Offline bbobcat75

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Re: rear end gears!!
« Reply #3 on: July 25, 2013, 09:40:43 AM »
ok well that doesnt sound too bad, it will go 80 at about 2400 or so rpm, so at 80 with new rear will be around 2700 that is still do able and not have the motor screaming!! if i ever get the 5 speed in it that should take it back down then right?!?!
 
thanks for the info!
 
should have added the car is a 2.3 with a 4 speed and 3.18 rear and going to swap only the rear to a 3.40!!
 
thanks guys and take care!!1
 
1975 mercury bobcat 2.8 auto
1978 mercury bobcat wagon 2.3l - soon to have a 88 tc drive line
1975 ford pinto - drag car - 2.3l w/t5 trans - project car

Offline 74 PintoWagon

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Re: rear end gears!!
« Reply #4 on: July 25, 2013, 10:28:08 AM »
Yep, 5 speed will bring it down more, plug in the final ratio on the overdrive and it'll give you the rpm.
Art
65 Falcon 2DR 200 IL6 with C4.

Offline Pinto5.0

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Re: rear end gears!!
« Reply #5 on: July 25, 2013, 12:26:29 PM »
Are you sure you have 3.18's in it now? 2400 @ 80 sounds more like 2.74's
'73 Sedan (I'll get to it)
'76 Wagon driver
'80 hatch(Restoring to be my son's 1st car)~Callisto
'71 half hatch (bucket list Pinto)~Ghost
'72 sedan 5.0/T5~Lemon Squeeze

Offline Wittsend

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Re: rear end gears!!
« Reply #6 on: July 25, 2013, 06:41:39 PM »
The T-5 is roughly a .80 overdrive. So, over a standard 1:1 transmission the RPM drop would be 20%.  While dropping RPM's sounds great (and a potential gas saver) there are other factors involved. If the torque of the engine can't sustain the load then the car will struggle as it encounters inclines and wind resistance due to greater speed.  Thankfully you can  go back to 4th gear, but the issue is how much time will you have to spend there while driving.  It may or may not be to your advantage.

Tire size has the same effect on engine RPM.  At one time I had 225-60-16" from my Turbo Coupe on my Pinto.  While I never did the math I'm sure that the effect was equal to (or greater than) the .80 of the T-5 5th gear.  With 3.40 my car was still struggling on any (even minor) hill.

Today I have a Turbo 2.3 with the T-5 and 3.00 gears. I've had 175-70-13's and 215-60-14's.  1st gear is doable but 5th gear is strictly level ground and 50+ MPH or it is time to downshift. While tire size is a factor it is my opinion that 3.25 gears would seem the best for a combination of performance and economy.  If you have an 8" (I know you don't) you go aftermarket or slide up to 3.40's as Ford basically left a hole between 3.00 and 3.40 for the 8".  Yes, Ford offered a 3.25, but it was very limited.

Offline Jerry merrill

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Re: rear end gears!!
« Reply #7 on: July 26, 2013, 01:59:59 AM »
I have a 71 with a 2.3 and 5-speed with 3.55 gears, even with 225-60-15 rear tires the 5-speed works well and only on really steep hills does it need to be downshifted. I even run 5th in town at speeds over 45. I am getting 28mpg or so on the highway and about 25 in town.

Offline bbobcat75

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Re: rear end gears!!
« Reply #8 on: July 26, 2013, 08:41:57 PM »
so I totally wasted 3 hours of my life today!!!   went to do the swap and thought about it and didn't want to have to bleed brakes swap shoes and so on, and I'm not too advanced in repairs to just swap the ring and pinion, plus was trying to keep it cheap and easy!!!!    so I wanted to just swap the axle housings with the gears already in it, no big deal pull axles and drain fluids and un bolt backing plates pull the old housing out of car after I unbolted the back side of the leaf springs and put new housing in and go to bolt up backing plates and!!!!!!!!!!!!!!       the holes will not line up!!!   so a 6 and 3/4 rear have different backing plates from 73 to 78 should have known!!! its a ford,        so  had one of the guys at my shop help me pull out the ring and pinion and went to finish swap.......... .... well need a new crush sleve for the pinion,   called dealer have 4 in stock,    get it in and its not right. so its still at work and a wasted day. should have left early like I was going to and do it on Monday!! o well get to finish it up then!!!            thanks for reading my ramble and have a great weekend!!  have to love a ford to drive one and work on one!!!
1975 mercury bobcat 2.8 auto
1978 mercury bobcat wagon 2.3l - soon to have a 88 tc drive line
1975 ford pinto - drag car - 2.3l w/t5 trans - project car

Offline 80_2.3_ESS

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Re: rear end gears!!
« Reply #9 on: July 28, 2013, 10:38:40 AM »
From 2010 till this summer, I was running a slightly built 2.3, stock 4-speed manual, and an 8" from a Mustang II. The rear end had 3.00's in it with an open diff. The back tores are 245-65-14's if I recall coreectly. Typical driving was never a problem, but off the line was a PITA. The cam I have is a racing cam, so powerbamd is like 4k plus. I cant just chug off the line by letting out the clutch, the car will stall.

I just recetly threw in a currie posi unit with 3.55's, and the car is a totally different animal. Tje car does run at a higher RPM on the highway in 4th, but it doesnt bother me. Hopefully by the end of this summer, I will have a built 2.5 stroker motor in the car with a T-5 from a 2.3 mustang behind it.I have most of the parts, but I am waiting on the clutch, shifter and head to come in.
Nick in CT

1980 2.3L Pinto ESS