trans-am rearend

[chipper]

got a good deal on a 78 t/a rear had a a 4 speed, but i will use an atuo this i believe will bring my top speed down ,am i correct? but i should be ok. to the corner store!!

 

[bob w]

I would think it is a pretty tall gear even if it came out of a 4 speed car. You can determine the ratio by preventing one wheel from turning, putting a chalk mark on the other wheel and on the driveshaft yoke. Rotate the yoke, counting revolutions, untill the wheel (or drum) completes one revolution. You will probably see between 2 1/2 and 3 1/2 yoke revolutions, or a 2.50 to 3.50 rear end ratio. Closer to 2.50 for economy and high speed potential if you have lots of horsepower. Closer to 3.50 means better stop light acceleration, more engine RPM at cruise speed and maybe a little less top speed.

 

[Rev Tex Devlle]

i have both trans and the rear ends ARE DIFFERENT RATIO,, the 4 speed will be lower,, but better, IMO

 

[hotrod preacher]

got a good deal on a 78 t/a rear had a a 4 speed, but i will use an atuo this i believe will bring my top speed down ,am i correct? but i should be ok. to the corner store!!

"high gear" in a true 4 speed and in a regular automatic are BOTH one-to-one ratio.
that means in 4th (on the 4 speed) and "drive" (3rd on regular automatic) for every revolution of the input shaft you get one revolution on the output

so the top speed is not affected by a swap from 4spd to auto as you have mentioned
just thought i'd share.........

 

[bob w]

HRP, I think chipper was referring to the fact that sometimes 4 speed cars are equipped with deeper rear end gears from the factory. Everything you said is true.

 

[Rev Tex Devlle]

"high gear" in a true 4 speed and in a regular automatic are BOTH one-to-one ratio.
that means in 4th (on the 4 speed) and "drive" (3rd on regular automatic) for every revolution of the input shaft you get one revolution on the output

so the top speed is not affected by a swap from 4spd to auto as you have mentioned
just thought i'd share.........

i had a four speed car , it had, like a 3.08 [i.e ]and the automatic car had like a 2.73[ i.e.]?,, trans are one to one,, all cars where one to one, till overdrive came along, overdrive trans work well with anything,, 3.50 or lower,, but i recommend not going lower than a 3.73 with over drive,,if ya going to drive every day, the 700r has a lower first gear,, good for take off with 373 .. and good for topend,, most late model trucks and vans like the astro,, ran this set up

 

[chipper]

T/A rearend

well I got the rear end and it should do fine it's a 3:42 gear raito, match that up to the 350/350 and off I go!!!!!