what gears do i need on differential?

[camaney]

Hi.can anybody tellme what gears do i have im not good at mat, on my truck i have a 454 engine 400 tranny 60/35/15 wheels and can only run on freeway about 45 to 50 miles p/h max. I dont want to put an other tranny just go 70 on the freeway does any body knows what numbers do i need to change in the differential and where is a good place to get them........... Thanks

[Bad70sbchevy]

You can either do two things, you can take the ring and pinion gears out or measure the overall diameter of your tire, then drive at any speed if your speedo is correct, but most times you need a gps to do this, and record the corresponding rpm of that speed. If you can give me that I can figure it out for you. 3.07s are a great highway gear (I got a Turbo 400 also), but if you want more of a street strip truck probably go with some 4.11 or 3.73s. You'll probably be turnin around 3600rpms with the 4.11s at 70mph compared to 2900 rpm with the 3.07s. This all depends on your tires though. Mine does2700 rpm at 60 with 3.07s but all of this also depends on tire size.

[camaney]

where can i get the parts?

[Sinister]

What rearend are you working with?

[292farmer]

how accurate is that speedo? is the truck shifting into third? my buddy had a th350 the linkage was so crappy and bent that when going down from neutral it actually went past the D selection into 2. never got past 50 in that truck till we figured it out.

[camaney]

its a12 bolt and it shifts to 3rd gear on tranny fine

[292farmer]

ok just thought i'd ask on the tranny, and summit and jegs will carry your gears heres one a 3.73 http://www.summitracing.com/parts/RMG-4902801/ this is for a 4 series if i remember lower gears are the 4 series and 3 series are higher gears in stock axles (divided at 3.73? someone please verify/correct me) please double check though as u need to match the series between your new gears and your diff. good luck

[Longhorn Man]

something is desperatly wrong. Even with a 4.10 gear, ytou should be able to go over 100 MPH. If you can't hit the speed limit, then something is way messed up on your truck.

[raycow]

Don't guess at your axle ratio. Take a few minutes to count it directly and then you will know for sure.

Put matching marks on the pinion yoke and differential housing. Jack one rear wheel off the ground, put the transmission in neutral, and the parking brake off. Turn the wheel exactly TWO revolutions and count how many times the driveshaft turns, estimating any fractional turn as closely as possible. That number is your axle ratio.

If the wheel is difficult or impossible to turn, you may have posi. In that case, jack both rear wheels off the ground and turn either of them only ONE revolution. Count the driveshaft turns the same way as for an open rear.

Ray

[gdogg14]

Originally Posted by Longhorn Man

something is desperatly wrong. Even with a 4.10 gear, ytou should be able to go over 100 MPH. If you can't hit the speed limit, then something is way messed up on your truck.

I have a similar problem. I am running 3.55 raito ring and pinion, The engine is a 305 and I think the tranny is a TH 400, The truck shifts fine thru all 3 gears but it turns 55 mph @ 2500 rpm (according to my tach and GPS)

[71meangreenc10]

Google Randy's Ring and Pinion, good folks to work with.


Smitty

[292farmer]

i doubt it but he could have 5.13s like me! have u got a tach? telling us the rpms at a given speed would really help.

[btullis99]

Originally Posted by 292farmer

i doubt it but he could have 5.13s like me! have u got a tach? telling us the rpms at a given speed would really help.

5.13's, i say god damn!! i thought my 4.10's were low

[capev86]

yeah....the 4.57 in the back of my 72 burb 3/4 ton is terrible. i shift into third gear at like 25mph so highway driving makes that 307 small block spin fast. from my figuring it is turning about 3200rpm at 60 and i usually keep it at around 50 or so because of that. hope to have a 4.10 third member installed real soon. it won't have much impact off the line (thankfully) but that 10% reduction means the faster i go the more rpms i am saving. looking to be around 2900 rpm at 60 after the swap. the 3 on the tree with the clutch is like a t350 with a lockup converter, but it still won't be good for long highway drives until i can get a borg warner OD unit installed on that saginaw. then 60 will be around 2000rpm. nice enough behind a small engine, but when i get my 406sbc it will be awesome. don't want to be sucking gas and spinning rev's unless i put my foot into it!

personally, i think anything between a 3.42 and a 4.11 combined with an overdrive trans is the best bang for the buck. the t400 is nice if you tow a lot more than you drive solo but with gas prices and environmental concerns, some modern concessions are worth their weight in gold. a big block or a diesel could get away with a 3.08 though (a diesel could still use an overdrive ratio). a 3.07 is too soft behind a 350 that is used for towing.

i want to keep the column shifter stick trans in my 72 burb, but if it had been a floor shift model, i would have kept the 4.57 and dropped in a 6 speed with 2 overdrive ratios (.8, .62 or .7, .52). you want your overall cruising ratio to be between 2.0 and 3.0 depending on configuration and primary use).

[paaw]

Easy to just pop off rear cover and look, gasket and oil is not expensive

[292farmer]

i believe i saw on this board somewhere 12 bolts never went lower then 4.57. which if he doesnt have a tach depending on his exhaust he may sound like hes redlining, so hes keeping speed low thinking hes about to blow

btullis99 yeah their low sounds like im racing nascar every morning on my way to work. dual cherrybombs get loud i never go above 45mph, have hit 55 but the 292 was SCREAMING!

[capev86]

a modern 6 speed behind a 292 would be awesome. i'd like to build an early 50's 1 ton panel truck with that setup. it would be so sleeper!

[292farmer]

i plan on trying to fit me and my dads c60 6 speed into my c25 behind it as it has a OD. heres my build thread if u guys wanna talk more, http://67-72chevytrucks.com/vboard/s...d.php?t=376520 i dont want to hijack/clutter this thread anymore, sorry cameney

[camaney]

No problem keep it coming I'm geting your ideas and sounds good

[Longhorn Man]

stock, the 4.10 (maybe it was 4.11) was the deepest gear offered in the 12 bolt. The 4.56 and 4.57 were in the corperate (eaton) and dana rear ends in the 3/4 tons and one tons.

[Longhorn Man]

whats the problem? You're good for well over 100MPH there. 110 MPH at 5000 RPM, and it redlines at 5500.

[gdogg14]

Originally Posted by Longhorn Man

whats the problem? You're good for well over 100MPH there. 110 MPH at 5000 RPM, and it redlines at 5500.

I guess the problem is mostly me. I would like to cruise down the road 70mph @ no more than 3000 RPM, I may get that with a 3.07 raito but will it have enough power to get itself going from a dead stop.

[gdogg14]

Originally Posted by gdogg14

I guess the problem is mostly me. I would like to cruise down the road 70mph @ no more than 3000 RPM, I may get that with a 3.07 raito but will it have enough power to get itself going from a dead stop.

To add ... I would like to keep the RPM down below 3 on the hiway because she will drink more gas than a drunk sailor in the last 15 minutes of Happy Hour. 2500 RPM seems to be the sweet spot on this motor.

[292farmer]

just thought of this if u don't have a lock up converter being an automatic they will slip, more then say one with a lock up converter, or a manual, especially im sure on an older untouched tranny, have u changed fluid or filters? so u may have decent gears that just seem a little lower then u realize.
longhorn man thanks on clarifying info on the 12 bolt gear ranges, like i said thought i saw it somewhere but wasnt sure.

[raycow]

Originally Posted by gdogg14

I would like to cruise down the road 70mph @ no more than 3000 RPM, I may get that with a 3.07 raito but will it have enough power to get itself going from a dead stop.

Easily. 3.07 was a factory option on these trucks, and GM doesn't like to sell parts combinations that are going to result in unhappy customers.

Ray