gearing

[1DOWN6TOGO]

it's come to this
i've been mod'ing the engine and drivetrain on my '77, and it's coming along great. she's got a stroker with lotsa torque, all preformance equipment under the hood, a 2800 converter, and a shift kit. yet i still can't see her power.
i'm not trying to run 120 on the highway or anything, i just wanna get some acceleration out of her. right now her power is best felt right after she shifts to second. she'll jump from 40 to 80 in a heartbeat, yet she takes her sweet time getting to 40.
i've been told it's because she's geared for highway and that i need to mod that if i wanna lay rubber at the green lights. i'm assuming that means her differential gearing. that's something i know nothing about.
can someone please explain this to me, and give me any helpful advice on how to mod her.

thanks guys!

 

[77-4speed]

The "gearing" refers to the ring and pinion gear in the differential. It is the final gear that the engines power passes through before turning the wheels. I'm not sure what the automatics had as a rear gear but the L-82 manuals had a 3.70 rear gear. It's great for acceleration but hard on the highway. I turn about 3500 rpm doing 70. Without changing your transmission you can have it 1 of 2 ways:

1: Quick off the line, with really high rpms on the highway (3.70)

2: Slugish off the line, with low rpms and good gas mileage on the highway (2.40)

A quick way to check your rear gearing is to jack the car up in the rear, release the parking brake. Now, not the orientation of the wheel and the driveshaft as well. Turn the wheel 1 revolution and count how many revolutions the driveshaft makes. The number of driveshaft revolutions is your rear gear ratio, i.e. if the driveshaft turns about 2.5 times, your rear end gear is about a 2.50:1.


Russ

 

[1DOWN6TOGO]

thanks for the explanation.
i'll have time to check the ratio out at lunch.

i'm pretty sure i'll want it geared higher for more acceleration, since i barely use her on the highway. i don't even need to drive the highway to get to work, so i can avoid it more than 80% of my time on the road.

if i am to mod the gear ratio. how would i go about doing that?

 

[77-4speed]

You can buy the new set of gears on an exchange basis and send the old gears back to the vendor. It is a job you can do by yourself but it is somewhat difficult to say the least. I imagine it would cost somewhere close to $600 to have the gears changed out, including parts and labor. I'm sure others that have done this will chime in soon.

Russ

 

[cntrhub]

Better have a "pro" change out the ring and pinion. First, you need the formula to get the correct shim for the pinion set inside the axle housing. You need special tools to "load" the crush sleeve on the pinion. You need at least two types of torque wrenches. One to crush the sleeve, and one to measure bearing drag of the pinion. The "foot print pattern" of the ring touching the pinion has to be spot on. If you don't line these two up, your rear end will sing....on lift and/or on throttle. Backlash is critical, becaue the axle grows when heated.... (more special measuring tools). To attempt all this, you still need to have both an array of shims for the pinion shaft and ring carrier, to get the all the "pre-loads" set in the axle housing. It is not that simple to do. Leave it to the experienced.

 

[1DOWN6TOGO]

i love working on my own car, i'm a fast learner, especially when i have some foundational knowledge to build upon. what i don't know i learn. but as i said before. i know nothing about differential, and i don't dare mess something up horribly by trying to learn. so i will take ur advice, and i will have it done by a pro.
thanks for the advice
and thanks 4-speed, for the insightful explanation and for the cost estimate.

sam

 

[Dave L.]

Try this outfit--www.ikerds.com.They are one of many companies that sell complete drop in carriers.They include new bearings and seals,clutch packs etc.These units are ready for install with out the hassle of setting tolerances.

Dave

 

[1DOWN6TOGO]

i'm looking there (www.ikerds.com) right now
and i'm trying to understand the ratio again.
-4speed, you say that a ratio like 3.x : 1 is better for acceleration than one like 2.x : 1 ?
that doesn't make sense to me
can someone explain why the closer the ratio the more sluggish it is?
thanks

 

[77-4speed]

It's all about torque.

Remember your old bicycle? If you had the chain on the smallest sprocket (2.40:1) you had to push real hard to get it moving, but once you were moving you wouldn't have to pedal very fast to keep up the bikes speed.

If you had the chain on the biggest sprocket (3.70:1) you could get moving really quickly but then your legs had to pump really fast to keep the bike up to speed.

Hope that helps clear it up some

Russ

 

[1DOWN6TOGO]

makes perfect sense now
bulb went off upstairs
thanks for the bike analogy

sam

 

[77-4speed]

Glad I could help.

By the way, I saw on Zip that you can get the 3.70 gears for $329. I had a local shop quote me $200 plus parts to rebuild the unit and $450 in labor to uninstall and reinstall the diff.

You can remove the diff yourself. I did with the help of a fellow CAC member and I've never done anything like it in my whole life. Then send it, or drive it to Stingray6974 in Dallas. He will be able to take it apart and diagnose what needs to be replaced. I guarantee you won't find a cheaper price or a nicer guy. He did mine and I saved hundreds!

Look him up here on the action center and send him an e-mail. He can give you an exact price quote for a new gear and the cost to install it. HIGHLY RECOMMENDED!!!!

Russ

 

[1DOWN6TOGO]

thanks
i'm glad you noticed i'm from up here and even more glad you knew of someone up here
that will help a great deal
i'm gonna look for him now
thanks

 

[77-4speed]

I've got his home and work numbers if you want them. Just pm me.

Russ

 

[Stingray6974]

I was wondering why my ears were burning!

Mike