Wilson

I am wanting to lower the RPMs on my numbers matching '70 442 with a TH 400. My buddy (the knowledgeable one behind the restoration) suggests putting a 2004R (because it bolts up without an adapter kit) in it with a lock up converter. Upon talking with the tranny shop guy, who says he can rebuild me one for $1000-1200, asked me why I didn't I just change the rear end gear.
I welcome your thoughts and knowledge.

edzolz

Depends on your driving. If you drive more on highway, the overdrive would be best. Around town, unless you want faster take off, change to higher numerically gears. Actually overdrive is the best all around choice.

don71

I understand your concern. Rpms, durability, mileage and fuel cost etc.

What engine size and current rear ratio do you have now? I assume its a 455 with a 3:90 posi from your other posts.

I feel if you change your rear ratio, you'll neuter your cars performance from a stand still. The factory built lots these to handle the power for this model. Thats kinda why they call it a 442 instead of a Cutlass. You should still talk to a drive line/rear guy and get his input too, as to cost. The 3:08 is a good compromise gear. I have a 3:23 and have no complaints.

I like the idea of an overdrive trans, but I think your buddy is a little low on price, and you'll find hidden costs in this adaptation. A little more to it, than the trans alone.

You've got a nice car, enjoy it.

oldcutlass

Look into a gear vendor overdrive unit.

Wilson

Thanks for your reply. We drive it to car shows, some times on the Interstate; even to Lansing for the Home Coming from southern Indiana. So, yes we need to get the RPMs down on the highway.

Wilson

Thanks for your reply. Yes, it's the original 455 with 3.23 gears. Yes, my buddy says it will be a pig if we change the gears. It wasn't my buddy who quoted the tranny cost; it was the tranny shop owner (and that price included the torque converter).

m371961

Just my opinion, not from specific experience with these cars, but with general auto knowledge. I think you would be much happier with overdrive. Still will have the power when you put your foot down and want to burn rubber, and give you more pleasure in long drives. You may even find yourself driving it more often. Changing the gears may be cheaper, but you are going to miss them.

oldcutlass

IMHO, 3.23 gears are not that bad, I wouldn't even worry about it. These cars were designed to drive all day long with those gears.

Fun71

You have 3.23:1 gears now, so what RPM are you doing on the highway?
My car has 3.23s, and with the old 245-60-14 tires (very short) the engine was spinning around 3400 RPM on highway trips. I had no problem with that. I now have 245-60-15s, which are 1" taller and dropped the RPM slightly - almost imperceptibly, actually - still no issues with that RPM on trips.

What size rear tires does the car have? A change from short 14" tires to tall 15" tires (275-60-15 = ~27" tall) can make a noticeable difference.

Note that there aren't very many ratios you can swap into your existing housing (assuming it's the original O-Type) to lower the RPM:
3.08, 2.78, and 2.56

I think in order to get any significant decrease in RPM, you would have to drop to the 2.56:1 ratio, which as said above, will kill your performance.

joe_padavano

The fundamental problem is that you want a wider range from first to top gear in the trans. Keeping your TH400 and changing the rear axle ratio sacrifices off-the-line acceleration for lower highway RPMs. Your tranny shop guy also doesn't realize how difficult it is to get gears for the Type O axle in your car (hint: it is NOT a "12 bolt", despite what the cover looks like).

Frankly, with 3.23 gears, I agree that you should leave it alone. Assuming a 26.5" diameter tire (225/70-14), you should be seeing about 2500 RPM in third at 60 MPH and about 2900 RPM at 70. Bump that up to a 28" tall tire (275/60-15) and RPMs drop to 2300 at 60 and 2700 at 70.

Now, the much wider ratio from first to fourth (OD) in the 200-4R means that you drop RPMs with the smaller tires to 1800 at 60 and 2100 at 70. At the same time, the steeper first gear improves off the line acceleration.

olds 307 and 403

Yes, $1200 is cheap for a 2004R overhaul, it needs line pressure boosted, a good servo, bottom feed filter and probably a billet forward drum. A 2004R is a very easy swap on a TH350 car, is the drive shaft the same length on a short tail TH400? A yoke change will need to be done at minimum, the 2004R uses the 350 yoke. Joe, that RPM calculation isn't taking torque converter slippage into account, add 250 to 300 rpm. With slightly taller 215/75R14 tires with a TH350 and 2.78 gears I run at 2400 RPM at 60 mph, checked with a GPS. With a TH2004R, it was 1700 RPM at 60 mph with it locked, my daughter ran it low on fluid and cooked it. I am planning on a TH350C, 300 RPM less does make a difference. This calculator is very accurate but add to 250 to 300 rpm for a non lock up torque converter, which is what you currently have.
http://tech.oldsgmail.com/axle_RPM.php

oldsmobiledave

Just drive it. It's not hurting anything.

Oldcoyote

Wilson
are you SURE you now have 3.23 gears?

Qwik71442

3.23’s plus the Gear Vendors is Perfect for Interstate or highway driving

3.23’s = 3000 rpm at 70ish (26” tire) not including convertor slip

3.23’s plus .78 GV Overdrive = 2300 rpm at 70ish (26” tire) not including convertor slip

Gerald Nickels

Slow down to the posted speed limit. That helps. Back when gas was under $ .50 with 3.91 I drove the heck out of it. I just never had a tach in my 64 Cutlass.

midnightleadfoot

A 2004r to take the torque of a 455 and live isn't a 1200. rebuild
It's 2200-2400 plus a good converter 300-500.
different cross member, tv cable brackets. speedo correction as nothing with a 2004r came with 3.90 gears.


At this point, go over and get a gear vendors o/d. That bolts to your th400.
It'll be cheaper in the long run and be stronger. and if the transmission takes a dump, to rebuild a th400 is much less than a 2004r is.


As for changing out the rear gears instead. How are you going to drive it.? If you have a 455 powered 442 because you are going to drive it and use the power. you might not like the gear change. If you will drive it like grandma 90% of the time. and don't care how much slower it might be/get. it will be the cheapest way out. But then why have a 455 powered 442.
only you know what is right for you.
I do doubt the torque of a 455 really "need" 3.90 gears. to still be quick. But again everyone's idea of quick is different.


They biggest question to ask yourself is this. Will you honestly drive this car so much on the interstate that the1200(your number) more like 2600 ish will pay for it self in fuel savings?
2mpg gain takes a long time(highway miles) to pay for itself when the buy in for it 2600.00
You won't gain much around town with the 2004r. or the g/v .
The going in and out of o/d while town driving does the 2004r no favors either.

Wilson

Thanks to all who have replied. Here are answers to some of the questions raised: Yes, I'm sure I have 3.23 gears; I did the calculation on the ring and pinion. I'm curious why you question that? I currently have 225/70R 14's on the car and according to the Tic Toc Tach, I'm turning about 3000 rpm at 60 mph. I'm getting ready to go with 275/60R 15's on the rear; which should help some. We don't run the ol' girl hard, she's got 78,000 now. But, I get what you're saying about not wanting a muscle car that drives like a pig.

Thanks

oldsmobiledave

What is it about 3000rpm that scares you? You are just spoiled by modern OD transmissions. Just get in and drive it. It is hurting NOTHING!!!!!!!!


The factory tac is ALWAYS way off. Olds did that on purpose to protect against warranty claims. When your Tic Toc Tac says 3000 rpm you are probably only turning 2500 RPM unless you re-calibrated the tac.


You state that you did the calculation on your ring & pinion but you took your tac as gospel. Get under your car & inspect the axle tube for the factory stamp or better yet pull the cover, inspect the crown & pinion & determine the ACTUAL ratio before you do anything else.

Wilson

Thanks to everybody for your input; very helpful!

Fun71

Spot on, Dave!
I just punched numbers into the online calculator below and for 225-70-14 tires and 3.23 rear gears it shows 2533 RPM at 60 MPH.

https://www.ringpinion.com/calculators/Calc_RPM.aspx