235cui/700R4/2.73:1 combo - would it work?

Just a quick question...I have a '47 Chevy Fleetline that I am restoring. I want to have the "original/vintage-look" with a '61 235cui engine and use a 700R4 tranny. I have a '73 Chevelle posi with 2.73:1 gears in the rear with a 4-link set-up. I plan on using 5.60x15 bias ply tires (28.5" diameter).

Will this be ok to simply cruise (no need fast take off's)?

Thanks.

 

Low powered, heavy car will need more gear. Figure on greatest efficiency at 2000 RPMs at 65 mph. Good trans choice with a deep first gear. Select a rear gear that will put you in that "sweet spot" in overdrive.

 

Not that this is an exact reference

I had 2 different cars with 4.3 TPI V8 - 4L80E trans - 2.56 posi (came ordered in some 94-96 Caprices). It was designated the "LO3" V8 and produced 170 hp and 255 lb·ft when new.

While I believe the 4.3 V8 winds up on the top end more than yours, around town it was low on torque with the 2.56 ratio for the heavier Caprice and Roadmaster. A stock 235 looks to be about 30lbs lower torque, but that being said the caprice combination was a great driver and awesome hi-way cruiser.

What about a better carb, intake and exhaust for your 235 setup? It may work well with with a 2.73 set.

 

it will fall on it's face when it hit's od. you need mid 3's in the rear.

 

I have an L03 in my truck. It is a 5.0l (305 CID) V8. The 4.3l V8 was last seen in 1977.

 

you'll hate it...nothing off the line (i know that's not important) and it will barely idle and run at 100mph. i have a 235 with a 700r4 and 3.73 gears....runs great at 75 down the freeway (approx 27.5" rear tire) to low of a RPM will make it a slug and it won't be in the motor's sweet spot to move. Step up the gears and i'll be happy

 

The 700r4 has a 3 to 1 first gear, you'll be fine coming off the line. That tranny was developed in the late 70's to try to make all those heavy GM barges get better gas mileage. Most of them had rear end ratios in the 2's also (2.2?, 2.56, 2.73) Your car might be a little lazy on the highway if you need to pass, but you'll have to try it and see.

I had an 80's Camaro with the 700r4 and 2.73's and I never had a problem with it on the highway.

 

If you are committed to the engine, the transmission is a great choice, but the rear gear is all wrong. You need at least a 3.73, probably more like a 4.11 rear gear. With a 4.11 and a 28.5 tire, you will be turning just about 2000 rpm at 60 mph. It is unlikely your six cylinder can pull much more gear than this on the freeway.

 

the od ratio is .73 you effective final drive in od is 1.99 to one.

I wouldn't go much under 3.55 unless you are driving on a billiar table all the time.

go to www.4lo.com and use their calculators to find rpm at speed or speed at rpms with different gears and tire diameter. I would shoot for 2300 to 2600 at 70.

As noted the low gear in the trans is pretty low so getting off the line shouldn't be a problem unless you are building a drag car.

I have one in my Studebaker truck behind the Studie 259 v8, coupled to a T bird 3.7 something rear. With 235 75 15 tires, it should be at 1950 at 60 and abpput 2200 at 70.

 

235 in a 54 210. I run a 2.93 w/ a 1:1 trans. about 2500 @ 70. it's real happy. I think this is the rpm to speed range you need to shoot for.

I ran this trans /rear with the stock engine and it pulled it great. The engine I;m running now is modified and works just as well. It will pull in high gear nice from 1000 rpm.

 

Per Dragdoc's recommendation, given your 28-1/2" tire, for 2000 RPM at 65 MPH, with a 0.70:1 4th gear, you'd need a 3.73:1 rear gear.

Gas Pumper's tires should (mathematically) be 29.55 inches tall, for comparison sake. If you wanted to match his performance with your 28-1/2" tire, you would need a (theoretical) 4.03:1 rear gear. Since that does not exist, you would be better off going to the next lower "real" gear (numerically higher), like a 4.11:1. You'd be at 73.67 MPH at 2500, instead of his 75 MPH.

Between a 3.73:1 and a 4.11:1 gear set, I'd go with the 4.11:1 one. Revving a little higher with better mechanical advantage is better than lugging under lower mechanical advantage.

Remember, tire circumference, figured out via tire height is often not exactly what the actual roll-out is.

 

wow, thank you to you all for the wealth of information! I am thinking I am going to just switch out the rear axle entirely since I dont want to mess with it...or? I was told it was a heavy duty 10-bolt rear axle and after counting the gears and referencing the code on the axle tube, it's 2.73:1. I was told it was off a '73 Chevelle.

What you all recommend, just swap out the gears on this rear posi or completely swap out the entire rear axle?

Yes, i am committed to the engine. I had thought about a 60's truck 3-spd transmission (3 on the tree) but was told that with the 2.73 gears, it would hesitate to take off ( I guess its like taking off on 2nd gear on my Toyota truck 5spd pick up, right?).

I think the original '47 Chevy rear axle (with the old torque tube) had 4.11 gears! I remember driving the '47 stock with the 216, 3spd, 4.11 gears and that thing rev'ed up HIGH on the highway!!

Image of the rear axle and car project:

 

My '89 Suburban ran a 700R4 and 2.73 rear. It's great on the flat if you want to cruise at 75-80 MPH, I pulled 17 MPG out of it with the 350. With a load on, on a hill, I was having to drop it into second or low to get up them.

You should be able to scare up a second gen Camaro or similar era Nova 10-bolt with a better gear in it, cheap, that will about bolt into the stock springs. Or look for an S10 4x4 rear, they're not hard to come by in mid-high 3's with a posi and fit well, although these need the perches moved a bit. I have a Camaro for my '50 Chevy that has a 3.42 in it.

 

Aeroman, seeing as you got the 2.73 , why not run a TH350 1:1 trans and sell the OD?

I am running a 3.50 1st Sag 4 speeed.

 

My old c10 had a 700R4 with 340's and a 305. It ran great but at highway speeds in overdrive it was a dog. Replaced the tranny when it failed with a TH350 and never regreted it.

 

I can't begin to imagine what a dog a Burb with 2.73's would be. I've had 2 or 3 Burb 350's with 3.73 gear and I considered those just Ok for pulling a load

 

I think you'll be very unhappy with the proposed combo as well. Something in mid 3's would be much better. Like Rusynewyorker says, look for an S-10 4x4 rear. Later ones are disk brakes as well, just grab the master cyl. while you're at it!

 

<meta http-equiv="Content-Type" content="text/html; charset=utf-8"><meta name="ProgId" content="Word.Document"><meta name="Generator" content="Microsoft Word 11"><meta name="Originator" content="Microsoft Word 11"><link rel="File-List" href="file:///C:%5CUsers%5COsito%5CAppData%5CLocal%5CTemp%5Cmsohtml1%5C01%5Cclip_filelist.xml"><!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <wunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <wontGrowAutofit/> </w:Compatibility> <w:BrowserLevel>MicrosoftInternetExplorer4</w:BrowserLevel> </w:WordDocument> </xml><![endif]--><!--[if gte mso 9]><xml> <w:LatentStyles DefLockedState="false" LatentStyleCount="156"> </w:LatentStyles> </xml><![endif]--><style> <!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0in; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:8.5in 11.0in; margin:1.0in 1.25in 1.0in 1.25in; mso-header-margin:.5in; mso-footer-margin:.5in; mso-paper-source:0;} div.Section1 {page:Section1;} --> </style><!--[if gte mso 10]> <style> /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;} </style> <![endif]--> Thanks for the info again fellas...again, I will using a 235cui with about 90-120hp...would this be a determining factor or would the tranny be more of the determining factor? Again, I simply want to take off from 0mph to a nice and easy acceleration rate. I will be mainly cruising slow and low, not towing a boat or anything for that matter.

I will look for an S10 rear axle. Are their certain years that are favored?

Thanks again...

 

The 700R4 has a lower first gear than any of the other GM automatics. Good for getting off the line.

S10 circa 1993-4 you can get one with a 4.11 ratio already in it, axle code HO4. Valid gear ratios in that range are 2.73 (GU2), 3.08(GU4), 3.42(GU6), 3.73(GT4), 4.10(GT5) and 4.11(HO4). So, what ever route you chose, there should be one for you in there.

Allied Auto Salvage, 1-877-784-0057, in Riverside, has two 4:10 units from a 1997 S10, for $150. Their stock numbers are 00001504 and 00003554.

 

Thanks Gimpy! Yeah, I am about 45 min south of Riverside. Thanks for the info! How did you find this out, lol?! Online?

 

I am a miracle worker.

No really, it is just a website. You know how the salvage yards talk about "the wire"? It is online and public, and apparently not well known. I just grabbed a Winchester, CA Zip Code at random, 92596, and typed that in.

http://www.car-part.com/

Give it a try!

 

Ah ha, thanks!!!!

 

What about simply swapping the 2.73 rear end gears for a 3.73 gear ratio? I can take it to a shop. If I go this route, where can I find the gears? Thanks!

 

Given the weight of the car, I might go all the way to 4.11/4.10. The gears alone will cost over $150, and the labor for a good shop to put them in can be killer.

Gears here:

http://www.ringpinion.com/

 

Much, much cheaper and easier to swap the entire rear. Here, the price for a rear axle from a U pick is about 50 bucks. I paid 150 for the limited slip Roadmaster rear for my wagon from my buddies high class recycler. How many hours will it take to properly set up a new gear set at 90 bucks an hour?

 

Transmission gear ratios ...

Power Glide.........1.76......1.0

TH350 .................2.52.....1.52....1.0

TH400.................2.48.....1.48....1.0

700-R4/4L60.......3.06.....1.63....1.0.....70

200-R4.................2.74.....1.57....1.0.....67

4L80E..................2.48.....1.48....1.0.....75

With the 700-R4 transmission you are using, it has a overdrive of 30 per cent. A 4.11 rear end is effectively in the 2.87 range when the 700-R4 is in 4th gear ( overdrive ).

First gear is 3.06.
With the 4.11 gear in the rear end, your effective gear ratio in first would be in the 12.5 to 1 range. That should really move the old Chevy off from the stoplight.



There is NO WAY I would run anything less than a 3.73 ... ( a 4.11 would be better ) in a vehicle has heavy as yours with no more than 235 cubic inches.

 

My 37 Chevy p/u has a 57 235 hooked to a T-5 with a 2.79 gears and it does ok but the gas mileage dropped after putting it togather,come to find out the original carbs were not designed for that motor to turn much slower so if you use those gears put a modern carb on it. I am tinkering with the original carb and making some progress but I was thinking of better gas mileage with the taler gears and overdrive but did not work out as I thought.

 

The 200-r4 has a lower first gear and its also the same size as a Turbo 350. I looked into the 292/ 200-r4 combo for a project. A 3.25 or 3.42 gear will work to depending on your tires size.

200-R4.............. 2.74.....1.57....1.0.....67

700-R4/4L60.......3.06.....1.63....1.0.....70

 

The reason being is that I have already welded the 4-link set-up n the axle. I'd have to start over with that. I wouldn't mind swapping the gears and leave the actual rear end alone. But I agree with you on the cost.

Fellas, originally, I was going to run a 350cui Vortec engine, stock engine, with the 700R4 and 2.73 gears. Lately, I have been itching to have the original inline 6 look, hence the dilemma with the combo questions.

I'm not looking for 1/4 drag take offs. I want a "normal", non-hesitant take off from the line, make sense? I had contemplated with using a 60's 3-spd transmission but it seems like the 700R4 has better benefits and it doesn't take away the stock look (mainly under the car). I currently have the body off the frame and so, hence all the questions here about using what for what. I want the nice highway speed with non-screaming engine rpm's - that's why I didn't keep it stock.

So, can I get away with 235cui, 700R4 ( or 3spd 60's Tranny), and 3.73 gears?

Has anyone ever gotten gears swapped out? I see it's about $150 for the gears, just not sure on the labor cost. Thanks!!!!!!!

 

I swap gears all of the time, as a regular business practice. The install labor varies depending on the the configuration of the axle (like shims v.s. threaded adjusters, etc.), and on weather or not it is still in the car.

Put that rear on my bench, and it is $510 (6x$85) +tax for the labor alone. The install kit would be about another $100. You could be at $760 +tax, to save re-doing the 4-link brackets, and you might regret the 3.73's.

How much are 4-link brackets?