I'm running a 250 6 / SM 465 granny low 4speed open drive and a 10 bolt with 3:08s in our 50 Suburban. Low gear is useless unless the trailer is hooked up, starts off well in 2nd. Freeway speed tops at 65 and is plenty fast for a 60+ yr old rig. We pull a 2500 lb 20' Avion a lot in the summer behind the burb and its a hill hating 35 mph struggle in 3rd, sometimes 2nd on the big ones and on flat land, 4th is very tired feeling at 50 - 55 mph. My plan is to swap rear end gears and toss in a 700r4 ( I drive it everyday 70 miles to work and back also running errands etc after work). Getting the best mpg I can with a 250 / 700r4 combo is high on the list, but being able to more comfortably pull the hills towing in 3rd would also be a plus. My question is: What rear end gears are you truck guys running with a 700r4 and occasionaly pulling a load at freeway speeds for a few hours through some hills?? I have seen 3:73s and 4:10s used and am wondering what you all would suggest with this set up. Here's our hound hauler/get out of town set up.
Stick in a chev 6.2 diesel and a 700r4. I drove a motorhome to Florida and back to Ontario with this combo, and got 29mpg at a constant 70mph! Don't know what rear axle ratio is, but could find out. Talk about having your cake and eating it! This rig flattened most hills and was easy driving. This is going into my 63 Step Van, so I can afford to drive it anywhere, just 'cause I wanna.
If I'm not mistaken the OP didn't ask about a diesel conversion he asked about rear gears for a 700R4. While I don't have the silver bullet answer for you If you dont have a 700R4 yet I would call up Gearstar trans (amazing service) they will ask you a bunch of questions, be able to give you advice on the rear gear choice and likely sell you a job rated awesome transmission as well...... I don't work for them, have no association with them whatsoever HOWEVER, got treated outstandingly well, they were very through and ensured I would be happy with my purchase. They ain't cheap but they will custom build you whatever it is you want and then back it up.
3.50 or 3.55s would be a nice gear with o/d but you might need a slightly bigger motor to make it happy pulling the trailer with whatever gear you decide to put in it.
You might try 3.73 or 4.10s with the four speed you have now. You may just need to spin the 250 up a little more!
Great looking rig you have there. 4.10s and the overdrive would be my choice, or leave the manual trans and run 3.50s.
I ran 3.73 with a 700r4 with 29" tall tires. The truck had a 250HP 327 and ran like a champ. Honest 24 mpg at 75 mph and could still pull the occasional car trailer. I would run 3.73/700r4 combo again in a heartbeat. (Beautiful setup too by the way.)
Thanks for the comments. I forgot about the tire height in the mix, I remember it making a big difference on one of Dad's trucks. I'll measure them and edit. A 292 would cool, but this 250 runs really nice. I have a 700r4 , lokar shifter, round boot etc, but mabey starting with 3:73 and keeping the 4sp? A truck is supposed to have 3 pedals, but I'm getting lazier the older I get and tossing it into D every day through 20 stop lights and 70 miles of highway sounds kinda nice. The 4:11s would make better sense for pulling the trailer and 3:73s for better economy seems to be the ticket, but cam , carb and tire size also play a huge roll in mpg from what I'm learning. Bumping it up to see if anyone else has input on what they have experienced. Thanks
my wife has a late model Silverado, with the six (262 ci), overdrive trans, and 3.42 gears. That truck kicks down all the time pulling a trailer. The engine is just too small. It gets great mileage when not towing, and lousy mileage towing. My 57 one ton pickup with a 454, SM420, and 3.73 gears (and tall tires) does a lot better, although it will go slow if I'm pulling a very heavy trailer through the mountains. Overdrive will help a bigger (350 ci) engine get better mileage when you're not towing. Good luck, sounds like you might have some more trials in your future...
I read somewhere that for the best fuel economy, top gear @ 60 should put the rpm's somewhere at the beginning of the torque curve. In you situation, I would think that OD should be at the lower end of the torque curve, and 3rd gear towards the top. Plug in the numbers, and play around with different ratio's here http://vexer.com/automotive-tools/speed-rpm-calculator
http://vexer.com/automotive-tools/speed-rpm-calculator thats a pretty cool calculator, but seems to run higher than I expected on the RPM's Anyone else with a stovebolt or inline 6, 700r4 combo and whats your rear ratio?
Needs More Cubic Inches !!!!....Try a beefed up 292 GMC six with more compression and a stump-puller camshaft...390 CFM four barrel and headers....leave the SM 465 alone !!!...change to 3:55s out back.
If you can find a 3.90 gear, that might be the best all-around set-up with the 250 six in a rig like that. If not, you have two compromises...go for a 3.73 or a 4.10 ratio. The 700r4 will get you going easier, but be sure you have the TV (throttle valve) cable hooked up and adjusted properly before you drive it an inch!!
Hey NewFisher, You may contemplate a steeper gear, and then adding something like a Ranger overdrive unit. I have a 64 C10 with a 292, and an SM420, and will be adding the Ranger here shortly. It allows you to split any gear with a 27% overdrive. http://www.high-impact.net/transmission_and_gear/rangeroverdrive.htm I know the sm420 and 465 often suffer a bit in that three/four area. A bit more rear gear, and the option to split gears may improve your situation. Just another option!
Depending on the vendor, I've seen them range from just under $1000, up to around $1500. Crazy that they vary that much, so, watch out when you go to buy one. I'm excited to get mine installed. With a 3.73 rear, and 30" tires, it should put me at 2150rpm at 70mph in my C10! Can't wait to see what it will do to my mileage.
Thanks guys. The pumped 292 would be cool, but last on the list. I'm digging the simple single carb and getting decent milage( keeping it simple for awhile). The ranger is cool, similar to a gear vendors unit theat I could get my hands on, but I'm kinda leaning ttowards ditching the manual for a more "6:00am, no coffee, 20 stop lights , then 30 plus mile drive to work" automatic. I know don't hate me, trucks need 3 pedals....I get it. It just seems easier right now. So back to the 700r4 swap behind a semi lethargic 250. The 3:90 gear set does seem to split the difference and may be my answer with this combo. Ill start looking for a set and see what's out there. 10 bolt car 7 3/4 is what I remember it having ( notes are at work). Thanks for all the input!
Quote ( I drive it everyday 70 miles to work and back also running errands etc after work). I always tune the drive train for what I plan on using it for the most. If you pull the camper you are more than likly on vacation so what's the hurry? You say you drive it 70 miles a day. I'd tune it to be happy going down the road every day..... I think your biggest problem is the 250. You have a truck, and the 250 just wasn't made to pull. It was more of a car or light truck engine. If your stuck on an inline I like the 292 suggestion. For economy? The best all around truck engine I have ever had was a 334 stroker. It's a 305 block and a 400 crank. It kicks a 350's ass on the low end, and is easy on gas. Not HAMB freindly, but I had to mention it because I think it fits your needs.
http://www.summitracing.com/parts/MGR-G875390/ Interesting....factory gearing in the old Chevy trucks from the 50s was, get this-- 3.90
I found out on my 66 F250 that a bigger motor with more torque helps out alot,I first went from 4.10 gears to 3.54s and the gas mileage stayed the same but dropped in a fresh 460 and if I keep my foot out of it I get better gas mileage then with the original 352 and plenty of power to tow what I want.
I really don't think that a drive line change is going to improve your fuel mileage. I really don't think that your towing performance will be helped by any thing other than the substantial boost in torque that would come with a bigger engine. Suburban+camper+every thing needed for a camping trip= like 7,000 plus pounds. 6 cylinder Chevy= 135 horses on a good day. You can have any thing you want, but you can't have every thing you want.
What are your rear gears now? I've never had a six cylinder truck but with overdrive and a stock six I would imagine you need 4 something gear to tow relatively comfortably. How often do you go on vacation with the trailer? If its not very often I would just set th truck up to be comfortable everyday and tow slow on vacation.
How about a 5 speed manual box with closer ratios than the current wide ratio four speed? Fifth is usually overdriven so it may improve your fuel consumption in the process.
The 2004R is the superior trans, no doubt... but the 700R4 is the better fit considering the weight of the vehicle and the dinky c.i. I imagine the 3.06:1 first gear will be welcome in his ride.
3:08s now and we camp nearly every other weekend in the nicer months with once a month in the spring and fall.
I'm doing the exact same maths on a tranny swap for my Packard, minus the towing capacity. The factory Ultramatic is getting tired and slippy, and after going through just about everything that you have so far, I've determined that the 200-4R is the right one for me. I'm running a stock 130hp Thunderbolt L8, a stock 3.90 pinion set and Coker 760x15s that measure 28.7" tall. Doubling the amount of ratios behind this engine will far better utilize the brutish torque it develops, and the .67:1 OD will lower cruising RPM @ 70 mph by nearly 1000. In my studies, I've found that many people consider the 200-4R a "weak" transmission because they are confusing it with the TH200 3 speed, which was infamously bad. In your application, I'd suggest hunting down the beefy version of the 200-4R that came with a Monte Carlo SS or Buick T Type/Grand National. It has lower ratios than the 700R4 and a taller OD, and a smaller case size which will make it much easier to fit in a car that's designed around a breadbox sized manual. The only rub to using either of the GM overdrives is the electric lock-up solenoid. If you're already running a 12v system, no worries. Install a relay on your brake switch circuit to unlock it on decel and you're golden. As was previously mentioned, a TV cable is also a good idea since it makes the valve body... behave better. My car is 6v and I really really do NOT want to make the change, since I like playing my optional Del-phi radio while I chase two little yellow globs around at night. I'm going to pick up a 200-4R this weekend that came out of an 85 Regal and inspect the lock-up solenoid to see if I can't figure out how to actuate it with 6v. The circuit is actually fairly simple. There's a mechanical pressure switch on the 4th gear hydraulic circuit that energizes the solenoid. It only needs battery feed to operate. Mechanical components don't care what voltage you run through them, as long as the amperage isn't too high. I think it will work. The big question mark is whether the solenoid will energize with enough force. I'll cross that bridge after I swim around it a few times, and I hope my rambling contains one or two pieces of info you can use.
I ended up with a 3:73 rr from a 68 C10 ( only 1/2 wider wms and same 1310 joint) and a 700r4 using the TCI lock up kit with the vacuum switch and added manual trigger for 3rd lock up when towing. Couldn't be happier. Soft 4th lock up smooth and great milage so far with the 390 Holley and the mild built 250 stovebolt
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