Burb Needs a New Transmission

[yevgenievich]

Well the answer is I'd like to do it tomorrow, but have already put it off for damn near a year. A couple of things are slowing me down. I currently have the 14B semi-float and have thought about swapping to FF, then deciding between 4.10 or 4.56. I guess I've delay it because I can't make up my damn mind!



If I was running a 454 there would be less of a decision to make because I'd 4.10 it. I have a 99 class C motorhome with 454 & 4.10 and it pulls that along reasonably well. So I also like to keep in mind the future with my gears. Currently has a 305, it's a good running solid 305 and I'm not going to ditch it until it's warn out. But what will I do when it's done, likely I'll go with a 350, it's a straight forward swap the 454 requires a little more work. I think that the 305 and the 350 would do well with 4.56's for my purposes but until I get around to doing it, I like to get first hand opinions. In the 60's and early 70's they 4.56'ed 1 tons with the TH400 from the factory, I had a friend with a 72 like that. The only thing was you didn't drive it much over 60mph. With OD I'd think it would be a lot less limiting.

4.10 with 33" tire is equivalent to 3.73 with stock tire. If doing more towing, 4.56 would probably be the choice with 33"tire. I don't tow too much, and above 70mph big block does fine in od towing reasonable size trailer(6kish) with 3.73 gears

 

[SirRobyn0]

4.10 with 33" tire is equivalent to 3.73 with stock tire. If doing more towing, 4.56 would probably be the choice with 33"tire. I don't tow too much, and above 70mph big block does fine in od towing reasonable size trailer(6kish) with 3.73 gears

So this afternoon, was a good example that did not involve the big trailer. I went and picked up feed for my farm, from another farm. This guy is 80 milesish round trip. Starting out at his place there is 20 - 25 miles of slow, hilly curvy country roads. Speeds vary from 20mph to 40mph. This is terrible loaded with 3.41s. At 40MPH that's a mear 1,400RPM out of the power band, so 3rd gear is about useless on this stretch, to avoid constant shifting, means running it in 2nd most of the trip, 2,400RPM which is much better, but also means not being able to lock the converter for that entire bit. Several hill climbs start after sharp corners which means I'm stuck in first at 20MPH, that's actually ok with me, I don't mind slow, what I really don't like is running in second and not being able to lock the TCC. And starting off on a hill loaded you have to lean into the converter way to much.

3.41 - 4.10 - 4.56 @40mph 31" tire
third 1,400 - 1,777 - 1,976
second 2,400 - 2,879 - 3,202

IDK seems like the 4.56 would be the winner for these speeds as well.

 

[RecklessWOT]

Well the answer is I'd like to do it tomorrow, but have already put it off for damn near a year. A couple of things are slowing me down. I currently have the 14B semi-float and have thought about swapping to FF, then deciding between 4.10 or 4.56. I guess I've delay it because I can't make up my damn mind!



If I was running a 454 there would be less of a decision to make because I'd 4.10 it. I have a 99 class C motorhome with 454 & 4.10 and it pulls that along reasonably well. So I also like to keep in mind the future with my gears. Currently has a 305, it's a good running solid 305 and I'm not going to ditch it until it's warn out. But what will I do when it's done, likely I'll go with a 350, it's a straight forward swap the 454 requires a little more work. I think that the 305 and the 350 would do well with 4.56's for my purposes but until I get around to doing it, I like to get first hand opinions. In the 60's and early 70's they 4.56'ed 1 tons with the TH400 from the factory, I had a friend with a 72 like that. The only thing was you didn't drive it much over 60mph. With OD I'd think it would be a lot less limiting.

The OD on a 700R4 is some ridiculously tall ratio. I forget what it is exactly bit IIRC it's like 60% or something absurd. You certainly wouldn't be limited to 60, though I seriously doubt you'd be able to break triple digits

 

[SirRobyn0]

The OD on a 700R4 is some ridiculously tall ratio. I forget what it is exactly bit IIRC it's like 60% or something absurd. You certainly wouldn't be limited to 60, though I seriously doubt you'd be able to break triple digits

The ratios are 1st - 3.06, 2nd - 1.63, 3rd - 1.00, 4th - .69, I've actually seen OD listed as .69 and .70, seems to depend where you look. I have heard people say just what you did, that the 700R4 has a ridiculously tall OD ratio, but if you compare it to other automatics of it's time period for example Chrysler's 42RH & 42RE both ran a .69 OD & the Ford AOD .67 OD so it's right there with them.

So with 4.56's in OD I'd hit 3,000RPM at 87MPH. 75MPH, 2,500RPM I'd be comfortable cruising that 2.5K RPM all day, even a little higher, but I know it's going to kill the highway MPG. It's all a compromise, isn't it.....

Oh 100MPH would be 3,495RPM, so yea I could hit that if need be but not an all day drive. I know SBC doesn't mind cruising with some RPM but that's a little much.

 

[RecklessWOT]

The ratios are 1st - 3.06, 2nd - 1.63, 3rd - 1.00, 4th - .69, I've actually seen OD listed as .69 and .70, seems to depend where you look. I have heard people say just what you did, that the 700R4 has a ridiculously tall OD ratio, but if you compare it to other automatics of it's time period for example Chrysler's 42RH & 42RE both ran a .69 OD & the Ford AOD .67 OD so it's right there with them.

So with 4.56's in OD I'd hit 3,000RPM at 87MPH. 75MPH, 2,500RPM I'd be comfortable cruising that 2.5K RPM all day, even a little higher, but I know it's going to kill the highway MPG. It's all a compromise, isn't it.....

Oh 100MPH would be 3,495RPM, so yea I could hit that if need be but not an all day drive. I know SBC doesn't mind cruising with some RPM but that's a little much.

Hah I feel you. That's one of the things I hate most about my '08 2500, it's limited to 99mph. I routinely cruise north of there without even realizing. But even 3500 RPM at 100 isn't horrible as long as you don't plan to stay there all day. Realistically 2500 at 75 ain't a bad cruising speed, even a tad higher at 80. You won't be killing it in the fuel economy department but as you said it's all a trade off. You got 3.42s and a 700R4, don't get much more MPG freindly on the highway than that unless go with 3.08s or something lol.

But if you want to be able to use your truck for truck stuff that may have to come to an end. You got your cake now, but I heard you can't tow **** with your truck and eat it at the same time, or something like that. So which'll it be oh brave Sir Robyn? When towing rears it's ugly head will he bravely turn his tail and flee, or will he stand up and fight those ugly MPG figures?

 

[SirRobyn0]

Hah I feel you. That's one of the things I hate most about my '08 2500, it's limited to 99mph. I routinely cruise north of there without even realizing. But even 3500 RPM at 100 isn't horrible as long as you don't plan to stay there all day. Realistically 2500 at 75 ain't a bad cruising speed, even a tad higher at 80. You won't be killing it in the fuel economy department but as you said it's all a trade off. You got 3.42s and a 700R4, don't get much more MPG freindly on the highway than that unless go with 3.08s or something lol.

But if you want to be able to use your truck for truck stuff that may have to come to an end. You got your cake now, but I heard you can't tow **** with your truck and eat it at the same time, or something like that. So which'll it be oh brave Sir Robyn? When towing rears it's ugly head will he bravely turn his tail and flee, or will he stand up and fight those ugly MPG figures?

NO! I DIDN'T! I NEVER! YOUR LIEING!

LOL thanks for that!

Seriously though I don't get on the freeway that much, but when I do it's long trips for the farm, some times all day drives, but I'm coming back loaded and sometimes with the trailer. Most of my driving is country roads where 55 is the limit and typically not realistic to go much faster. My commute is country roads, to a 3 miles of freeway, and then a few blocks of city traffic. With all the country roads I drive I might actually see an increase in my day to day MPG since it'll be easier on it on the hills and such.