Is there something Seriously wrong with your ZF5?

 

I've been pondering the swap as well. Here's a link to a decent write up zf6 swap

 

Some synchronizer problems. But also thinking about things down the road? Pros and cons of the swap. Better pulling? Better cruising? Better both or a waste

Thanks for the link

 

In all reality none of what you are expecting. But if you do a lot of heavy towing the low gear in the 6 speed is lower than the 5 speed. As for cruising the top gears are so close that you won't really notice a difference.

 

I did a swap in a obs for a customer and he said the od ratio was a few hundred rpm lower in overdrive

 

OD is actually HIGHER on the ZF5 than the ZF6


S42 ZF5
Close Ratio
1st Gear:
4.14
2nd Gear:
2.37
3rd Gear:
1.42
4th Gear:
1.00
5th Gear:
0.77
Rev Gear:
3.79

S47 ZF5
Close Ratio
1st Gear:
5.08
2nd Gear:
2.60
3rd Gear:
1.53
4th Gear:
1.00
5th Gear:
0.77
Rev Gear:
4.66

ZF6


1st Gear:
5.79
2nd Gear:
3.31
3rd Gear:
2.10
4th Gear:
1.31
5th Gear:
1.00
6th Gear:
0.72
Rev Gear:
5.23

 

With the ZF5 it take more engine RPMs to make the same speed as the ZF6

With the ZF6 you should see lower RPMs@ the same speed..


Just take you gear ratio times the overdrive ratio of the transmission.. that will give you your final drive ratio..

 

Lower reverse, more overdrive, and less rpm gap between 1st-4th shifts. Tell me why so many people say this swap is a waste of time and won't change anything?

Those gear ratio's look 100 times better to me for trying to pull anything.

 

I have driven all 3 of the transmissions listed above. The S47 Zf5 is the best one.
They shift like butter.
Reveres is where it should be.
They dont cost a ton to buy OR fix.
They came in these trucks, they bolt right in with NO CUSTOM parts.
You are looking at ONLY 60 RPM difference in OD

The only plus I see, is they are rated at 50 ft/lb/tq more

O did I also mention you HAVE to run a trans cooler with a ZF6

Do I need to go on? That is just my take on them

 

I respect your opinion on the subject, I guess my views are different.

I have all three transmissions as well, I don't see a difference in shifting in any of them, except my S47 has a bad third gear synchro.

I'm not too concerned with the price difference, reselling the existing trans takes out most of the sting there.

There is no "right" spot for reverse to me. I have and have had several different transmissions with reverse in different spots.

I'm not really interested in lower cruising speed rpm, most of my driving is 55, with 65 on occasion.

My complaints are with the S42 in my 95. It is pretty much worthless for towing anything over 5k lbs compared to most of my other trucks. 1st gear is too fast and the rpm jumps between gears are too large to keep the engine in a happy spot. My biggest complaint is that reverse is too fast, it seems really hard on the clutch trying to back a trailer in.

As it is, the 95 is the last truck I hook to a trailer which is sad because I really like the truck and would like to use it more. I'm not real fond of custom parts either, but this swap doesn't seem like it needs that much custom work to me.

 

If i ever find a good deal on a zf6 I'll be in for that swap.

 

I realize that, the 97 has the S47. It still has the big gaps between 1-3, that I think make the old 7.3 struggle. Don't get me wrong, I think it would help but if I was to go through the trouble of finding a trans and tearing my truck apart, why not get the best of everything?

 

You must be reading the chart wrong. The zf 5 actually has a CLOSER pattern than the ZF6. The zf6 just has a lower 1st. So that negates that. What else do you like about the ZF6?


Gear differences........... zf5...... zf6
1-2 shift .....................2.48........2.48
2-3 shift ......................1.07.......1.21
3-4 shift .......................0.53...... 0.79
4-5 shift .....................0.23 ........0.31
5-6 shift ......................n/a..........0.28

 

I see what you're saying, but if you look at a final gear ratio chart, the rpm gap is less between gears for the zf6.

I'm still liking the zf6 for a lower first gear and reverse, as well as less rpm drop between shifts getting a trailer going. Please tell me how I'm wrong here and save me the work of doing this because the more I look at the numbers, the better this swap starts looking.

 

1-2 shift is the Same
2-3 shift you have LESS rpm drop with the ZF5
3-4 shift you have LESS rpm drop with the ZF5
4-5 shift you have LESS rpm drop with the ZF5

So the gear gap is LESS with the ZF5 NOT the ZF6

That is why I dont understand your thinking that the ZF6 is better, because it is NOT. Other than the CREAPER 1st and Reverse, I just dont see it. ANd if you need that LOW of 1st and reverse, just pop it in 4 low. But my 97 w a ZF5 and grossing out at 20,000 I have absolutely no issues with the ZF5. And mind you I have 35s. But what do i know. Go spend 1600+ on a ZF 6 + another 500 on a Tcase and what ever the driveshaft mods cost, its not my money

 

using Brads gear ratio numbers for the two transmissions I get a different result. it is early morning so I might have the math wrong so feel free to fix it.

% rpm drop between gears for a zf5
1-2 is 49%
2-3 is 41%
3-4 is 34%
4-5 is 23%

% rpm drop between gears for the zf6
1-2 is 42%
2-3 is 37%
3-4 is 38%
4-5 is 24%
5-6 is 28%

the red is the gears you are actually going to be using and the extra gear is going to allow you to keep the rpm closer to where you want it.

maybe look at it backwards? cruising on the highway in your top gear and come to a hill to climb. on the first downshift the zf5 has a 23% drop vs zf6 a 28% (zf5 is better), as the hill gets steeper and you need to drop another gear the second downshift the zf5 has a 35% drop to contend with vs zf6's 24% (zf6 is better), still climbing you have to drop another gear and the zf5 has a 41% drop vs zf6 38%

 

No reason to get snippy, I'm honestly wanting to hear reasons for or against.

The part I'm having a problem with your reasoning is the rpm gap between gears. I realize that the difference between gear ratios is the same or less with the zf5, however if you throw those figures in a final drive calculator it shows a different picture. I think it's because the ratios are higher numerically on the zf6, so the same drop numerically actually creates closer final drive???

For a rough example, Transmission A has a 1st gear ratio of 4.0:1 and second gear of 2.5:1

Transmission B has a 1st gear ratio of 5.5:1 and second gear 4.0:1

Both transmissions have the same 1.5:1 difference in ratio, but transmission B is going to have less rpm drop than A by far. This is a crazy comparison but I think it explains why looking at just the ratio differences between a zf5 and zf6 it looks like there is little to no difference when what we really need to look at is the difference in actual rpm difference between gears and not just the difference in ratio between gears.

I'm still on the fence, and I am learning a lot about final drive ratio. Every calculator I've tried shows the zf6 to have less rpm drop between gears over the 5. It makes sense to me now, does it you?

 

The reason your final drive I believe is trowing a loop is because of a 5 vs 6 speed.
The ZF 5 has an "average" difference between gears of 1.69
the ZF6 has an "average " difference between gears of 1.44

 

ZF5 S47

RPM MPH per gear
1 2 3 4 5

1250 5.5 10.7 18.2 27.8 36.1

1750 7.7 15.0 25.4 38.9 50.5

2250 9.8 19.2 32.7 50.0 64.9

2750 12.0 23.5 39.9 61.1 79.3


ZF6

RPM MPH per gear
1 2 3 4 5 6

1250 4.8 8.4 13.2 21.2 27.8 38.6

1750 6.7 11.7 18.5 29.7 38.9 54.0

2250 8.6 15.1 23.8 38.2 50.0 69.4

2750 10.6 18.5 29.1 46.6 61.1 84.9


For those interested in a cruising speed comparison, the S47 is 64.9 @ 2250 rpm, while the ZF6 is 64.8 @ 2100 rpm. The faster you go, the more the difference increases.

These figures are with 235/85/16's and 4.10 gears (what I run since I'm thinking of doing the swap) Draw your own conclusions from the numbers but it looks like a pretty worth wile swap for what I want (not need) out of my truck especially considering I have the S42 which would show an even greater difference vs the ZF6, but I don't feel like taking the time to graph that one out also.

No offense to anyone, not trying to step on anyone's toes, I just wanted to see some hard numbers that show the difference between transmissions verses opinions on the difference. To sum it up, I'm on the hunt for a zf6 to replace my S42.


On Edit; Darn it, my graphing skills lack, but you get the picture

 

Very nice write up...

When I did the ZF6 swap.. I went from 4.10's to 3.55's.. Now All I need to do is get it backon the rado so I can see if I like it or not...

 

ZF6 has a bigger input shaft and you can get a higher HP clutch for it.

 

That right there swayed my decision on the zf6 swap