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Gear Ratio for ZF

littlejess

Jr. Member
Joined
Feb 4, 2011
Messages
80
Would appreciate :D some feedback on what the best ratio for my ZF conversion. 302 with headers, 4B and will be running 33's,60/40 street to trail. I have seen the charts, but would like to hear some actual road time stuff so I can take full advantage of the swap and the OD.
 

blubuckaroo

Grease Monkey
Joined
Jun 11, 2007
Messages
11,795
Loc.
Ridgefield WA
Your ZF has a close OD ratio to my NV3550. I have 32" tires and 4.11 gears an wouldn't change a thing. With your 33" tires and your teeny bit more OD, I'd go with 4.30 gears.
 

AZ69EB

Sr. Member
Joined
Jun 8, 2006
Messages
680
EFI 302, 2 into 1 exhaust with BC shorties, ZF, 4.88, and 33's

65 mph = 2700 RPM's in OD
75 mph = 3000 RPM's in OD

That's pulling a tent trailer full of gear last weekend.
:)
 

bigmuddy

Contributor
Bronco Guru
Joined
Dec 28, 2004
Messages
6,994
Loc.
Marthasville Missouri
I run 35's, (34 actual size) with 4.56 gears, EFI 5.0 with my ZF. Offroad, I don't need anymore, in the hills I need to shift down into 4th but otherwise it works great.
 
OP
OP
L

littlejess

Jr. Member
Joined
Feb 4, 2011
Messages
80
ZF gearing

Thanks for all the input, the rpm data is great how about some more?

BC
 

Ranchtruck

Sr. Member
Joined
Feb 7, 2008
Messages
766
4.10s for 35s, 3.55s for 31 or 33s.

You guys are overgearing these things for the highway.

You'd hardly get to use 5th gear on the highway with those gears.

The point of overdrive is being able to run a deeper axle gear without loosing fuel economy. The 0.76 overdrive ratio means a 4.10 is the equivalent of 3.12's. Good luck pushing 35" tires down the highway with that.

4.56's would be a good match for 33's and give you a little room to grow on the tires later.
 

Dave

Contributor
Bronco Guru
Joined
Aug 25, 2006
Messages
2,190
I ran one behind a peppy 5.0 HO with the factory 3.55 gears and 31" tires. It was a little low. I think 3.73 with 31" tires would have been perfect for highway driving. If you do the math, I believe that would be pretty close to 4.11 with 33" tires. If you go any higher 1st gear on the road will be useless and you will be starting in 2nd. Low range and 1st gear was plenty low for anything I did on the trails.
 

Ranchtruck

Sr. Member
Joined
Feb 7, 2008
Messages
766
If you go any higher 1st gear on the road will be useless and you will be starting in 2nd.

With the ZF and most other pickup transmissions with a granny first, starting in 2nd is normal. 2nd is also the same ratio as the stock 3spd's 1st gear. You want the axle ratio to be high enough to let you start easily in 2nd with the zf.
 

76Broncofromhell

Bronco Totalitarian
Joined
Jul 30, 2001
Messages
4,226
Loc.
Reno, NV
You'd hardly get to use 5th gear on the highway with those gears.

The point of overdrive is being able to run a deeper axle gear without loosing fuel economy. The 0.76 overdrive ratio means a 4.10 is the equivalent of 3.12's. Good luck pushing 35" tires down the highway with that.

4.56's would be a good match for 33's and give you a little room to grow on the tires later.


Maybe I missed the part where you had experience with this engine-gear combo .... or any other combination for that fact.


A 3.12 with 1:1 would be fine on 35s - just every other gear would suck. In fact I've run a truck on 37s with 3.08s. It went great on the highway but didn't do too well accelerating or rock crawling. I later re-geared it because it's a rock crawler and that was the plan all along, but I digress.

4.56s and 33s is way overgeared in my opinion. If you were running a 22R-E powered Toyota, I would agree with that, but not a V8 Bronco.
 

broncnaz

Bronco Guru
Joined
May 22, 2003
Messages
24,341
A lot of it is based upon how the engine is built and engine size. but still the stress on clutches no matter manual or auto is a big factor as well you need the lower gearing to keep the clutches happy. Small v8's still need to rev to stay in the power band. While I agree can run 33 in tires with 3.50 gears or 35 in tires with 4.11 gears and be fine but once you add a OD tranny into the mix your OD becomes kinda useless at speeds below 75mph and small hills.
You yourself even say the mismatched gearing you ran sucked in everything but 1-1 on the hiway so your comments dont really compute. Yes you can run mismatched ratios but you pay the price along the way. I highly doubt you have the market cornered on gearing knowledge. There are other people out here that have knowledge as well. While you may find your gearing mismatches acceptable others do not. Were all entitled to our opinions.
Just for info 33in tires with 4.56 geairing and a OD tranny would have about the same outcome as just running 3.50 gearing with 33in tires and no OD except that with the OD/gearing swap you gain better lowend gearing without having to over rev the engine on the hiway.

also not a bad idea to slightly over gear as the way mods go one day he may step up to 35in or larger tires.
 

Ranchtruck

Sr. Member
Joined
Feb 7, 2008
Messages
766
Maybe I missed the part where you had experience with this engine-gear combo .... or any other combination for that fact.

In fact I've run a truck on 37s with 3.08s. It went great on the highway but didn't do too well accelerating or rock crawling.

Our bronco has a 4b 306, 4.11's and 32" tires. With the stock 3spd, I have to be more abusive to the clutch than I would like to get it moving. It will also do 110mph in 3rd without much fuss, so it has plenty of gear range. 4.56's or 4.88's would make it much happier off the line (same situation with a zf starting in 2nd like it should) and the OD of 5th makes the 4.56/88 an acceptable highway cruiser gear. I've been doing a lot of looking into this because I have a zf sitting on the floor of the shop waiting to go in.

Thanks for calling me an ignorant douche by the way, it makes your opinion that much more valuable.
 

Dave

Contributor
Bronco Guru
Joined
Aug 25, 2006
Messages
2,190
With the ZF and most other pickup transmissions with a granny first, starting in 2nd is normal. 2nd is also the same ratio as the stock 3spd's 1st gear. You want the axle ratio to be high enough to let you start easily in 2nd with the zf.

And you have that option. Personally, I like being able to start out in first with today's gas prices. Less skinny pedal to get going. Especially if you have something on behind. I got great gas milage with my engine tranny combo. Too low or high on the gearing and you are not in that sweet spot on the power curve at your normal driving speed. There are a lot of factors involved and you definitly can not use the one size fits all phylosophy. Years of engineering lead Ford to use 3.73 gears behind a .76 OD with a 5.0L and 31 inch tires on vehicles that were intended to drive a bit faster than most like to zoom down the highway in an 40 year old Bronco. (And yes, I acknowledge that Ford also used other gear ratios for different applications)
 

AZ69EB

Sr. Member
Joined
Jun 8, 2006
Messages
680
Did I say 13.8 mpg while pulling a 2000 lb tent trailer loooooooaded with gear doing 65 + mph.

Steep hills with long up hill grades, not a problem. Just drop to 4th and just hit that skinny peddle. Nothing like hearing that little 5.0 EFI, start to sing up to 4.5 K RPM’s.;)
 

Matthutchinson2

New Member
Joined
Feb 10, 2013
Messages
1
Will be a daily highway driver, what would be the best gears to match with my zf transmission. Does anybody have any advice on the linkage to a j shifter transfer case while using adapter from bc bronco
 

Ranchtruck

Sr. Member
Joined
Feb 7, 2008
Messages
766
What size tires are you running? Do you have plans to go bigger down the line? What engine?

Ours with 32's, 4.11's and the ZF is the minimum I'd recommend. It's good for highway cruising but it could do with a lower axle gear for extra punch around town and lugging it down on the trails. The plan is to put in a 351w rather than regear.

I'm using the NP205 so I can't help you on the transfer case shifter question.
 
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