Manual transmissions first gear ratios

[TAC71]

What did you use for an adapter to the D20?

Trans has 28 spline output that matches the D20. I made the adapter to bolt them together.

 

[Broncobowsher]

Trans has 28 spline output that matches the D20. I made the adapter to bolt them together.

So super coupe trans, 4WD truck tail housing, your own custom adapter to the D20 with the super coupe output shaft passing through straight into the D20 with 28 spline matching.
Pretty slick!

 

[TAC71]

So super coupe trans, 4WD truck tail housing, your own custom adapter to the D20 with the super coupe output shaft passing through straight into the D20 with 28 spline matching.
Pretty slick!

That's correct

 

[ba123]

Do you know what differential gear ratio your friend is running? Tire size?
That might be why a high-three, or low-four first gear feels too low for his tastes.
Hah! I remember when that was not a thing. Not possible to have too low of a first gear!
Bring on the NP435s!

Paul

Just like Paul references here, there is SO much more to this equation than the transmission gear.

It has to be geared correctly AFTER you decide which transmission to use, not before. You pick the trans you want, the tire size, the xfer case if applicable and if changing, then the decision of which gears in your differentials that ACTUALLY make the real difference (imho).

 

[ntsqd]

I target the desired cruise RPM with the gearing of the chosen trans and size of tire at 60 & 70. In the Wagon that led me to the fairly uncommon 4.27 ratio. I ran the calc with 4.56's and I just didn't like how much the RPM rose with those gears, and 4.11's were way too tall. I had the LM7's donors specs so that I could work it backwards to get the ideal RPMs for those road speeds.

 

[ba123]

I like this calc:

Gear Ratio Calculator

I ended up with 5.13 but no way would that have worked with a 4:1 ratio 1st gear. I'd have to start in second! My first is only 2.84!

 

[ntsqd]

I just use an Excel spreadsheet. That way I can tweak the formula to get any one of the variables.

 

[jamesroney]

Young whippersnappers probably never heard the phrase "granny gear" or "compound low" or one or two others that I can't think of at the moment.
Just speaking a foreign language.

Paul

Hey Paul...what's the name of that low first gear they are putting in the 6G Bronco with the ZF manual? It had some funny sounding name.

Maybe "crawl" or something? I'd have to look at one...

 

[DirtDonk]

Something else in the "GOAT" category then? Mosey would probably be appropriate.
Haven't paid near as much attention to them as I probably should.

Paul

 

[Broncobowsher]

I'm surprised that no one has swapped in a 6G 7-speed manual. Sure it will need adapters. With as much other stuff that has been swapped, I wonder what is stopping people?

 

[ntsqd]

I'm going to guess awareness as I had no idea that even existed.

 

[DirtDonk]

Here too. Who makes it, what kind of adaptage will it take, and how many are in the junkyards?
How much they cost would certainly have the biggest effect on how quickly people start adapting.
Heck, we're still adapting old 4-speed and 5-speed transmissions!
But it sounds intriguing.

Paul

 

[Oldtimer]

Transmission Gear Ratios
The Ford Bronco's 7-speed Getrag MT88 manual transmission

• Crawler (C): 6.588:1​

• 1st Gear: 4.283:1​

• 2nd Gear: 2.365:1​

• 3rd Gear: 1.453:1​

• 4th Gear: 1.000:1​

• 5th Gear: 0.776:1 (Overdrive)​

• 6th Gear: 0.646:1 (Overdrive)​

• Reverse: -5.625:1​

 

[ntsqd]

Could run a pretty tall axle ratio with that and still have a decent crawl ratio. Were I to guess though, I think that 5th should be closer to 4th, and 6th not quite as tall. This is based on comments from guys driving the 6 speed autos in Tacos. They end up gearing their trucks down low enough so that their 6th is pretty close to the same overall ratio as my all stock 5 speed auto. And from driving an AOD with a 3.50 axle. And also from having a Gear Vendor's OD behind a 4 spd OD auto. Really tall OD's are not terribly useful.

Better yet make 6th 1:1, all of the others less than, and use an appropriate axle ratio. Somebody once claimed to see the logic in persisting with OD's and I fail to understand it. As I understand gear-train losses 1:1 has the least parasitic loss. An axle ratio that makes up the difference will also have lower parasitic losses. The guys designing these things aren't dummies, so there must be reasons to don't make sense to me to keep doing it this way.

 

[Broncobowsher]

The really tall 6th is probably paired with the direct inject engine that likes to be lugged down low to hit the CAFE numbers
The 1-5 are actually really close to my daily driver Xterra 6-speed. 4.3 first and .75 OD. But don't have the crawl, or the double overdrive. There are a few times I've reached for that 7th gear, so one more might be nice at times.

Have not checked if they are in production yet. I thought I heard they were working on an Atlas for the 6G? At which point all you would really need is an engine adaptor to whatever you want.

 

[ntsqd]

What engine does the 6G come behind? I'm assuming that "6G" is another term for the MT-88 that @Oldtimer posted about above? If not, what does the MT-88 come behind?

 

[toddz69]

What engine does the 6G come behind? I'm assuming that "6G" is another term for the MT-88 that @Oldtimer posted about above? If not, what does the MT-88 come behind?

6G refers to the 6th gen 2021+ Bronco. The MT-88 comes behind the 4 cylinder in the Broncos - 2.3L.

Todd Z.

 

[ntsqd]

Thanks! I wondered.