Ring and pinion depth question?

[lagbolt]

How does this pattern look to you guys? It’s my first time doing a gear change. I have my back lash a 10 and my pinion inch pounds of resistances at 18.


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[Yeller]

I’d run it.

 

[.94 OR]

Are you running a spool?

 

[lagbolt]

Are you running a spool?

No sir. It’s a truetrac 5.13 gears.


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[bax]

front or rear? high or low pinion?

 

[lagbolt]

front or rear? high or low pinion?

9” small bearing.


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[okie4570]

Run it

 

[lagbolt]

Did just the back to test the ratio if I like it with my 4r70w and 35” tires. I read a bunch of different threads and 5.13 seemed to be what everyone said for my setup but man I drove it and it just seems like the rpm’s are too high now.

Maybe switch to 4.88s?


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[jamesroney]

Did just the back to test the ratio if I like it with my 4r70w and 35” tires. I read a bunch of different threads and 5.13 seemed to be what everyone said for my setup but man I drove it and it just seems like the rpm’s are too high now.

Maybe switch to 4.88s?


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35 inch tires? After 40 years, the ideal ratio has been identified. Unfortunately, the 6 speed Auto has broken the mold...and it will take another 10 years to come up with the right ratio for those.

For a Bronco, a 302 with an AOD and 35's, I would be very happy with 4.11's.
35's with ZF5 / NV4500 like 4.56.

Far too many people "engineer" the gear ratio for either crawl performance, or spirited driving, or highway economy. But the world is full of compromise.

With 5.13's and the "W" part of the AOD. (4R70W) you will be out of first gear way too soon, and when you are on the freeway at 75 MPH, you will think the engine is running too fast. Not "it's going to blow up" fast, but just "it's kinda high RPM...I wish it had another gear" fast.

How do you intend to use the Bronco, and what is your driving style? Anyone that tells you to go with 5.13's and a 4R70W is probably running a Dana 20, and wants to crawl. So they have compromised the wrong way for YOU.

My advice is to borrow a friends EB that has the "correct" ratio and see if you like it. That's a lot easier than swapping gears.

 

[DirtDonk]

With 35 inch tires and 513s it is definitely set up for crawling. Or for very quick acceleration. Assuming the tires have traction…
Don’t guess at your next gear ratio. Figure out the RPM you wanna run at and put the correct gears in for your tire size.

Questions you will have to ask yourself are:
1. will you be running 35 inch tires for the life of the vehicle? Or will you go larger eventually?
2. Do you want to run hard technical trails a lot? Or are you going to use it primarily on the street?
3. If on the street, is it just gonna be a casual weekend go to the ice cream store rig? Or are you going to get on the freeways for long trips Or both?
4. And whatever variation on all of those questions you think you might run into.

Have you figured out exactly what RPM your engine is running at? Get an exact tire size by measuring from the center of the hub to the ground. Then let’s use one of the calculators to figure out what you actually are running, rather than assuming what your next ratio needs to be.

Right now with those gears and a presumed 33.5 inch tire height, your engine speed at 65 miles an hour in overdrive is 2500 RPM or thereabouts.
I don’t remember exactly what the final ratio is of the 4R70W so I used .75 as a generic overdrive.

 

[Apogee]

Did just the back to test the ratio if I like it with my 4r70w and 35” tires. I read a bunch of different threads and 5.13 seemed to be what everyone said for my setup but man I drove it and it just seems like the rpm’s are too high now.

Maybe switch to 4.88s?


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Paul makes some good points, but what's your actual RPM at highway cruising speed now? Do you have a tach? Actually "being high" and "sounding high" can be two different things. I have a flex fan on my '77 F150, and the RPM's sound high, even when they aren't. That said, based on the Grimmjeeper gear ratio calculator, you should be at 2241 RPM at 65 MPH...2586 RPM at 75 MPH assuming full Ø35" diameter tires, neither of which I would classify as "high" for a 302/5.0 or 351W engine. I don't know how fast you drive, but I don't tend to push much past 70-75 MPH in mine on the freeway so that I can flow with traffic.

Given that you have Ø35" tires, I probably would have gone 4.88's with a 302/5.0 and maybe 4.56's with a 351W given the extra grunt provided by the torque converter, but given the relatively small difference between 4.88 and 5.13, roughly a 5%, I'd be looking at getting a tachometer first and swapping gears maybe not at all. A quieter exhaust, some door gaskets, clutched mechanical fan, etc can all go a long way towards reducing the perception of high-RPMs if/when the tach doesn't support it.

Tobin

 

[DirtDonk]

I found out that exhaust is definitely a huge change in engine RPM. Well, not actual RPM, but perceived RPM.
I went from dual glass packs to quiet turbo mufflers with an equalizer/crossover tube and thought I had changed gear ratios!

 

[okie4570]

Even if you don't have a tach, you can still find the rpm. https://purperformance.com/p-29669-rpm-calculator.html

Running 70mph and assuming that your 35" tires are actually 34", you should be at 2484rpm, at 65mph it would be 2306rpm, 55mph is 1951rpm

 

[lagbolt]

I have no tach at the moment and will have to measure exact tire height. It’s a explorer 302 with 4r70w all stock, All street as of now and nothing over 60( all back country roads ). The tires are brand new bf good wrench, I’ve been thinking about going to 37” tires is one of the reasons for 5.13s.

I wonder if I can hookup my OBD2 scanner and get rpm’s at 50 and 60 mph? I’ll go check it out and get back to everyone.



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[lagbolt]

Even if you don't have a tach, you can still find the rpm. https://purperformance.com/p-29669-rpm-calculator.html

Running 70mph and assuming that your 35" tires are actually 34", you should be at 2484rpm, at 65mph it would be 2306rpm, 55mph is 1951rpm

Thanks. I used this one from Yukon and seems to be a good rpm but I’m going to physically Check tomorrow.


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[DirtDonk]

That works. And with potential 37's in the future, thing long and hard about any gear changes before the fact.
The larger tires are not only larger, but heavier by quite a bit too, and so we often put lower gearing than would be called for just so the engine can keep some of it's pep.
Your engine setup is just like mine. Stock Explorer and I know that with my 31 BFG's (measure barely 30" more like 29.5) I could easily pull 3.50 gears and only suffer off-road. On the road it would be sweet I'm pretty sure, since the engine runs strong right out of the gate.
But with my current 4.56's it would be a beast off-road if as long as I have the ground clearance.
And with bigger tires in the future, my next experiment is 4.11 instead. Probably be the perfect sweet spot.

Paul

 

[bax]

On the gear set up, I think you are not deep enough into the ring gear. I would put my pinion a little deeper and the move my ring gear into it and see what you come up with. We need to see both sides of the set up , drive and coast. Also on a new gear I go a little smaller on my backlash. Its going to wear a little and the lash will get bigger. I shoot for seven on a new set up. Ten is great for used gears. But thats just me.

 

[spap]

I know I’ll get yelled at but just redid mine and I am 4.56 with 35s and a 4r70w. The 4R isn’t as deep as the AOD. But I really like the combo
I wanted gear to be able to drive on the freeway in ca.
remember bfg s are really a 34.5 Tall tire
i have plenty of grunt down low and cruises good at 70/75 At around 2300. I have a low pro 5.0 but it has decent torque low like 280 lbs at 2000/2200

 

[bax]

I run 4.56 with the 33'' BFG 3's. 4r70 W trans. Works great for me. I had 4.11 before I switched and I like the 4.56 better.

 

[lagbolt]

On the gear set up, I think you are not deep enough into the ring gear. I would put my pinion a little deeper and the move my ring gear into it and see what you come up with. We need to see both sides of the set up , drive and coast. Also on a new gear I go a little smaller on my backlash. Its going to wear a little and the lash will get bigger. I shoot for seven on a new set up. Ten is great for used gears. But thats just me.

That is the drive and the coast side in the pics.


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