Bad Trans? Engine?

[DrunkenPelican]

Hi Everyone!

Very new to the early bronco scene. I recently purchased a 66. Below is what was told to me by the old owner.

It has the original 6 cylinder engine. 3 speed manual transmission with new James Duff floor shifter and new clutch. Dana 20 gear drive transfer case. Dana 30 posi front end and a posi ford 9 inch rear end. Not sure the gear ratio. 4:11 or lower. Also has front and rear axle trusses. It has a 3 1/2 inch lift, new shocks and bushings.

My question is: When getting up to 55 mph is seems to be revving real high (Like it has reached it's max speed) and feel like I'm pushing her limits. Is this because of the trans or is this an engine issue? Can this be fixed? Any help would be great.

 

[DirtDonk]

Hey there, welcome to classicbroncos!

What you're describing is pretty normal, especially for newer owners not familiar with the way the old trucks sound (especially a little tiny six-banger!) at speed.
Even though the 33's should lower the rpm at 55 pretty noticeably, you could have the lower 4.56 gear ratios and that would raise the rpm back up.

So while you're probably not over-revving at that speed, it's still working pretty hard. The lower power of the six, even though it has decent torque for it's size, is making it work harder to not only roll the larger, heavier tires, but to push that "phone box on wheels" through the air at highway speeds.

Without a tachometer though, we really don't know what the engine is running at. You might be able to put a temporary tach in to see what it's doing so you can from there start to tell what it sounds like at different speeds.
You can also measure the tires exactly from the center of the hub to the ground with the weight on it (rolling radius), then we can use one of the tire size/gear ratio calculators to determine what your engine speed should be with either the 4.11 or 4.56 ratios.
That'll at least tell us if you're doing any harm to the engine or not. My guess is that it's not the revolutions per minute that are any issue, it's just that small engine trying to push the big heavy and lifted (aerodynamics coming into play) big tired truck down the road.

Good luck! And have fun with your new rig. Congrats on the purchase.
Oh, and if you have some pics, we'd love to see them. It's always fun checking out the new rides.
And if you find one of the threads where the '66 owners are seeing who's is the earliest and latest and what all was on the vehicle when bought originally, join in the conversation too.

Paul

 

[Broncobowsher]

On the left is a Bronco tach, in it there is a simple axle ratio checker. See if you have 4.11 or 4.56 gears. I'm betting 4.56.

They were not speed demons when new. They used a lot of gear to get a little engine to work. I have 4-cylinder engines that are larger then the I6 in your Bronco. You are probably just reaching the natural limitations of a small engine bronco.

 

[DirtDonk]

Forgot to mention, the way the forum is set up, you can't post images directly to the thread unless you become a contributor for the 13 buck fee per year. Since you're just getting here and likely want to check the place out a bit more before forking over hard earned cash, you can also post images to another online hosting site like SuperMotors or the like, then link them here so we can see the images.

Good luck

Paul

 

[TDubya]

I didn't see in his post where he gave tire size, am I missing that?

 

[DirtDonk]

You're right. Not sure where I got the 33 stuck in my mind from, but maybe from a previous discussion today.
So we're still up in the air. Maybe if he's got 31's or so, with 4.56's, then the engine would have an easier time pulling the load, but would definitely be spinning pretty fast.

Paul

 

[DrunkenPelican]

Wow! Thanks everyone for the quick replies. To answer the question on tires it has new 31 inch Chaparral tires on aluminum directional rims. Should I consider changing these?

Thanks!

 

[TDubya]

I have a 69 with the 170, 3 speed, 4.11s and 30" tires. I may change to 4.56s in the future to get it closer to stock gearing, but it is just a trail rig and does not see freeway speeds. It all depends on what you want to with yours.

 

[DaveLev]

Perhaps we're overlooking a few things:

Could it be the clutch is slipping due to weight/resistance?

Might speedo be telling him wrong data with his tires? Solution: Install Waze app on cell phone, and have it tell you your MPH.

RPMs may sound loud, but may be low. Unsure without a tach. $50 or less new at your local parts warehouse, or go with nice steering column mounted pod-style. Could not find any at WH or James Duff, but found some here:

http://www.summitracing.com/parts/atm-3708/overview/

I'm sure there are others.

If dana 30 up front, how likely is a posi on a 6 cyl vehicle?

Wonder if front and rear gears were both done, or prior owner did posi+gears up front and never did rear?

For free images, I recommend Imgur.com. Free, fast, drag and drop, BBcopy feature. Although for $13/year, why didn't I go the paid member route? Did not ever see that in FAQs (I did look).

 

[needabronco]

If you have limited slips front and rear from Ford I'd venture to guess you may very well have 4.56 gears assuming everything is factory? If that's the case 55 MPH is going to be max speed for your rig, and it likely is screaming. My 66 had 4.11's and 265/75/16's (32"s) and with the little 170 it would barely do 50 at full throttle, it too sounded like it was about to launch out of the hood.

This isn't an engine or a transmission issue, your just plain out of the limits the Bronco was designed to be operated in. Those flat tapped cam'd 170's are pretty loud engines anyway. Plus they aren't really designed for high RPM operation, they are more like tractor engines that will work OK for highway duty.

 

[DrunkenPelican]

Thanks Everyone!

I have a lot to learn about her and it is great to have a place to ask questions. I will post some pics and update my profile when I get some more time.

 

[DaveLev]

Looking forward to those pictures!