I have two Broncos - an '83 and an '86. This post pertains to combining the engine from one and the tranny from the other Bronco and is a continuation of the conversation had here: https://www.ford-trucks.com/forums/1...g-matchup.html

My '83 has a 4.9 engine with a 4-speed Tremec RTS OverDrive transmission and a mechanically actuated clutch. The truck runs amazingly with over 100k miles on it. But, sadly, I rolled it while on an off-road trail ride. The drive train is still sound though, proven by the fact that after returning the greasy side down it started right up and I drove it away.

My newly purchased '86 is destined to provide the replacement body and parts to make my '83 chassis whole again. The '86 has an EFI 302 with either a 4-speed Borg-Warner T-18 manual or a 4-speed New Process NP435 manual transmission and a hydraulically actuated clutch. The tranny has a granny first (non-synchronized). If it matters, I will know which transmission in a day or so when I get it on a lift to inspect. For expediency I will refer to this transmission as a "T18" unless proven otherwise.

I want to combine my 4.9 engine with the T18 tranny and the transfer case it is attached to on my '83 chassis (I have done a frame-off, powder coated restoration and a 4 inch suspension lift) and then cover it all with the (non-squished) '86 body.

My questions are as follows:

1) Which clutch would be better to keep (mechanical or hydraulic)? The '86 body has the hydraulic already in place, but I'm thinking the mechanical would be more reliable.

2) Can I use the flywheel from the 4.9 on the input shaft of the T18 with the existing hydraulic clutch that was previously mated to the 302 (basically bolting the 4.9 and T18 together with the 4.9 flywheel but no other major modifications)?

3) Alternately, could I utilize the entire bell housing and mechanical clutch from the 4.9, mating this bell housing from the Tremec RTS to the T18 tranny?

4) Would there be any additional parts required other than the ones I already have on one of the two trucks?

5) Would there be any issues with the starter on this new 4.9 / T18 setup?

6) What are the "gotcha" mistakes that I should be careful to avoid making?

7) Finally, I have 4.10 gears on the '83 with 33" tires. With this setup I didn't notice a major difference in RPM in any gear from when I had small wheels and stock gears (this was the intent when we calculated which gears to utilize). With this in mind, would you say that the 4.10 gears are a bad idea with the T18 tranny?

Wow, that's a lot! Thanks in advance for your consideration!

Zach

 

 

I don't have a whole lot of info on exact particulars, but I can give you my experience.

I have two Broncos that I drive all the time. One's for my wife, and one's for me. They both have 300s in them.

The '81 has the same Tremec O/D trans as your '83.
The '84 has the NP-435 granny trans. (BTW, you can identify it because, towards the rear of the vehicle, there's a big NP inside of a circle on the casing. It's right out in the open and easy to spot.)

Both clutches are very reliable, but I prefer the hydraulic. The mechanical needs adjusting about once a year or it'll start to catch. Plus, it takes a bit more leg strength to hold it down (not that I have a problem with that.) The hydraulic is just smooth and easy every time.

As for the gearing, it obviously depends on what you use it for, but I think you'll go crazy with the 4.10s and no overdrive with the T18/NP435.
With 33" tires, you'll be at 2500 RPMs @ 60mph where you'd normally be at 1780 with the overdrive.
65mph = 2700RPMs
75mph = 3150RPMs

Plus, with the insane granny gear that non-overdrive trans has (no matter which one it is), you'll never need those 4.10s unless you're doing something absolutely crazy.
In low range and granny, with my 3.55s and 31" tires (in the '84), I'm at around 4mph if I rev it up to 3000 RPMs. That's crawling...
Plus, I'm begging for an overdrive on the interstate. I can't imagine 4.10s.

 

That's good information. Thanks! By the way, how did you calculate the RPM's with a given gear / tire combo? Is there software that can do this? I could obviously do the math, but if there is an easier way, that would be cool.

Anyone know details about the flywheel?

 

There are some, but it's just simply:

Engine RPM = (Speed * Transmission Gear * Final Drive * 336) / Tire Diameter

 

Well, I am confident that it is in fact a T18 because it does not "have a big NP inside a circle on the casing" but does have "Boerg Warner" stamped on it

Has anyone had experience with taking this tranny off the 302 and mating it onto a 300?

 

Thanks to some info I recently got from some other members here the bellhousing bolt pattern should be the same between the 2 engines. Not sure about overall length but maybe you can used the driveshafts out of the same one as the trans is coming out of.

 

I'm certain you are right. Thanks for the info!

What I am really needing is confirmation that I can mate the 300 flywheel up to the 302 clutch plate in the bell housing from the 302 without any other modifications. I've never tried this type of swap before . . .