Dana 21

Crusher · Post by **Crusher** » Wed Sep 05, 2007 11:56 am

Hello folks. My name is Anthony Terry. I'm with Stone Crusher Steering. I've built quit a few Broncos from Full size to Early to Bronco II's and am in the process of building a Bronco II to hopefully compete in some rock crawling competitions. The drive train I'm going to be running is a 3.8 injected engine backed by a NP435/Dana 20. 44 in the front and 9" in the rear. 5:38 gears with lockers.

I have a question that I'm hoping one of you may be able to help me with. I came across an article( http://www.broncoii4x4.com/dana20-21/dana20-dana21.php ) and am wonder who this was done by? I have access to an NP435 with a Dana 21. I'm wondering if I can change the 21 out for a 20 and if the person that did this tech article could possibly give me some insights.

Anyway, just found the site and am looking forward to chatting with some of you.

Anthony

Post by **Nobody** » Wed Sep 05, 2007 12:56 pm

Welcome to the forum Anthony.

I took those pictures a long time ago when I did the V8 conversion on my Bronco II. I was looking into using the dana 21 adapter with a dana 20, but ultimately decided not to and I bought the AA adapter.

It can be done. There used to be a webpage where a guy did it. I saved the page but unfortunately didn't get the pics. I'll post the text below.

The main advantage of the aftermarket NP435/20 adapters is it keeps the driveshaft lengths the same on the Early Broncos. Since you don't care about that, I think there are some folks making spacer type adapters to mate the stock bronco 3 speed adapter to the NP435. Or you can cut and weld the 2wd NP435 tailshaft housing to the 3speed adapter.

If you do build a comp Bronco II, I'd love to see it. Keep us posted!

Here is the text from the Idaho Bronco webpage

NP-435 Install:
Updated 03-25-01
I used a tranny from a 75' F-100.
Below are some pics and notes of my conversion.
I just got finished with my NP-435 install. I used one from a 75' F-100 and used the factory adapter. It turned out to be by no means a direct bolt in. The F-100 appears to use the 2wd tranny, so the 28 spline output shaft worked great. The Dana 21 uses a 6 bolt pattern similar to the Dana 20, but it's about 1/4" narrower. The round locating boss from the adapter is the same size and worked on the Dana 20. The F-100 didn't have an intermediate bearing between the tranny and t-case, so I thought I'd try it without one also. I used the grinder on the t-case side of the adapter to open the bolt holes into slots, then welded some pieces of metal around the slots to make ears for the bolts to tighten on. The t-case lever mount is right next to where the shift Rods are, so I welded a piece of 3/4" pipe to the top for a place to mount the shifters. While I was at it, I converted to twin sticks. The stock tranny mount couldn't be persuaded to fit, so I fabbed a new one from 1 1/2" square tube. The stock skid plate went back on without to many problems. It was late so I only took it for a spin around the block, but it shifted fine and seemed to work great. The next day I went wheeling with a couple of Chevy guys to see how it would hold up under abuse. It worked great all day and hasn't given me any problems yet.

Total cost:
Tranny with adapter $225
1 1/2" square tube $5
Nuts and Bolts $3
Gear oil $12
Total $245.

This is the T-Case end of the stock EB 3 spd. tranny.
You will need to remove this gear. Then remove the bearing behind it, and finally the short shaft connecting the tranny and transfer case.
Back of F-100 Tranny.
Take the nut off of the shaft, and remove the gear.
The overall length of both tranny's with adapters is the same, so no driveline changes are needed.

This is the modified adapter.
The holes were cut into slots using a grinder. Then some steel ears were welded around the slots to provide a better place to bolt to.
The Dana 20 input gear is placed back onto the 3spd output shaft. I used the inner bearing race as a spacer to correctly position the input gear. Everything is held inplace with a snap ring.
Twin stick shifters.
The F-100 adapter doesn't have a good place to mount the t-case shifter, so I welded some 3/4" pipe on and converted to twin sticks.
Tranny/Transfer case combo.
This is the whole thing put together. I didn't use any gaskets between any of the pieces. Instead I used RTV to seal them together. This allowed the 3spd intermediate shaft to ride on the 4spd output shaft and not have any slop in the T-case. The F-100 didn't have an intermediate bearing, so I thought I might try it without one. The option to this would be to take the adapter to a machine shop and have one cut into it. The F-100 adapter has a round boss that mates perfectly with the Dana 20 to center it.
Tranny in action.
I love that low first gear.

Crusher · Post by **Crusher** » Wed Sep 05, 2007 1:26 pm

Thank you. Yeah I've put 20's behind 435's and T-18's that came from 2 wheel drive trucks. I used the 3 speed adaptor and re-machined the pilot for the transmission bearing. What I have is a 435 dana 21 from a 76 F100 that I'm wanting to use. What I'm trying to find out is if I can use a 20 adaptor and a 20 in place of the 21. I've talked to Advance Adaptors and they are doing some research also. If push comes to shove, I'll have to replace to out put shaft on the 435.

I'll be glad to keep you informed on the Bronco II build. I'm hoping to get it started this fall if time allows. I've just about got all my parts together. I'm pulling the C-4/20, 44 and 9" from my EB to put into the II. That's why I need the 4-speed to go back into the EB along with the HP 44 and 31 spline 9" that came from the F100. I'm going to stretch the II 7" to give me a 100" wheel base. I haven't completely decided on which tires to run but with the cost of them I'm leaning towards the Pit Bull Rockers.

Post by **Nobody** » Wed Sep 05, 2007 2:06 pm

You shouldn't have to swap out the output shaft on the NP435. It should already be a 28 spline.

Crusher · Post by **Crusher** » Wed Sep 05, 2007 5:01 pm

This is true, it is a 28 spline but most 4-wheel drive 435's output shaft is too long. That is why most people use a two wheel drive 435 when putting a 20 behind it. Like in the outline in your other post. He used a two wheel drive transmission from a F100. All you have to do on a two wheel drive is cut the threads off the end where the nut threads on to hold the yoke. The 4-wheel drive version does not have these threads and the splines are further down the shaft. I'm just not sure on this one considering it has the Dana 21. If I had it in my hands I could do some measuring but it's still in the truck some 100 miles away. Just trying to get my ducks in a row before I tow it home and start the tear down.

Post by **Nobody** » Wed Sep 05, 2007 6:28 pm

I'm pretty certain you can use it as is. The exception is the NP435's mated to the NP205's and 203's, and (208's if that was an option). Those have a 31 spline output shaft which would require swapping the output shafts.

On both my 2wd NP435's I didn't have to cut the threads off, but I have heard of that needing to be done. I think the difference may be with NP435's used in other makes, ie dodge. I know those have different gear ratios, and can different length input shafts too.

Crusher · Post by **Crusher** » Thu Sep 06, 2007 4:08 am

That's what I'm hoping for. That with 435 being mated to the 21 I can change it out without too many problems. I guess I'll have to wait until I actually have everything in my hands where I can see what fits and what doesn't. I do appreciate your help and willingness to discuss the possible problem areas. I also appreciate your quick response to my post about the pictures. If all works out, I’ll post a tech write up with pictures. There are quite a few of these 435/21 combos out there and if we can make a 20 or 205 work without too many problems….could make for some easy crawl ratios for our Broncos.

Bob Myers · Post by **Bob Myers** » Sun Sep 16, 2007 8:19 am

The 3,8 would be a novel idea. One question though, why waver from other tried and tested methods? I like to be different too but, a 4.0 can be mated to a 435 with an available kit, so why use a heavier-not more low end torque engine?
My c5 with double 1350/1354 case will sit and spin on the rocks at 1200rpms until you decide to stop, and the 4.0 is almost 100% plug and play.