The Stovebolt Site Forums The Shop Area Engine Shop Is this a NV3500? mating to 250 inline help

Hey guys. I just got a hold of what I beleive is a nv3500 trans. I want to swap the sm420 trans out of my '49 Chevy pickup and I already have a '73 250 L6 motor installed. I was able to get the clutch, clutch disc, pressure plate and slave cyl with it. Not sure if I'll be able to use all those or not. I did buy new clutch and pressure plate when I swapped the motor so hoping I can reuse those.

I need help from someone who has done a similar swap. I'm not very familiar with making a hydraulic clutch work in an older truck. I know I need the master cylinder, maybe different clutch pedal etc but what else? What exact clutch package did you use that worked best?

I would really like to use this trans since I have it, but would I be way better off getting a T5 or nv4500 instead? I know the 4500 are much stronger but also much more expensive. And the t5 is kinda weak. I DO NOT have the $$ to go out and buy the perfect trans. I was lucky enough to get this one. This trans is electronic so I won't have speedo I guess- don't have one now so I'm used to it. Didn't see a tag on it, just the numbers cast in the side. I already swapped the rearend (already had half open/ closed driveshaft- something the previous owner cooked up) but I'll have to get a different driveshaft anyway. I hope you guys can help me out so this swap won't be a major pain. Hoping to maybe get it done in time for the Lone Star Roundup in Austin! Thanks,
Jeremy

http://s245.photobucket.com/albums/...20Chevy/?action=view&current=025.jpg

http://s245.photobucket.com/albums/...20Chevy/?action=view&current=026.jpg

http://s245.photobucket.com/albums/...20Chevy/?action=view&current=022.jpg

http://s245.photobucket.com/albums/...20Chevy/?action=view&current=028.jpg

A t5 would likely be an easier swap, as would the nv4500. The t5 should be plenty strong to go behind a 250. The nv3500 has that integral bellhousing to complicate things. In my opinion it would be easier to get a 54-55 first series bellhousing crossmember, 55-67 v8 truck bellhousing and mechanical clutch linkage, and a T5 to go behind it. You would likely need a new clutch disc to match the T5.

With the transmission you have, you would have to remove the bellhousing crossmember, fabricate a new transmission support, figure out how to run the hydrallic clutch, and eventually convert the electronic speedo signal to work with the mechanical speedo. Not all that much work or figuring, but more work and figuring than I would like to do.

I believe the NV4500 is probably too much transmission for you, but it is interesting to note the 1994-1997 Dodge 2WD version can be made to work with the mechanical speedo very easily. I have the NV4500 in my 1959 GMC 1/2 ton and love it.

I think the biggest thing I'm worried about is making the hydraulic clutch work. I've already got the slave so I just need to get a clutch master cylinder and either make it work with the stock pedal or get a new clutch pedal to work with it. I've been looking at the Wilwood pedals and master cylinders but I didn't know how those pedals would work with the angled floor. Any ideas? I've gotta fab up a trans mount anyway- that's not a big deal. I'm open to suggestions, I just really want to try and make this trans work since it's a good one and I already have it.

What year and model is your truck? Knowing that could make a difference.

I'm going to disagree with the approach SwingDaddy suggested. While the '54/'55 1st cross member with a later bell housing is a good approach when using the original motor I think in a case like yours there is a better way.

The 250 does not front mount, it needs to be side mounted. If you go with a V-8 type side mount cross member in the front and a similar transmission mount at the rear, you're good to go with that integral bell housing and its hydraulic clutch support.

I've not done it, but that's the way I'd approach it if I were doing this.

From there the question becomes pedal and cylinders as you suggest.

Are you planning to run power brakes? Dual master cylinder for the brakes?

The usual approaches to floor mounted pedals with dual master and a power brake cylinder make the area under the floor somewhat crowded. But you could still mount a clutch master on the frame ahead of the pedal pivot. You'd need to stay away from the exhaust but otherwise it should be a straight forward project.

I didn't say it couldn't or shouldn't be done. I have very little experience setting up hydraulic clutches, so I said I wouldn't go this route, and when I said I, I actually meant me personally. It actually seems like a pretty straight forward swap, as the 250 should bolt right up to that transmission. Again this is not my area of expertise, and I haven't done this swap, but I would assume the bellhousing crossmember will need to be removed, and another crossmember fabricated, as well as sidemounts for the engine. I realize this is done everyday when swapping a v8 with an automatic transmission. The frame may require extra strengthening to cope with the loss of that crossmember.

The route I mentioned only has the advantage of keeping a crossmember in the original location, and possibly using the stock clutch linkages. The v8 bellhousing would bolt right up to that crossmember. Again... I haven't done that swap either, so it is still not my area of expertise.

You have the transmission I say go for it!

I think the half-closed and half-open drive shaft you mentioned and have pictures of is the front torque-tube half of a 3/4-ton drive shaft as used 48-53. Of course you won't reuse that if you make that NV3500 or another trans work. Good luck!
(Edit) I should have looked at the pics of your truck first - it is a 3/4-ton! How did you get the 6-lug hubs/wheels on the front? (edit, again) I should have read the captions too - it has a 1/2-ton front axle, duh. And after you get that red rear end under it you'll have a longbed heavy-duty half ton. Cool.

OK - I have been studying your pictures. Great looking 49 3600 by the way. It looks so solid with very little rust. The cab floors, inner cowls, cab corners and everything you can see looks solid. I'm jealous! Congrats on a good find.
I also gather that the blue 250 and SM-420 were already in it?? And you swapped in a good 72 (red) 250. I know that this swap has been done in a lot of trucks over the past 40 years or so. In this picture you can see a bent piece of steel bar supporting the bellhousing up from the X-member. It also shows a heavy steel X-member under the tail of the trans. Looks like its been that way a long time. Apparently the person who did the original transplant did not use a 63-72 truck bellhousing that has the ears to mount to the X-member.
I have seen that in other pictures. Is this common? Anybody seen this before? Also the SM-420 normally does not have a tail mount. The reason I noticed it is that I am still thinking about a 292 swap in my 50 3600.
Thanks!

Yeah SwingDaddy I could have said that better... Basically if it were me I'd take an alternate approach than yours. No offense intended and certainly none taken here.

I looked a little more at the pictures and realized it already has a 250 in it. Step one is figuring out just what was changed or possibly hacked to make that swap work. It may limit what you can do next.

I need to update the pics actually. It now has a 3" drop front axle (that I dropped myself with a jig I built), the red '58 rearend is now under the truck. The truck had a 230 motor with the sm420 trans already when I got it. The motor was locked up from sitting for 15 years. The driveshaft was already "custom" as well. It almost looks like a cut up Model A axle that was used for the rear trans mount. I plan to leave the original drum brakes, so I would just upgrade the clutch pedal if necessary, but didn't know how that would work since the floor board is angled. So I may have to fab up a new bellhousing cross member then? Thanks for the help guys!

"So I may have to fab up a new bellhousing cross member then?" I believe this crossmember is eliminated, and a new transmission tail support crossmember is added. This gives you a triangular motor mount setup. 2 mounts up front on the sides, and one mount on the rear at the tail of the transmission.

I didn't know if the truck still needs some sort of crossmember there for strength/frame rigidity? And I guess that is for sure a nv3500? Just hoping it wasnt the nv1500 model....

That heavy factory crossmember that goes under the bellhousing IS a structural member and should not be eliminated, without something to take its place. Look at the frame; its a ladder with only 4 or 5 rungs.

That is why I originaly reccomended the other crossmember, bellhousing, and transmission. The swap with the integral bellhousing transmission is similar to a v8/automatic swap. I believe that crossmember is removed for the v8/automatic swap. I don't know how that problem is solved for that swap, but I assume it will be the same solution for the swap here. Maybe someone who has done the v8/automatic swap can chime in here.

If nothing is added as support the cab may sag because the mounts move without the cross member. Also that cross member adds stiffness where the front springs mount.

But if you add both an engine cross member and a transmission cross member you are replacing some of that strength.

So does that solve the problem? I've not crawled under enough modified trucks to know for sure.

So I'm fixing to install the nv3500 trans but I'm having trouble figuring out which throwout bearing I should use. When I installed the motor a few years ago I had put in a new pressure plate, clutch disc and throwout bearing. I got the flywheel, pressure plate, clutch disc and bearing with the nv trans when I got it. The bearing I had in the truck is about and inch longer than the one I got with the new trans. The flywheel I got with the trans was new and barely cleared the bellhousing but did fit, but I'd have to buy a new starter. I opted to use the new clutch package I had bought not long ago since it was in almost new shape but is smaller.
I bolted both clutch packages to each of their flywheels to compare installed heights and set them next to each other on the table. The package I had pulled out of the truck is about 1/2" longer than the package I got with the trans. I don't know which bearing would be best to use?
The input shafts on the NV trans and my old sm420 trans are the exact same length and size. Any help you guys can give me is greatly appreciated!
Jeremy

There is a short bearing, and there is a long bearing. If you are 1/2 inch taller, maybe use the short one. Usually the bearing is dictated by the style of pressure plate you use. I think the borg and beck get the short bearing, and the diaphram clutch gets the long bearing, but there are exceptions to these rules.

Doesn't a borg and beck style have only 3 fingers? Both pressure plates have normal amount of fingers- 12 or so. I'm just confused because the clutch package I got supposedly was used with a 350 motor and should be the same as my 250 and the NV trans has the same measurments as my old sm420. If that's the case why aren't both bearings the same?