47-55.1 Asking for a friend :)

[simicrintz]

I am over on another portion of this page (have a '71 K5 Blazer) but have a question for you fellers over here: My Father-In-Law has a '51 Chevy 1/2 ton truck with a 4 speed trans. Sounds like the trans to the rearend is shot and he has a 4 speed from a '57 along with the gears and housing. He would like to remove the torque tube in between the trans and diff and just put the gears in the existing housing. He knows that it will require an open driveshaft and he is okay with that. He feels that he would have to mess with springs if he replaced the rear diff if he has to replace the housing. His best case scenario would be to unbolt the torque tube and just replace the gears and keep the existing housing.

A. Does this make sense, and B. is he heading down the right path? He is in Montana and I am in San Diego so I cannot see it and he is not online. Please let me know what you know or what info I can get to make any of this clearer.

Thank you!!!

[mr48chev]

I have heard of people doing that but never personally have seen it done. I have helped a few guys put the 55/59 open drive rear axle under 48/54 trucks though and outside of welding on a pair of new spring pads and finding U bolts it is a pretty well straight on deal.

When you take the torque tube out you have to figure out how to mount the rear axle housing solid as it pivots on the pad that bolts to the springs in it's normal setup using the torque tube to keep it lined up Past experience that wasn't good says that welding up the old setup to have it stay in place doesn't work and you have to come up with some way to hold the housing in place.

Classic parts and a couple of others sell the mount to use the later axle and locate it properly https://www.classicparts.com/1947-54...ctinfo/93-317/ They also sell the complete kit with U bolts and brackets but there is about a 3 week wait on it to be shipped from their supplier.

[dsraven]

I am thinking the same as mr48, gonna be a problem waiting to happen if you just change the gears. like he says, the original axle is on a bracket that allows the axle to torque up but the tube to the trans keeps it from flopping around. there are easy ways to get it done though. you need a new spring pad that is probably offset from the spring center. if you check your old one you will likely see the axle tube is not centered over the spring center bolt.

-try to get a diff the same width from flange to flange, that is gonna have the gears you want. a 6 bolt pattern would be nice to keep all the wheels the same but the old trucks had pretty low gears. thats up to you though
-grind off any spring pads that are there on the new housing,if they are in the wrong place
-set it in place so the wheel base is the same, grab some new spring pads and slip them between the housing and the springs
-install some u bolts and snug things up
-double check your wheel base measurements and ensure the new housing is square in the frame and also centered
-tack the new spring pads on the housing
-recheck if everything is good
-weld the spring pads onto the housing. do this a bit at a time so you don't warp the axle tubes
-connect the brakes etc
-connect the driveshaft etc, prolly need to have one built for you. make sure to check with the driveshaft guy or simply drop it off at the shop so they can make a new shaft for you. ensure the truck is complete so it sits at ride height

[simicrintz]

You guys are the best; thank you! I have to leave (road trip!!) to Montana on Friday and will see my F-I-L by Saturday night if all goes well. I will most likely try to print all this and have it ready to take with me so that he and I can talk about it and he can formulate his plan.

Thank you both again for the input; and if there are any more concerns or roadblocks to avoid to make this go as smoothly as possible that is also much appreciated!!

[1project2many]

Is this truck a fairly new purchase or has he had it for a while? The straight cut gears in these old rigs make them scream in any gear but 4th.

[simicrintz]

Originally Posted by 1project2many

Is this truck a fairly new purchase or has he had it for a while? The straight cut gears in these old rigs make them scream in any gear but 4th.

I have known him for 15 years now and he has owned it for at least that long. I do know that he put it together many years ago (if I remember the story correctly it was for his F-I-L) and then got it back sometime after that. If I were to guess I would say he has probably owned this truck for 30 years or more if you count the time he had given it away.

He is very mechanical and enjoys doing this kind of stuff. He is excellent at researching stuff but does not use the web; he is better at getting the info firsthand, but has come to a bit of a road block in this case.

Are the '57 gears straight cut as well? He is not trying to hotrod the truck but I do believe he is looking to address what is bad currently and make it more enjoyable to drive as well.

[mick53]

I have a 53 1/2 ton that I bought in 1980 when I got out of the Navy. I was 23 broke and renting an apartment. No internet. It was my construction work truck. I changed the drive line to open. I went to the junkyard and with a tape measure picked out one with 6 lugs out of a huge pile of rear ends for $50. They cut off another set of perches for me for free. Picked up a longer than I needed drive shaft for $10. I had a friends dad weld them on where I wanted them. Had the drive shaft shortened and balanced for another $20 by a small shop. Since then I have put well over 100k miles on it. I did this in my parking lot a 23 years old and broke. Point being it's not that hard. Measure well, do your homework and be safe. Good luck. BTW it turned out to be a 12 bolt with 373's

[simicrintz]

I love those kinds of stories, Mick! Years ago I would put SBC engines in my Datsun trucks, never really knowing that they would tear up front and rear ends; I just wanted a 350 SBC in a Datsun truck! Sometimes being "too dumb" to know better makes stuff happen; good for you for doing this in the parking lot!!!

[dsraven]

the kit from the link above includes the u bolts, the u bolt plates with shock mounts and some frame shock mount brackets. you could probably fab up all the stuff from a set of trailer axle spring mounts by drilling another set of holes to center the diff in the same position as stock, buying new u bolts, fabbing up some u bolt plates and some frame mounts for the shocks, but really, for the price of the kit, it is probably not worth it by the time you drive all over to pick up the stuff, then spend time and supplies fabbing it all up. your time would be better spent finding the right rear axle with the gears you want. while you're at it maybe think about upgrading the brake master cylinder to a dual system. also, try to get a diff with something close to the same size brakes on it so you keep the bias the same

[mr48chev]

If he is worried about having to spend money twice on rear brakes I am pretty sure that most of the rear brake pieces will swap over from the 51 axle to the later axle. If he has a good axle housing and axle shafts that is. There may be more than one reason he wants to use the original housing. If he were so inclined he could fab up a track bar that ran from the rear axle housing up to the crossmember much like some of the 4th? gen Camaros use. To take place of he torque tube. That's a lot more work and expense than putting a pair of spring pads on though.

[simicrintz]

More awesome info; thank you!! I am going to try and touch base with my F-I-L sometime today and share this. He is loading the truck onto a trailer and will be taking it to Arizona for the winter where he will be working on it and he is wondering how much other stuff (trans, diff, etc.) he should also load. I am positive this info is going to help him make that decision!

Now I have to find a way to get this all to him! He would like to be loaded this week and I won't see him until Saturday. He does not get email and does not have a fax and mail would be too slow if I print and send! I'll try to read all the info and maybe then print this out and take with me as well. Great info!!

[simicrintz]

Just wanted to thank you guys again for all of the help. My F-I-L has decided that he will take the truck to Arizona but will save this portion of the project until he gets back to Montana in the Spring. The decision was made with the input from you all, and he asked me to send his thanks!

[simicrintz]

Hello again! The torque tube conversion has been completed to open drive shaft and all '57 components (trans, drive shaft) and is performing well. My question is: there is now no support for the trans with this setup; what have you guys done in this case?

Much appreciated; thank you!!

[1project2many]

there is now no support for the trans with this setup;

The early trucks and cars supported the engine at the front and at the bellhousing. The transmission hangs off the bellhousing and there is no support at the back of the trans. This method of mounting engine and trans actually continued in medium duty trucks until well into the '80s.

If you look at this line drawing you will see the back of the transmission of the 55-59 truck is not supported.
http://chevy.oldcarmanualproject.com...55ctsm0010.htm

[simicrintz]

Interesting, 1p2m. So do I follow that it is then okay and we are concerned for no reason? This truck is in AZ currently (and I am in San Diego) so I can't see it; just going on what my FIL tells me. He thinks things through really well and I know this has him concerned.

I will pass this on; thank you! I know he wants to do this right so all help and info is appreciated!

[1project2many]

I would say you are worrying about a non-issue. If you can get pictures from your FIL the folks here can review them to see if we note any potential issues.

[simicrintz]

Again, appreciated 1p2m! Let me see if I can make that happen (FIL is still on a flip phone and does not do the internet!). I'll see if he can find a way to get that to me.

A million thanks again!!