thegnu

55 roadmaster ,complex driveline modification questions

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I have this idea in my head that I can swap the rear end in my 55 to something more modern , an im not absolutely positive if it will work so this may be lengthy any input is very much appreciated. I will start at the beginning. I would love to retain the dynaflow transmission,{ I still have the oem nailhead an a conversion kit that will accept any gm transmission is fairly expensive} an this is where it gets complicated.
1. I understand there is first the torque ball an u joint to deal with an that I would need a slip shaft to account for the rears movement . the oem ujoint assembly is bolted to the output shaft(no slip there) . I assume that by removing the tourqe ball an installing a hybrid u joint assembly with a slip yoke on the driveshaft side I could effectively account for the movement of the rear axle as the shaft lengthens an shortens as it moves up an down with the rear axel. what possible issues could I have here an is the tourqe ball the transmissions "rear seal" essentialy?
2. drive shaft , would have to be custom made similar to one from a 4x4 with a slip yoke at the front an matching rear as the rear end of choice. here the queston is would vibration , fluid seals, bearings, or other modifications be a serious issue on the transmission?
3. rear axel an suspension, clearly a 4 link an panhard install makes the most sence with coilover shocks , or possibly retaining my coils an adding shocks. (a) whats a good gear ratio to look for in that rear axel ? an the dynaflow is a 2 speed. (b) rear axle width ? recommendations or best donor axels?
any out side input or issues I have overlooked is very much appreciated before I start spending cash on something that may not work .

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You could investigate Rolls-Royce SSI/SS2 and Bentley T-Type rear suspension. They use a torque arm arrangement that is flexibly mounted to a crossmember between the transmission and rear end. It should give the basic concept of how to fabricate what you want. The RR arms are pictured. Many are being parted out, but a lot have damage from tow hooks and rust.

 

I wouldn't do it myself, but I have put about 20,000 hobby miles on my Dynaflow over the past 15 years and see no reason to change it. In drive mine has infinite ratios. I have a 6 speed ZF electronic automatic, V12 BMW. The drive train feel is nearly identical on both cars.

 

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1 hour ago, 60FlatTop said:

You could investigate Rolls-Royce SSI/SS2 and Bentley T-Type rear suspension. They use a torque arm arrangement that is flexibly mounted to a crossmember between the transmission and rear end. It should give the basic concept of how to fabricate what you want. The RR arms are pictured. Many are being parted out, but a lot have damage from tow hooks and rust.

I saw a (small series) 56 Century with an adapted transmission and Jaguar xj6 rear suspension.  Might be able to adapt the torque tube since the differential like the RR and Bentley is fixed.  The Jag might be too narrow for the 55 Super.

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56 minutes ago, old-tank said:

I saw a (small series) 56 Century with an adapted transmission and Jaguar xj6 rear suspension.  Might be able to adapt the torque tube since the differential like the RR and Bentley is fixed.  The Jag might be too narrow for the 55 Super.

yes jag is way too narrow I have some experience with them .no access to rolls or bently rears in my area.  if I am understanding both of you the torque ball is the rear seal for the dyna flow?

I have an axle from a 70 chevy c10 ( have not measured it yet) . that torque ball is the key to this whole thing .

a torque arm like an iroc Camaro has would eliminate my need for upper parallel bars .

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Russ Martin at Centerville Automotive in Grass Valley, CA offers a torque tube elimination kit tha simplifies this conversion.  Google "Russ Martin nailhead" and look for it in his parts section.  Dynaflows after 1960 had an open driveline.

 

Or use the long trailing arms found on 60 - 72 era Chevy C-10 and GMC pickups and make this a fairly easy swap using your transmission of choice.  The bell housing size of the Dynaflow got smaller in '57.  If theres some interchange between years 56 and prior and 57 and later is a question for someone else. 

 

There's an article on the Jalopy Journal website titled "55 Buick truck arm suspension......"  Look at it and you'll get the scoop on how to set up a rear end under your car using the axle of your choice.  Find a 60 - 72 Chevy C-10 pickup and cannibalize the rear suspension - after you've read the article so you know everything to get.

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In the world of '67-'72 GM light truck rear suspensions,  The Chevy models used the rear coil sprig suspension metioned above.  The similar GMC used a rear leaf spring suspension and a a Dana-sourced rear axle.  It all went into the same place and were interchangeable as a complete unit.  BUT, the leaf springs were option on the Chevys and the coil springs were optional on the GMCs.  Just as the Chevys came with a steel bed load floor, the GMCs had a wood bed floor.  But the Chevys could be ordered with the wood and the GMCs could be ordered with the steel load floor.

 

Using rear leaf springs (as Olds did back then) could simplify things a big lot in your conversion.  Provided you can find the spring length can fit the rear of the frame's "kick-up".  It's my suspicion that the similar Olds rear suspension might be very close to working on a Buick, but haven't really researched it, given some of the unadmitted to commonalities of the higher GM carlines' frames.  To me, it would be nicer if another OEM set-up could be used, rather than something "aftermarket", for the current benefit and also that of possible future owners.  Just leave a list of what it all came from!

 

Just some thoughts,

NTX5467

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So, what is the issue with the current original set up?

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21 hours ago, old-tank said:

So, what is the issue with the current original set up?

I've got noises coming from it and a vibration right in the middle of the car that I cannot pin down, 34 years in the auto repair an painting industry an I have never had this problem , an the thought of having a more modern rear suspension is very appealing.

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8 hours ago, thegnu said:

the thought of having a more modern rear suspension is very appealing.

Nothing wrong with that.  I researched and even found some examples and other than the jag rear conversion, none were satisfactory.  On those the ride could be described as brutal:  unexpected bumps, jolts and kicks...more truck-like than sedan.  And those had noise and vibration problems too.  One owner was always grinning while driving and after he gave me a ride it was probably more of a grimace.  The jag conversion rode and handled well, but the experience was marred by the turbo 350 with a "shift kit".

There probably is no easy way to convert the dynaflow to open drive.  And even if you did the rear gears selected would work best at the original 3.4:1 ratio.  3.6, 3.9 would be more fun, but 3.2 would be a slug (like driving uphill).  The converter stall, tires, engine hp/torque have been matched pretty good at the factory.

Nobody can help with your noise and vibration without being there.  Even then some or a lot of 'disassembly required' would follow.

The original rear setup is different technology, but can be serviced and repaired.  New and used parts are available and guidance is right here.  If you decide to dive into the existing setup, post here or you can even PM to me for phone conversation.  But always start with a service manual.

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9 hours ago, thegnu said:

I've got noises coming from it and a vibration right in the middle of the car that I cannot pin down, 34 years in the auto repair an painting industry an I have never had this problem , an the thought of having a more modern rear suspension is very appealing.

Sounds like the joints inside the torque tube.  Slide the assembly out from the back of the dynaflow and replace the joints.

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There wasn't any u-joints in the driveshaft prior to 1957. Only one u-joint in the rear housing of the Dynaflow. 

I would suggest checking that the exhaust system is totally isolated from frame or body contact. Made a huge difference in my '56.

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You could potentially find an old "Hydramatic" Dynaflow and swap tailshafts.

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thanks all  , all avenues I have suspected an considered my service manual is helpful . more suspect is the single u joint or the bearings on either side of it  but being that its enclosed in the torque ball makes it a difficult diagnosis even harder still to describe here, but I will try maybe someone will be able to form some opinion based on this. it is definitely a rotating assembly it is a low note an mild vibration that increases with rpm when  driving barely audible at low speed an noticeable at 40mph an above. i've considered removing the rear diff cover to have a look but its definitely in the center of the car you can feel it in the toe boards an hear it same local . I have thought the torque tube may be transmitting this forward in the car but cant be sure.  i've ruled out front wheel bearings as they are correctly tightened an well lubed an do not feel " lumpy "or loose.  any thoughts?

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Just roll her out and have a look inside.

RR4.thumb.JPG.5c9ed2f02e565d81e8ecf94a3bf7cfac.JPG

 

It is not that big a job. I had a little squeak, squeak, squeak at slow speeds, only one way to figure it out. And I never would have found this looking and listening.

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That's my '60 with a different configuration but a worn out piece buried deep inside. It's a $15 part and a few hours of work. The dangerous part is getting carried away and doing a bunch of other stuff.

It doesn't have to go back in like this

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Edited by 60FlatTop (see edit history)
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On ‎10‎/‎23‎/‎2019 at 10:37 AM, 60FlatTop said:

Hahaha. yes sir that's me I could get in there an just fix everything.

I would love to just swap up to more a modern trans an rear but its not in the budget. the hot rodder in me says just do it, an the restorer says fix it the way gm intended it . its been a real reliable an fun car so far . an based on all the info I have gathered an all the input from everyone here I will be ordering the ujoint ahead of time an quite possibly the bearings  before an after it then just drop it out an physically see whats happening in there.

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