What is best to use the frame mount or torque rod that goes from the tcase to tranny and engine block?
CK5
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tcase torque rod or frame mount - what is stronger
- Thread starter wazzabie
- Start date
I'd say the frame brace is far stronger...whether that makes it "better" is debateable...GM decided the truss rod was good enough,so I guess it was adequate...perhaps they decided to go with the bar instead because during extreme off roading,the frame might twist enough to stress the transfer case and possibly crack the tail of the tranny?...
To me, those two pieces serve completely different purposes.
I am not a big fan of the frame mount piece, I believe it over-constrains the system and that's part of why it's common to see broken transmission housings and adapters. Basically, because the mount is so far off of the center of the drivetrain, it has lots of extra leverage and it makes the transfer case mount stiffer than the motor mounts. That's hard on the parts in between (i.e. trans case and adapter). I think there's a reason that GM got rid of them on the later trucks.
The strut rod is a great idea. They tie everything together a little which helps but I think their intent is to resist push from the front driveshaft. When the front is under power, the splines on the driveshaft don't want to slip as easily. So if you're hitting the gas and going over bumps, the driveshaft doesn't want to compress easily and pushes on the t-case. That has potential to break the aluminum t-cases and again, potential to break adapters/transmission cases. I think the strut rod really helps prevent that.
I am not a big fan of the frame mount piece, I believe it over-constrains the system and that's part of why it's common to see broken transmission housings and adapters. Basically, because the mount is so far off of the center of the drivetrain, it has lots of extra leverage and it makes the transfer case mount stiffer than the motor mounts. That's hard on the parts in between (i.e. trans case and adapter). I think there's a reason that GM got rid of them on the later trucks.
The strut rod is a great idea. They tie everything together a little which helps but I think their intent is to resist push from the front driveshaft. When the front is under power, the splines on the driveshaft don't want to slip as easily. So if you're hitting the gas and going over bumps, the driveshaft doesn't want to compress easily and pushes on the t-case. That has potential to break the aluminum t-cases and again, potential to break adapters/transmission cases. I think the strut rod really helps prevent that.
tommartin
Registered Member
My 79 has the rod, I heard gm removed them a little later because of it cracking the t-case... I still have mine and it seems to be fine... Just had the t-case out too to do the trans to adapter ring because of a bad leak. The t-case looked to be in good shape.
The bolt that holds the support rod to the tranny and engine block sheared off. I was able to remove the remains of the bolt from the engine block.
I believe there is a washer that also goes between the support rod and tranny as there is a small gap.
I believe there is a washer that also goes between the support rod and tranny as there is a small gap.
Iirc, it's a stud with a nut made on it so you can torque down and then there's another threaded section that sticks out for the support rod and another nut.
I guess GM tried a lot of different ideas and no one alone is ideal?..the truss rod idea helps prevent the tail end of an automatic from cracking when a heavy NP-205 or 203 is hanging off it,but one 3/8" stud was maybe not sufficient to handle the load by itself..the aluminum cases put less stress on it being lighter,so I can see it being better when used on a NP-208 or 241..
I can see the frame bracket being TOO rigid and causing troubles in certain situations..I never had any issues on street use with them though..
I recall seeing a few "rare" SM465/NP203 setups with NO brace or truss rod whatsoever--a friends dad bought a new '77 K5 with that drivetrain and the T-case didn't even have the 9/16" holes drilled or tapped in it,but the "pad" was casted into it!...I guess GM felt the SM465 wasn't at risk even with the ingot NP-203 hanging off it..
My 82 pickup has a TH400 someone swapped in it,by the looks of it it is a "car" or 2wd case--no cast aluminum flywheel cover ,it has a tin one,so no place to bolt the 2 small truss rods going from the motor mount brackets to the tranny dust cover...doesn't seem to be a "must" because I have worked the truck heavily plowing for over 10 years and nothing has cracked yet!..but it has a NP-208 so its not like a heavy NP-205 is hanging behind it either..it does have the long truss rod going to the bellhousing bolt though..
I can see the frame bracket being TOO rigid and causing troubles in certain situations..I never had any issues on street use with them though..
I recall seeing a few "rare" SM465/NP203 setups with NO brace or truss rod whatsoever--a friends dad bought a new '77 K5 with that drivetrain and the T-case didn't even have the 9/16" holes drilled or tapped in it,but the "pad" was casted into it!...I guess GM felt the SM465 wasn't at risk even with the ingot NP-203 hanging off it..
My 82 pickup has a TH400 someone swapped in it,by the looks of it it is a "car" or 2wd case--no cast aluminum flywheel cover ,it has a tin one,so no place to bolt the 2 small truss rods going from the motor mount brackets to the tranny dust cover...doesn't seem to be a "must" because I have worked the truck heavily plowing for over 10 years and nothing has cracked yet!..but it has a NP-208 so its not like a heavy NP-205 is hanging behind it either..it does have the long truss rod going to the bellhousing bolt though..
Thanks, good advice. I just placed a washer between the support strut and engine block and ran a bolt from the strut, washer and engine block. I can see what you suggest as being stronger.
Fred_M1010
1/2 ton status
This makes sense to me.
I worry all the time about breaking my tc (np208) with my front square driveshaft (they bind a lot...).
And as an old musclecar guy, I know of the golden rule, to never have a tighter tranny mount than motor mounts,
so the motor mounts takes up all the rotational force, to avoid cracked trannys.
But now as I'm planning to build a doubler setup, I've been looking into how people are mounting their doublers.
And I'm surprised to see that a lot of people are using really tight poly bushings, that are spread out pretty wide, giving it a very high rotational stiffness...
Are there other things that comes into play with a doubler, or how is that?
72blazerguy
3/4 ton status
I used the 203 mount, the doubler plate, and the 205 side frame mount (all with rubber bushings). A lot of people broke their doublers from not supporting the 205 properly. FWIW
