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Broken t-case adapter

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mason72

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Any ideas on why this happened.
72 blazer
350 700r 205 1 tons 5.39's 40's
Cross member rubber mounts in good condition
Side brace to frame bushings not good condition
Engine mounts good condition

b93ec8ab-4efe-436c-9c2b-651e754d7935.jpg

86de67b7-aa20-44ff-abfb-7bec49f6d8bc.jpg
 
mason72 said:
Any ideas on why this happened.
72 blazer
350 700r 205 1 tons 5.39's 40's
Cross member rubber mounts in good condition
Side brace to frame bushings not good condition
Engine mounts good condition

View attachment 508293

View attachment 508294
Click to expand...
Wow, that’s impressive breakage !

I’m certain most will reply with the side torque mount as the sole culprit ( and it may have added to the issue in the overall picture ) but the victim is usually the aluminum trans case that gives from frame flex combined with the rigid ‘69~’75 side mount.
Was there any history of long term bad/worn mounts that may have caused stress cracks ( before the good mounts were in place ) ?

Can you give really good close up pics of the cracked portions of the mount - sometimes the damage can help tell the story by indicating an old age and worn portion of damage and fresh breakage that more recently gave up the ghost.

Also, can you give an example of how this rig is used - meaning hardcore off-road with lots of flex or just a driver ?
I’m assuming more on the hardcore side judging by the rest of the drivetrain described.

Get some good pics of each section posted and let’s see if they help paint a better picture of how this may have come about.
 
Floppy mounts and some history of abuse. It’s a fairly common failure actually

Source another one and plan on replacing engine and transmission mounts
 
Sloppy engine mounts. The t case frame as well there is reason GM abandoned it.

Is the engine/trans/ t case level, ei oem hight front and rear?
 
Frame twisting, weak engine mounts, get rid of the t/c side mount.
Engine mounts should minimize rotational movement.
Trans mount only needs to support the weight, not keep anything from rotational movement.
 
It is a bobbed and narrowed rock crawler that also gets used in the dunes.
Engine and trans mounts appear to be in perfect condition. Trans housing doesn't have any cracking.
The rollcage goes through the floor and welded to the frame. It is much stiffer not much frame flex.
I will ditch the frame mount even though I can't wrap my head around it being the problem.
Are the later adapters without the bearing interchangeable with the this one?
Thanks for the replies.image.jpg20250715_162112.jpg20250715_162131.jpgIMG_20201126_151247441_HDR.jpgimage.jpg
 
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Well it is living a rough life.
Something is bothering me here, it definitely started cracking a while ago and finally snapped but I see some marks like it was cut with a circular blade in one spot.
It could just be rub marks where the crack started until it broke which seems like more than just a day.
 
The ‘73 on up TH350/NP205 adapter with no bearing is a direct replacement - IIRC there is still a grove in those later ones for the snap ring that retains the bearing so you could use one if desired along with the older coupler.

Those early style motor mounts are known to have the rubber separate while still appearing in good condition from an outward position - an upgrade is highly recommended !

BTW, nice rig !
 
Are these cast steel? Any thoughts on welding it back together and adding some reinforcement to get by until a better solution arrives?
 
I have one of the newer bearing less style adapters but I got my son in Phoenix to pick me up the same type with a bearing. I would rather use the bearing type only because I've had a few trucks with 205's and the bearing less ones had more issues with the seals going bad and filling the t-case with trans fluid.

What motor mounts do you upgrade to?

It is cast. I weld but never had really good luck welding cast exhaust manifolds. My buddy has a fab shop and is going to weld and gusset it to keep for a back up
 
Roostius_Maximus said:
This stuff all exists in the stock car world, I believe Allstar Performance has them. I don’t have enough signal to load their page right now.
Click to expand...
DIY4X engine mounts are the BEEF! I’ve not seen others that compare.
I used the DIY4X mounts to replace brand new Summit Racing steel engine mounts, the DIY4X mounts are thicker steel in every way. Plus a poly bushing for that bit of give.
I’ve not looked at stock car stuff though. So, give em a try.
 
mason72 said:
Any ideas on why this happened.
72 blazer
350 700r 205 1 tons 5.39's 40's
Cross member rubber mounts in good condition
Side brace to frame bushings not good condition
Engine mounts good condition

View attachment 508293

View attachment 508294
Click to expand...
I’ve got the flanges all scanned etc and am about to pull the trigger on making these in steel,
Wes Harden said:
unfortunately the comp mount aren't available from ORD for a 1st gen.

https://www.summitracing.com/parts/ens-3-1156g/make/chevrolet/model/blazer/year/1970 probably these, you need to keep an eye on them they will fail eventually, just not as fast as stock replacement chinesium. Be sure to match mount material trans/t case-engine all Polly or all rubber.
Click to expand...

K, forget ORD on the engine mounts, there are similar mounts in the stock car and hotrod world. I’m not in the shop today or I’d dig up a couple of options.
And if I find that nobody makes what we’re looking for anymore then I’ll make them.

On the transfer case mount, I’m cutting it from steel, it’ll be a component style kit with th350/400 transmission flanges and the figure 8 205 style flange. I haven’t measured the other flange style or it could be cut also.
I’m making these mounting tube that spaces the flanges variable so some mix matching can be done with either stock couplers of for my own application of a 2wd 4l80 into a crew cab I can get that t-case further back yet and a longer - lower front driveshaft angle by also clocking the t-case down some too.
 
Well damn, didn’t realize that ya had full-on shop fabrication at hand - that’s great !

While your at it fab up a side T-case bar ( mounts to the holes where the torque mount previously was ) that goes to a bellhousing bolt location.
This is a great piece to have and is a major insurance policy for your trans case.
If ya need visual ides look for ‘78 on up squares ( some manuals didn’t get the until later ).

Best thing done for protection of the trans case especially on a capable rig that gets worked ( like it should ) regularly.


Please keep us updated with pics !
 
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