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Tii Rear Trailing Arms Difference


justinevert

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I think that other than the "boxed in" design they are the same.  One of my '02 books mentioned that once the tii arms are rusted they may not be any stronger than a standard '02 arm.  Mine are pretty rusty and I don't think there is a way to see or correct rust on the inside.  Hopefully the tii experts can confirm or expand on this.

'71 MGB - sold   '74 2002 - sold

'89 XR4Ti - sold  '94 Miata R Package - sold

'73 tii - restoration project - sold

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I am in the process of rebuilding a rear sub-frame on the bench. It is the one I got from Roadhog, which came out of a '73 and will be put in my '76. I recently acquired a set of tii arms, but do not know what year they belonged to. I am putting all this out there in case the "tii experts" can shed some light on any subtle differences over the years. I recently inquired about boxing the arms I am installing and learned that this is overkill for anything but a racecar and there is a chance of distortion and the possibility of trapping dirt and water and encouraging rust . Now that I own a set of tii arms, the question of whether to use them comes up, but my answer is no. Another question I have is how to tell a factory set from a home-boxed set? I am pretty sure mine are originals, but still a little curious. Interesting to compare weld quality on the boxed portion to the rest of the sub-frame. The boxing welds are not quite as nice, so it got me wondering... the starting and stopping points are more apparent and a little lumpy, but they are outside corner welds. One upgrade I have been considering for trailing arms is to weld a portion of a 14mm socket to the inside of the arm where the flexible brake line goes through, because those connections are often referred to as a PITA to get at. On standard arms it seems like a flare nut wrench will just lay in there and the walls of the arm would keep it from spinning; but in the tii arms, you cannot get a wrench through that little hole. I am tempted to chop off a couple of 14mm deep sockets and weld them into those holes on the tii set for their future owner to enjoy, unless someone here tells me this is a stupid idea. 

 

Tom

     DISCLAIMER 

I now disagree with some of the timing advice I have given in the past.  I misinterpreted the distributor curves in the Blue Book. 

I've switched from using ported-vacuum to manifold, with better results. 

I apologize for spreading misinformation.  

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Well the tii and turbo came with boxed trailing arms so as far as the factory is concerned they are fine for road cars. I am not aware of any differences over the years, I do not believe parts numbers changed at all. It is true that an old set of tii arms can hide rust--more likely if the car was driven on salt-treated roads. If I had a factory new set the first thing I would do would be to tape up all the openings, pour in some POR-15 and slosh it around to coat the inside. If someone did a good job boxing some standard arms it would be hard to tell the difference from factory. I would look at how smooth the bend of the inner added plate is and look at the fit of that inner plate at the bushing bosses. If welds are really pretty would likely be non-factory! I made my own boxed arms recently and as others have said, one must be very careful they do not warp from welding--the ends tend to pull in toward each other from the heat and cooling. A good jig is required...and in my case a 20-ton bottle jack to correct minor fit problems.

 

Fred '69 & '74tii

Edited by FB73tii

--Fred

'74tii (Colorado) track car

'69ti (Black/Red/Yellow) rolling resto track car

'73tii (Fjord....RIP)

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One upgrade I have been considering for trailing arms is to weld a portion of a 14mm socket to the inside of the arm where the flexible brake line goes through, because those connections are often referred to as a PITA to get at. On standard arms it seems like a flare nut wrench will just lay in there and the walls of the arm would keep it from spinning; but in the tii arms, you cannot get a wrench through that little hole. I am tempted to chop off a couple of 14mm deep sockets and weld them into those holes on the tii set for their future owner to enjoy, unless someone here tells me this is a stupid idea. 

 

Tom

Welding a 14mm socket (nice idea, btw) or alternate is mandatory on self-made boxed trailing arms.  the factory welded up an appropriate 6-sided 14mm hex made of a stamped section of thick steel to keep the flex brake line from rotating during tightening and loosening.  IIRC, i bolted my trailing arms to a spare rear crossmember while i tacked the plate in place.  i did not have alignment issues on the finished part.  if you are lucky enough to have access to a nice stamping press you can have the brake line hole stamped out and it will look very much like a factory job.  and yes, the original factory welds were not pretty, so it's okay to not sweat over looks if you want to simulate original tii trailing arms.  Done with care, these are probably better than original if rust was/is a concern.

Former owner of 2570440 & 2760440
Current owner of 6 non-op 02's

& 1 special alfa

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as said, no need to weld something into a tii arm...the factory already did it.

 

but...an option i am considering for my rear suspension build this winter is to not run the brake line through the trailing arm at all.  may just run it through a U tab on top of the trailing arm so when i pull a trailing arm i do not have to open the brake system.

2xM3

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  • 2 years later...

You can weld and make them look like the tii ones very easily. .

A copy will always be  a copy (made in china reverse "engineering")

Another  important item on tii rear axles :the factory did have a different part # on the flanges (old days before the internyet),after sending bathes of hubs and axles for non destructive hardness testing (race car building days)   ,they did come back with a much higher Rockwell hardnes # ,the factory must have done there homework on the tii.

And if you look further down the monkey line, the "real turbo" even had a larger diameter stub axle.

Dah they felt the need to do it (more vroom vroom vroom=more boom)

No need to look further ,lots of rear axle/bearing/hub failures lately.

When rebuilding rear axles ,take a close look at the axle and the flange splines,before setting up correct bearing clearances.

Jack Fahuna

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