70 series axles on a 40 series

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Jun 30, 2004
Denver, CO
Has anyone else done a 70 series axle swap on a 40? I put the front axle in last night and was reminded very quickly about the tie rod end differences. I have the tie rod from the 70 that goes between the knuckles, but I don't have the end that connects to that and goes to the center arm. I can probably find a 60 series or 70 series rod and cut it down to fit the length, but I will once again have a difference in tie rod end size when I get to the center arm. I suppose I could have it reamed to fit the larger end.....or I could have the right side 70 series TRE welded and reamed to fit the 78's TRE. Whatever I do, I don't want to spend too much $$$ since this may be temporary. If the 13BT conversion won't clear the factory style steering box, I'll need to go to a 60 series steering box and won't have any TRE conversion issues.
You can check my link in the sig line if you want to see pics of this.

A 60 series relay rod would work, but it would need to be modified for the 78's TRE at the center arm or the center arm would need to be reamed larger. 60 series would still be larger than a 78's TRE's
tre 001.jpg
tre 002.jpg
You can see in that first pic just how much larger the 70 series tie rod is than the 40 series relay or drag link.....can't remember which it's called. I'm not positive that the center arm is enen large enough to accept the taper from a 70 series. It would probably wind up too thin.
When I had a double arm and 60 ps I had to shorten the relay rod to accept the 60 box to the 40 tre. I basically mated 2 rods. Took it off 6mos later when I bought hysteer. The 70 tres are for the most part the same as a 60 except for length. I'll have to see if I have that rod still kicking around you might be able to use it.
simple short term is use late fj40 arms and the standard set up.

I have a set of joint fuji aftermarket late arms if you need them-hit me pm.
Ahhh...I may be in luck. It appears that a mini truck LHT TRE will fit into the 70 series tie rod and thread into the stock 40 series relay rod. I'll check tomorrow on the fit, but that would be SWEET.
Hmmm...must be more to it than that. As I read around it looks like most people use a spacer bushing in the ream to fix this. As a temporary fix, I know this will work, but I'll still see if the threads on a mini TRE will thread into the stock rod.
Just an update....mini rod ends not only fit the 70 series knuckle arms, but they also thread right into the stock tie rods on the 40 series. The only catch is the length of the relay rod.....which must be shortened.

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