12 Bolt Pinion Yoke Strap Finish

[Edgemontvillage]

In the process of restoring my 1969 12 bolt diff I'm unclear if the finish on the yoke straps (that hold the U-joint) were originally natural steel, zinc plated or phosphated? The survivor / original straps I've seen are all dark due to age however not often rusty. They were exposed to road debris and road spray as well as to fluids so I'm looking for some input on what's original?

Pinion Yoke Strap (typical)


My 12 Bolt Pinion Yoke

[Edgemontvillage]

Anyone know this?

[Kelley W King]

I remember buying them over the counter at Cheverolet in the 70,s that were natural. But I guess that does not prove what the factory did. I also can,t remember cleaning any originals that showed signs of paint or plating. Hope this helps.

[Tinkerr]

There is a guy on Yenko.net that has what he says are NOS U-bolt straps for sale. They look zinc plated. I don't know how to add a link. I don't know if you can extrapolate from that the straps you have were zinc plate or not.

[Mike S]

One way to test if there are traces of zinc on a steel part is to place the part in a diluted mixture of Mauriac acid & water and if it fizzles, then is has zinc on it.

Mike

[Edgemontvillage]

Thanks for all the input. I did receive one answer by email from a well known expert who stated the straps should be "natural steel". I have often seen them restored using manganese phosphate and as the steel tends to darken over time its not obvious to me how they were finished originally. NOS examples are often a good proxy for the original however not always reliable. I also like the "acid test" - will have to try that.

[olddragracer]

Having seen many U joint to pinion yoke straps and U bolts for 60's and 70's GM cars and trucks. I do not recall seeing any that were not "raw' or "natural" steel.

[olddragracer]

   If you use diluted muriatic [hydrochloric] acid to test for zinc plating you should be aware that both zinc and iron oxide [rust] will produce foaming. There may be a difference in color of the foam.

[68camaroz28]

Agree Lloyd, natural steel.

[bcmiller]

I have been looking at this topic for a while. Straps in 69 were probably natural steel.

Yoke is a different story. I am not finished researching. 67 and 68 finish on the yoke and deflector ring may not be the same as 12 bolt yoke for 69.

[Edgemontvillage]

I have been looking at this topic for a while. Straps and bolts were probably natural steel.

Yoke is a different story. I am not finished researching. 67 and 68 finish on the yoke and deflector ring may not be the same as 12 bolt yoke for 69.

I assume you're referring to your 67/68 model research when you state the strap bolts are natural. For 69 I've  only ever seen the bolts manganese phosphated?

[bcmiller]

I was mixing topics. Not a good idea.

I went back and fixed what I said.

You are correct on the bolts.

It seems that 67 and 68 yokes for both the 10 bolt and 12 bolt - and the 69 10 bolt yokes - used u bolts. The 69 12 bolt yokes had threaded holes. They used manganese phosphated bolts and bare steel straps.

[Kelley W King]

Thanks for the input Bryon. I never really knew where the line on ubolts vs straps was but your post seems correct to me.

[Edgemontvillage]

I was mixing topics. Not a good idea.

I went back and fixed what I said.

You are correct on the bolts.

It seems that 67 and 68 yokes for both the 10 bolt and 12 bolt - and the 69 10 bolt yokes - used u bolts. The 69 12 bolt yokes had threaded holes. They used manganese phosphated bolts and bare steel straps.

Thanks for clarifying.

[bcmiller]

Thanks for the input Bryon. I never really knew where the line on ubolts vs straps was but your post seems correct to me.

Thanks.

I am looking for examples of low mile original unrestored cars 67 to 69 to verify the finish of the yokes and deflector rings.  67 and 68 may not be the same as 69. I may start a new thread.