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Old 02-18-2016, 02:22 PM   #1
ahirt
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Default How far to screw in end plug on tie rod ends

I have a question about how far to screw in the end plug on tie rod ends (and drag link). Les Andrew’s book says to screw in the end plug and after the end plug contacts the tie rod ball, screw it in an additional 1 to 1.5 turns. He follows with a note that the spring must be compressed 25%.

Both Bratton’s and Mike’s catalogs have a note that says to measure the spring and to tighten the plug one fourth the length of the spring after it contacts the ball. So I measured the spring and it was about 15/16 inches long. 25% of this is a tad shy of ¼ inch. In fact I calculated .234 inch. I asked myself how to know when I had tightened the plug this amount and it occurred to me that if I measured the threads on the end plug, I could calculate how many turns were required. It looks to me like the end plug is 20 TPI, so each full turn is 1/20 inch or .05 Thus to get .234 inch compression, I need to tighten the end plug about 4 .5 turns.

There is a huge difference between 1-1.5 turns and 4.5 turns. Both of these cannot be correct.

Les’ note says that the spring needs to be compressed 25% but he does not provide any additional detail, so I tried to research the definition of how coil spring compression is measured. What I know is this. A coil spring has an uncompressed height (free height) and a fixed height (the height when it is fully compressed and all the coils are sitting one on top of the other). The difference between these two numbers is the deflection height of the spring. Out of curiosity I measured the fixed height of the tie rod end spring by putting it in a vice and cranking it all the way down. The fixed height of the spring was 11/16 inch, so the deflection height for the spring is 4/16 or ¼ inch.

It occurs to me that if 25% compression means 25% of the deflection height then it is easy to see that 25% of ¼ inch is 1/16 inch or .0625 inch Tightening the end plug 1 to 1.5 turns would be putting it within a range of .050 to .075 inch - or exactly in the middle of a 25% compression of the deflection height. So Les’ instructions are accurate IF 25% compression means 25% of the “compressible” length.

On the other hand, compressing the spring almost 100% of its deflection height (I.E. .234 inch of a maximum of .250 inch) may be what was intended. I do not know enough about front end geometry and the force that Ford intended to be exerted on the tie rod ball. Suffice it to say, at almost full compression if you use 25% compression of the springs height as the correct figure, then the force on the tie rod balls is significant.

So what is the correct figure?? Help!!
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Old 02-18-2016, 02:38 PM   #2
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Default Re: How far to screw in end plug on tie rod ends

I don't no how right it is ,but I've always turned mine in a 1/4" after contact. To me that is 25% compression.
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Old 02-18-2016, 03:00 PM   #3
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Default Re: How far to screw in end plug on tie rod ends

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Originally Posted by ahirt View Post
It occurs to me that if 25% compression means 25% of the deflection height then it is easy to see that 25% of ¼ inch is 1/16 inch or .0625 inch Tightening the end plug 1 to 1.5 turns would be putting it within a range of .050 to .075 inch - or exactly in the middle of a 25% compression of the deflection height. So Les’ instructions are accurate IF 25% compression means 25% of the “compressible” length.

So what is the correct figure?? Help!!
I don't know the correct answer but I would go with your Option #1 (above). I don't believe that having the spring collapsed to within 1/16" of coil bind was what was originally intended. Not to mention it would be pretty tight.
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Old 02-18-2016, 05:42 PM   #4
Larry Jenkins
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Default Re: How far to screw in end plug on tie rod ends

Many years ago I read where the plug should be turned in just far enough to allow the cotter pin to be inserted. This supposedly positioned the plug in the right compression.

Kinda makes sense.

Many thanks to all for all the great comments and encouragement that prompted a decision to return. Let's just hope the Barn survives..

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Old 02-18-2016, 05:45 PM   #5
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Default Re: How far to screw in end plug on tie rod ends

With good balls I screw the plug in until the slot is even with the holes for the cotterpin.
The plug will be flush with the rod or a hair more
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Old 02-18-2016, 11:42 PM   #6
Chuck Sea/Tac
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Default Re: How far to screw in end plug on tie rod ends

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How ever far you screw it in, too far and it steers hard(er), too loose and you'll get shimmy!
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Old 02-19-2016, 01:55 AM   #7
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Default Re: How far to screw in end plug on tie rod ends

It seems obvious that you can't compress a spring down to "0.00" inches. The spring itself is metal and full compression may be 1/3 or 1/4 of it's original expanded length. I don't have a clue as to what the spring measures when fully compressed, but it's not "0.00" inches. So, 25% of it's compression may only be a turn or two, but NOT 4 or 4.5.
I suppose you would have to measure the fully compressed spring and subtract that from a fully extended spring. Then compress it 25% OF THAT FIGURE.
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Old 02-19-2016, 02:14 AM   #8
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Default Re: How far to screw in end plug on tie rod ends

Just did mine, made them flush.
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Old 02-19-2016, 06:34 AM   #9
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Default Re: How far to screw in end plug on tie rod ends

To tighten the plug flush or enough for the cotter pin to drop in is not consistent because springs, seats, plugs and bore depth can be dimensionally different. It's best to tighten plug till all free play is removed and then tighten an additional 1 to 1.5 turns. This compresses the spring about 25% of it's free travel and gives the rod end a nice feel. Tight but not too tight.
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Old 02-19-2016, 09:03 AM   #10
Kurt in NJ
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Default Re: How far to screw in end plug on tie rod ends

I have not found any documentation from Ford, but I have looked at other cars of the era that use similar systems, there were some variations, but tighten to coil bind and back off 1/4 to 3/4 turn, on big trucks it was coil bind and back off 3/4 to 1-1/2 turn----if there is any wear on the balls you make the adjustment with the wheels turned to the least worn area (all the way left---or right)

The shop manual for my 2cv Citroen which uses a smaller version with cups, spring and plug says to tighten cup plug till it bottoms, back off 1/6 turn

most every tie rod (even new cars today)end has a spring in it to take up wear, when they are first installed the spring is almost at coil bind----as it wears there is more play the spring takes up

if the spring that is used can't take being compressed to coil bind then it is a "GYP" part. when you hit a pothole or other impact that tries to turn the wheel the spring will be compressed----if too much movement is allowed the parts will beat themselves to death and the wheel alignment won't be kept where it is set

if the balls are worn and the adjustment is made too tight it will cause hard steering or even prevent the turning to full lock---I learned this on my car a long time ago, the first adjustment I made with the wheels straight, but found they got stiff when turned and wouldn't go to full lock , perhaps the non standard adjustment methods are ways to deal with worn and gyp parts, i have not seen any documentation in any factorygy shop manual for any car that says to compress the spring 25%---only to bottom it out , then back off a small amount
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Old 02-19-2016, 09:06 AM   #11
H. L. Chauvin
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Default Re: How far to screw in end plug on tie rod ends

Hi ahirt,

You are no doubt a Ford Barn Hero by adding your very detailed scientific findings followed by what keeps this Ford Barn alive ...... not just answers, but very interesting "questionable" questions.

Not like so many of us in the past, where we "still" test Model A HP increases for different HC heads by driving with a wet finger held out of the window to calculate the increase forces of the breeze, as opposed to using a dynamometer. LOL

FWIW: Years ago I read where Manufacturers' recommendations were specified in the 1934 Motors Handbook, for spring loaded tie rods; e.g., to check for excessive looseness.

And for spring loaded "drag link" adjustments:

----------------------------------------------------------------------------------
"For 1934 Buicks, Cadillacs, Chryslers, Dodges, LaSalles, and Plymouths, (similar to tightening spring loaded ends of tie rods), specific Manufacturers' tightening was recommended back then as follows:

Springs are provided on the ends of "drag links" to take up wear and absorb shock. When either end of the drag link is assembled to the ball joint, an adjustment of spring tension is necessary on both ends. To make an adjustment, tighten the plugs on the ends, (both plugs, on both ends), of the rod until "solid" ..... then back them off 1/4 to 1/2 turn on each end."

-------------------------------------------------------------------------------

If ends of drag links and ends of tie rods are similar to your findings for Model A Fords, i.e., 20 TPI, and also similar where a Model A spring is 15/16" uncompressed, and 11/16" fully compressed, it appears that the 1934 Motor's information is recommending:

A. Tightening the rod ends until the spring is fully compressed at 11/16" long.

B. Next, back off 1/4 to 1/2 turn, where:

(1) 1/4 turn / 20 = .0125" = about 1/8"; and,

(2) 1/2 turn /20 = .025 = about 5/16"; and,

(3) The average between the two, i.e., [1/8" + 5/16"] / 2 = about 1/4".

C. So, correct setting appears to be is slightly below 1/4" as determined by your findings. (Naturally, taking into consideration minor ball wear and slightly overstressed springs.)

Looks like your findings can make us put our wet finger back inside the car.

Last edited by H. L. Chauvin; 02-19-2016 at 09:18 AM. Reason: typo
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Old 02-19-2016, 01:43 PM   #12
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Default Re: How far to screw in end plug on tie rod ends

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Originally Posted by harleytoprock View Post
To tighten the plug flush or enough for the cotter pin to drop in is not consistent because springs, seats, plugs and bore depth can be dimensionally different. It's best to tighten plug till all free play is removed and then tighten an additional 1 to 1.5 turns. This compresses the spring about 25% of it's free travel and gives the rod end a nice feel. Tight but not too tight.
That's about where mine are flush, after I take her out for a test drive, if it feels to loose I can always crank it down to where she feels right.
That's the wonderful thing about Model A's, you always get to work on them.
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Old 02-19-2016, 02:00 PM   #13
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Default Re: How far to screw in end plug on tie rod ends

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That's about where mine are flush, after I take her out for a test drive, if it feels to loose I can always crank it down to where she feels right.
That's the wonderful thing about Model A's, you always get to work on them.


Yep, sounds about right to me. These can be forgiving creatures.
I replaced those springs on mine a decade or so ago [ originals were broken] and they were over an inch in length and set them at about 3/4".[ Seems that they were flush and just enough to fit the cotter]. Set toe and ran it for a few years. Decided to snug them up for the heck of it giving them a half turn I think. Rechecked the toe, and, went for a ride. Haven't worried about them since.
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Old 02-20-2016, 05:20 PM   #14
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Smile Re: How far to screw in end plug on tie rod ends

Thanks for all the responses. Clearly the Model A is a truly robust vehicle. No wonder there are so many of them still running!
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