Shims and knuckle preload.

Joined
Aug 30, 2015
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203
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maine
using the sst tool I end up with a negative number for my bottom shim --

pulling 10 pounds of preload to adjust for what will be probably 33's
I get a total 2.20 mm of shim thickness for my total shim thickness, a difference of 2.20mm between my scribed lines (measurement D). My bottom shim (E) would then be 2.20mm (D) minus 3.0mm.
-.80mm?

do i simply NOT use a bottom shim in order to keep my center and preload?

thanks in advance
 
Joined
Dec 13, 2012
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985
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KY
I'm a little confused with changing the bearing pre-load based on tire size. I thought the idea was to set pre-load on the bearing period and tire size was not part of the equation. That means any value between 6.6 and 13.2.

Since you can't have a negative number shim I would say that you go without a shim in that position.
 
Joined
Aug 30, 2015
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203
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maine
Thank you gents. Ive read much on the topic. Even on this forum some say if you will be running oversize tires
the preload should be set higher. A larger heavier tire would move the knuckle much more easily than a stock tire
therefore a bit more resistance would be prudent so as to avoid wobbly steering at upper speeds.

I have a 79 "40". Im using a 1980 FSM. 4.0- 8.4 pounds of preload not 6.6- 13.2. But even when i do the numbers at
a lower preload eg. 7 pounds, well within the FSM range for preload, I still end up with a number that would indicate no lower shim or a
negative number. Is it possible that the new bearings are the issue ? (Marlin crawler seals and complete knuckle kit from marlin)

To what was in there before: 2.50mm worth of shims total, the orientation is now unknowable,
truck is a complete frame off due to its condition and I wouldn't trust the original configuration of the shims especially due to the fact that both knuckles were already leaking.

"BYRON" thanks for "no shim" vote. thats what im heading toward.
 
Last edited:

Pin_Head

 
 
 
Joined
Feb 6, 2002
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14,861
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OC, CA
I doubt that there were 25 mm of shims. This is about an inch.
Getting a negative number suggests that you may have made a mistake in measurement.
 
Joined
Aug 30, 2015
Messages
203
Location
maine
sorry .. meant 2.5 mm

The bottom shim is supposed to be the difference between the marks indicated on the rod between the housing and the knuckle. that number is 2.20 mm.
2.20mm - 3.0mm. Ive done the measurements at least 6 times.

I'll try again today and report back. not sure what I could be doing wrong. I've read everything and all the threads. I even measured the knuckle with and without the sst lever as this would effectively lenghthen/shorten the length of the measurement.

Thanks Pin-head
 
Joined
Aug 30, 2015
Messages
203
Location
maine
update: after countless hours and measurements i am at a loss
Preload 7 pounds
Measurement (A)= 167mm
Measurement (B)= 165mm
Total shim Measurement (C)= 167mm- 165mm= 2mm

This is where i am stumped. When I scribe my line using my sst at 7pounds
with the lever mounted for the spring scale (mounted between the the bolt head and the rod attachment)
I scribe my line. I then measure for (A). I disassemble.
Then i affix the spindle to the knuckle. Insert the rod and adapters without the lever for the spring scale.
I tighten just enough to be able to spin the rod. I do this with the knuckle in the proper position matching the
north south orientation that it was installed on the housing.

When I scribe this line it is exactly the same as my initially scribed line when installed on the housing.
This would mean my measurement would be -3mm?
If i keep the spring scale lever intact I get a measurement of 2.45mm after scribing a line.
The lever is 2.10 mm. meaning my measurement without the spring scale would be .35mm.
Measurement E would still be -2.65mm.

Additionally i measured the difference between the old knuckle bearing in its respective race and the new bearings and races
and this produced a total of about .10mm per set. or .20mm overall. This still would not make up for the gross negative
measurement.

Any ideas greatly appreciated. Im wondering if my 40 has a different knuckle and housing from a differnt year or model.
 
Joined
Aug 30, 2015
Messages
203
Location
maine
Ok ok.

See this thread... knuckle centering ?so everyone knows im not the only one.
always make sure the nut on the sst is at 12 oclock and not at 6 oclcock. The head of the
rod should be at the bottom shim position.
 
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