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GMT-400 to GMT-800 brake conversion tie rod discussion

SmithvilleD

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St Joseph, MO
#22
The 706 was a gasser & bought new the year I was born. Was both main tillage tractor & chore tractor when newer. Good, very handy size, tractor - but that gas engine needed & got rebuilt more times than I can count.

Diesels are definitely better for longevity.
 

schiker

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#23
Just fyi I don't know about these automotive tapers but a degree is a pretty course measure of locking tapers. Probably the nominal taper might be expressed as an angle. When tapers get precise from what I have seen they are expressed in inches of taper per foot. Included or per side. Usually measured on a sine plate with jo blocks.
 

Big T

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Thread starter #24
I think I've got a solution - still needs to be bolted on the truck & aligned to confirm. Tie rod combination measures right.

So got the O'Reilly store brand ES409R to mock up & see if it could work. The taper didn't fit the GMT800 knuckle as is. I had an Allstar Performance 9.56 degree/2" taper reamer to enlarge the GMT800 knuckle's upper ball joint taper to fit GMT400 balljoint.

So in addition to reaming upper balljoint hole, I reamed the GMT800's tie rod hole to fit the ES409R tie rod. It fits tight.

I'm not certain if this tie-rod is 10 degree or 7 degree taper? Not easy to discern that 3 degree difference. May do the math on big/small diameters & see which it comes out to.

Dirt track racer friends tell me it won't matter as a mismatch 7 to 10 degree taper interference fits tight regardless? Anyone have experience with this?

The tie rod stud has a castle nut/cotter pin, so have same safety backup as stock setup.

View attachment 46924
Are those forged Lower Arms from the GMT-400 or GMT-800?
 

SmithvilleD

Active Member
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Location
St Joseph, MO
#25
The ES409R tie rod taper info is 0.676" - 0.593" = 0.083" diameter difference over it's spec 0.66" taper length. (the taper length spec was throwing me because the actual stud tapered portion length is notably longer than that).

But believe they give the spec that way to get to inches per foot taper. The reamer I have is 2"/foot.

0.083" / 0.66" = 0.1257 "/ft

0.1257 inches per foot X 12 inches per foot = 1.509 inches per foot.

So if my understanding is correct, this tie rod stud should mate into a taper reamed with a 1.5"/ft reamer.

Yes, forged arms are from the GMT800 chassis.
 

schiker

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#26
Yeah, that looks right.

IF I remember how to figure it the included angle of those diameters comes out to (Inverse Tangent of 0.0415/0.660) *2 = 7.1959047274 degrees.

Perfect world no distortion it comes out to something like 1.5091 inches of taper per foot included for the stud.

When I googled for a 1.5" TPF reamer several reamers were on ebay listed as GM tie rod reamers. So I guess that is what they are called.

Looks to be just slightly tight to the stud and the stud distorts it to a locking taper when its drawn into the taper.

I did see some 7.15 degrees reamers too. 1.5 TPF included comes to 7.152668 degrees included. So I think its just rounded off and either are correct.

7.152668 does not equal 7.195904727 so again I think the stud is slightly bigger to distort the female and lock.
Anyone see something else close to compare??? I am not sure I would try to split a couple hundredth's of an angle. Could be tolerance or some spring effect of the female to make a locking mechanism.
 

SmithvilleD

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St Joseph, MO
#27
Yes. I think I should have reamed the GMT800 knuckle's tie rod hole with a 1.5"/foot reamer. That would have enlarged the GMT800 knuckle's tie rod hole/taper at the correct 1.5"/ft taper and fit the ES409R outer tie rod end as designed.

Overall adapting GMT800 knuckle would then require both 1.5"/ft & 2"/ft reamers to do the job right.
 

Big T

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Thread starter #30
Any chance that there's some Moog upper and lower ball joints that would fit both upper and lower control arms plus have the right tapers to fit the steering knuckles.
 

SmithvilleD

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St Joseph, MO
#31
Don't know. Does your Burb have the stamped steel lower A arms, or forged? If forged, the hole the ball joints press into may well be the same. If that is so, could then just buy & press in the GMT800 ball joint to match the GMT800 knuckles lower taper.

I didn't compare the GMT800 stamped/welded upper A arms to GMT400 stock arms much before they got discarded.

The Moog 800 # is above. Don't know how likely it is they feel comfortable in helping outside of stock/OEM engineered applications?
 

Big T

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Thread starter #32
My lower arms on the '99 are the forged arms where the ball joints press in.

The upper arms are forged and the original ball joints that were riveted on have been replaced with Moog problem solvers, which are booted on after drilling out the rivets. If that mounting pattern were the same for a 2" taper ball joint, I could avoid the team job.
 

SmithvilleD

Active Member
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Location
St Joseph, MO
#33
Here is a pic of the GMT800 ball joint section that presses into the forged arm, showing OD. Compare that diameter & depth it seats to the balljoint part# you pressed into your '99's forged lower arms. 20160119_232339.jpg
 

Big T

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Thread starter #34
Here is a pic of the GMT800 ball joint section that presses into the forged arm, showing OD. Compare that diameter & depth it seats to the balljoint part# you pressed into your '99's forged lower arms. View attachment 46953
I checked on RA and the press fit measurement is smaller:

Front Lower; Includes Powdered-Metal Gusher Bearing To Allow Grease To Penetrate Bearing Surfaces; 47.89mm/1.885" Press Fit Diameter; For Forged Arm.

Now if I could find one that has the above press fit and the 2" taper, Problem solved.
 

Ttoyota

New Member
Messages
13
Likes
5
Location
Tn
#36
I think I've got a solution - still needs to be bolted on the truck & aligned to confirm. Tie rod combination measures right.

So got the O'Reilly store brand ES409R to mock up & see if it could work. The taper didn't fit the GMT800 knuckle as is. I had an Allstar Performance 9.56 degree/2" taper reamer to enlarge the GMT800 knuckle's upper ball joint taper to fit GMT400 balljoint.

So in addition to reaming upper balljoint hole, I reamed the GMT800's tie rod hole to fit the ES409R tie rod. It fits tight.

I'm not certain if this tie-rod is 10 degree or 7 degree taper? Not easy to discern that 3 degree difference. May do the math on big/small diameters & see which it comes out to.

Dirt track racer friends tell me it won't matter as a mismatch 7 to 10 degree taper interference fits tight regardless? Anyone have experience with this?

The tie rod stud has a castle nut/cotter pin, so have same safety backup as stock setup.

View attachment 46924
Hello, First time poster. How did everything work out? I'm right at this stage. My truck is k2500 3/4 8 lug 8600gvw. I'm not wanting to ream out the upper part of the outer tie rod if I don't have to. Would rather go in thru the bottom. Going thru the top seems to put the tie rod really close to the steering stabilizer. So to confirm, The inner tie rod in the pic is standard gmt 400. The adjusting sleeve is standard gmt400, but your new outer tie rod stud is the same diameter and thread pitch as the inner? You still have to ream out the lower outer tie rod hole as well? How is everything working out. Any thing you would have done different or is truck steering working out good? Thanks for everyones help. This was so nice to find and do.
 
Last edited:

Ttoyota

New Member
Messages
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5
Location
Tn
#37
man thx for the likes but i need some love... really all i need to know is the pn for the inner tie rod he use. That's if its the same for the 8600 8 lugger. Need to have parts waiting for me when i get off this rig. Ol girl needs some work.
 
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