Mack King Pins:

[Rob]

Good morning. Got me a question starting from finding a left side king pin sloppy in my R612ST. This thing has a shake at 43mph and goes away right at 46-47mph all to way to governed speed, (80mph+). My daughter will run "chase" tonight to isolate further, but It needs new king pins and that's not a big deal. My question is why are these things called "adjustable"? I have the adjusting socket/tool and after rebuilding the assembly with new pins, bushings, and bearings, you install the top cap, thread in the bottom plug, adjust it up snug seating the tapered king pin into the tapered socket of the axle beam, and install a cotter key to keep the plug from backing out. If my understanding is correct, the taper of the king pin and socket keeps the pin from rotating in it's respective bore, but the wear surfaces are the upper, and lower bushings, along with the thrust bearing in the bottom between the spindle, and axle beam. The tapered portion of the pin should never wear if logic is correct.

Is the "adjustment" just a preliminary install item and is never touched again for the service life of the king pin and knuckle assembly, or do these things require periodic adjustment to compensate for wear of the thrust bearing for instance?

Rob

[bobo]

Uncle Rob the "adjustment" is real to set the camber when "loaded", but many people hear adjustable and think its to tighten up the pins. bobo

p.s. I always change BOTH kingpins! and so should you!

[Rob]

Uncle Rob the "adjustment" is real to set the camber when "loaded", but many people hear adjustable and think its to tighten up the pins. bobo

p.s. I always change BOTH kingpins! and so should you!

And I will change both sides. The kit was ordered this morning and I should have them Friday. Be a nice little project for Saturday as there is nothing in the shop pressing.

I didn't know these were used to set camber angle. I'd assumed this was still done by bending, (shhhhhh) the axle beam.

Thanks,

Rob

[bobo]

Its an easy way of cheating to get more life out of pin that wasn't greased enough! The problem I have seen with the set up is the top cap some times doesn't want to stay in, I've tried "green" locktite but still pop out as they are hand press. If you use air grease gun, the pressure will blow cap off! I think it would have been better if mack would have made it threaded like the bottom and use the same key. bobo

[Rob]

Its an easy way of cheating to get more life out of pin that wasn't greased enough! The problem I have seen with the set up is the top cap some times doesn't want to stay in, I've tried "green" locktite but still pop out as they are hand press. If you use air grease gun, the pressure will blow cap off! I think it would have been better if mack would have made it threaded like the bottom and use the same key. bobo

The left side pin has about 1/4" free movement at the top of the tire. There are no top caps on either side! (Go figure) The right side seems to be tight but I'll not replace only a single side as you mention cause they both must be worn. The truck will be apart so get it done right! I actually had the truck jacked up by the front engine xmember to check for spring pin bushing wear, and grease it up really good. While under there, I found the loose king pin, greased the front end moving parts very well, adjusted the clutch brake for better operation and adjusted the clutch for exactly 1.5" free pedal at the top, and 1.5" clutch brake squeeze from the floor.

I also discovered there is only about 1/8th inch of front brake shoe lining left. This is below allowed so looks like new brakes too. Hope the drums are good and I'll find out on Saturday when I haul everything into the vendor.

Thanks again!

Rob

[terry]

I always thought the "adjustable" part was to keep moving the bottom thrust bearing upward as it wears to keep the axle beam from dragging on the spindle. terry

[theakerstwo]

I always thought the "adjustable" part was to keep moving the bottom thrust bearing upward as it wears to keep the axle beam from dragging on the spindle. terry

Thats right.Some times they can get lose and you can adjust them and take some slack up and down out.

[Stingray698]

They are designed to have up and down as in lateral but if you push in or out on top or bottom of wheel there should be none , if they get too tight they can press themselves out of the axle , how do the tires look are they choppy or cupping on outer side , also on top cap i always peen them in 10 or 15 spots , after setting them i run nut up till its tight then back off until next slot lines up ,then check for up and down ,then after another lesson learned i always grease them right after final adjustment is made -there again if there too tight and you grease them they will lock up then your taking the spider back off and re adjust , they are designed to have some play to tight will wear axle beam , Also i tried a stemco no reem kit in the tapered style and will never use one again , I ended up removing it and returning it , goes to show you aftermarket is crap every time you would grease it it would push the spiral bushings and move them and make adjustment super tight after adjusting, just my 2 cents Ive done probably 10 sets and every one sets up a little different, also i checked a garbage truck for referance once and i bet it had 3/8 up and down , customer didnt want to fix i looked at it 6 month later and it was same way and tires wernt even wearing bad , strange but no lie

[Rob]

The tires on the steer axle show no abnormal wear at all. I was chasing the vibration, or hop at speed is what had me notice the play in parts. I've only installed one set of these tapered king pins and had the bushings reamed to fit but it was a new axle beam replaced from collision. Never have done a set of tapered pins on a working truck. I have the OTC adjusting socket and figured it was to tighten to take up play in the thrust bearing so I just tightened till snug, then backed off to next slot to shove cotter pin through. I didn't know if this is a periodic adjustment or not. The caps I just drove in with a drift and the front took grease just fine.

I ordered a Euclid brand kit that is supposedly complete. Should have it tomorrow afternoon and will take the truck apart then. They vendor will press the bushings and ream to fit, (if needed) for me on Friday and I should be putting it back together on Saturday if all goes well. I also ordered new "P": series shoes for the steer axle and hardware kits. The axle is a 12,000# FA(W) 537 so pretty common stuff.

Remembered and proved another problem with this truck tonight also. If the truck is idling in the shop, the compressor cuts in at about 105, and out at 120 very evenly. If the idle is held to 1400+, it will exceed 150psi with the safety relief valve blowing. I discovered this driving as it sounds like a 22 short going off under the truck. The tanks drain clean, there is no air dryer, the governor is replaced with a shop spare, and the lines are clear and connected correctly. The compressor is a Midland 1300 series and I put a new unloader kit into it about six months ago. This problem is not new, and it's been there since I've had the truck. Tonight I did notice the compressor is bleeding back through itself when the engine is shut down. I'm thinking the head will need to come off of it for evaluation and check the inlet and discharge valves.

Rob

[Stingray698]

As for the compressor i agree sounds like the internal valves in the head , and for the king pins you can do the bushings yourself they are brass and very thick and a needle bearing they do not need to be reamed i just take a small brake hone and pb blaster clean the spindles , then press new ones in also another trick i figured out is take one of the old grease seals and emry down the outer lip so it will fall into spindle by hand then you can determine depth of bushing and needle bearing so when you put the seals in they dont protrude out past the spindle and rub on the axle ,also make sure the grease seals are put in with the lip facing out so it actually looks like the seal is in backwards , it will lock the spindle up when you grease it , if the lip faces the bushings, one other thing when i remove the top grease caps i weld a 1/2 fine nut on the cap and put a small style slide hammer and they usually come right out

Edited May 18, 2012 by Stingray698

[Rob]

As for the compressor i agree sounds like the internal valves in the head , and for the king pins you can do the bushings yourself they are brass and very thick and a needle bearing they do not need to be reamed i just take a small brake hone and pb blaster clean the spindles , then press new ones in also another trick i figured out is take one of the old grease seals and emry down the outer lip so it will fall into spindle by hand then you can determine depth of bushing and needle bearing so when you put the seals in they dont protrude out past the spindle and rub on the axle ,also make sure the grease seals are put in with the lip facing out so it actually looks like the seal is in backwards , it will lock the spindle up when you grease it , if the lip faces the bushings, one other thing when i remove the top grease caps i weld a 1/2 fine nut on the cap and put a small style slide hammer and they usually come right out

Thanks a bunch for the tips. The kit came it today but I was unable to get there due to commitments in the shop. Seems air conditioning is really important to people when it starts to get warm outside...... After getting a couple of cars pulling down into vacume I brought my drop deck into the shop, jacked up the rear getting all eight tires from of the floor, and set the trailer on jack stands. It was then I remembered Jaime backing over my hub oil drain pan last winter splintering it!! I just changed all the hub oils to synthetic so I'd like to keep it. I'll get a pan tomorrow when picking up the king pin kit.

I looked and PAI does market a cylinder head rebuild kit for this Midland compressor, so I ordered it. The kit has the valves, seals, springs, gaskets and some small parts so I'll attempt this over the weekend probably. The vendor did have a reman compressor on the shelf for $280.00 exchange so that can be a backup if something is AFU.

Thanks for the tips.

Rob

[Freightrain]

I remember doing my king pins. Was simplier then I ever imagined. Few hours and it was in pieces ready for new bushings and install. Took them to buddys shop for press work and put it together.

I was curious too about up/down movement as I think after 10 yrs mine has some(not sure how much, need to jack it up again). Never really worried too much, just screwed the plug in the bottom til snug and then found nearest hole for cotterpin. Keep it greased and seems to steer fine after all this time.

Barry got me my kit, pretty cheap if I recall.

[39 Baby Mack]

Mack part #301SQ47CP1 if I remember is the latest Mack kit with later heavy duty caps for the top bores.
With this kit, I used to just use a bushing driver to install new bushings and needle bearings (top).
As was said before seals go in with lip toward axle beam they seal water out not grease in.
Never had to ream them as as the lower shell bushings were already pre- sized.
When installing lower bushings make sure grease grooves run out to bottom of spindle to make sure thrust buttons get greased.
Another trick I was taught years ago is how to set taper of pins in eye of axle.
Making sure eye of axle is clean and dry with brakleen, insert pin up through spindle and axle then take bottle jack and jack up under pin to take weight of truck off other support so all weight is holding pin in axle eye, smack axle beam behind eye (inboard) from eye to set pin in axle eye.

This takes the place of a lot of settling in when first put together and also insures a good set in the axle.
Dutch fit top bore to help secure late style plug using stud and bearing mount lock tite.

These late style caps are also threaded for a puller bolt so they can easily be removed if you ever have to do it again.
Always raise vehicle off the ground when greasing Mack king pins.