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GMC Truck Steering


R Cubed

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Here is another section of the overhaul, the steering box, king pin bearings.

 

The steering box is a real pain to get out, you need to remove the steering drag link between the two front wheels and also the winch propshaft so you can get the exhaust down pipe off, once this is all done the steering wheel has to be removed, mine came off with a clout from a club hammer and a piece of wood, after undoing the centre nut ( watch out for the key way falling out ) then the cross shaft drop arm, this is splined and tapered, undo nut a bit then using a hub puller force the drop arm off, I needed to apply some heat for this. Then there are the four bolts holding the box to the chassis rail, these have nuts and lock nuts on the outside of the chassis rail, so you need to hold the bolt and undo the nuts. Then with a wiggle and a bit of force get the box out..

 

Steeringbox.jpg

 

This pic is after it has been cleaned up ready for stripping down, stay tuned.

 

Moving on from this, to the replacement of the steering king pin bearings of which there are four, one each side at the top and one each side at the bottom of the swivel housings on the front axle, a handy note here is these bearings are the same for the Banjo and split axles,

 

Bearing numbers are: outer 41286, inner 41125.

 

Strip down hubs by splitting the two halves and remove top and bottom bearing caps, watch out for shims under these as you will need them again. After I inspected mine it seems that the bottom bearings need replacing as these get all the pounding and carry all the front end weight of the truck, the top bearing just keeps it all upright.

 

This is a complete bearing.

 

Kingpinbearing.jpg

 

Here you can see the wear marks generally in the straight ahead position as this is where the bearing sits most of the time so getting most of the shock.

 

More to come as I work through it all.

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Right then this is what's inside your steering box.

 

Gearsoutofbox.jpg

 

The red shaft is the one from the steering wheel ( steering shaft ) this has a worm grove cut in it at the end and a block fits over this which also has a worm grove cut in it, between the two groves there are ball bearings, these are fitted and removed by taking out the two steel tubes on top of the block and removing the balls then the block can slide off the steering shaft worm.

 

 

Steeringshaft.jpg

 

 

These types of steering boxes are know as recirculating ball steering boxes, because the balls in the worm groves recirculate around the steel tubes !! This was a great advance when the trucks were designed and was a key selling feature of them as it was like having power steering.

 

The cap at the end of the steering shaft is the one at the bottom of the steering box

 

Steeringshaftbearingandcap.jpg

Steeringshaftcap.jpg

 

 

The large adjusting slot and lock nut are only for adjusting slack/play in the steering shaft ( so only up and down movement on the steering wheel )

 

The only other shaft ( the cross shaft ) is the one which pokes out through the chassis rail and has the large drop arm on it.

 

 

Crossshaftandcap.jpg

 

 

The crescent gear meshes with the block gear on the steering shaft, this cross shaft is fitted in the steering box in plane bronze bushes these are prone to wear and gives play in a front to back movement by the drop arm ( my problem ) the cap at the engine side of the box allows the cross shaft to be adjusted from left to right in the box and enables some play to be removed between the two sets of gears, I think have not confirmed this yet

 

Crossshaftandgear2.jpg

Crossshaftstripeddown.jpg

 

 

R Cubed

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Thanks Jack, dont get much in the way of pics and explanations of the repairs people have done so I thought as this looks like a active forum I would start, so to try and build up articles of how something comes apart and what is in it.

 

The problem I had was much over 35 MPH I would get severe wheel wobble to the extent that the only way to stop it was to break hard and then carry on slower, I have traced this down to several things, the main one I think is the steering king pin bearings on the swivels, the bottom bearings having stamp marks in the outer shell in the straight ahead position this leading to excessive play in each wheel, but also found when turning the road wheels left and right when jacked up, that the actual cross shaft which comes through the chassis rail from the steering box was moving forwards and backwards not just rotating !!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

R Cubed

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Ok bit of an update to the steering box sarga, I have removed the plane bronze bearings from the steering box along with the cork oil seal on the cross shaft, and will be getting some new ones.

For what ever reason if you want to take the toothed block off the steering worm you need to remove the two recirculating ball tubes and then all the balls dont loose any !!!!

 

Recirculatingtubes.jpg

 

These two tubes are split in half so you have 4 bits these are all the same and does not matter which way round they go into the holes, as long as they go between 1 and 2, 3 and 4.

 

 

Wormblocknumbered.jpg

 

 

The number of balls you get out must be split in half, there should be 106 in total, one set of balls goes in hole No1 untill they start coming out of hole No2, NOTE you must make sure that no balls run across the top of the worm in hole 1 or hole 2, then the remaining balls go in the split tube, then this fits in to holes 1 and 2, the balls are now traped and can not escape if some do they have got over the top of the worm,you have to start again. then repeat this for holes 3 and 4. NOTE you must make sure that no balls run across the top of the worm in hole 3 or hole 4.

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  • 4 weeks later...
  • 2 weeks later...

I have fitted the new bronze bushes and a new liped oil seal inplace of the old cork one in to the box and as they say the assembly is the reverse procedure of disassembly, well the only problem I had was the insertion of the geared cross shaft, you MUST get the geared block which is on the steering shaft in the centre position ie: turn steering wheel to end stop and count turns to other end stop then go back half way, which gives you the half way point, otherwise you get more steering one way than the other :-o :-o

You adjust the large screw adjuster at the end of the box first, to get the correct load on the steering wheel, 1 to 1 1/2 pounds pull to keep the steering wheel in motion, measured and the outside rim of wheel.

 

Steeringshaftcap.jpg

 

Then the small screw on the side of the box to mesh the gears together so as not to get any binding throughout the travel of the steering wheel from far left to far right. recheck pull now should be 2 to 2 1/2 pounds pull to keep the wheel in motion.

 

Crossshaftandcap.jpg

 

Once this is all done ensure all nuts, bolts ect are tight and the side bolts on the box wired up with lock wire, and dont forget to fill the box with oil to the fill plug, dont use Hypoid oil as this will eat those nice new bronze bushes, I used Morris ST 90 as with all diffs and gearbox and transfer box.

 

R Cubed

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  • 2 weeks later...

Well these are the old bearings, notice the pitting on the outer part.

 

D4100123.jpg

 

Also the rollers on the other part of the bearing are not so good either.

 

D4100122.jpg

 

Here are the two bits together.

 

D4100124.jpg

 

Well I have just picked up the new ones nice and shiny but a bit dear.

 

D4100130.jpg

 

Well you cant have it all ways.

So now I can get on and fit them and shim up to get the correct pre-load on them, I have got a shim kit, genuine NOS still in its very well wrapped packing with part number on it.

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  • 5 months later...

Yes it has sorted out the wheel wobbbbbblllleee fine, still need to do the steering tie bar bushes and pins between the two wheels and that will conclude the steering sarga, might check the king pin drag and steering box this winter and poss take the shims down a bit more but we shall see.

 

Next jobs all prop U.J. joints and check pillow block, a rear torque rod, engine crank inspect and sort out ignition timing.

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I ll hope the weather cooperates and isn't too wet or windy , Having tried working outside it basically s**** as my fingers quickly go numb and the wrench slips causing new cuts and bruises . Bad enough having to do the work but to have doing it in winter is worse times 10 .

Glad to hear that your going to be toasty while sorting yours out :tup:

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  • 5 months later...

Tie bar pins now done and toe in adjusted, so we shall see how it goes but a road test the other day seems very promising.

 

New new distributor now fitted and timed up by ear !!!!!!!!!!! the old one was, well very old, so much so with the gear drive in one hand you could easily turn the rotor arm about 10 degrees from one side to the other with no resistance and not moving the gear drive, eeeek also it had variable points adjustment in that the bearing was so worn that you could wobble the shaft sideways as well and alter the gap of the points, how it kept running I don't know !!! so a good move to put a nice new distributor in it...

 

Have gone down the boy racer route and fitted a rev counter !!!!!!!!!!!!!!!!!

 

Did you know the best revs to change gear in a GMC is 2000 any lower or higher and the gears crunch so there you go.

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Ummmmm

 

 

The wiring !!!!!!!!!!!!!!!!!!!

 

 

 

Oops sorry could not resist that !!!

 

Well I have had a 6 cylinder electronic rev counter lurking around for ages, so I thought I would use it on the truck there is a Positive wire, goes to a switched live. Negative goes to a ground connection and the last one is a trigger which goes to the connection on the coil which links the coil and points ( not the HT wire ) just like that, but as it's max reading is 7000 RPM the truck only revs to 2750 RPM, it does not move much but nice to know what revs the engine is doing when on a long dual carrigeway.

My speedo does not read very accuratly so not a good judge of engine revs.

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  • 1 month later...

HI,

 

I have a White Scout car and have been told that it uses the same spliut froint axle as a Jimmy, my question is on the stering knuckle bearings you reaplaced was there a thrush washer under each bearing? as I seem to have 'lost' any space for the shims to be able to be placed back to preload and I have a feeling the Greek army when replacing the bearings back in the 70's 'lost the spacers' on replacement.

 

Cheers

Paul

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Hi to you Paul, I dont think the Scout car are the same, but if its any help the shims fit on the big square caps which bolt over the bearings, with more shims in, the cap can not be bolted down so much so the bearing is looser, by taking out shims and or swapping for thinner ones you can obtain the correct pre-load on the hubs, NOTE you MUST fit and remove or put in the same number and thickness on the top and the bottom so as to keep the hub in a central position in relation to the axle.

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