The Stovebolt Site Forums The Parking Lot Tons 'o Fun 1-ton front disc brake dumb idea?

To install front discs on a 3800 why couldn't you simply remove the drums from the hubs and mount REAR disc rotors (with lug holes instead of studs) onto the hubs, then fabricate a bracket to mount the calipers? That way no need to find an integral rotor/hub that will fit the spindle.

Yes, I know Hollister makes a front disc brake kit but I don't want to use it because it spaces the wheels outward another inch on each side.

Worth looking into, you might figure out a new way to do it.

Otherwise the Holster kit is a reasonable solution, not unlike what you're suggesting.

I have the Hollister kit on my one ton and it works well. Not really a lot of money and the power brake booster fits in the stock location even with the PTO!

Looks like that's what they've done.

Spacing wheels out another inch as stated above modifies original steering geometry, center point steering modification puts larger load on wheel bearings, wears tires more.

Ed

You could buy stock GM wheels with a wider offset so that's not accurate. It doesn't change the center point because it's still at 90 to the center point, Weight of the truck isn't changed so larger load on the bearings is not accurate either. Look at a 3/4 ton a 1 ton and then a 1.5 ton and tell me one will do any of the thing you've stated. each has a different off set wheel and track width due to wheels and all share the same axle and the same center point.

It doesn't change ackerman either. even though they are outward 1" they are still well within the wheel wells

If understand Ed's comments correctly..
In an ideal situation the kingpin centerline intersects the ground at the center of tire contact patch with the ground.
If wheels are spaced out this changes to a little less than ideal, results in more tire scrub when turning.
Load on wheel bearings does change, the weight is now carried at a different point between the two bearings, so some leverage different than how bearings were intended to cary the load. Also dynamic load while turning, is increased. Yes same weight sitting still, but applied differently to the bearings.

With 1/2" per side none of that has changed much, but for sure there is a difference, and I agree likely not enough to bother.

For an extreme example of all above think about the 4x4 pickup guys who put wheels significantly wider and or different offset than original resulting in much wider track with, wheels that hang half or mostly out of fenders.
They do have much increased steering effort, tire wear, and bearing failure.

So at some point changing (effective) wheel offset does matter.
1/2" might not, but it is a change.

Grigg

Grigg,

That is correct.

Ed

This seems to show something different, the single front wheel is a 0.5 offset wheel 4" bakespace so it's not very close to the king pin center line.

Single wheel front hub
Single rear wheel front hub set out 1"

Dual front hub
Dual wheel front hub with the wheel mount outboard of the outer bearing.

Same axle, same spindles, same bearings, same center line. except the tread does not center on the kingpin on either.
The dual hub wheel mount is significantly out board of the single hub wheel mount and doesn't seem to have created a bearing load issue The front tread is almost 3/4" different on stock axles between dual and single rear wheel, and again all other parts are the same.

So i'm thinking that if it were a problem all 3800 and up dually trucks would already have the problem.

The 4x4 scenario is usually when the wheel offset is very exaggerated past what I show in the pictures.

We did a lot of research on the kit before we released it for sale, I checked the rumor for ball bearing failing when discs were added or radial added. Not one place could I find a first hand example. We checked if it would affect steering while braking, Turn radius, Ackerman, you name it. We have several hundred of these out now so someone would have said something if it had issues.

I am on your side, I think you make a good kit and the original poster or anyone else shouldn't be worried about using it.
I also think this is a good discussion about what matters for changing wheels or axle parts and what to think about and look for.
Understanding the original or ideal design considerations helps evaluate effects of changing the relationship of parts, and at some point if changed enough it does matter.


The dual wheel trucks use different wheels with lots of offset compared to the single wheel.
Making the center of wheel again in approx same location relative to the wheel bearings, so not an issue at all for bearing load.


Different matter,
It's true the kingpin is not in the center of the wheel. And that the wheel turns about an axis defined by the center of the kingpin, like a hinge turns about the hinge pin.
The kingpin is inclined, and that incline lets the pivot point of the wheel on the ground (the kingpin axis extended to the ground) come close to center of tire tread on ground.

So changing wheel offset will move tire contact patch on the ground relative to turning point on the ground.
Big changes like some of the 4x4 crowd with extreme outset wheels makes a difference, harder to steer, more tire wear because of more scrubbing when turning.
If driving dead straight all the time this wouldn't be an issue. (Not considering wheel bearings)

On a 3600 you could have an offset of 7/16 on a 17" wheel or 3800 with the same offset both being SRW. But the 3800 DRW that had 18" had an offset of 4-9/16" with a DRW front hub. the axle length was the same , bearing position the same, The DRW just has the hub extended. If you look at the alignment section of the manual it shows the kingpin sitting at the inner edge of the wheel about 3" from the wheel centerline. You just can't have that much pin inclination and still drive it. Does it actually incline into the tread area , yes, That's the scrub area and it only changes that slightly. you can get a larger change for swapping to late model wheels.

I'm looking at the alignment section in the 1949 100-450 GMC maintenance manual.
The picture with alignment chart is illustrative, not accurate.

Note that king pin inclination is 7-1/6* and camber is 1-1/2*
Added together the kingpin is at an 8.6667* angle with wheel centerline.
Figure a 32" tire, or 16" radius.
Tan 8.6667* X 16" = 2.438" meaning the kingpin centerline at the ground is that much further out than at center of wheel.

I measured best I could front hub and spindle on a 3/4 ton (single wheel) AD axle.
At center of wheel the wheel mounting surface (hub surface) is 3.25" outside of center of kingpin.
Subtract from that the nominal 7/16" inset of stock wheels (is this right?) gives 2-13/16" center of tire tread to kingpin center at center of wheel.

Difference then in the calculated offset due to camber and kingpin inclination and physical offset of hub from kingpin is about 3/8" between center of tire on ground and point it turns on the ground.
Any less offset in wheel or adding wheel spacers increase that offset, more scrub.

So the factory setup is pretty much ideal and good for ease of steering and better steering tire life.

Sorry if that's hard to follow in words. I can make up a drawing if it helps anyone, just ask. (And if I made a mistake it'll become apparent in a drawing)

Grigg

I think that s pretty much my point, The change minimal at best for an SRW kit and no change on a DRW kit. If that little of an offset and scrub difference mattered an entire industry would close down because we couldn't use aftermarket wheels and every time someone used a ford rim, which is a rim of choice on these, with a 5 or 6 inch back space vs the 4.5 original I think it would be very common knowledge that wheel bearing were failing and steering was greatly affected. But I do see that anywhere of hear about is much past theory. It would certainly show up here on stovebolt if it were happening.

did you ever try that rear disc idea? how did it turn out?

Someone who claims to be able to solve my problems by selling me something always makes me wonder if he's got an agenda that's more about making a profit than actually following sound engineering practices. Changing a tire's scrub radius and the load geometry on a bearing might be OK, or maybe it's not. The original designers probably did their homework pretty well before they decided on a specific configuration. When my engineer brother does contract computer modeling for Ford, General Motors, Chrysler, or U. S. Navy missile guidance systems, he charges his time out at a rate of $1,000.00 a day. I wonder how many aftermarket parts suppliers can afford that kind of research?
Jerry

Not sure of the point you're trying to make but scrub is most critical in front wheel drive vehicles (newer cars) and vehicle with diagonally split brake systems( not used any longer). Rear wheel drive straight axles and front to rear split brake systems are minimally affected by scrub unless its drastic. GM didn't have a specific configuration noted by the number of wheels and offsets you could get on the same axle.

Positive or negative scrub can be changed merely by changing the size of the tire say from a 650 to a 750, or a 16 to a 17 with no offset change and the reverse of that. It is most noticed in FWD cars on acceleration and deceleration causing bump steer. On a straight axle its most noticeable on low speed turning such as getting into a parking spot. It's really a non issue for the trucks we have, unless your adding huge mudding tires.

Now I can't say I've ever gotten paid a $1000 a day but I have stayed in a Holiday Inn Express

Changing offset causes torque steer on FWD vehicles- - - -not bump steer.

I'll agree to disagree with you on this, mainly because causes of torque steer has nothing to do with what everyone is working on here and I don't want to have the thread go down a rabbit hole to some other topic

My point was that scrub is inconsequential on our vehicles unless its drastic.

As a practical rubber-meets-the-road matter, small changes in wheel offset don't cause bearing failure in my experience. I abandoned the 17" three-piece wheels about 20 years ago and found the Ford wheels now so widely used. Fine except they're ugly. So I found some Centerline wheels with enough backspacing and I'm using 235/85X 16 tires. So the offset is outboard by about an inch to clear the tie-rod end as you all know. The tires are somewhat smaller diameter than the original 7.00X17s so that compensates some for the greater offset but they are wider and much stickier.

I've run the truck loaded with a gross of 7800 to 9100 pounds ever since. I had to replace one wheel bearing set (inner and outer) about ten years ago but that was the side with the original bearings from '51. The other side I replaced in the mid-seventies.

In the past 20 yrs I've run the truck ~ 120,000 miles and am on the second set of steer tires. Yes the steering is heavy but is that because of sticky radial tires, greater offset, more weight on the front axle or arms that are 20 years older? Take your pick. With both fuel tanks full it's a chore to move around in a parking lot.

Off topic but for those of you who do not know Dave Chapman of Hollister Road Co. passed away January 5, 2018.

Further info and discussions here
https://www.stovebolt.com/ubbthread...28/dave-chapman-thoroco.html#Post1251128

Who sell a disc conversion kit for 1 tion huck brake ? Any help is greatly appreciated.

What year is your truck?

I fabricated disc brakes for my '38 1 ton.

This is for single wheel 3600&3800 trucks.

https://www.ebay.com/itm/350973126802?item=350973126802&viewitem=&sspagename=ADME%3AX%3ARTQ%3AMOTORS%3A1123&vxp=mtr&rmvSB=true

This is for single wheel 3600&3800 trucks.



Tomshttps://www.ebay.com/itm/350973126802?item=350973126802&viewitem=&sspagename=ADME%3AX%3ARTQ%3AMOTORS%3A1123&vxp=mtr&rmvSB=true

Ok. So does this still fit and clear on a 47-55 axle? Has anyone had any luck with this EBay kit? Does anyone know what will happen to the Hollister Road Design?

There is a post on another site showing how to make some, http://67-72chevytrucks.com/vboard/showthread.php?t=647049
I'm sorry to hear about Dave, I had considered getting his kit, but I have been thinking about changing out my Hucks for 20 years...

I have this thread as well. Good ideas. Will keep researching. Thanks.

It's not on his site yet as I type this, but Sid Drapal (http://droppedaxles.com/) of Nostalgia Sid's posted on Facebook today that he is now carrying 3/4 ton and 1 ton AD truck disc brake kits.