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Re: 1-ton front disc brake dumb idea? [Re: Jay Zed] #1234646
Wed Sep 13 2017 08:27 PM
Wed Sep 13 2017 08:27 PM
T
thoroco  Offline
Shop Shark
Joined: Dec 2006
Posts: 673
Houston, Tx
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.


Dave Chapman
The Hollister Road Company
713-937-0387
info@hollisterroad.com
www.hollisterroad.com
www.thoroco.com
Re: 1-ton front disc brake dumb idea? [Re: Jay Zed] #1234691
Thu Sep 14 2017 12:53 AM
Thu Sep 14 2017 12:53 AM
G
Grigg  Offline
Master Gabster
Joined: May 2005
Posts: 9,297
Lexington, VA
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


1951 GMC 250 in the Project Journals
1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-
Re: 1-ton front disc brake dumb idea? [Re: Jay Zed] #1234707
Thu Sep 14 2017 04:08 AM
Thu Sep 14 2017 04:08 AM
T
thoroco  Offline
Shop Shark
Joined: Dec 2006
Posts: 673
Houston, Tx
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.


Dave Chapman
The Hollister Road Company
713-937-0387
info@hollisterroad.com
www.hollisterroad.com
www.thoroco.com
Re: 1-ton front disc brake dumb idea? [Re: Jay Zed] #1246527
Mon Dec 11 2017 06:27 PM
Mon Dec 11 2017 06:27 PM
E
ethanm90  Offline
New Guy
Joined: Dec 2017
Posts: 17
IN
did you ever try that rear disc idea? how did it turn out?


55 3800
Re: 1-ton front disc brake dumb idea? [Re: Jay Zed] #1246609
Tue Dec 12 2017 04:58 AM
Tue Dec 12 2017 04:58 AM
H
Hotrod Lincoln  Online
Boltergeist
Joined: Feb 2004
Posts: 16,107
Dellrose, TN
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


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: 1-ton front disc brake dumb idea? [Re: Jay Zed] #1246666
Tue Dec 12 2017 08:30 PM
Tue Dec 12 2017 08:30 PM
T
thoroco  Offline
Shop Shark
Joined: Dec 2006
Posts: 673
Houston, Tx
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


Dave Chapman
The Hollister Road Company
713-937-0387
info@hollisterroad.com
www.hollisterroad.com
www.thoroco.com
Re: 1-ton front disc brake dumb idea? [Re: Jay Zed] #1246709
Wed Dec 13 2017 01:24 AM
Wed Dec 13 2017 01:24 AM
H
Hotrod Lincoln  Online
Boltergeist
Joined: Feb 2004
Posts: 16,107
Dellrose, TN
Changing offset causes torque steer on FWD vehicles- - - -not bump steer.


The murder victim was drowned in a bathtub full of Rice Krispies and milk.
The coroner blamed the crime on a cereal killer!

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
Re: 1-ton front disc brake dumb idea? [Re: Jay Zed] #1246719
Wed Dec 13 2017 02:41 AM
Wed Dec 13 2017 02:41 AM
T
thoroco  Offline
Shop Shark
Joined: Dec 2006
Posts: 673
Houston, Tx
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.


Dave Chapman
The Hollister Road Company
713-937-0387
info@hollisterroad.com
www.hollisterroad.com
www.thoroco.com
Re: 1-ton front disc brake dumb idea? [Re: Jay Zed] #1251094
Mon Jan 15 2018 10:12 PM
Mon Jan 15 2018 10:12 PM
1
1Ton_tommy  Offline
Wrench Fetcher
Joined: Jul 2014
Posts: 68
Seattle
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.


51 3800 PU, 55 235 (w/cam, headers, 2 carbs, MSD ign.), SM420 & Brown-Lipe 6231A 3spd aux. trans, stock axles & brakes. Owned since 1971.
Re: 1-ton front disc brake dumb idea? [Re: Jay Zed] #1251120
Tue Jan 16 2018 01:52 AM
Tue Jan 16 2018 01:52 AM
D
draglink  Offline
New Guy
Joined: Dec 2006
Posts: 8
Gallatin, Tennessee, USA
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

Last edited by Grigg; Tue Jan 16 2018 01:35 PM. Reason: add link

Jas
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