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Old 11-30-2011, 01:13 PM   #43
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It's the right idea, but doesn't it apply more to the front?
Zep
More'r to the rear...offset weight transfer advantage, pretty much.

Bob
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Old 11-30-2011, 10:28 PM   #44
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Quote:
Originally Posted by ROBERT CROSS View Post
More'r to the rear...offset weight transfer advantage, pretty much. Bob
Bob, ol' buddy, you're using flat earth physics. If you put your valve in that way, your back end is going to be leading your front end ... here's a quote from a web site that I have no personal connection to (underlines added by your truly ):
The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.
If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force.
So, more brake pressure to the front.

Over and out,
Zep
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Old 12-01-2011, 12:48 AM   #45
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Quote:
Originally Posted by Zeppelinium View Post
Bob, ol' buddy, you're using flat earth physics. If you put your valve in that way, your back end is going to be leading your front end ... here's a quote from a web site that I have no personal connection to (underlines added by your truly ):
The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.
If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force.
So, more brake pressure to the front.

Over and out,
Zep
Hi, this is close, but not necessarily the whole story. It's not all in the hydraulic pressure going to the brakes. Other factors are that many vehicles had disc brakes in front and drums in the rear. [un-equal brakes] Also vehicles with four wheel disc brakes, such as my Lincoln, have much smaller calipers and brake pads in the rear compaired to the front brakes.

So, more braking force to the front.
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Old 12-01-2011, 05:43 AM   #46
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Originally Posted by ROBERTSUNRUS View Post
Hi, this is close, but not necessarily the whole story. ...
So, more braking force to the front.
Darn, I hate learning something new every day. It's all those pesky little details.

Aside from the issue with front/back brake design on the tow vehicle (I don't think GMC is going to change based on my ideas), I appreciate this discussion because I'm thinking of using disks on my Safari--it already has the '70s disks and I'm wondering if it's worth keeping them (with new Dexter axles) and getting a Carlisle controller, or just going with Dexter. Hmmm.

Man, I though I had you down for the count.

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Old 12-01-2011, 06:43 AM   #47
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Is your old system compatible with the new stuff? Calipers, rotors, etc. Piston diameter and number of pistons plays a roll.

Perry
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Old 12-01-2011, 06:50 AM   #48
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I've been told that the rotors and pads are "maintainable," so evidently parts are available. As far as matching piston diameter to pump output, I need to investigate that, but I don't see any reason that that couldn't be done unless the volume of fluid required exceeded pump capacity.

I just don't know if the bolt pattern will match the Dexter axle--that's the first step. A major reason for wanting to retain the old calipers and rotors is that the new disks (Kodiak, for example) will not fit inside the '70s aluminum wheels.

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Old 12-01-2011, 07:03 AM   #49
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Well if your calipers are good then you might need seals for them. I would recommend DOT5 brake fluid because it will prevent corrosion. I put the stuff in my Eclipse when it was new 20yrs ago and I have never had to replace any wetted brake component. It also won't boil real easily. You will never need to change it.

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Old 12-01-2011, 09:58 AM   #50
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Quote:
Originally Posted by Zeppelinium View Post
Bob, ol' buddy, you're using flat earth physics. If you put your valve in that way, your back end is going to be leading your front end ... here's a quote from a web site that I have no personal connection to (underlines added by your truly ):
The amount of brake force that can be applied to a wheel without locking it depends on the amount of weight on the wheel. More weight means more brake force can be applied. If you have ever slammed on your brakes, you know that an abrupt stop makes your car lean forward. The front gets lower and the back gets higher. This is because a lot of weight is transferred to the front of the car when you stop. Also, most cars have more weight over the front wheels to start with because that is where the engine is located.
If equal braking force were applied at all four wheels during a stop, the rear wheels would lock up before the front wheels. The proportioning valve only lets a certain portion of the pressure through to the rear wheels so that the front wheels apply more braking force.
So, more brake pressure to the front.

Over and out,
Zep

Zep,

More like "level toe-rig" phisicks.

I set up for level with the proper str axle transfer.

TV only,(loaded)

rig no bars

rig WD set for travel

Please....if you see something rong.

Bob
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Old 12-01-2011, 11:50 AM   #51
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Bob,

I think it's impressive that you actually checked the effectiveness of your WD setup. I don't do that--I know approximately what the tongue weight is for each of my Airstreams and I use the appropriate WD bar, then just hitch the chain up until the rig comes back up to level. I'm different in another way, too, in that my diesel is always heavier on the steering axle.

I don't think it's critical to get the load on both TV axles the same, just get the rig back to level (which tells you you've done a good job of distributing the tongue weight proportionally). With the Airstream attached, you don't get the forward pitch (eg, rotation which lifts the tail slightly) of the TV when you slam on the brakes, so you don't get the same amount of weight transfer, but you do get some. So it's good that your steering axle is slightly underloaded under static conditions.

I'm no expert, it would be great if a vehicle dynamics person chimed in here. I sure don't see anything wrong--your setup looks good to me.

I don't know if you use an anti-sway damper. It's always recommended, but my TVs are both diesel so the Airstreams never seem to have any tendancy to sway (even in 50 kt crosswinds in Kansas this spring that unrolled the Zip Dee out of storage along I-70--the Airstream remained calm [not me, of course]), and they sure don't control the trucks, the trucks are always in control. That being said, if you experience any sway that doesn't die in 1/2 cycle, you need to add the anti-sway bar. It may also be helpful to transfer a bit more weight forward with heavier WD bars (based on the lighter loading of your steering axle), but this is something an expert ought to comment on.

I also tow with a lighter TV, an Explorer, and the best I can do is get it level, use an anti-sway bar, and keep the speed below 60. The wheel base is too short to do much else.

Zep
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Old 12-01-2011, 12:16 PM   #52
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Originally Posted by ROBERT CROSS View Post
Zep,

More like "level toe-rig" phisicks.

I set up for level with the proper str axle transfer.

TV only,(loaded)

rig no bars

rig WD set for travel

Please....if you see something rong.

Bob
Bob.

Ideally, there should be a balance between the front and rear axle on the tow vehicle.

However up to a ten percent difference of the total weight of the tow vehicle weight can be on the rear end, but no more.

By your numbers, the tow vehicle is 8320 pounds.

Therefore the rear axle can be no more than 832 pounds heavier than the front axle. If it is greater, the steering suffers.

Your numbers show a difference of 1040 pounds.

That means 208 pounds needs to move, divided by 2, or 104 pounds.

Adding that 104 pounds to the front axle, leaves the rear axle with 104 pounds, making the transfer of weight at it's maximum difference.

Again, ideally your rig would handle better if you moved 200 to 300 pounds forward.

Andy
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Old 12-01-2011, 01:34 PM   #53
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Welcome back Andy did you have a nice vacation?

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Old 12-01-2011, 01:42 PM   #54
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Welcome back Andy did you have a nice vacation?

Perry
I didn't go anywhere.

The next big trip is in March.

Andy
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Old 12-01-2011, 02:54 PM   #55
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Nice to see scale tickets, RobertCross

Per the ever-handy Ron Gratz chart:

Weighing #1 -- TT attached and Weight Distribution Activated

Let Front Axle Load be "FA1" 3640

Let Rear Axle Load be "RA1" 4680

Let TT Axles Load be "TT1" 7640

Then, while in same position on scales, take
Weighing #2 -- TT attached and Weight Distribution Not Activated

Let Front Axle Load be "FA2" 2980

Let Rear Axle Load be "RA2" 5520

Let TT Axles Load be "TT2" 7480

Then, drive off scales and drop TT. Return to scales and take
Weighing #3 -- TV only -- TT Not Attached

Let Front Axle Load be "FA3" 3740

Let Rear Axle Load be "RA3" 3600

From the above values, you can calculate:

TV weight = FA3 + RA3 7340

Gross Combined Weight = (FA1 + RA1 + TT1)
- should also be equal to (FA2 + RA2 + TT2) if scale weights are correct

[15,960]
[15,980]

TT Weight = Gross Combined Weight - TV Weight 8,640

Tongue Weight = (FA2 + RA2) - (FA3 + RA3), or

8500 - 7340 = 1,160 [13.6%]

Load Transferred to TT Axles
when WD System in Activated = TT1 - TT2 160

From a baseline FA 3,740
To a hitched 3,640
With an interim 2,980
Achieved 97% of unhitched value [short 100/lbs]

The rule of thumb nowadays is 75/25 as the TW is distributed onto the rear axle and TT axles where the FA remains at the unhitched weight. Your TV manufacturer instructions (Tow Guide) are the lead, here.

Looks like room to play with, TT especially, and FA somewhat.



If we use the older formula of 1/3 - 1/3 - 1/3 as a start, then:

Of a TTW of 1,160-lbs, (one-third being 386#)

We would assume (from values above)

FA 4126
RA 3986
Total: 8,112

TT 7866

Looks like even more to play with. To slay the dragon means to have tried all possible configurations as suggested by the numbers.



Bob.

Ideally, there should be a balance between the front and rear axle on the tow vehicle. However up to a ten percent difference of the total weight of the tow vehicle weight can be on the rear end, but no more.

By your numbers, the tow vehicle is 8320 pounds. Therefore the rear axle can be no more than 832 pounds heavier than the front axle. If it is greater, the steering suffers.

Your numbers show a difference of 1040 pounds. That means 208 pounds needs to move, divided by 2, or 104 pounds. Adding that 104 pounds to the front axle, leaves the rear axle with 104 pounds, making the transfer of weight at it's maximum difference.

Again, ideally your rig would handle better if you moved 200 to 300 pounds forward.

Andy



As Andy suggests (and what I can perceive) I think you could have some fun in making more/different adjustments. Check my math, the phone rang

There's the [1] white-knuckled SOB hitch-up; [2] the palm-of-the-hand-firmly-against-rim-adjustment-with-no-close-traffic; and, [3] the yawning sort-of-a-fingertip-on-the-wheel-as-two-big-rigs-rush-by-with-a-hairy-crosswind-otherwise adjustment.

Would be nice to see the TV door sticker numbers for:

GAWR, FF & RR
GVWR
GCWR

.
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Old 12-01-2011, 03:41 PM   #56
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(edit time cutoff)

The rule of thumb nowadays is 75/25 as the TW is distributed onto the rear axle and TT axles where the FA remains at the unhitched weight. Your TV manufacturer instructions (Tow Guide) are the lead, here.


TW is 1,160-lbs

With WDH activated, then

290-lbs onto the TT axles
870-lbs onto the TV axles
(with FA returning to unhitched value), or,

TV = 8,210
TT = 7,770

From scale tickets,

TV = 8,320
TT = 7,640

Difference:

TV = 110# over
TT = 110# under

The scale tickets show 160# "transferred" onto TT axles, and we would be looking for near to 290# for the "75/25" rule. (130# short)

Then, up to 386# assuming I have the old "1/3" rule correct. (The usual scale discrepancies of 10-20-40 pounds per different tickets factored in). (220# short)

The door sticker numbers will show overall how much one can play with per axle.

I haven't played with Andy's numbers polish, but am digging using it as a final guide.

As before, I see working the numbers as a baseline. From there it is a matter of more scale tickets to verify the general working range, tire pressure adjustments, and some up/down/around WDH fine-tuning to get the best feel given experimentation via road, load, weather, etc. Asphalt and gravel; windy, etc. Gotta have a baseline to return to each time.

.
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