Drum brakes on rear and large calipers on mid

[emerystora]

>> What about leaving the rear dumbs as they are but replacing the mid drums
>> with 13-inch discs? I would think the mid discs would brake harder than
>> rear drums while the rear drums would still brake some.
>> *John Phillips*
>
John
If people are replacing drum brakes Dave Lenzi’s kit for the large caliper on the mid axle has instructions for leaving the drums on the rear while replacing the drums on the mid. This still allows the use of the original master cylinder which gives more pressure at the rear than the P30 master cylinder.

In my case I had 11” disks on all 4 rear wheels and I had to use the P30 to get enough volume at the rear brakes.
So I decided to go back to the original master cylinder and just eliminate the rearmost brake. I have exceptional braking. The best I’ve ever had sin buying my GMC in 1981.

I am in the middle of installing Dave Lenzi’s kit on the mid axle of Gus Nottberg’s GMC and leaving his drum brakes on the rear so that he’ll still have a parking brake. We are installing Dave’s sensitized booster and a new original master cylinder. When we get it all installed and bled we’ll be able to compare his setup and mine. I’ll report on the result when it’s done.

I have used my new setup on a couple of trips now including going 1600 miles from Denver to Amana and back.

As Matt Colie recently posted, the far rear drums don’t give much braking. That is why the reaction arm was developed.

Dave’s system, in my opinion is a really great solution. It utilizes a massive caliper with two pistons with a 13” disk and was utilized on single rear axle trucks that weighed loaded 30,000 to sometimes even 40,000 pounds. Far greater than our GMC even dragging a toad.

Emery Stora
77 Kingsley
Frederick, CO

 

[jim kanomata1]

Emory,
There are several people in another camp that has been testing and using
the 6 wheel disc with reaction arm that are questioning the massive
intermediate unit as it raises some question.There will be some testing
conducted on the massive unit this Winter using the Lenzi unit to either
disspell the belief one way or other.
Just like the One Ton front end system.

On Sat, Oct 20, 2018 at 9:24 AM Emery Stora via Gmclist <

>

> >> What about leaving the rear dumbs as they are but replacing the mid
> drums
> >> with 13-inch discs? I would think the mid discs would brake harder than
> >> rear drums while the rear drums would still brake some.
> >> *John Phillips*
> >
> John
> If people are replacing drum brakes Dave Lenzi’s kit for the large caliper
> on the mid axle has instructions for leaving the drums on the rear while
> replacing the drums on the mid. This still allows the use of the original
> master cylinder which gives more pressure at the rear than the P30 master
> cylinder.
>
> In my case I had 11” disks on all 4 rear wheels and I had to use the P30
> to get enough volume at the rear brakes.
> So I decided to go back to the original master cylinder and just eliminate
> the rearmost brake. I have exceptional braking. The best I’ve ever had sin
> buying my GMC in 1981.
>
> I am in the middle of installing Dave Lenzi’s kit on the mid axle of Gus
> Nottberg’s GMC and leaving his drum brakes on the rear so that he’ll still
> have a parking brake. We are installing Dave’s sensitized booster and a new
> original master cylinder. When we get it all installed and bled we’ll be
> able to compare his setup and mine. I’ll report on the result when it’s
> done.
>
> I have used my new setup on a couple of trips now including going 1600
> miles from Denver to Amana and back.
>
> As Matt Colie recently posted, the far rear drums don’t give much braking.
> That is why the reaction arm was developed.
>
> Dave’s system, in my opinion is a really great solution. It utilizes a
> massive caliper with two pistons with a 13” disk and was utilized on single
> rear axle trucks that weighed loaded 30,000 to sometimes even 40,000
> pounds. Far greater than our GMC even dragging a toad.
>
> Emery Stora
> 77 Kingsley
> Frederick, CO
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502

 

[emerystora]

Jim

You say Lenzi’s design “raises some question”.

What is that “question”?

I’m happy with it and haven’t noticed any problems.

Emery Stora
77 Kingsley
Frederick, CO

>
> Emory,
> There are several people in another camp that has been testing and using
> the 6 wheel disc with reaction arm that are questioning the massive
> intermediate unit as it raises some question.There will be some testing
> conducted on the massive unit this Winter using the Lenzi unit to either
> disspell the belief one way or other.
> Just like the One Ton front end system.
>
> On Sat, Oct 20, 2018 at 9:24 AM Emery Stora via Gmclist <

>
>>

>>>> What about leaving the rear dumbs as they are but replacing the mid
>> drums
>>>> with 13-inch discs? I would think the mid discs would brake harder than
>>>> rear drums while the rear drums would still brake some.
>>>> *John Phillips*
>>>
>> John
>> If people are replacing drum brakes Dave Lenzi’s kit for the large caliper
>> on the mid axle has instructions for leaving the drums on the rear while
>> replacing the drums on the mid. This still allows the use of the original
>> master cylinder which gives more pressure at the rear than the P30 master
>> cylinder.
>>
>> In my case I had 11” disks on all 4 rear wheels and I had to use the P30
>> to get enough volume at the rear brakes.
>> So I decided to go back to the original master cylinder and just eliminate
>> the rearmost brake. I have exceptional braking. The best I’ve ever had sin
>> buying my GMC in 1981.
>>
>> I am in the middle of installing Dave Lenzi’s kit on the mid axle of Gus
>> Nottberg’s GMC and leaving his drum brakes on the rear so that he’ll still
>> have a parking brake. We are installing Dave’s sensitized booster and a new
>> original master cylinder. When we get it all installed and bled we’ll be
>> able to compare his setup and mine. I’ll report on the result when it’s
>> done.
>>
>> I have used my new setup on a couple of trips now including going 1600
>> miles from Denver to Amana and back.
>>
>> As Matt Colie recently posted, the far rear drums don’t give much braking.
>> That is why the reaction arm was developed.
>>
>> Dave’s system, in my opinion is a really great solution. It utilizes a
>> massive caliper with two pistons with a 13” disk and was utilized on single
>> rear axle trucks that weighed loaded 30,000 to sometimes even 40,000
>> pounds. Far greater than our GMC even dragging a toad.
>>
>> Emery Stora
>> 77 Kingsley
>> Frederick, CO
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
> --
> Jim Kanomata
> Applied/GMC, Newark,CA
> jimk
> http://www.appliedgmc.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

 

[jim kanomata1]

Under severe braking is where we have concern at this moment till we do
testing guided by Rick F and others.
I had not paid attention this till several people started contacting me. So
now we will spend a weekend doing actual pannick stops and see if it is
worth the concern or not.
Just like the One Ton unit.

On Sat, Oct 20, 2018 at 11:59 AM Emery Stora via Gmclist <

> Jim
>
> You say Lenzi’s design “raises some question”.
>
> What is that “question”?
>
> I’m happy with it and haven’t noticed any problems.
>
> Emery Stora
> 77 Kingsley
> Frederick, CO
>
> > On Oct 20, 2018, at 10:58 AM, Jim Kanomata

> >
> > Emory,
> > There are several people in another camp that has been testing and using
> > the 6 wheel disc with reaction arm that are questioning the massive
> > intermediate unit as it raises some question.There will be some testing
> > conducted on the massive unit this Winter using the Lenzi unit to either
> > disspell the belief one way or other.
> > Just like the One Ton front end system.
> >
> > On Sat, Oct 20, 2018 at 9:24 AM Emery Stora via Gmclist <

> >
> >>

> >>>> What about leaving the rear dumbs as they are but replacing the mid
> >> drums
> >>>> with 13-inch discs? I would think the mid discs would brake harder
> than
> >>>> rear drums while the rear drums would still brake some.
> >>>> *John Phillips*
> >>>
> >> John
> >> If people are replacing drum brakes Dave Lenzi’s kit for the large
> caliper
> >> on the mid axle has instructions for leaving the drums on the rear while
> >> replacing the drums on the mid. This still allows the use of the
> original
> >> master cylinder which gives more pressure at the rear than the P30
> master
> >> cylinder.
> >>
> >> In my case I had 11” disks on all 4 rear wheels and I had to use the P30
> >> to get enough volume at the rear brakes.
> >> So I decided to go back to the original master cylinder and just
> eliminate
> >> the rearmost brake. I have exceptional braking. The best I’ve ever had
> sin
> >> buying my GMC in 1981.
> >>
> >> I am in the middle of installing Dave Lenzi’s kit on the mid axle of
> Gus
> >> Nottberg’s GMC and leaving his drum brakes on the rear so that he’ll
> still
> >> have a parking brake. We are installing Dave’s sensitized booster and a
> new
> >> original master cylinder. When we get it all installed and bled we’ll be
> >> able to compare his setup and mine. I’ll report on the result when it’s
> >> done.
> >>
> >> I have used my new setup on a couple of trips now including going 1600
> >> miles from Denver to Amana and back.
> >>
> >> As Matt Colie recently posted, the far rear drums don’t give much
> braking.
> >> That is why the reaction arm was developed.
> >>
> >> Dave’s system, in my opinion is a really great solution. It utilizes a
> >> massive caliper with two pistons with a 13” disk and was utilized on
> single
> >> rear axle trucks that weighed loaded 30,000 to sometimes even 40,000
> >> pounds. Far greater than our GMC even dragging a toad.
> >>
> >> Emery Stora
> >> 77 Kingsley
> >> Frederick, CO
> >> _______________________________________________
> >> GMCnet mailing list
> >> Unsubscribe or Change List Options:
> >> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >>
> >
> >
> > --
> > Jim Kanomata
> > Applied/GMC, Newark,CA
> > jimk
> > http://www.appliedgmc.com
> > 1-800-752-7502
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502

 

[78 Barbi]

Jim K. writes; There are several people in another camp that's been testing and using the reaction arm system that are questioning the massive
intermediate brake unit.

ITEMS TO CONSIDER WHEN UPGRADING TO LARGE MID WHEEL DISCS ON GMC-MH

1/ Frank Condos made the following statement back in Dec. 2000 regarding possible problems one could encounter when using the mid wheel Harrison disc
system.
" The configuration with the large 12.5" discs clearly shifts much of the braking to the rear. Under dry pavement conditions this high percentage of
rear braking may not be a problem. However with wet or icy conditions an emergency stop can cause rear lock up and loss of control with excessive rear
braking (the reason ABS is standard on most pickup trucks)."
2/ One must remember that it's not your rotors, your brake pads or your calipers that ultimately stops your coach , It's your tire patch in contact
with the road surface that stops your coach. For those folk that are relying on 4 discs instead of 6, you are potentially sacrificing 1/3 of your
total braking capacity .
3/ With the design of our forward bogie arm we have not only the standard " pitch forward component " to contend with but also the " pitch forward
component " caused by the " pole vaulting " effect of said forward bogie. Even with 4 OEM rear drums at approx. 950 pounds braking force per wheel ,
it is possible to skid the rear most wheels due to bogie lift. This phenomena has been documentated many times by coach owners, myself included. The
" Reaction Arm " systems eliminated this problem completely and afforded owners maximum braking on all 6 wheels.
4/ With a " pitch forward" component of slightly greater than 50% , one winds up with 6000 pounds plus on the two front wheels , this is where the "
One Ton" front kits shine because they have the capability to address such loads. With that said; this leaves approx . 6000 pounds or slightly less
shared by the 4 rear wheels, But with between 0 and 175 pounds down force on each rearmost wheel , the weight load on the mid wheel set is still
approx. 6000 pounds shared by essentially 2 wheels at maximum braking with an OEM master cylinder at 1,000 PSI.
5/ Depending upon tire composition, temperature , road surface composition and whether the road surface is wet or dry , the friction component between
tire patch and road surface can vary from 0.85 G all the way down to 0.25 G. With the Harrison mid wheel disc system , the braking capability per
wheel at maximum braking of 1,000 PSI on an OEM master cylinder is 2,700 pounds braking force per wheel, assuming the worst case of a full 3,000 pound
load on the mis wheel , 2,700 pounds braking force / 3,000 pounds down force on the wheel , equates to 0.9 G braking force on said wheel. Therefore
even with maximum traction on dry a dry road surface , the Harrison system has the capability of locking the mid wheels in a panic stop situation .
Obviously at a higher master cylinder pressure or a larger rotor or caliper , the risk of lock up would be higher. Therefore the Harrison system
cannot even come close to competing with a reaction arm system when addressing a panic stop on a GMC motorhome , for every day general use the
Harrison system is fine BUT all brake systems are engineered for that ultimate " panic stop " situation . As the old saying goes " Pays your money and
takes your chances" .

Albert Branscombe
78Barbi the 23 foot Birchaven
Tiverton, ON

 

[Ken H.]

For braking safety, there's absolutely no doubt in my mind that reaction
arms on the center wheels are mandatory. And on the rears, 'though they're
no where near as important there.

Of all the brake configurations I've tried, the one I have NOT, but wish
someone would, is no (or only slightly effective) brakes on the center
wheels and "big" brakes on the rears. Fact is, since those braking forces
are opposite the "pole vaulting" of the centers, applied rear brakes
actually tend to apply MORE down-force on the center and rear wheels. How
effectively that fact can be applied is not clear to me; either empirical
tests or simulations are needed. It could be that we should put our
largest brakes at the rear -- even with reaction arms.

Another factor to remember in establishing center and rear braking forces
is that if one of those locations has little braking, those wheels will not
lock up as soon as the other four and will tend to stabilize the rear
("keep it behind the front").

I'm not likely to be doing any more brake tests, nor changes from my
One-Ton and Manny Brakes, but I'm still interested in Y'All's tests -- keep
'em coming.

Ken H.

On Sat, Oct 20, 2018 at 8:56 PM Albert&Sheila Branscombe
wrote:

> ...
> ITEMS TO CONSIDER WHEN UPGRADING TO LARGE MID WHEEL DISCS ON GMC-MH
> ...
>

 

[78 Barbi]

Ken Henderson writes : Of all the brake configurations I've tried, the one I have NOT, but wish
someone would, is no (or only slightly effective) brakes on the center
wheels and "big" brakes on the rears.

Good point Ken, seems a bit weird ( only because nobody's ever tried it ! ), but I don't readily see a down side to it. The braking physics numbers
appears to say it's OK and perhaps rotor cooling
would be enhanced with the bigger brakes on the rear. I know my mids always ran significantly hotter than the fronts due to the forward part of the
rear wheel wells blocking air flow to the mid
rotors. A drum or 2.6" parking brake caliper could be applied to the mid for parking brake use if required . Food for thought, perhaps someone can
chime in as to potential down sides.
Cheers.....Albert Branscombe
78 Barbi, The 23 foot Birchaven
Tiverton, ON

 

[RF_Burns]

My farmboy physics thinks there would still be a rotational force around the rear bogie pin that will transfer weight onto the front bogie. Though
since the front bogie is not lifting there would be more weight staying on the back wheel. The more braking, the more the rear wheel will still lift.

I still think you would be losing braking power compared to more brake power on mid axle.

--
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that

 

[Jim Hupy]

The reason for less braking on the rear/rears is weight transferring to the
front of the coach. Particularly when the front torsion bar adjustment is
out of whack. 40 plus year old springs, be they flat bar, coil wound, or
twisted bar stock, do not improve with constant use or age, either.
Everything in the coach tries to rotate around the front spindle
centerline during braking forces, increasing until tire traction ceases to
exist.
Any mechanical linkage that counters that force is a good thing in
heavy vehicles. Traction bars, floating backing plates or rotors, anti-dive
linkages, all play their parts in this.
Which is superior? Beats me. If it is an improvement over a worn out
stock braking system, it can't be all bad.
It is like Ford vs. Chevrolet. No actual way to prove which is
better. But, that won't stop folks from taking sides in the discussion
about which one is better. Just the way it is, I guess.
Jim Hupy
Salem, Or

> My farmboy physics thinks there would still be a rotational force around
> the rear bogie pin that will transfer weight onto the front bogie. Though
> since the front bogie is not lifting there would be more weight staying on
> the back wheel. The more braking, the more the rear wheel will still lift.
>
>
> I still think you would be losing braking power compared to more brake
> power on mid axle.
>
>
>
>
> --
> Bruce Hislop
> ON Canada
> 77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.1 ton front end
> http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
> My Staff says I never listen to them, or something like that
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>