RE: SER1 1954 86" Series I with SII /109" front axle.

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For predictable results, I'd recommend keeping the braking system consistent
with regard to a wheelbase: all LWB parts or all SWB parts, at least for the
four wheels.  That said, some details for information purposes only:

1) Front wheel cylinder pistons are larger than rears in order to exert more
pressure on the fronts.  On a IIA, 88 front wheel cylinders are used on the
109 rear.  On Series I, the castings are different, but the piston size
follows the idea.
2) The piston size for an SWB master cylinder is smaller than  LWB master,
corresponding to the smaller of wheel cylinders.  If a SWB master is
retained while changing the wheel cylinders, you have increased your
hydraulic advantage for the system.  While the pedal mechanics will exert
the same force on the piston of whichever master cylinder is fitted, the SWB
master has a smaller piston surface area, and the result is actually higher
hydraulic pressure in the braking system.  For example, 50lbs applied to a
piston with a cross section area of 2 square inches will yield a pressure of
50/2 or 25psi; 50lbs applied to a piston with a smaller 1 square inch of
area will yield 50psi.  
3) With a larger piston size, the LWB master cylinder moves more fluid in a
stroke than the SWB master.  Indeed this is handy, as the wheel cylinders in
a LWB are also larger and will use that additional fluid to move them the
same distance as compared to a SWB system.  If you upgrade the braking
system on all four wheels from SWB to LWB but retain the SWB master
cylinder, in addition to gaining braking power, brake adjustment becomes
critical.  As less fluid is moved for the same pedal travel, the shoes will
now move less distance for the same pedal travel and "out of adjustment"
will come sooner.  A saving grace is that once LWB braking components become
bedded in, they stay in adjustment for long periods of time, depending of
course on driving technique.

Again, for informational purposes only; I am not advocating any
modifications.

Randy

> -----Original Message-----
> From: series1-host@xxxxxxxxx.xxx [mailto:series1-host@xxxxxxxxx.xxx] On
Behalf Of
> Jeremy Brooks
> Sent: Wednesday, September 08, 2004 8:38 AM
> To: series1@xxxxxxxxx.xxx
> Subject: RE: SER1 1954 86" Series I with SII /109" front axle.
> 
> Hi Jamie,
> 
> a guideline is to not mix and match LWB and SWB brake components. Wheel
> cyliders and master cylinders in particular are not interchangeable. Your
> current set up is not good - the 2a 109 axle has dual wheel cylinders but
> the original 86" master cylinder cant pressuize them sufficiently.In fact
I
> bet you have worse braking with the 109 axle than you would have with the
> original 86 axle.
> 
> My suggestion is to install a MC from a LWB or to take the 109 LWB axle
off
> and use a SWB axle.
> 
> Jeremy
> 
> From: Jaime Campos <jcamposbb@xxxxx.xx>
> Reply-To: series1@xxxxxxxxx.xxx
> To: series1@xxxxxxxxx.xxx
> Subject: SER1 1954 86" Series I with SII /109" front axle.
> Date: Wed, 8 Sep 2004 15:39:02 +0200 (CEST)
> 
> 
> Hi all,
> I am restoring a 1954 86" SI and I've seen that it has a SII 109 front
axle
> and need some advice about it.
> Is there any problem having different size axles: front 109, rear
> semi-floating 86?
> If there is no problem, will the the 86 master cylinder be OK using 11"
> brake drums? or is it better to use a 107/109 master cylinder?
> 
> 
> Many thanks
> 
> Jaume Campos
> Barcelona (SPAIN)
> 
> 
> 
> 
> ---------------------------------
> 
> 
> 
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