[Fot] Rear brake help needed

Fri May 7 16:03:16 MDT 2021

Greg

When we looked at it at the track the knob for the bias was way in the back
on the driver shaft tunnel. I'm sure it is a smooth run from there up under
the bonnet to the bias bar but maybe the cable arrangement could hold a
clue. Might it hang up somehow causing the rears to change to dragging
while getting off and on the peddle? Running with it disconnected would
tell a story.

Bob Kramer

On Fri, May 7, 2021 at 3:01 PM Greg Blake via Fot <fot at autox.team.net>
wrote:

>
> 
>
> Fellow racers and breakers of parts,
>
>
>
> This past weekend we had wonderful racing at Eagles Canyon Raceway.
> Ownership turned over a couple years ago and they have finished a
> multi-million dollar renovation of the track, it is truly amazing now.  ECR
> has always been high on my list because of its potential with the natural
> terrain, but the lack of good construction methods had held it back since
> it opened.  That has all been corrected now and it is truly amazing…well
> enough on that for now.
>
>
>
> *My problem*
>
> For the past two years I have not been able to finish a race weekend w/o
> completely destroying my rear brakes.  Usually related to heat build up
> that manifests as a blown wheel cylinder or brake shoe linings that start
> cracking and chuncking off the shoe causing further rapid wear.  This last
> weekend, I had a total rapid failure of the rear brakes when the right rear
> cylinder let go under hard braking from 100+ mph, I may have blown another
> seal in the drivers compartment when that happened, but will spare those
> details.  Luckily, my dual masters allowed me to get the car slowed
> reasonably with just the front brakes.  For any of you that have had this
> happen before, you understand that with a balance bar setup, you don’t end
> up with full brakes when one end fails.  The balance bar rotates
> significantly to the side that has zero resistance.  In my case I’d
> estimate that I had about 20% of my front brakes available to slow the car,
> like I said, interesting experience that I’d rather not repeat again.
>
>
>
> *My setup*
>
> Twin Wilwood 0.7 master cylinders with a custom balance bar.  Stock front
> TR6 calipers and stock 9” TR drums with 0.75 wheel cylinders (I’ve tried
> everything from 5/8 up to 7/8”).  I also run a hydraulic proportioning
> valve to be able to fine tune the rear hydraulic pressure.  I was running
> with the aluminum rear drums until I destroyed the linings last year in one
> of the incidents when the rear shoe linings cracked and broke completely
> off allowing the shoe to cut groves into the drum linings. My routine setup
> is to put the car on jack stands to adjust the brakes.  I start by running
> the rear drum shoe adjusters in until I perceive slight drag, then back off
> two clicks.  Then I adjust the rear mechanical bias with the balance bar
> until I have the front and rear brakes engaging (dragging) at approximately
> the same point of pedal travel.  I then fine tune the adjustment to dial
> back the rear bias until I can threshold brake at speed and lock the fronts
> slightly before I lock the rears.  This allows me to trail brake with
> confidence that I’m not going to swap ends because of too much rear brake.
>
>
>
> I have used stock, portifield, and TSI drum linings all with the same
> results.
>
>
>
> I’m looking for a couple things from the group (no disc conversion ideas
> please):
>
>    1. What is wrong with my rear brake setup and adjustment approach?
>    2. What is your setup and adjustment approach?
>    3. Do you like the amount of rear brake you get with your approach or
>    is it a compromise to keep the brakes from failing?
>    4. Lastly, I hate our wheel cylinders, its is a terrible design and I
>    think we have real junk on the market today.  I have a theory that the
>    sliding wheel cylinder assemble is part of the root cause of my failures,
>    along with heat.  The piston and seal are dealing with some severe side
>    loading once the cylinder starts sliding around to do its job and I don’t
>    think it is up to the task, especially what we get these days.  Has anyone
>    modified their backing plates and shoes to use a modern day twin piston
>    wheel cylinder that is bolted to the backing plate?  Or has anyone ditched
>    the TR drums all together for another 9” or 10” drum backing plate and guts
>    from another source.  I’m open to all drum brake ideas at this point.  I’m
>    really tired of not racing because of rear brake failures.
>
>
>
> Sorry for the long post and thanks in advance for your ideas.
>
>
> Greg
> _______________________________________________
> fot at autox.team.net
>
> http://www.fot-racing.com
>
> Donate: http://www.team.net/donate.html
> Archive: http://autox.team.net/archive http://www.team.net/pipermail/fot
> Unsubscribe/Manage <http://www.team.net/pipermail/fotUnsubscribe/Manage>:
> http://autox.team.net/mailman/options/fot/rkramer56@gmail.com
>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://autox.team.net/pipermail/fot/attachments/20210507/3e2f0864/attachment-0003.htm>