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Rear Brake cylinder connection

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warwick-steve

warwick-steve

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Hi all
I am in the process of stripping down the n/s rear brake drum on my BT7 due to an occasional sticking on of the brakes/handbrake? . After the last run the brake drum was really hot.
The drum is now off and although there is no leakage from the cylinder the piston is pretty stiff so I will replace with a new cylinder. When looking at removing it I noticed that there is no flexible hose to the cylinder. The metal (copper)? line is connected directly to the cylinder but there is a gentle bend/loop before connection presumably to allow the slight movement of the cylinder in the back plate.
The car was professionally restored by someone with a very good reputation so I presume mine isn't the only car done this way. Does anyone else have experience of this and why it would be done as I would have thought it offers unnecessary resistance to the movement of the cylinder. However, up to recently the brakes have worked fine although I note from my records that 4 years ago the cylinder on the offside was also replaced due to "sticking on".
Would be very interested in your comments
thanks
Steve
 
RAC68

RAC68

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Hi Steve,

As I remember, the rear flexible brake hose provides the flexibility for movement of the rear suspension and connects the solid brake chassis line to the solid brake line on connecting the left and right brakes. It is not necessary for there to be flex lines on each slave cylinder as these slaves are solidly fixed to the rear wheel plates and don't move separately from the rear suspension.

Hope this helps,
Ray(64BJ8P1)
 
RAC68

RAC68

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Steve,

Am I missing something? As I understand, the clips holding the wheel cylinders to the brake plate secure the slaves. I do not expect the slave to do any moving as, to do so, would potentially disturb the hard connection and, over time, cause a fluid leak. No matter how the brake line was bent, movement would stress the line and eventually damage it.

I still have my original brake lines in my Healey that date back to 1964 and find their integrity to be still pristine. Although I have rebuilt the slave cylinders, they too are originals. Due to its function and action, I have replaced the connecting flex pipes a few times during the same period. Since my lines and connectors are originals and still have no signs of stress, I can't see how these connections would have any movement as a part of its function and feel the slaves are quite solidly fixed in position once mounted.

Did I misunderstand your response?
Ray(64BJ8P1)
 
steveg

steveg

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Travel is about 3/16" - probably centers once then doesn't move after that:

screenshot.1149.jpg
screenshot.1148.jpg
 
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warwick-steve

warwick-steve

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Thanks Guys
My understanding is that the cylinder must slide in the backplate to perform its centralising action to get both shoes to contact the drum. Steve confirms that the movement is about 3/16 and I assume that the slight partial loop in the pipe before it is screwed into the cylinder body will allow this movement to take place.
From what Ray has said it sounds as though he has the same arrangement i.e. a flexible hose to the 3 way connection on the axle case then solid pipe to each cylinder.
Having looked at the AH parts list which shows the circuit it does look like this was indeed the original configuration. If this is the case I was wrong in my original understanding that there was a short flexible hose to each cylinder. So, I apologise if I caused confusion which was in part caused by a report in a car magazine Austin Healey 3000 Brake overhaul which talks about clamping the flexible hose to minimise fluid loss.
Thanks again for your valuable information
I have now removed the shoes and determined that the cylinder is corroded and in need of replacement I am waiting for a new cylinder to be delivered and looking forward to trying to unclip the locking plates!!!
Cheers
Steve
 
RAC68

RAC68

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Steve,

I agree with you in that, once the wheel cylinder is centered, it stays fixed. It is not a floating component or would not be a candidate for solid line connection. Even a constant 1/16" float would cause stress in the solid lines over time and anything more would make it a candidate for a flex hose connection. Keep in mind that there is no play in the brake line's connection to the slave cylinder and any movement would cause the line to bend. I believe that once secured on the back plate much of the centering, if not all, is compensated hydraulically by the cylinder's piston and is exampled by what happens when the brakes are adjusted.

Good discussion,
Ray(64BJ8P1)
 
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Jack T

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warwick-steve said:
I have now removed the shoes and determined that the cylinder is corroded and in need of replacement I am waiting for a new cylinder to be delivered and looking forward to trying to unclip the locking plates!!!
Cheers
Steve
Click to expand...
Steve, I hope you ordered new clips to go with your new wheel cylinders. By the time you bend, pry, chisel, and beat your old ones off you will probably need them. Whoever came up with the design to hold the wheel cylinders on never accounted for the car to be driven in all sorts of weather and its effect on the clips after several years.

Good luck
 
Bob_Spidell

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"I agree with you in that, once the wheel cylinder is centered, it stays fixed."

Hmmm ... I don't have my shop manual handy, but I recall that it states that the drum brakes are of the 'self-energizing' variety. My understanding of this--marginal at best--is that when the leading shoe is applied it does move slightly to engage the trailing shoe, hence the 'self-energizing'--or servo--effect.

Some discussion here--WRT to Cadillacs--but it explains the principle:

https://forums.cadillaclasalleclub.org/index.php?topic=130490.0
 
RAC68

RAC68

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Good article Bob. It presents the application of a leading shoe and this is also true in the Healey, established through the use of the single piston wheel cylinder.

Considering that the rear brake adjuster is fixed (attached with 2 bolts) and would provide the minimal clearance between shoe and drum. Also, the wheel cylinder has a fixed side and one piston. Now consider that when applying the brakes, force would be initially applied to the leading shoe by the activation of the piston. Once making contact with the drum, the leading shoe and continued piston pressure would now push the cylinder back to apply force to cause the following shoe, attached to the cylinder's fixed side, make contact and apply pressure to the drum. Although this analysis would reflect the presence of wheel cylinder movement, this movement must be small so as not to cause stress on the secured brake line. However, its movement and potential stress effects could be handled if this line movement is transferred over a long enough distance.

Steve, although I still contend that constant 3/16" cylinder movement is excessive and would adjust brakes to keep movement to a minimum (no more then 1/16"). Although I still contend continuous movement could cause stress on the line over time, I do now agree with your initial contention that the wheel cylinder is not solidly fixed as I contended.

Its great to learn something every day,

Ray(64BJ8P1)
 
steveg

steveg

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RAC68 said:
Good article Bob. It presents the application of a leading shoe and this is also true in the Healey, established through the use of the single piston wheel cylinder.

Considering that the rear brake adjuster is fixed (attached with 2 bolts) and would provide the minimal clearance between shoe and drum. Also, the wheel cylinder has a fixed side and one piston. Now consider that when applying the brakes, force would be initially applied to the leading shoe by the activation of the piston. Once making contact with the drum, the leading shoe and continued piston pressure would now push the cylinder back to apply force to cause the following shoe, attached to the cylinder's fixed side, make contact and apply pressure to the drum. Although this analysis would reflect the presence of wheel cylinder movement, this movement must be small so as not to cause stress on the secured brake line. However, its movement and potential stress effects could be handled if this line movement is transferred over a long enough distance.

Steve, although I still contend that constant 3/16" cylinder movement is excessive and would adjust brakes to keep movement to a minimum (no more then 1/16"). Although I still contend continuous movement could cause stress on the line over time, I do now agree with your initial contention that the wheel cylinder is not solidly fixed as I contended.

Its great to learn something every day,

Ray(64BJ8P1)
Click to expand...

Since the cylinder sildes easily, I'd argue the retracting springs would return it to its normal position in the center of the slot. When pressure is applied the cylinder and piston would move equally in opposite directions. I'm guessing the 3/32" travel on either side is more than enough for the shoes to work if properly adjusted.
 
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warwick-steve

warwick-steve

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Hi Jack, being aware of the challenge ahead I did order new clips.
The workshop manual states "The brake shoes are allowed to slide and centralise during braking operation---" My understanding is that as Steve suggested there could be a one off centralising of say 3/16, but under normal braking conditions once the shoes have been adjusted the movement will be very small and easily accommodated by the "flexibility" of the connecting pipe. Important is the ability of the cylinder to slide albeit by a very small amount.
So, the new cylinder has just arrived (I ordered both a reproduction version and a Girling TRW quality one) I was intending to try to match with what is on the other side if I could identify it without removing that drum and returning the other. However I would prefer to fit the better quality one.
Thanks for helping my understanding
Steve
 
Bob_Spidell

Bob_Spidell

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"... I ordered both a reproduction version and a Girling TRW quality one ..."

Please let us know how they compare. I recently installed one of the repops, and was quite happy with its quality.
 
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