Caledonian Chipmunks

Author Topic: Brake Dilemma  (Read 349 times)

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Offline yakxx

  • Posts: 171
  • Country: pt
Brake Dilemma
« on: Sunday September 16, 2018, 09:18:39 UTC »
Having just completed a 2500 mile wonderful Chipmunk trip I experienced a rather strange brake issue and before I tear out the whole system I would welcome any comments ... ( I also had a trim cable jam or break which meant the last 900 miles without trim control...just manually set to works pretty well ) ....back to brakes:   It happened twice and both at the same airfield in Spain which happens to be 3000ft and to taxi to the pumps takes at least ten minutes of zig, I reached the pumps and applied left brake I had absolutely no pressure....had to hit mags off and hit the right brake  which of course swung me around the other way just missing the pumps and the fuel man who thought I was insane....I say it happened twice because on an earlier visit the same  brake became soft but workable , but this time I had absolutely no pressure...I pumped and pumped..nothing, then after about ten minutes pressure started to come back and then it was normal...I then flew another 500 miles stopping many times without would seem it may have overheated but why zero pressure....If the pads had stuck in or out....I should still have pressure....If its the master cylinder why would it happen and then come back.....both times after a long taxi....and at 3000 elevation.   Brake fluid tank is full....I can only think that its a seal issue in the master...but why would the brake come to life after sitting stationary for ten minutes........air bubbles in the line boiling like an F1 car.....dont think so.....naturally I will be replacing the total system , seals  ....but would love to hear any comments....
On the trim cable.....I haven't even taken a look yet.....after two solid weeks flying, I dont want to see her.....for a few days

Offline Bob

  • Posts: 348
  • Country: 00
Re: Brake Dilemma
« Reply #1 on: Monday September 17, 2018, 21:04:42 UTC »
I'd go for boiled fluid due altitude/temp.I take it they are the original Dunlops?

Offline speedbird1

  • Posts: 541
  • Country: us
Re: Brake Dilemma
« Reply #2 on: Tuesday September 18, 2018, 00:27:39 UTC »
A friend here in the US just had a similar issue when he had to taxi a very long way, with a crosswind, at a major airport.  5606/OM15/DTD585 will do this when it gets hot and Dunlop brakes don't help either.

Offline yakxx

  • Posts: 171
  • Country: pt
Re: Brake Dilemma
« Reply #3 on: Tuesday September 18, 2018, 16:48:47 UTC »
Yes, very similar....big crosswind and at least ten minutes taxi....

My system has always used DOT 4 ( Car fluid) ...for the last 25 I dont want to change to Red aircraft fluid now unless I change all the seals right through.....

thanks for your comments ....

Offline Dick Gower

  • Posts: 293
  • Country: au
Re: Brake Dilemma
« Reply #4 on: Tuesday September 25, 2018, 07:05:29 UTC »
Doesn't car fluid absorb water over time and this lowers the boiling point?  A friend of mine had this happen in a car until he learned not to drive like Fangio.
Dick Gower

Offline speedbird1

  • Posts: 541
  • Country: us
Re: Brake Dilemma
« Reply #5 on: Tuesday September 25, 2018, 15:38:42 UTC »
So does OM15/DTD585/5606.  ie: the Red stuff, absorbs water as well.
I have seen several stuck pistons in accumulators that don't get operated very often and it is always corrosion where the water sat under the piston and its seals.  Also the accumulators were mounted horizontally.
Speedbird 1.

Offline Nigel Stevens

  • Moderator
  • Posts: 245
  • Country: fr
Re: Brake Dilemma
« Reply #6 on: Friday September 28, 2018, 11:56:32 UTC »
Agree sounds like boiling brake fluid. Car brake fluids do absorb water over time. Most high performance cars now  have recommendations to flush the old brake fluid out of the system with new fluid on either a two or four year cycle. This may apply to low performance cars as well!!!!   Pressure pump systems are avaialable which fit on the car master cylinder and then force the new fluid through until clean new fluid comes out of the purge fittings. Unfortunately they are too large to fit on the Chipmunk MC without some modifications, but flushing new fluid through should cure the problem.

Offline rod brown

  • Posts: 2
  • Country: gb
Re: Brake Dilemma
« Reply #7 on: Saturday October 13, 2018, 22:58:21 UTC »
Nigel has hit the problem head on and best suggestion would be to change the fluid for some new DOT
4. Chances are that it will be old and dis-coloured. Having read about brake bleeding problems here
on Cal Chips some time ago I found it best to draw out the old fluid from the reservoir, fill up with new fluid and bleed one side at a time until new fluid flowed through.
Research shows that DOT 4 has a temperature range a bit higher than the Shell Type 41 which has
replaced DTD 585 here in the UK so not much point in changing the fluid type. There is some good
information available from Shell by typing DTD 585 or  into Google.

Offline devonchip

  • Posts: 5
  • Country: gb
Re: Brake Dilemma
« Reply #8 on: Sunday October 14, 2018, 16:30:50 UTC »
We have had a similar issue that turned out to be the brake push rod jamming against the master cylinder circlip tags.  We had all the symptoms of brake fade/ fluid
issues etc. Brakes would not bleed because the piston was not returning fully.


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