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Author Topic: Brake issues - technical question  (Read 461 times)
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DavidHill
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Posts: 18


« on: 10 January, 2022, 09:18:34 AM »

Morning,

After getting my Aprilia on the road after around an 8 yr and counting restoration i found that the brakes were really weak.  So have now taken all the drums off to investigate.  Have found the following: front brakes: drivers side shoes hardly move at all, passenger side shoes also hardly move at all and have a leaking cylinder. Rear brakes: Drivers side both shoes move well, passenger side one shoe moves well, other less so.

So can I conclude that the master cylinder is working ok, or could it be the issue causing both front brakes to hardly move?  (My car is a series two with a master cylinder labelled P25-30.)

cheers
David.
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davidwheeler
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« Reply #1 on: 13 January, 2022, 11:25:05 PM »

I would suspect all the seals and renew the lot.  Get a full set from Omicron, take off all the cylinders, unseize clean and restore them and do the same with the master cylinder which is itself a very simple thing compared with modern ones.    I would renew the hoses whilst I was at it also.    You may also find the aluminium shoes are binding upon the steel pins?pegs? on which they sit because of subtle corrosion.    Waste not 8 years work for threeha'pence. 
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David Wheeler.  Lambdas, Aprilia, Fulvia Sport.(formerly Appia and Thema as well).
simonandjuliet
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« Reply #2 on: 14 January, 2022, 07:32:22 AM »

Also consider sending the cylinders and M/C to "Past Parts" in Bury st Edmonds (from memory) to get it all checked over. They will measure everything accurately and assess what is repairable. Over the years many cars have had 1st ser cylinders added to 2nd ser cars because the later stuff has been more difficult to source.
They have done several sets for me and I've been pleased at both price and service

Happy New Year
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S1 Aprilia Cabrio, S2 Aprilia, S2 camioncino, S2 furgoncino, , R4 Sinpar, R4 Rodeo, '65 Mini Moke,R60 Tractor,R60 S, Moto Guzzi Ercole, Disco 3, Mini ALL4 JCW, Moto Guzzi Cardellino 63,Fulvia Berlina GT, 2019 Royal Enfield Himalayan,JTD Ypsilon - Mathilda
DavidHill
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« Reply #3 on: 14 January, 2022, 04:54:31 PM »

thanks for the replies David and Simon,

I managed to take the whole Master Cylinder off the Aprilia yesterday and today after some battling with a screw that blocks the piston from coming out once the circlip has been removed from the end, i dissembled the master cylinder.  The piston itself looks ok- as do the two seals. But on inspection of the bore i noticed that there is some small corrosion at the far end of the bore...this explains why the rear brakes were moving, but not the front - as the far end of the cylinder is supplying pressure to the front brakes and that's where the small corrosion is!  so now have to see whether it can be re-bored and sleeved or source a new one from Cavalitto's/Omicron....I also plan to replace all the wheel cylinder seals - just in case whilst they are off the car anyway...all the bores look pristine on the wheel cylinders...will keep you posted on progress...

Many thanks
David.
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davidwheeler
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« Reply #4 on: 16 January, 2022, 11:07:46 PM »

My master cylinder has only one outlet, on the end thereof.  Dual brake circuits were not, to my knowledge, employed on Aprilias.    Thus the pressure acts equally on front and back.    I still think your front cylinders/shoes are seized.


* IMG (Copy).jpg (348.87 KB, 758x1050 - viewed 9 times.)
« Last Edit: 17 January, 2022, 09:52:22 AM by davidwheeler » Logged

David Wheeler.  Lambdas, Aprilia, Fulvia Sport.(formerly Appia and Thema as well).
DavidHill
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« Reply #5 on: 17 January, 2022, 05:27:51 PM »

Hi David,
see attached pic of my Mastercylinder.  it has two outlets, the first one going to the rear brakes and the end one to the front. See also in the picture the brass piston from inside the cylinder. This has two seals and two pistons that are connected together via a shaft and a spring..so they can move independently a bit (not much)...so i think either one of the seals is not great, or there is pitting affecting just one seals, or the mechanism that allows the pistons to move slightly is not working? Does that make sense?


* mastercylinder.jpg (2776.97 KB, 3024x4032 - viewed 8 times.)
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lancialulu
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« Reply #6 on: 17 January, 2022, 06:33:57 PM »

Just out of interest where does the master cylinder reservoir feed in?
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Its not the winning but taking part! or is it taking apart?
1955 Aurelia B12
1967 Fulvia 1.3HFR
1972 Fulvia 1600HF
1972 Fulvia 1600HF
1972 1600 Fulvia Sport
1988 Delta 1.6GTi
1998 Zeta
DavidHill
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« Reply #7 on: 18 January, 2022, 08:38:06 AM »

yes good question...from the steel top of the middle pipe out of the cylinder, the brass part of that pipe takes the feed to the rear brakes...
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davidwheeler
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« Reply #8 on: 19 January, 2022, 10:32:30 AM »

Your cylinder is different from mine then and is perhaps a later modification.   Mine (SeriesI/II) has only the single cylinder.  The diagram (Tav.27) is from the series II book.   I am still not sure how it works as all the dual circuit cylinders I have worked with have two pressure outlets and a separate inlet from the reservoir.  Very strange...  Perhaps there is a non return valve in the line from the reservoir?  Otherwise, the pressure would merely displace fluid from the reservoir.


* IMGP4057 (Copy).JPG (589.83 KB, 1400x1050 - viewed 6 times.)
« Last Edit: 19 January, 2022, 10:39:59 AM by davidwheeler » Logged

David Wheeler.  Lambdas, Aprilia, Fulvia Sport.(formerly Appia and Thema as well).
Kari
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Posts: 127


« Reply #9 on: 19 January, 2022, 01:26:40 PM »

The master brake cylinder of David Hill looks like a SABIF P25-30. Here you'll find a description of it and how it functions. Sorry, Italian language.

https://www.registroaprilia.it/wp-content/uploads/2017/05/La-pompa-dei-freni-SABIF.pdf

Its stated that there is one connection at the front for all 4 wheel cylinders and the connection on the centre top accepts the pipe from the reservoir.

I hope that helps.

Karl
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DavidHill
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Posts: 18


« Reply #10 on: 21 January, 2022, 09:00:36 AM »

Dear Kari,

thank you very much for pointing that out. My master cylinder is a Sabif P25-30 and the picture from the TAV does indeed show both front and rea brake lines coming off the same exit from the master cylinder, with the other fitting connecting the master cylinder to the brake reservoir. My rear brake lines were fitted to the reservoir point too, which is clearly wrong! I will have to fix that before refitting the master cylinder.  Many thanks!
David.


* brakes thumbnail_IMG_2752.jpg (548.25 KB, 960x1280 - viewed 9 times.)
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davidwheeler
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« Reply #11 on: 23 January, 2022, 02:27:56 PM »

Thanks for the Tav which I have put into the technical information thread.
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David Wheeler.  Lambdas, Aprilia, Fulvia Sport.(formerly Appia and Thema as well).
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