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 Rear brake cylinder bore
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EdinburghJoe
V4 Beginner

United Kingdom
65 Posts

Posted - 05 Aug 2019 :  14:46:08 Show Profile Reply with Quote
Hi all,

Ive stripped the rear hubs on my 1973 96 to fix a brake imbalance (it failed the MOT). I found one of the pistons was seized in the offending wheel, so Im wanting to replace the cylinder and pads on both wheels.

Ive got the cylinders off, and realised that they are 3/4 inch, and the eBay replacement (Borg and beck bbw1551) are 5/8 inch.

Ive read here (and in Haynes) that 5/8 is the right size for the car, but I cant fit them because the end of the brake line will not screw into the new cylinder. Its the right width, but I suspect the thread pitch is wrong. They certainly look similar by eye.

Does anyone know what the difference might be between the thread dimensions of the old and new cylinder? Im going to get a new pipe length made up and it would be handy to know what to ask for!

Thanks,

Joe.

melle
V4 Guru

United Kingdom
2831 Posts

Posted - 05 Aug 2019 :  17:19:59 Show Profile Visit melle's Homepage Reply with Quote
The standard thread is 3/8 UNF; it would surprise me if the new ones are different. Are you sure the threads on the brake hose aren't damaged? Bill at Saabits sells nice stainless HEL brake line kits, if you're a UKSaabs member he'll give you a 10% discount.

Unless there is a lot of pitting in the cylinders, cleaning and reassembly with brake grease normally is enough to give them a new lease of life.

www.saabv4.com
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StefanM
Starting Member

Sweden
34 Posts

Posted - 06 Aug 2019 :  13:46:23 Show Profile Reply with Quote
These lockheed cylinders is pretty common back then and most likely they have used whatever they could find and they had 10mm thread perhaps. Late mini or Ford Transit perhaps or whatever.
The correct V4 cylinders is 5/8" bore with 3/8" UNF thread as mentioned.
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melle
V4 Guru

United Kingdom
2831 Posts

Posted - 06 Aug 2019 :  14:08:04 Show Profile Visit melle's Homepage Reply with Quote
Also see here: http://www.uksaabs.co.uk/UKS/viewtopic.php?f=12&t=193802&p=1828710

www.saabv4.com
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EdinburghJoe
V4 Beginner

United Kingdom
65 Posts

Posted - 07 Aug 2019 :  21:46:53 Show Profile Reply with Quote
Thanks for the replies. I took the pipes and new cylinders to our local garage and he made up a new set of pipes for me, and they definitely fit the new 5/8 cylinders. Ill ask hiim what size he used when I see him for the retest, but Im guessing it would have been 3/8 unf as suggested here, and my old cylinders must have had something different, maybe metric?

Now all Ive got to do is get it all back together (with new shoes) and hope it passes...
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andydeans3
V4 Guru

United Kingdom
1194 Posts

Posted - 22 Aug 2019 :  04:55:40 Show Profile Reply with Quote
Joe

How did you get on with the MOT?

1978 LHD SAAB 96
1978 MGB Roadster
2008 LHD "Classic" Renault Twingo
1991 Nissan Figaro
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EdinburghJoe
V4 Beginner

United Kingdom
65 Posts

Posted - 27 Aug 2019 :  16:19:37 Show Profile Reply with Quote
Passed - thanks for asking!
The brake test printout showed that the rear brakes are now even, though less powerful than before (compared to the previously 'working' side). I guess that will be down to having the smaller bore size, or maybe new shoes not yet bedded in. Anyway, the MOT guy said it was much better so I'm hoping this is now all taken care of.
Joe
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Derek
V4 Guru

United Kingdom
1872 Posts

Posted - 28 Aug 2019 :  12:23:45 Show Profile Reply with Quote
The hand brake is mechanical so the cylinders don't come into play. Yes, should improve a bit as the shoes bed in. Were the rears down a bit when the brake pedal was used? Poor hand brakes often caused by wear in the levers. Very common and can be fixed by welding and redrilling. I think Malbrad has replacement levers, maybe on exchange. Not particularly cheap but time-saving for a quick changeover.
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