Replacing wheel cylinders

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James k
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Replacing wheel cylinders

Post by James k »

Hi,

My brakes have started pulling to the left. I have found that one of the right hand cylinders is leaky. All the front cylinders are a similar age so I have decided to replace all the front wheel cylinders and shoes as a precaution.

The procedure as I understand it is:
-Top up master cylinder and block vent hole
-Remove wheel and brake drum
-remove adjusters and shoes
-remove cross pipe between cylinders
-unbolt wheel cylinders
-pull cylinder and hose through backplate and remove flexi hose by turning the cylinder.
-inspect and clean parts
-fit new cylinder to flexi hose with new copper washer.
-bolt cylinders to backplate and refit cross hose.
-refit shoes and drum

I have a few questions on things I'm unsure about:

-Should I bleed the cylinder immediately after replacing or wait until I have done both sides, then bleed the whole system?
-Is there a good rule of thumb for how tight the unions should be?
-If using the plastic bag method to seal the master cylinder, how do you avoid it getting torn up by the threads when refitting the cap and contaminating the fluid?

Any tips would be greatly appreciated.

Thanks,
James
simmitc
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Re: Replacing wheel cylinders

Post by simmitc »

If the flexible hoses are in good condition and fully serviceable (I'm surprised that they don't also need replacing) then the best thing would be to clamp them with a proper brake pipe clamp whilst the cylinders are off, then no need to seal the master cylinder. Bleed each side as soon as you have finished it.
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Re: Replacing wheel cylinders

Post by mowogg »

James

I would replace the flexis at the same time if you can. It's suprising how flexible and spongy they can get. It's the time to replace them. You will not want to go back to them once you have installed the new cylinder.

I have never used brake clamps but I know other do. I put a plastic bag under the master cylinder cap and replace all the cylinders before starting to bleed. I usually bleed a front and rear to make sure no air has got in but always do the front first. Assuming you have standard dot4 fluid it's good to flush the system through in any case

It is handy to have a spare brake pipe to connect the Cylinder should the old ones not come off without damaging

I always add a smear of red brake grease under the cylinder caps whn fitting. It's important to only use red grease hear. I have found this prolongs the life considerably
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Re: Replacing wheel cylinders

Post by King Kenny »

I would agree with the last post. Best to drain the old fluid and refill with brand new when you have finished. It is the only way you can be sure there is no air in the system. You will probably need to replace the old brake fluid anyway.
1969 Traveller in Almond green. Owned since 1979.
James k
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Re: Replacing wheel cylinders

Post by James k »

Hi,

Thanks for the comments. This talk of flexi hoses has put me in a real bind now (pardon the pun). I wasn't planning to replace the hoses - they seem okay and not cracked or bulging - but now I'm thinking that I should do them anyway. The problem is that I didn't buy any so I can't change them tomorrow. Therefore, the choice is between doing the job tomorrow and not changing them or waiting until next weekend so I can order the hoses. The choice seems obvious but not doing the job tomorrow means that I can't drive the car this week.

Although, if I drained and disassembled the system tomorrow and refitted next weekend, I'd know if I also needed to order any new cross pipes.
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Re: Replacing wheel cylinders

Post by Dogsdad »

Hi James. I have just done this job.
I feel that you will be lucky to reuse the bridging pipes.Mine snapped on removal from the cylinders.
The flexi-hoses were very hard to loosen from the cylinders. A good fitting thick open ended spanner and a tap with a hammer
were required (before loosening the cylinder from the backplate.) I find many modern style thin spanner’s can mangle nuts and bolts.
Of course just cut the flexi- hose if you decide to replace them.
Not too bad a job really.
Good luck.
simmitc
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Re: Replacing wheel cylinders

Post by simmitc »

If replacing the flexible hoses, then a good soaking of releasing fluid (such as Plus Gas) on the static end will help to avoid damaging the fixed pipes. Also clean with a wire brush and wash with paraffin to remove all debris. Old installations can get very dirty and bind on the pipe, twisting it as you try to undo the joint. You don;t want to get dirt in your nice new components.
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Re: Replacing wheel cylinders

Post by mowogg »

It's worth bearing in mind you need to break this joint even if you are keeping the flexis
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Re: Replacing wheel cylinders

Post by James k »

Okay, I've decided to do it next week so I can change the flexi hoses. They're not ancient so I'm hoping they come off without too much trouble.

I'm terms of the bridge pipes, if I can loosen the nuts slightly without the pipe bending, can I assume they'll come off undamaged and able to be reused? I'm thinking that I can do this check to work out if I need to order new pipes. I'd like to avoid it if possible to keep the cost down. I've also currently got the short pipes that fit neatly behind the backplate. From what I've read, the new ones are a lot longer and require different routing.

Mowogg, I'm changing the pipes anyway but for future reference, why does the joint need breaking when retaining the hose? I thought it would just stay connected at that end. Also, whereabouts does the grease need to go and how much?

Thanks
simmitc
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Re: Replacing wheel cylinders

Post by simmitc »

It's normal to undo the static end so that the flexi can be unscrewed form the cylinder, but you were proposing to release the cylinder and then pull the flxi pipe through the backplate so that you could unscrew the cylinder from the pipe. I stand to be corrected, but I would describe that as "unconventional" but still a valid approach. Remember to fit new copper washers or at least anneal the old ones is they are serviceable.

Brakes are safety critical and you should not worry about skimping on cost. I do understand how costs mount up, and we've all been there. An interesting point about the spec of the new bridge pipes - it's something that I have not encountered as I always make my own. In the future, you might want to invest in a brake pipe flaring tool so that you can do the same. Most Minor owners build up useful tools over a long period.
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Re: Replacing wheel cylinders

Post by ManyMinors »

Maybe the OP's car is an early model with the 7" brakes? On such cars they did indeed have shorter bridging pipes which fit - rather more conveniently -
to the outside of the swivel pin. Replacement pipe kits do contain the longer pipes which suit the later 8" brakes and travel around the other side of the swivel pin.
James k
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Re: Replacing wheel cylinders

Post by James k »

Hi,

The technique of drawing the pipe through the backplate and unscrewing the cylinder is a tip I've seen a few times on here and seemed like a good method.

My car has 8" brakes but the pipe is not routed around the swivel pin. It just comes out of the cylinders and bends so it's right up against the backplate. Routing around the swivel pin seems like a strange arrangement to me as it prevents removal of the brake assembly without removing the pipe. The pipe also seems like it would be more susceptible to damage in this position. If that's the standard way though, I'll do it that way.

I'll probably invest in a brake flaring tool in the future. I have indeed slowly built up a collection of tools from working on the Morris. Usually, buying the tool is cheaper than paying a garage for the work and then you have it forever.
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Re: Replacing wheel cylinders

Post by mowogg »

Brake flaring tools of sufficient quality to use with cunifer pipes are quite expensive when compared with premade brake pipes.

If you have a standard set up I think you would be better just to buy premade kits for the car or the ones you need.

Your brake pipes sound to routed as bmc installed them from your description. A photo might make it clearer
ManyMinors
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Re: Replacing wheel cylinders

Post by ManyMinors »

I have described the bridge pipe fitting incorrectly in my earlier post: It is indeed the later 8" brakes where the bridge pipe fits around the backplate and to the outside of the swivel pin. It is the earlier 7" brakes where the bridge pipe, rather inconveniently, travels around the inside of the swivel pin. I must be suffering from a combination of old age and too much sun :roll: The bridge pipes for the 7" brakes should be shorter however.
James k
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Re: Replacing wheel cylinders

Post by James k »

Hi,

I've now got the new flexi hoses and bridge pipes and am going to start the job either tomorrow or Monday. I'll probably be doing it in the evening when it's a bit cooler.

I've got some red rubber grease for the cylinders but I'm not quite sure where it should go. Do I need to withdraw the pistons slightly and smear them or just dollop it under the cap?
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Re: Replacing wheel cylinders

Post by myoldjalopy »

Pull the pistons out and grease them and replace before fitting to the car.
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Re: Replacing wheel cylinders

Post by oliver90owner »

myoldjalopy wrote: Sun Jul 17, 2022 10:44 am Pull the pistons out and grease them and replace before fitting to the car.
With the correct lubricant, of course…
James k
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Re: Replacing wheel cylinders

Post by James k »

oliver90owner wrote: Sun Jul 17, 2022 12:45 pm
myoldjalopy wrote: Sun Jul 17, 2022 10:44 am Pull the pistons out and grease them and replace before fitting to the car.
With the correct lubricant, of course…
Red rubber grease, right?
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Re: Replacing wheel cylinders

Post by myoldjalopy »

oliver90owner wrote: Sun Jul 17, 2022 12:45 pm
myoldjalopy wrote: Sun Jul 17, 2022 10:44 am Pull the pistons out and grease them and replace before fitting to the car.
With the correct lubricant, of course…
If you had read through properly, you would have noted that James had already said he is using red rubber grease! :roll:
Yes, James, red rubber grease..........
James k
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Re: Replacing wheel cylinders

Post by James k »

I've just spent a few hours on it and now have everything disassembled. The screws holding the cylinders to the backplate were rounded off so were a bit of a struggle to remove but I got them off eventually and will order some new ones.

The bridge pipe undid absolutely fine but the unions to the flexi hoses were seized to the pipes on both sides so the pipes snapped when undoing.

I'll be able to continue on Tuesday or Wednesday now, once the new pipes and screws have arrived. I'm hoping that, since everything is now disassembled, I won't run into any more trouble!
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