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Drum To Disc Conversion Hints And Tips Please


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#1 unburntfuelinthemorning

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Posted 04 December 2019 - 07:10 PM

I've worked on plenty of cars with disc brakes but the Minis I've had have all had drums so I've never worked on Mini disc brakes.

 

Is the information about the brakes in the Haynes manual sufficient or are there other things to consider when working on them which the Haynes manual doesn't tell you about?



#2 nicklouse

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Posted 04 December 2019 - 07:33 PM

Nothing else really. 
 

the drive shafts are the same so you only need to change the CVs.



#3 Moke Spider

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Posted 04 December 2019 - 07:39 PM

One thing that's likely in there but not well high lighted is the Rear Wheel Cylinders will also need to be swapped out.

 

5/8" Cylinders will be fine with any Disc Brakes, as long as you are running some sort of Rear Wheel Brake Shut Off Valve.

 

There can be some small (very small) advantage to possibly going to 11/16" Cylinders with some set ups.



#4 cal844

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Posted 04 December 2019 - 08:16 PM

Just curious, what rear cylinders would be recommend for a 1980 estate, (Black tag MC, FAMwtf front to rear split system) with S disc conversion...


Apologies for the thread hijack but it saves cluttering the forum

#5 Moke Spider

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Posted 04 December 2019 - 11:11 PM

Just curious, what rear cylinders would be recommend for a 1980 estate, (Black tag MC, FAMwtf front to rear split system) with S disc conversion...


Apologies for the thread hijack but it saves cluttering the forum

 

Cal, you'll be safe with 5/8" Wheel Cylinders, but sometimes Estates and Vans, being a little longer and with possible loads in mind, may benefit from 11/16" Cylinders. Of course, the 'thing' to look out for is locking of the rear wheels, which you want to avoid under any circumstances.



#6 unburntfuelinthemorning

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Posted Yesterday, 10:40 AM

The Haynes manual says to tighten the hub nut with the wheel on the ground but is it not better to tighten it whilst the wheel can still be turned to check for bearing bind?

 

I'll have to check what rear wheel cylinders I have.  Whatever size they are they have been great for use with drums on the front as they show a high efficiency on the MOT rollers but never lock before the fronts.

 

I've always been confused about the best size to fit, I thought the 3/4" bore ones would be the ones as Minispares says 'as fitted to all cars from 1970 except "S" '.

 

I have the FAM7821 limiter valve fitted, does the above advice about bore size assume this is fitted, or not, or does it make no difference to the required wheel cylinder size?

 



#7 cal844

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Posted Yesterday, 10:52 AM


Just curious, what rear cylinders would be recommend for a 1980 estate, (Black tag MC, FAMwtf front to rear split system) with S disc conversion...


Apologies for the thread hijack but it saves cluttering the forum


Cal, you'll be safe with 5/8" Wheel Cylinders, but sometimes Estates and Vans, being a little longer and with possible loads in mind, may benefit from 11/16" Cylinders. Of course, the 'thing' to look out for is locking of the rear wheels, which you want to avoid under any circumstances.

I can lock all 4 wheels but the pedal has a fair amount of travel before locking the wheels. The fronts lock up before the rears so that's a good thing 😁

#8 sonscar

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Posted Yesterday, 01:32 PM

I like to tighten wheel bearings whilst turning the wheel so you can detect any premature binding and also to spread the load on the balls/rollers.You will probably need it on the ground to achieve the final torque.Steve..



#9 Moke Spider

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Posted Yesterday, 05:47 PM

The Haynes manual says to tighten the hub nut with the wheel on the ground but is it not better to tighten it whilst the wheel can still be turned to check for bearing bind?

 

I'll have to check what rear wheel cylinders I have.  Whatever size they are they have been great for use with drums on the front as they show a high efficiency on the MOT rollers but never lock before the fronts.

 

I've always been confused about the best size to fit, I thought the 3/4" bore ones would be the ones as Minispares says 'as fitted to all cars from 1970 except "S" '.

 

I have the FAM7821 limiter valve fitted, does the above advice about bore size assume this is fitted, or not, or does it make no difference to the required wheel cylinder size?

 

I'm not sure why the Haynes suggest tightening the Nut with the wheel on the ground, an assumption here is that it's an easy means of locking / holding the hub 'still' to torque the nut up. It does need a fair bit of holding force.

 

I used to do it this way in the early days and it works OK, but these days, I have a holding jig and so I can do them on the bench.

 

In regards to the Wheel Cylinder Size, what you read on the Mini Spares site, while incomplete, is correct. Where it's incomplete is that the 1275GT also would not have used 3/4" Cylinders as it too was fitted with Discs. I'm sorry here too, I think I gave you a bum steer. Looking in the one Haynes Manual I have (the Blue covered 59 to 95 one) it's a bit light, actually, very light, on information. It's not all in the Haynes Manual !!

 

I've just trawled through some of the easy access Factory Info and while it's there, it's very easy to get confused from it the way the UK info is laid out. The Australian Data is considerably better, but could be confusing to apply to UK built Cars and Models.

 

Basically it's like this;-

 

Front Brakes              Rear Wheel Cylinder Size

 

Drums                                  3/4"
Discs with Limiter Valve        5/8" and in some cases, 11/16" * (5/8" is 'safe')
Discs without Limiter Valve   1/2"

 

* The 11/16" Cylinder is generally used when a Stepped Bore Tandem Master ('Yellow Tag') is fitted, but can be worthwhile trying in other Disc Brake set ups, as it wasn't exclusively fitted here.

 

To further confuse matters here, there was at least 6 different Rear Limiter Valves used in the Single Circuit set ups, from 250 PSI to 450 PSI (250, 340, 350, 370, 390, 450 Shut off PSI), . The choice here comes down to many factors related to Hydraulic Pressure developed in the system and the wheel base / use for the intended vehicle. a simple way out, is to fit a low pressure Valve or an adjustable type. Note though, that an Adjustable Valve does have limits and is only really a fine tune on the Correct Rear Wheel Cylinder size, it's not a substitute for that.

 

 

 

 

 

 

Just curious, what rear cylinders would be recommend for a 1980 estate, (Black tag MC, FAMwtf front to rear split system) with S disc conversion...


Apologies for the thread hijack but it saves cluttering the forum


Cal, you'll be safe with 5/8" Wheel Cylinders, but sometimes Estates and Vans, being a little longer and with possible loads in mind, may benefit from 11/16" Cylinders. Of course, the 'thing' to look out for is locking of the rear wheels, which you want to avoid under any circumstances.

I can lock all 4 wheels but the pedal has a fair amount of travel before locking the wheels. The fronts lock up before the rears so that's a good thing

 

 

All the same, it does seem to me there's still too much rear brakes here.



#10 DeadSquare

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Posted Yesterday, 05:59 PM

When racing, I used to put a ball bearing in the mouth of the input pipe to the limiter, so that the rear brakes didn't work at all.

 

Much safer than having a lock-up and loosing the back-end.



#11 unburntfuelinthemorning

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Posted Yesterday, 07:23 PM

If I stick discs on the front I probably don't need any rear brakes but as I have to have them 5/8" bore wheel cylinders sound like a reasonable size to use if I'm understanding correctly.  I have the yellow tag master cylinder.

 

Anyone got a drawing of the internals of the FAM7821?   I've always wondered what's on the inside.



#12 unburntfuelinthemorning

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Posted Today, 10:31 AM

Anyone got a drawing of the internals of the FAM7821 brake limiter?   I've always wondered what's on the inside.

Or has anyone got any photos of one that has been dismantled?



#13 nicklouse

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Posted Today, 10:54 AM

 

Anyone got a drawing of the internals of the FAM7821 brake limiter?   I've always wondered what's on the inside.

Or has anyone got any photos of one that has been dismantled?

 

similar

https://www.moke.com.../90-5-way-valve






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