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Close Call: Full Breaking Spun Me 90*


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#1 luismx123

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Posted 17 April 2019 - 12:40 PM

Hey all,

Well, as the title says, I had to do a full break on a country road. It got kinda hairy as the car started spinning clockwise. I managed to catch it before losing the tail and having me go off the road...

Is there a way to adjust the brakes sothat this wont happen again?

Im driving a 1990 998 with 7.5 discs upfront and drums in the rear. Also, its a LHD vehicle. 

Thanks



#2 cal844

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Posted 17 April 2019 - 12:45 PM

Did it lock the rear wheels? You may have it over adjusted

#3 luismx123

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Posted 17 April 2019 - 12:54 PM

Did it lock the rear wheels? You may have it over adjusted

not exactly sure. The rear began over-taking me so Id guess so.

How do i do that?



#4 Icey

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Posted 17 April 2019 - 01:17 PM

 

Did it lock the rear wheels? You may have it over adjusted

not exactly sure. The rear began over-taking me so Id guess so.

How do i do that?

 

 

You can't adjust the brake balance but noticing you're running 7.5" setup on a later Mini, did you check what size rear break pistons are required? If you have too much rear break effort you'll need to change them.



#5 Ivor Badger

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Posted 17 April 2019 - 01:17 PM

Got to be careful doing what you did to the brakes with a split braking system. If the same as one I did, there was no brake limiting valve on the rear. Had to pipe the system as separated front/rear and not diagonal split. There has to be a better/ more legal way now, I did it many years ago with less restrictive type approval.

#6 luismx123

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Posted 17 April 2019 - 01:24 PM

 

 

Did it lock the rear wheels? You may have it over adjusted

not exactly sure. The rear began over-taking me so Id guess so.

How do i do that?

 

 

You can't adjust the brake balance but noticing you're running 7.5" setup on a later Mini, did you check what size rear break pistons are required? If you have too much rear break effort you'll need to change them.

 

 

This all sounds chinese too me so I'm guessing I havn't :/
What am I looking for here? Id like to read up on some infos but not sure where to start



#7 viz139

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Posted 17 April 2019 - 02:04 PM

If all the above sounds Chinese to you I would suggest you leave it to an expert. You had a lucky escape this time, many don't. Assuming you still have a dual master servo with the 7.5 discs this setup was never fitted as standard on any mini and so you need to know what if anything was done with the whole system.



#8 Icey

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Posted 17 April 2019 - 03:56 PM

 

 

 

Did it lock the rear wheels? You may have it over adjusted

not exactly sure. The rear began over-taking me so Id guess so.

How do i do that?

 

 

You can't adjust the brake balance but noticing you're running 7.5" setup on a later Mini, did you check what size rear break pistons are required? If you have too much rear break effort you'll need to change them.

 

 

This all sounds chinese too me so I'm guessing I havn't :/
What am I looking for here? Id like to read up on some infos but not sure where to start

 

 

Start with this:

 

https://www.calverst...ias-adjustment/

 

...and see where you get to. The general gist is that the Mini breaking system is balanced by matching master cylinder to front calipers to rear pistons. If you change one component you need to understand how it has affected the overall pressure generated in the system when you press the pedal.

 

As a general rule, the smaller bore rear cylinders will generate less brake effort. So once you know what you have you can look at replacing them with a smaller option. As an example, on a Yellow tag master with Metro 4-pots I had to use GWC1126 pistons (the smallest there is - 1/2") to stop the rears locking under heavy breaking.

 

While I generally recommend people do their own work, this is a safety critical system and this is all 'at your own risk' - so if you don't feel comfortable, you should have a suitable mechanic either confirm the details or do the work.



#9 johnR

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Posted 17 April 2019 - 05:03 PM

Spelling alert - devices to arrest movement of car = brakes, result to car if they don't = breaks :)

#10 paulrockliffe

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Posted 17 April 2019 - 08:02 PM

Is it possible to fit an adjustable bias valve for the rear brakes and use that to dial out rear locking if you take it somewhere safe to try some emergency stops?

#11 Moke Spider

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Posted 17 April 2019 - 08:10 PM

For that set up, I'd suggest just fitting 5/8" rear wheel cylinders.

I'd almost certainly say this is the issue.



#12 sonikk4

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Posted 17 April 2019 - 08:18 PM

OP you need to clarify exactly what your brake setup is. Post a picture of your engine bay to let us see what setup you have. 

 

At the moment we are guessing and as this is safety critical you need to stop driving the car.



#13 cal844

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Posted 17 April 2019 - 08:44 PM

OP you need to clarify exactly what your brake setup is. Post a picture of your engine bay to let us see what setup you have.

At the moment we are guessing and as this is safety critical you need to stop driving the car.


This is good advice, I'd also say to do research on the sizes required

#14 luismx123

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Posted 18 April 2019 - 07:53 AM

 


 

Start with this:

 

https://www.calverst...ias-adjustment/

 

...and see where you get to. The general gist is that the Mini breaking system is balanced by matching master cylinder to front calipers to rear pistons. If you change one component you need to understand how it has affected the overall pressure generated in the system when you press the pedal.

 

As a general rule, the smaller bore rear cylinders will generate less brake effort. So once you know what you have you can look at replacing them with a smaller option. As an example, on a Yellow tag master with Metro 4-pots I had to use GWC1126 pistons (the smallest there is - 1/2") to stop the rears locking under heavy breaking.

 

While I generally recommend people do their own work, this is a safety critical system and this is all 'at your own risk' - so if you don't feel comfortable, you should have a suitable mechanic either confirm the details or do the work.

 

ah thanks! Ill have a read up in the future.
I did the fronts myself and bled the system so that wasnt too hard. Also replaced the rear shoes and serviced the rear brakes under the supervision of a 30yr+ mini restorer friend guy. I guess he forgot to mention swapping the rear cylinder but thats ok. 

I really wasnt aware that there were different cylinders.I thought it would be adjustable via some sort of valve or similar...woops!

 

 

OP you need to clarify exactly what your brake setup is. Post a picture of your engine bay to let us see what setup you have. 

 

At the moment we are guessing and as this is safety critical you need to stop driving the car.

 

Ive added 2 old photos from a while back but nothing changed since then.
Are these sufficient?
 

Attached Files



#15 Ethel

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Posted 18 April 2019 - 08:40 AM

Can we assume there's a FAM7821 brake valve hiding under the servo? If there is your only options are smaller wheel cylinders or replace it.

 

Of course, lacking ABS, there's always the possibility of locking up the rear particularly on loose or uneven surfaces. Start by servicing and checking the rear brakes, handbrake cables... They can get out of balance pretty easily.






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