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Rear brake imbalance. (drums on my mini)


mjrstar

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So I took the mini for some wof action this morning, and the only thing it failed on was rear brake imbalance, due to the miniature size of the umboosted drums it managed a whopping 90 on the r/h and 40 on the l/h.

Oddly it is for both the handbrake and the foot brake (exactly the same figures)

So as you can see this is outside the 20% imbalance.. which is a bit of a pain in the arse because it only give me a maximum allowable difference of 19 left/right.

I have scuffed up the drums and shoes and taken it back for a recheck and it's still no good..I'm happy that i have the adjusters set correctly.

I have since chucked some new pads in it and swapped drums from side to side. and will be taking it back AGAIN tomorrow..

I had planned on getting the drums machined but the brake shop didn't want to do them due to not having a taper in the centre bore?? they also said they looked ok (they have probably done less than 2000 miles in the last 10 years)

So basically i'm after any other sneaky tricks I can try to get this sorted out, i had contemplated getting the drums sand blasted since machining was not an option in case my sand-papering was not enough to remove any glazing..

Also i am un-keen to take to another wof shop which does not have rollers as the car was not picked up for any other faults.

Cheers

Matt

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new shoes and swapped drums should have sorted it. get the brakes nice and warm before you turn up. also slam it on another set of rollers if it still happens. perhaps the low weight and braking effort a mini has is too intricate for a slightly out of sync brake rollers.

scuffing up old shoes may not be the key. if anything you should swap one from each sdide. somebody may have relined one side at some point, perhaps witha slightly differnt COF of lining, or had one side contaminated by a slightly leaking wheel cylinder at some stage. looks like a shoe problem to me, though.

with the new shoes: take it for a good run with lots of light braking, not getting them tooooo hot, to bed them in to the unmachined drums first. tell the guy that you've done a reline on it before it goes over the rollers.

also of note : equalise tyre pressures and make sure even the tread pattern and depth is the same. I've seen a vehicle get thrown out @ 20% imbalance for that alone. hah.

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Fingers crossed for tomorrow....

good point on the tyre pressures dude.. I also noticed that due to a reasonable about of slam the car is almost touching the middle of the machine between the rollers when it squats.. so we played with the position of the car a bit (both left and right)

It HAS to be a friction based problem as the handbrake takes the hydraulic side of things out of the equation.. Had considered cranking the adjusters up some more although did not want to cook the poor little drums. I also had a go on the machine and applying progressively more pedal pressure (compared to the weak old man) I was able to get them a bit closer than the was (about 90 & 65).

The plus side is the bunch of old fellas at the testing station are all pretty good blokes and were willing to fiddle with the test a bit to try and get a better reading.

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Scuffing up the drums wont have much effect.

I used to cunt around with trying to patch up shit brakes. But nowdays I just get the drums skimmed, buy new shoes, and replace wheel cylinders. I get discs/drums machined for $20 a pair. and the last time I did rear up, I paid $20 for wheels cyls, and about $25 for shoes. assemble, then set and forget.

Unless you are uber poor, I would just fix it properly.

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I had planned on getting the drums machined but the brake shop didn't want to do them due to not having a taper in the centre bore??

Matt

Yeah I have no problems with doing things properly.. I took the drums to a brake and clutch shop in frankton today but they were unkeen to give them a machine up, i even tried to find some replacement cooper s drums but they just looked at me funny...

The drums were brand new when i certed the car and mileage has been minimal, (750 miles in the last 5 years) 8) they do still look like new inside..

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^ yuh i always use emery tape to clean off any glazing, and finish with a good rinse with brake cleaner.

works well.

always do 30 or 40km while making heaps of brake applications (i'm tlaking distance of normal speed drivng, not drive at 30-40kph) to bed them in to any small imperfections in the drum. unless they're scored quite badly they wont need a skim. even then, skimming alters how much of the shoe's circumference will contact it.

sounds like you'er on the right track, though.

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Sounds like you have tried the usual tricks, did you replace shoes on both sides? It not the other side reading too high?

If the other sides shoes have been contaminated you will never get them equal, and last face it Mini brakes don't normally trouble those machines the needles barely move. If all new shoes then as above take it for a decent drive, I use the handbrake to slow sometimes to speed the bedding in process.

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  • 11 years later...

I'm back, 

 

This time it's my falcon ute with rear imbalance.. 

First test was L200 - R240 (listed as 27% imbalance) but my maths says 20%

 

Stripped slider pins, cleaned and re-greased there was a bit of crud on the left ones,they move nice and free in the bore. 

 

Went back for a re-test now L300 - R360 so new 26%

Discs and pads have less than 10,000ks on them and look mint, no uneven wear..

 

Is there a chance if the lsd setting on the roller machine isn't done incorrectly that you could get an out of wack reading? 

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The two times i've had rear imbalance, where pissing with the rear didn't solve it, it was the proportioning valve(?). On the car it controlled the left / right split part of the system, i'm not good with terms. Different car though so could run a different setup. Both times it was a tiny bit of crud inside the valve and when cleaned out balanced up perfectly. Just an idea anyway, no idea on that car setup. 

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2 hours ago, Bling said:

The two times i've had rear imbalance, where pissing with the rear didn't solve it, it was the proportioning valve(?). On the car it controlled the left / right split part of the system, i'm not good with terms. Different car though so could run a different setup. Both times it was a tiny bit of crud inside the valve and when cleaned out balanced up perfectly. Just an idea anyway, no idea on that car setup. 

Yeah had the same thing with an ae111 corolla, one rebuilt bias valve later it was happy days. It had huge performance on the rear on one side so was a bit easier to spot. 

 

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7 hours ago, mjrstar said:

I'm back, 

 

This time it's my falcon ute with rear imbalance.. 

First test was L200 - R240 (listed as 27% imbalance) but my maths says 20%

 

Stripped slider pins, cleaned and re-greased there was a bit of crud on the left ones,they move nice and free in the bore. 

 

Went back for a re-test now L300 - R360 so new 26%

Discs and pads have less than 10,000ks on them and look mint, no uneven wear..

 

Is there a chance if the lsd setting on the roller machine isn't done incorrectly that you could get an out of wack reading? 

we often had semi-seized pistons in the Falcons, especially the utes . maybe from burnouts or too many heavy loads rooting the prop. valve

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8 hours ago, smokin'joe said:

we often had semi-seized pistons in the Falcons, especially the utes . maybe from burnouts or too many heavy loads rooting the prop. valve

This is interesting, I haven't noticed a lever / height operated prop valve like the old hiluxs had, but that's not to say it doesn't have one.. 

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