GM Hydraulic brake caliper

[Bedmountain]

I finally bit the bullet and splashed out on a GM rear 160 hydraulic brake kit. For my previous build I didn't use the cut off brake levers and stuck with my stock hydrauilic brakes.
I had real issues with the back one binding on the motor housing. I shaved off some 3-4mm off the actual brake housing which worked until the housing burst one day as it was now too thin to hold the pressure of the brake fluid...

So I thought it was time to have the added safety feature of the motor cut-off and buy a brake that would surely fit between disc rotor and motor housing (big thanks to Gary S by the way for shipping so quickly to the UK - not so big a thanks to her majesties customs that charged me a ridiculous amount ...)

After a couple of hours of messing about, shouting at things and butchering the brake mounting bracket I've come to the conclusion that the 160mm caliper and rotor just will not fit.
With the caliper adjusted as far as possible towards the dropouts it just will not clear the motor housing. I even shaved some material off the caliper bracket so I could move it further away from the motor but it quickly became obvious that it starts to distort the disc rotor before it clears the housing.

I'm a bit surprised. It can't be anything to do with my bike or even the way I'm installing it. The room to fit it in is simply just not there.

I'm guessing that if I fit a 200mm rotor then the caliper will be high enough to clear the raised middle of the motor housing which is what I will do next. I'm hoping I can buy a mounting bracket that will lift it up to fit otherwise I will have to space it with some steel tube or lots of washers.

I don't see much around on this forum about this problem - there was a post a few weeks ago but that seems to have been sorted by buying the GM caliper.

No-one else had this issue?

[Bikemad]

Ben, it might be worth spacing the disc further away from the hub by adding some suitable washers in between the disc and the mounting flange (making sure the washers are all the same thickness and that the bolts are threading in sufficiently.).

This should hopefully allow the caliper to fit without distorting the disc.

big thanks to Gary S by the way for shipping so quickly to the UK - not so big a thanks to her majesty's customs that charged me a ridiculous amount ...

You forgot to thank the nice delivery company for charging you an excessive handling fee just for paying the VAT on your behalf without your knowledge, permission or consent! 

Alan
 

[Bedmountain]

ooooh - now there's a simple answer that makes me feel simple

I'm sure I read somewhere that that was not a good idea but I can't think of any reason why it wouldn't be so it was probably a dream...

Thanks Alan

Still seems like it should fit without any mods with it coming from the same factory as the wheel....

[Bikemad]

I'm sure I read somewhere that that was not a good idea but I can't think of any reason why it wouldn't be so it was probably a dream...

I think you must have been dreaming about the freewheel spacer:

The Magic Pie is supplied with a couple of spacer shims (narrow washers) tie wrapped to the axle:

 

These should only be used if there is not enough clearance between the freewheel and the hub without them.

The freewheel should screw easily onto the threaded boss, and excessive force should be avoided. If it doesn't thread on easily first time, remove it and try again, taking great care to ensure it is aligned correctly so as to prevent any possibility of cross threading it.

If the freewheel binds against the hub, fitting a single shim will hopefully be enough to cure the problem.
The shim is easily fitted by simply placing it on the threaded boss on the hub before the freewheel is screwed on.

If one shim doesn't provide enough clearance, it might be wise to consider using a different freewheel instead of additional shims.
Fitting more shims will further reduce the amount of thread available for fixing the freewheel, making it more prone to stripping the soft aluminium threads on the hub under heavy pedal pressure.

The shim occupies a small portion of the threads visible in the picture on the right, which will prevent the freewheel from being threaded on too close to the hub.
This photo was taken before the freewheel had been fully screwed on:
(With my freewheel, a shim was not required and is therefore not shown in these photos)

   

Fitting the brake disc (Magic Pies only)
Feed the centre of the brake disc over the wiring and attach to the hub as shown below using six Allen headed bolts screwed into the appropriate set of threaded holes suitable for the disc, and then tighten the bolts securely.
Applying small amount of thread locking compound onto the threaded portion of each bolt prior to fitting will ensure that they don't come loose.

 

If you need to space the brake disc on a Magic Pie in order to give a little bit more clearance for the brake calliper, make sure you use identical washers (or sets of washers) between the disc and the hub on each of the six fixing bolts.
If you're using the fixing holes nearer to the axle, you may need to file or grind a flat on each of the washers to ensure they clear the disc locating lip (the sticking out bit) on the hub.
The easy way to check for clearance is to put a washer on a bolt and thread it into one of the holes your disc uses. If the washer can slide down the bolt and lay flat on the hub it should be OK to use as it is. If it's tight against the locating lip then it (and all the other washers used) will need to be filed away until it fits.

[IMGhttp://www.arhservices.co.uk/GoldenMotor/Disc%20spacers_zpsw9xomavl.JPG[/img]

Please Note: the above freewheel spacer shims should not be used for spacing a brake disc which bolts directly to the hub on the Magic Pie.
The brake disc must have a suitable flat surface area where it contacts the hub to ensure it can be correctly tightened without causing any distortion of the disc.

Alan
 

[GM Canada]

After a couple of hours of messing about, shouting at things and butchering the brake mounting bracket I've come to the conclusion that the 160mm caliper and rotor just will not fit.
With the caliper adjusted as far as possible towards the dropouts it just will not clear the motor housing. I even shaved some material off the caliper bracket so I could move it further away from the motor but it quickly became obvious that it starts to distort the disc rotor before it clears the housing.

Is it possible to upload pictures of the issue. I can't get my head around the fact that it does not fit between the rotor and the motor. This makes no sense to me either. I have sold a lot of these and no one has ever mentioned they didn't fit. I don't get it.

Gary

[Bedmountain]

Thanks Alan - I think it was that image with the warning not to use the freewheel spacer that had stuck in my mind...

Gary - Please see image below. The disc rotor is as far as it can go within the caliper but the caliper and motor housing are still touching...

[Bikemad]

Ben, I have just been studying your photo and I cannot clearly see the washer on the axle which should clamp against the inside edge of the dropout.



Without this washer, it can seriously damage your frame when the axle nuts are tightened.

If it isn't fitted, it would also explain why you needed to shave away part of the caliper fixing bracket to prevent the caliper touching against the hub.

I would suggest spacing the disc until the caliper clears the disc mounting flange on the hub and then
space the axle from the dropout using the correct width washer (if it is not already fitted) or add an additional washer if necessary.

Unless it's an optical illusion (or camera lens distortion) the disc rotor itself appears to be quite buckled in the photo and will probably need to be straightened so that it runs true within the caliper.
(It should be possible to use an adjustable spanner slipped over the disc to perform the necessary tweaking.   )

Alan
 

[Bedmountain]

Oh Alan - Is it not clear from the picture that I am trialling GM's new transparent washers - It is quite hard to spot in that picture  .

Of all the times I've installed a pie (I've only owned 2 but they have been on and off more times than I can remember...) I'm pretty sure that's the first time I've left that washer off which makes it the perfect time for me to take a picture of it and post it on this forum lol 

Ok - the washer is back in place and thanks very much for spotting that - I won't be doing that again 

Obviously I still have the issus with the rotor needing to be spaced away from the hub.

I think, rather than space it, find out it's not enough/too much and repeat over and over with my rageometer clicking up a notch each time it would be easier for me to buy a 203mm rotor and mount adaptor.

Surely that will move the caliper far enough away from the motor housing that it cannot interfere.

Unless of course there is something I haven't thought of that makes this a bad idea?....

[Bikemad]

I think, rather than space it, find out it's not enough/too much and repeat over and over with my rageometer clicking up a notch each time it would be easier for me to buy a 203mm rotor and mount adaptor.

Make sure you can get the required adapter to suit or the 203mm disc might cause your rageometer to go off the scale.



According to the following chart, the standard 160mm post mount can be replaced with adapter mounts suitable for 170mm, 180mm or 200mm discs but not 203mm.



It might be better to limit the choice of disc diameter to 200mm max. unless you are 100% sure that you can get the required adapter to suit your caliper.

Also, be very careful when you remove those transparent washers as they can be very difficult to locate when dropped on the floor!


Alan
 

P.S. According to this diagram, Bracket no 5 should allow a 203mm disc to be fitted if your frame's caliper mounting is IS:



Check you measurements carefully to make sure the hole spacing is correct:

[Bedmountain]

Thanks Alan

It's an IS mount - I've ordered a rear IS adaptor for 203mm rotor. What could possibly go wrong? 

The thing I've ordered looks quite like the adaptor in your picture - I'm sure all the holes will be in just the right places...

If not I have a tube of 'no nails' glue I'm not afraid to use and if that doesn't work I'll fit a brake pad to the heel of my left boot.

[GM Canada]

I really am shocked this caliper did not fit. So I decided to try it myself and you are correct. I removed the disk and added 6 washers and no problem. it is still quite close to the motor but I can slide a sheet of pager in between no problem. I can only assume those that have ordered them from me have added washers to adjust the fit on the smaller brake disks. Please send me and email so I can determine what order was placed on the site by you.

Gary

[Bedmountain]

Hi Gary

I was surprised the caliper didn't fit without spacing or at least GM didn't make it clear that spacing would be required as it must have been obvious for them in the factory.

All is well though. I bought a 203 mm disc (180 would have probably cleared it) and added a mount adaptor and all is fitting nicely.

[Bedmountain]

Just a quick note for anyone out there who might be thinking about ordering from Gary at GM Canada...

If you read this thread you will see I ordered a GM product that wasn't quite up to scratch in terms of it not fitting straight out of the box (with a handful of washers it works fine (this is a DIY hobby after all...)) - or in my case a bigger disc.

After a quick chat with Gary (he has live chat now via the site), bearing in mind I was not complaining I was just touching base as he had asked me to email him, he apologised for it not fitting without spacers (not his fault) and then re-imbursed me the cost of the 203mm disc and mount adaptor I bought (I didn't ask for any kind of refund - I was simply letting him know I had got around the issue and everything was ok).

Now that is customer service you will not find anywhere else in my opinion...

I don't get commision from GM Canada  - just wanted to let people know what they can expect in terms of service from this company.

[Klatuu]

Gary's live chat is great!  I recently used it to get a few questions answered about his products and got a ton of good advice  ultimately purchasing the MP Edge with which I am very happy! 

[GM Canada]

Gary's live chat is great!  I recently used it to get a few questions answered about his products and got a ton of good advice  ultimately purchasing the MP Edge with which I am very happy!

Thank you for the positive comments!

Gary