1975 1500TC rear disc conversion - NOW ROAD TESTED!

[bazyerma]

Hi
On stripping my rear axel for new bearings, seals and a freshen up I decided to fit rear discs.

**At this point please take note before commenting, I have not tested these on the road yet *Now tested 09/05/21 - Success!*, and I am aware many will know this is a pointless / un-necessary modification, but I wanted to do it, so that’s reason enough for me (and it was fun!) **

Planning phase

In the past I had butchered my backing plates to fit MG TF wheel studs, as I am running MG wheels (drilled a hold in them so I could fit them without taking out the half shafts as I could not remove the hub) so I wanted to replace them and clean up my drums.

On strip down I found both rear cylinders were leaking, and the drums and shoes were worn and could not re-used. I estimated the cost of replacing the lots at approx. £220 so although rear discs would cost more than this, at least I had a cost to compare to! EG - Shoes - £20, Drums - £110, Cylinders - £40, Back plates - £20, Clips / Pins / retaining kits - £30

Plan – Due to the use of MG TF studs and knowing the PCD is the same I decided to go with MG TF discs, calipers and hoses, with a bracket to fit them to the axel bolts.

FITTING

Back plate

With the axel stripped and new bearings on the has shaft, the first modification I did was using the grease catcher (104582) as a template I marked the outline on the backing plate and cut out the centre to size (you could make this from 2mm plate if your back plates are worth saving or going back to stock). With this fitted I put everything on the axel together ready to make up bracket

[bazyerma]

Discs

Trail fitting the discs I found the drives size fitted but the passenger side was catching the hub. 2 minutes with the file removing the casing marks on the hubs and it fitted.

**IMPORTANT – as per the photos show, the disc centre hole is larger than the lugs (spigot) of the hub, and therefor the discs are only centred on the wheel studs, and disc retainer bolts cannot be fitted. I am happy with the centerisation of the disc and the run out, but I have not had a road tested yet, and I am sure plenty of engineers would not be happy either. **

Bracket

Using a large nut on the wheel studs with the wheel nuts I fitted the disc, then holding the caliper with pads in place I made a carboard template to suit the 70mm od of the axel tube spacing to match the caliper carrier. When drawing up the bracket in paint I extended the legs 10mm with the radius of the curve continuing to help it “hook” into place.

I decided to make the bracket out of 8mm plate as the flange on the axel is approx 5mm and the carrier is 12mm so I decided 8mm would be strong enough.
The drawing was sent to a local machine shop with a water jetting machine and they turned it round in 2 days for £40. There is online companies but they needed a proper drawing, Cad ect but the shop local to me did the drawing ect.
Trail fitting the bracket it was tight, so I filed down the bottom leg flat and it went on with a nice tight fit. I measured up for the bolt holds and drilled out the axel size to 8.5mm and the caliper side 11mm.

[bazyerma]

Build
The brackets are fitted with the centre line matching the weld across the axel tube with two of axel flange bolt holes using M8x40mm high tensile bolts.
Calipers are fitted onto the bracket via M12x1.5mm BMW caliper bolts I had, but I think MG part number is BAU5631.

Brake hoses

For the hoses and lines, my car is a single line to the rear with a flex over the axle. I have used MG TF hoses, linked via a M10 3 way splitter with 5 male M10 fitting, then a cross over pipe to the correct 3/8in female fitting with 3/16in copper pipe.
PHOTO / Sketch

Handbrake (work in progress)

The plan was to try something with MG TF cables, but it looks like I can use the standard cables, with the caliper hand brake arm hole drilled out to 6.5mm to accept the original pin.

[bazyerma]

TESTING

Now the car is still awaiting a refurbished cylinder head, so this is still untested (all just prototype stage!).

As brake down of the costs to me are approx. £300 with all new parts. I already had MG TF wheels and studs fitted so take that into account as it will add to the costs.

Calipers with pads and carriers - £170
Brackets - £40
Hoses - £25
Discs - £30
Bolts, pipe fitting ect - £35

WEIGHT

As per attached photos my disc conversion added an extra 5.4Kg to the rear axle weight.


Parts list

Rimmers links but it’s a lot cheaper to shop around, and get the calipers with carriers
MG wheel Studs – RB FAM8419K16 / eBay - FAM8419 - £66 for 16
https://rimmerbros.com/Item--i-FAM8419K16
MG wheel Nuts – RB NAM9077P1 / eBay NAM9077 - £96
https://rimmerbros.com/Item--i-NAM9077P1
MG Rear discs – RB SDB100461 - £55 pair
https://rimmerbros.com/Item--i-SDB100461
MG Rear Caliper – Right (SMC000460) and left (SMC000470)
https://rimmerbros.com/Item--i-SMC000460
https://rimmerbros.com/Item--i-SMC000470R
MG rear caliper carrier – Right (SXP000070) and left (SXP000060)
https://rimmerbros.com/Item--i-SXP000070
https://rimmerbros.com/Item--i-SXP000060
MG Rear Caliper Mounting Bolt – RB EJP6293 x 4 £8
https://rimmerbros.com/Item--i-EJP6293
MG rear hose RB SHB000880 £18 x 2
https://rimmerbros.com/Item--i-SHB000880
M10 female Brake hose Tee – eBay example
https://www.ebay.co.uk/itm/Female-brass ... xy07FRjG3n

[new to this]

Nice mod,i used rover 45 brake calipers







Dave

[bazyerma]

Hi Dave

That's some nice looking brackets, I am tempted to make back plates after I have test everything.

Regards

Barry

[new to this]

hi barry

have you upgraded the front brakes ? what style/type of MG wheels are you using

Dave

[Carledo]

I was gonna say much the same thing, but Dave beat me to it above^^^^

I would think you need a TJ kit up front (if you don't have one already) either that or some sort of pressure limiter for those rear calipers, otherwise your front/rear bias will be all to cock!

I ran an unlimited Sprint rear setup on the Carledo briefly, it's propensity to change ends under heavy braking was disturbing, to put it mildly! A Cavalier pressure limiting valve fixed that until I could afford the TJs.

Steve

[Latham_F2]

That looks very similar to the setup I ended up with during first lockdown.
I used a pair of new Renault Scenic calipers, bought a while ago from Ebay for about £35(!) after using an online brake bias calculator to work out a suitable piston diameter to avoid overbraking the rear.
Since I'm already running 6R4 4pot calipers on the front, these were fine.
The front will be getting Wilwood calipers soon anyway.

Main difference seems to be that I picked up on 5 of the 6 axle flange bolts.
This did mean that I was limited on where I could put the caliper, because the gap also has to avoid the grease nipple on the back.

I also found out the reason why my brakes were so crap - turns out both axle seals had been leaking.
Not enough to be obvious, but boy did the shoes stink of oil!
Fixed that using the gearbox seal mod recommended on this forum.

Like yourself, I haven't had chance to try them out on the road.
But a quick run up and down the driveway certainly showed a huge improvement.

[new to this]

That looks very similar to the setup I ended up with during first lockdown.
I used a pair of new Renault Scenic calipers, bought a while ago from Ebay for about £35(!) after using an online brake bias calculator to work out a suitable piston diameter to avoid overbraking the rear.
Since I'm already running 6R4 4pot calipers on the front, these were fine.
The front will be getting Wilwood calipers soon anyway.

Main difference seems to be that I picked up on 5 of the 6 axle flange bolts.
This did mean that I was limited on where I could put the caliper, because the gap also has to avoid the grease nipple on the back.

I also found out the reason why my brakes were so crap - turns out both axle seals had been leaking.
Not enough to be obvious, but boy did the shoes stink of oil!
Fixed that using the gearbox seal mod recommended on this forum.

Like yourself, I haven't had chance to try them out on the road.
But a quick run up and down the driveway certainly showed a huge improvement.

Hi sorry dont know your name,have you jacked up the rear wheels,to test for clearance,only asking as when i did my brake set up, originaly had my brake calipers at a similar angle to yours,but when i jacked up the rear wheel the brake hose got traped between the body frame and caliper,thats why i moved the caliper round a bit more

Dave

[Latham_F2]

Hi Dave, it's Tony.

The car is on axle stands in the pics, plenty of clearance.
But on these calipers the brake pipe exits from the caliper going forwards and down, it won't catch anything.

[SprintV8]

That looks very similar to the setup I ended up with during first lockdown.
I used a pair of new Renault Scenic calipers, bought a while ago from Ebay for about £35(!) after using an online brake bias calculator to work out a suitable piston diameter to avoid overbraking the rear.
Since I'm already running 6R4 4pot calipers on the front, these were fine.
The front will be getting Wilwood calipers soon anyway.

Main difference seems to be that I picked up on 5 of the 6 axle flange bolts.
This did mean that I was limited on where I could put the caliper, because the gap also has to avoid the grease nipple on the back.

I also found out the reason why my brakes were so crap - turns out both axle seals had been leaking.
Not enough to be obvious, but boy did the shoes stink of oil!
Fixed that using the gearbox seal mod recommended on this forum.

Like yourself, I haven't had chance to try them out on the road.
But a quick run up and down the driveway certainly showed a huge improvement.



What are the 6R4 callipers your using.?

[Latham_F2]

Metro 6R4. Probably from an early one.
I read that later ones had vented discs so required a spacer between the 2 halves.

[soe8m]

Probably std. Metro turbo calipers. The 6R4 had alloy AP racing calipers.

Jeroen

[cleverusername]

I was gonna say much the same thing, but Dave beat me to it above^^^^

I would think you need a TJ kit up front (if you don't have one already) either that or some sort of pressure limiter for those rear calipers, otherwise your front/rear bias will be all to cock!

I ran an unlimited Sprint rear setup on the Carledo briefly, it's propensity to change ends under heavy braking was disturbing, to put it mildly! A Cavalier pressure limiting valve fixed that until I could afford the TJs.

Steve

Yes that was my thought, why would a 1500 need rear disk brakes? The big drums on the Sprint need a valve to stop the brakes locking up and you're likely to need a similar system for this conversion, unless the fronts are upgraded as well.

To be honest I am not a fan of all disk setups on front engineed cars full stop. Most of the braking is done by the front brakes, so rear disks are pretty pointless. They just complicate the fitting of a handbrake, at least until electronic parking brakes were introduced. Drums are perfectly fine for rear brakes.