Sprint Brake Discs

[sprint-revival]

Hi All,

Finally returned XLK to the road last weekend. Had no less than three break downs on the first run out, but soon worked out the inline fuel filter was oversized robbing too much pressure from the system, a smaller filter resolved cutting out issues. Really enjoying driving XLK, I have been very surprised by the performance, which far exceeded my expectations. A few small issues have been identified, the 2nd fuel tank I have fitted to the car leaks fuel at approx. 1/3rd full. The other main issue is the brakes.

Today I took the car into work (Im a mechanic). A colleague put the car on the rollers and carried out a brake test which uncovered that the rear brakes (fitted with new old stock Girling brake shoes and the original drums) are nicely balanced, with minimal/no run out. The fronts however are a different story, the balance wasn’t to bad 240/210, but the run out is horrendous! I watching during the test and the needles on the gauges could be seen bouncing around wildly, in particular for the NSF. The front brakes were fully rebuilt, with the callipers being stripped and new seals fitted, new hoses, set of Pads, and a new set of brake discs supplied by R.Bros (standard ones, manufactured by a company called Auto National). My colleague advised that the discs aren’t flat/true and should be changed (easier said than done). There is a slight hissing noise behind the brake pedal that can be heard in the cabin, when the pedal is pressed the noise goes away, however my colleague who conducted the brake test advised that he was not concerned at this as the servo functionally seems to operate as intended and holds a vacuum.

So the question is, what discs do I go for, as the standard ones are clearly poor quality/not properly machined, any NOS sets around? Had several issues with poor repo part quality in returning XLK to the road - rad caps, dizzy caps, points, condensers, 5 3/4" H4 lamp units to name just a few. Wouldn't mind but it is not great having to revisit jobs on the car so soon due to poor quality parts!

To add insult to injury the Dolly ran out of fuel on the way home. Note to self, trust the fuel light, not the gauge that read ¼ tank.

Thanks for any advice in advance.

Olie

[new to this]

My advice would be upgrade the front brakes to a tracker jack kit, uses Vented disc instead of the solid type

Dave

[xvivalve]

Robsport have a pair of standard discs on eBay at the moment

[ClassicFan]

A few small issues have been identified, the 2nd fuel tank I have fitted to the car leaks fuel at approx. 1/3rd full.

A friend had a similar isue with a leaing tank. It was repaired at a local radiator repair shop (Advanced Radiators). Apparently most do fuel tanks as well these days. Basically it was cleaned then coated internally and externally (don't know what with). Added benefit now is that there is no old 'gunge / rust' in the fuel system so a filter isn't really needed in the line (but one is fitted anyway)

[killysprint]

I experience a similar problem when I was a slip of a lad, with what I thought was poor quality brakes, and warping after replacement at a local garage.

Stripped them back and the mating surfaces of the disc and hub on one side weren't clean, had some debris and detritus on them, cleaned them up and rebuilt them, the vibration under braking was massively reduced. Think I had left it too long before investigating the problem. May be worth a look.

Today, as one of the other posts have said - I've ran trackerjack brakes for over 10 years - and driven hard on them - never flickered. Well worth the price.

[Richard the old one]

I had the same problem with some new discs from the same supplier a number of years ago. I overcome the problem by fitting some I had kept from a scrap car.

I believe John Abra had the same problem a couple of years ago and ended up getting the discs skimmed on the car. I do not know how much it costs but if you do a search for "Skim my disc" details should come up and you can find out what garages have the equipment. I live in Bristol and was surprised to find that there is a garage within 3 miles of my house.

[gmsclassics]

I would be surprised if a new disc would be at fault. I agree, from experience, with the previous comment about ensuring the hub and disc mating surfaces needs to be spotlessly clean (with no paint on the hub surface). Also double checking the wheel bearing/hub tightness and setting play at the lower end of allowable range (and rechecking a few miles after fitting).

When I was racing a Sprint I also found it necessary to check the disc run-out using a dial indicator suitably mounted. To get the run out to as close to zero as possible I shimmed the surface between the disc/hub until I reduced even the minutest run out to effectively zero. In fact I used small pieces of 80gsm printer paper, which I slightly wetted to hold in place until the disc was bolted in place. Worked every time.

Geoff

[sprint-revival]

Thanks for the input everyone, I really appreciate it.

I have ended up sourcing a set of EBC discs for only a few £ more than standard discs from most suppliers. I had a quick look at one of the standard discs currently fitted, they have 'Troy Made in UK' stamped on them. I remember this name as I had a wheel bearing for a classic mini from this brand fail after only a few hundred miles a few years ago, so would rather avoid this brand again. Purchasing another set of standard discs would be a lottery if I end up with the same again; I imagine all suppliers must be sourcing these from the same place. I know EBC have mixed reviews on here, but have fitted to other cars in the past without issue, so worth ago. I have some NOS Unipart Pads to fit along with the new Discs.

I will spend more time cleaning the hub mating surface, I’m usually pretty good at this but will be doubly careful.

Fitted the 3rd second hand replacement tank today, which thankfully is leak free, seems to be a later aftermarket tank, as seems to be lacking baffles like the originals, and didn’t line up as nicely as the original, but it’s in and holds fuel so I’m happy.

Went for a spin, and you guessed it broke down!, brake down number 5! This was different to the others though. Doing 60mph on a fast A road, and all of a sudden was like someone applied the handbrake! a frighting few seconds! Got a few hundred yards up the road and found somewhere safe to pull in. I could smell burning from rear brakes and the pedal was right at the top of its travel. I jacked up and rears were locked solid! Oddly by the time I had the wheels off and gathered the tools together to remove the drums, the brakes had freed themselves off. I stripped and cleaned and de adjusted slightly (still reasonable handbrake holding on 7 clicks), then proceeded to drive home (Approx. 25 miles), without further incident. Most bizarre, the brakes are almost all new - New club single line master, front callipers rebuilt, discs + pads, rear wheel cylinders, shoes, LSV rebuilt with club seal kit, all new brake hard lines, brake flexi’s etc. In fact the only original component is the servo.

I think the car is trying to tell me it’s not quite ready to awake from its 26 year slumber, despite covering 120 miles in the last week. When I pulled back onto the drive I also noticed that the tail lights are on whether you like it or not, ignition on tail lights on, this can’t be right, they remain on with the side/headlights, but would have thought this would only be on with sidelights and headlights?

Been lucky on each occasion I have broken down that the Dolly has chosen somewhere relatively safe and convenient, but I’m not going to be taking the risk again until I’m 100% happy to venture out again.

Olie

[Carledo]

More likely it's the brake lights that are coming on with the ignition, rather than the tail lights, check the position and integrity of the brake light switch, it's a horrible bit of cheap plastic that falls to pieces if you look at it a bit funny! And the bent tin bracket that holds it up isn't much cop either, but at least it's easy to bend to the right position!

Steve

[xvivalve]

You say you have new flexi hoses, but as both rear brakes were locked I suspect the rear flexi might have an internal issue creating a ‘valve’ that prevented fluid from returning back; this would tie up with a gradual release whilst you jacked up and removed the wheels. It’s a common problem with NOS rubber hoses that could have been sitting on a shelf for up to 50 years now!

[Richard the old one]

I can assure you the problem I had was that the discs sides were not parallel I found this out using a micrometer. I cant remember how much variation there was but it was sufficient to make the brake pedal pulse.

John Abro also had this problem and that is why he had his discs skimmed on the car. I did enquire yesterday to find out how much the local garage charges to skim discs it turned out to be £90 so not cheap.

[sprint-revival]

More likely it's the brake lights that are coming on with the ignition, rather than the tail lights, check the position and integrity of the brake light switch, it's a horrible bit of cheap plastic that falls to pieces if you look at it a bit funny! And the bent tin bracket that holds it up isn't much cop either, but at least it's easy to bend to the right position!

Steve

You were quite right Steve, had a look under the pedal this afternoon and the switch was loose on the bracket. Nipped it up and now brake lights are off. Thanks for pointing me in the right direction.

Olie

[sprint-revival]

You say you have new flexi hoses, but as both rear brakes were locked I suspect the rear flexi might have an internal issue creating a ‘valve’ that prevented fluid from returning back; this would tie up with a gradual release whilst you jacked up and removed the wheels. It’s a common problem with NOS rubber hoses that could have been sitting on a shelf for up to 50 years now!

This thought had crossed my mind when I was at the side of the road. Hoses all round were brand new from R.Bros purchased August 2020 and fitted March 2023. Probably worth sourcing a new rear hose from an alternative supplier. I do heed the warnings in Dolly Mixture for certain NOS items. The only other thing I thought of was perhaps an issue with the LSV, however that was fully rebuilt, odd that issue only became apparent after approx. 90 miles of driving!

[sprint-revival]

Spent some time sorting out a few niggling issues today with the brake lights (as above), and tightened the fan belt as this was slipping slightly, viscous fan seems to engage better now and will sit comfortably idling on the drive without the temp rising above half.

Since returning to the road a whistling noise/air leak has been getting progressively worse. I finally think I have tracked down the source. I can feel significant movement in the carb butterfly spindles, you can feel and hear the movement. When I rock the spindles side to side with the engine running you can change the note of the whistle/hiss noise and also alter the idle of the engine. I’m guessing this will require a full rebuild of the carbs (something I didn’t touch at all during the engine rebuild). Probably something nice to rebuild during the winter. Proabably worth while switching to club alloy mounts while im at it. A quiestion I have regarding the mounts is how do you remove them? I see the mounts have cut outs for spanner access, but I couldnt get a 1/2" spanner on the bolts. Is there a special low profile spanner/tool for this? The studs and nuts on the other side (carb side) are obscured by the carbs themselves

Link to video with noise below (video makes it sound worse than it is, in person it sounds like a kettle just starting to boil/hiss).

https://www.youtube.com/watch?v=HUG6WsSxRI8

Olie

[sprint-revival]

Just an update with the locking up rear brakes.

Over the last couple of weeks I have replaced the rear brake hose and fitted a new rear load sensing valve (Hyundai H100 van part), thoroughly bled the system and went for a spin this morning. All was going well, filled up with fuel and got just over 5 miles, until I could feel the car holding back, and started to smell that all to familiar burning smell, pulled up in a layby after about 300 yards. The brake pedal was solid with no travel at all. This time however both front and rear brakes were smoking. Checked master cylinder fluid level which was unchanged. Let the car cool off for 20 minutes and nursed it home.

I am a bit stumped now with this. The system is all but new. Club single line master cylinder, rebuilt brake calipers, new brake lines front to back and back axle, new load sensing valve, brake hoses all round, and wheel cylinders. The only parts not replaced are the engine bay brake hard lines (as were in good condition) and the brake servo. I am slightly suspect of the servo as a whistling noise can be heard in this area that goes away when pedal pressed. Is it possible that the servo could lock the brakes up intermittently.

Any advice welcome.

Thanks,

Olie