Brake lock up

[80Sprint]

I have had a Trackerjack set up for some time now with original Sierra discs and callipers. They were much better than standard but I never locked up no matter how hard I braked. I read that you don’t need the brake balance valve with this set up so I removed it when I refurbished the back end. I then replaced the discs with new Brembo discs and Ferodo pads. I also changed from spax adjustables, lowered with a slight nose up attitude. I the replaced with AVO and have it lowered still with a nose down attitude this time The brakes grab really well now and seem better than before, however braking hard to a roundabout from 60 and it starts to lock up where I get tyres squealing. Strangely it can sometimes do it braking on a. Large roundabout that has lights on it and I may only be doing 30. 30 in a straigh5 line isn’t usually ok. I do also get a slight pull to the right on heavy braking from speed

My first thought is to stick the balance valve back on but wondered how others have managed without or is it just the new disc and pad combo is very effective ? Track day in October so I need to get it sorted soon.

[Carledo]

The balance valve (or load sensing valve to give it it's full title) only affects pressure to the REAR brakes. It's there to stop the rears from locking up prematurely because the stock front discs aren't man enough to outbrake the stock rear drums (Stolen from the TR4 which had bigger wheels and therefore could run bigger discs up front)

Once you fit the TJs you get a restored balance that no longer needs the LSV. I routinely delete the LSV when I do a TJ conversion and have had no problems running without it, even under track conditions. TBH, 95% of the LSVs i've encountered have been seized solid anyway!

But from your description the problem seems to be with the front brakes "grabbing", sometimes unevenly (if you have a brake pull) Since it only started when you fitted the more upmarket discs and pads to the front, that is where you must seek the answer!

Steve

[80Sprint]

I have had them apart again Steve . Made sure the pins are cleaned and greased.
I did spent ages trying to get the disc run out right but never got it as low as I think it should be. I don’t get any judder ( which was the original problem before new brakes) so I am not sure if that could be an issue.
I can also bleed them again but any other ideas what may make them grab? Callipers were also new when I did the original conversion some years ago now.

[gmsclassics]

Could be due to tyre contacting the road, pads differing in gripping the discs on each side or even perhaps front suspension setup, so:
1. recheck that the new shocks (and springs?) are setup identically
2. were the pads bedded in correctly (the Ferodo DS3000 I used had a specific bedding in process to use). Otherwise you could get glazing on the pad surface. Sometimes sanding and starting again may help.
3. Assume tyres are the same brand/type all round and haven't got any minor flatspotting or lost a wheel balance (which may not be enough to cause judder though). Even slightly uneven tyre pressures could contribute.

I always used to be pedantic about both wheel bearing (Timken only) play and disc runout. I aimed for a max of 50% of what the standard setup says is allowable, given I was using larger and heavier rotors. Any run out can cause your symptoms so minimising both can only help.

Hope something here is of help.

Geoff

[Carledo]

I know that when Jon builds his kits, he does a very fine face of the outside hub section of his discs. This is because, on the standard Golf they are sourced from, this is not critical, only the wheel goes on this outside face. On a Dolomite however, this face directly mates to the hub and can give runout if not completely flat and square. Something to think about.

However, my own personal suspicion is that this is not the problem. I suspect it lies in the particular mix of disc and pad you have employed, with maybe a side order of caliper inequality and/or perhaps a slight flexi hose defect. Are the Brembo discs drilled and/or grooved? And have you fitted competition Mintex pads? It might be an idea to pop down to the factors and get a cheap and cheerful set of lesser quality pads and see how it behaves on those. Cheap pads are just that, CHEAP! but if a softer lining solves it, it's worth changing them more frequently in the long run.

Steve

[trackerjack]

When I had a TR4 I had a severe brake judder (this was in 1979 by the way) and I stuck some emery cloth using Araldite to the braking face of some old worn out pads. I then drove the car very gently and applied the brakes gently too. This trued up the disc nicely and ensured they were parallel. I then replaced the pads with new and hey ho brakes were fine. Since using only Mintex discs I have not needed to skim the outer face of the disc because their machining tolerances are so good.
The Sprint has never been pictured during it's racing years with a nose down attitude and perhaps the car lowered too much is having too much negative camber which lessens the tyre contact, or perhaps the drag links are shot. I never had any on road or on track problems with front or rear locking up, however the car was always slightly nose up.
Always fun finding the fault

[Carledo]

I run the Carledo with a slightly nose down stance and I have let nature take it's course with camber, so it's running around 3 degrees neggy. I've not tried to dial it out with extra shims as it drives fine as it is and doesn't wear tyres out excessively quickly. If it ain't broke.......

On locking up, I CAN lock up the Carledo on a dry road with the TJs fitted - but I have to be REALLY trying! And the Carledo is VERY light (760kg kerb weight vs around 1100kg for your average fully trimmed Sprint) which may, along with the 195/50/15s, explain the fact that I can do it at all.

I've noticed on other cars that having a massive footprint is not always beneficial, particularly on lighter cars, go too wide and you run into a law of diminishing returns that quickly becomes positively detrimental if you go too mad with tyres. With the Carledo, I reckon i've reached it's practical limit. The Dolomega will run an altogether more conservative 185/60/14s both for improved ride quality of the higher profile and to save me from rolling the arches to get them in! It won't be anything like as low either!

Steve

[80Sprint]

Always fun finding the fault

Mmm , i would rather be driving it Jon.

I had cheap discs and pads before and had lots of vibration. I changed to Brembo for quality but only went for standard discs as i felt grooved discs were for show. I fitted Ferodo pads, again for quality and not race type pads either. I do feel the stopping power is much improved if it were not for the break in traction. Front and rear have new Superflex poly bushes which if anything feel softer than the ones that came off.

I ran a nose up attitude before but thought i had read the Sprint was the opposite to the Ford Escort and suited a nose down attitude. Track Sprints are lowered so i don't see why on a smooth road it would be any different but perhaps from the replies here, there lies the problem, or part of it if i get it back to a nose up stance.

I suppose i need to do one thing at a time and see what happens, unfortunately with all the suspension and brake changes it is difficult to say what has affected this but it looks like i am back to some fun in the garage and some road testing. Either way at least i know i should not have to fit the LBV back again and just go from here.