Rear disc brakes

[new to this]

I know some of you have fitted rear disc brakes on your Dolomites, did you need a rear bias valve,or was it okay without the need for one

Thanks Dave

[Mad Mart]

I've never fitted them but would imagine you would definitely need a bias valve.

[jikovron]

If you size the brakes front and rear in proportion to each other then the load sensing valve can be avoided.

I used rover 45 calipers all round which is a similarly front weight biased car and tbh I would say the rear brakes had less initial grab than the sprint drums, however without the unmetered variable levels of self servo action the disc brakes were fairly linearly progressive to pedal pressure, smooth at any speed, never prone to fade and allowed for barely any pedal travel.
HTH

[RichardHyde]

Was there much work involved converting the tears to discs ?

[jikovron]

I turned the hub in a 4 jaw to reduce the diameter of the disc location boss, also I removed the oil seal guard then reattached it with sealant and some m4 bolts, the drum back plate center is cut out so that it can continue being a bearing shim.
Then it's just a case of making a disc brake bracket and spacer for the caliper of your choice, I actually have a few hub and bracket sets buried in the shed as it happens.

[new to this]

I turned the hub in a 4 jaw to reduce the diameter of the disc location boss, also I removed the oil seal guard then reattached it with sealant and some m4 bolts, the drum back plate center is cut out so that it can continue being a bearing shim.
Then it's just a case of making a disc brake bracket and spacer for the caliper of your choice, I actually have a few hub and bracket sets buried in the shed as it happens.

Jikovron

Thanks im in the middle of doing the rear disc mod now, still got to get the caliper mounting brackets,i was going to use MGF calipers,you said you reduced the diameter of the disc location boss,was that on the disc or the hub ? i take it you also used MGF disc

Thanks Dave

[new to this]

Was there much work involved converting the tears to discs ?

Im in the middle of doing the mod,you need a caliper mounting bracket,the disc holds on to the hub using the same drum hold screws,some people do away with the back plate,but im making a new back plate that is only there to protect the disc

Dave

[new to this]

I've never fitted them but would imagine you would definitely need a bias valve.

Thanks

[jikovron]

yeah i reduced the hub location diameter to suite the mgf disc center bore .

edited to add, mgf calipers have larger pistons than what i used which are setup to suite the rear weight bias of the mid engined car so might need some trial and error to get the brake balance right via the load sensing valve or an adjustable brake line limiter.

[cleverusername]

Is there any advantage to rear disc brakes? Most of the braking is done at the front and the big advantage of discs is they cool quicker. I doubt that the rear brakes on a dolly overheat in normal road use. Plus drums make far more effective parking brakes than discs.

[Carledo]

My own experience says I can't see the point in wasting time effort and money on rear discs when the stock Sprint drums are MORE than adequate for the task. The original cars were plagued by the demon of having rear brakes that were TOO good and overpowered the rather weedy fronts, leading to the use of the load sensing valve, which is there PURELY to resolve this one issue!

With the advent of the trackerjack kit, the lousy front brakes are fixable (other solutions also work, but, IME, The TJs are easiest) and if you fit a TJ kit, the balance is better and you no longer NEED the LSV.

But you don't REALLY need anything better than that. Much bigger brakes and you lose "feel" and the wretched thing will lock all 4 wheels if you breathe too hard on the pedal! You have to bear in mind that even a Sprint at it's MOT testing weight of 1170kg is still a very light car by todays standards. Less weight means less inertia and less stopping power needed than on a 15-1700kg modern in the same class, say a Golf GTi or Astra SRi. And it's a geometric progression, not a linear one. I've noticed this particularly with the Carledo, which (without my bulk in it) is around 760kg kerb weight, I had it weighed on the council truck scales, just out of curiosity. When my Sprint servo failed, not having a spare, this being before the club restarted the recon process, I fitted an 1850 servo as stopgap. But I found to my surprise that I actually liked it better that way, so it has stayed!

And the drums, without even compo linings have stood up to everything I have been able to throw at them, i've not had one incident of fade since fitting the TJs despite several track days and fairly severe road work usage in between. The thing just stops, end of!

I'm not saying don't fit rear discs, if you want them, knock yourself out! I'm just saying that, in my opinion, they are not necessary to the car's braking performance, you'd be fixing a problem that doesn't exist!

I'm so confident that i'm willing to sell the pair of half shafts I have here that have already been modified (not by me) to accept MGF rear discs, £50 the pair! (or swap for your stock ones)

Steve

[jikovron]

Its correct to say that discs on the rear are not a one size fits every car but for those wanting to fit them then there is no harm done when configured right,and indeed there are a number of people who have successfully done it without complaint, additionally surely any modification is a waste of time and money but is done to make you feel better about the car even if on paper it may only be 6 and two 3s, I advocate discs purely because the brakes on my car were complementary of the power level I had available and I liked how direct the pedal feel was as there is no slack to take up.
The bottom line realistically is that drums v discs is a personal perspective matter.

[new to this]

I started this as one mod leads on to another Ive changed the PCD on my car and have fitted Stag wheels 14",ive got the Tracker jack brake but up it to 260mm disc,on the rears i was going to use 240mm disc but they wouldnt fit over my modified rear hubs,so needed to up them to 260mm

Thanks Dave

[new to this]

My own experience says I can't see the point in wasting time effort and money on rear discs when the stock Sprint drums are MORE than adequate for the task. The original cars were plagued by the demon of having rear brakes that were TOO good and overpowered the rather weedy fronts, leading to the use of the load sensing valve, which is there PURELY to resolve this one issue!

With the advent of the trackerjack kit, the lousy front brakes are fixable (other solutions also work, but, IME, The TJs are easiest) and if you fit a TJ kit, the balance is better and you no longer NEED the LSV.

But you don't REALLY need anything better than that. Much bigger brakes and you lose "feel" and the wretched thing will lock all 4 wheels if you breathe too hard on the pedal! You have to bear in mind that even a Sprint at it's MOT testing weight of 1170kg is still a very light car by todays standards. Less weight means less inertia and less stopping power needed than on a 15-1700kg modern in the same class, say a Golf GTi or Astra SRi. And it's a geometric progression, not a linear one. I've noticed this particularly with the Carledo, which (without my bulk in it) is around 760kg kerb weight, I had it weighed on the council truck scales, just out of curiosity. When my Sprint servo failed, not having a spare, this being before the club restarted the recon process, I fitted an 1850 servo as stopgap. But I found to my surprise that I actually liked it better that way, so it has stayed!

And the drums, without even compo linings have stood up to everything I have been able to throw at them, i've not had one incident of fade since fitting the TJs despite several track days and fairly severe road work usage in between. The thing just stops, end of!

I'm not saying don't fit rear discs, if you want them, knock yourself out! I'm just saying that, in my opinion, they are not necessary to the car's braking performance, you'd be fixing a problem that doesn't exist!

I'm so confident that i'm willing to sell the pair of half shafts I have here that have already been modified (not by me) to accept MGF rear discs, £50 the pair! (or swap for your stock ones)

Steve

Why do people modifiy the hub to take a MGF disc,why not open up the hole in the disc its self,that way you can always go back to the original setup if you need to

Dave

[jikovron]

The drum back plate is also a difficulty to revert back haha, but yeah it's just for quicker consumable replacement .