Sprint Brakes

[Bish]

RESULT

[xvivalve]

Well done...perseverance pays off in the end.


...but does the pedal drop when you start the engine now?

[Carledo]

Well done...perseverance pays off in the end.


...but does the pedal drop when you start the engine now?

Yes it does, I wasn't in a position to road test, but I was able to fire it up with my foot on the brake and feel it drop. So I was confident when I left that it would be fine.

Steve

[sprint95m]

For anyone who wants to know

Glad you have it sorted now Bob.
It is not uncommon for there to be more than one fault.

I am right in thinking there may have been nothing wrong with the first brake servo?
In the end did you update the brake failure warning system
(I am doing this using a Mini reservoir cap)?


Thanks
Ian

[Carledo]

For anyone who wants to know

Glad you have it sorted now Bob.
It is not uncommon for there to be more than one fault.

I am right in thinking there may have been nothing wrong with the first brake servo?
In the end did you update the brake failure warning system
(I am doing this using a Mini reservoir cap)?


Thanks
Ian

It's an early car, updated with the dual circuit system from a late one, including the blankety-blank PDWA (now deleted) but the wiring for the warning light was never there. A job for another day maybe!

Steve

[10yearsafter]

Ian, I see my Rep. has answered your question about the wiring. I suspect that there was nothing wrong with the 1st servoso my apologies to Rimmers for even thinking that it was NBG. I would point out that the "Yoke " was wrong in both cases.

Next job is to trace suspected dodgey O/D wiring. Blown bottom fuse but I think it is only when trying to operate the O/D switch, otherwise the fuse seems to remain intact.
Bob

[new to this]

Ian, I see my Rep. has answered your question about the wiring. I suspect that there was nothing wrong with the 1st servoso my apologies to Rimmers for even thinking that it was NBG. I would point out that the "Yoke " was wrong in both cases.

Next job is to trace suspected dodgey O/D wiring. Blown bottom fuse but I think it is only when trying to operate the O/D switch, otherwise the fuse seems to remain intact.
Bob

Check the wiring that runs through the gear stick, ive got to do mine

Dave

[new to this]

There are several separate issues here.

Firstly is the "bias valve" which I presume is the factory fit (on a Sprint) LSV, or load sensing valve, which is situated at the body end of the rear brake flexi hose. These have a habit of seizing in one position which completely negates their purpose. Although the club can supply a seal kit to refurbish the LSV, it's my experience that you'll have great diffuculty freeing it off enough to service it and it won't STAY free for long, even when reconditioned by an expert. If you have TJ brakes on the front, you can safely and comfortably delete this. But it won't affect the quality or feel of the brake pedal, nor will it make bleeding difficult, even if seized solid.

Secondly is the TJs themselves. Because they use a bigger piston in the front calipers (54mm vs 48mm stock) it has a tendency to produce a somewhat "long" pedal. This can be partially offset by using the 1500/1850 5/8" bore rear wheel cylinders. But I find on my TJ fitted cars, that I need to keep the rear brake adjustment (I know they are technically self adjusting, but they never work IME) bang on or the pedal gets uncomfortably long.

Which brings me onto the rear adjustment, if it's not right, you will struggle to get a decent pedal. The cylinder needs to slide easily, the H plates in the handbrake shoes need to be there and not worn, The handbrake actuating arms need to pivot easily, shoes must be in good shape and drums need the rust lips on the outer edges of the wearing surface ground off so they slip over the shoes easily when manually setting up adjustment. The adjustment should be done with the handbrake cables disconnected and only once it's perfect should the cables be reconnected, adjusting the cable length if required. Don't FORCE the cables to fit!

Finally, you have a dual circuit master cylinder. If the car is a series IV Sprint (VA 30,000>) this is correct and the car will also be fitted with the notorious and almost completely useless Pressure Differential Warning Assembly (PDWA) on the bulkhead. This thing CAN make bleeding a nightmare, even when you THINK it's bled, it isn't! Since it doesn't tell you anything you don't already know (it only puts the light on when pressure in one circuit is lost, your foot will tell you that!) it's my habit to delete the troublesome and useless thing. I can provide a delete kit which incorporates a brass 3 way for the front pipes, an inline joiner for the rears and 3 new metal pipes for m/cyl > 3way and 3 way > both front flexis. The pipes are needed because the front circuit pipes on the PDWA use 7/16" UNF unions and I can't get a 3 way piece with 7/16" holes (I have tried!) To replace the PDWA's function, but more efficiently, I fit a level sensing m/cyl cap (a Saab 9-3 one fits) and connect it to the existing wiring, you only need to add an earth lead from the cap.

If your car is pre VA 30,000 and doesn't have a PDWA, ignore the last paragraph!

HTH, Steve

Steve i know you replace the PDWA valve with a 3 way union,would this work , just remove the shuttle valve from inside the PWDA unit ?

Dave

[soe8m]

Steve i know you replace the PDWA valve with a 3 way union,would this work , just remove the shuttle valve from inside the PWDA unit ?

Dave

No, then you would have a single system again. You can block the valve by only screwing in a bolt with copper washer in place of the switch. This way you can leave all in place and the shuttle valve can't move anymore.

Jeroen

[new to this]

Steve i know you replace the PDWA valve with a 3 way union,would this work , just remove the shuttle valve from inside the PWDA unit ?

Dave

No, then you would have a single system again. You can block the valve by only screwing in a bolt with copper washer in place of the switch. This way you can leave all in place and the shuttle valve can't move anymore.

Jeroen

okay thanks

Dave

[Carledo]

Steve i know you replace the PDWA valve with a 3 way union,would this work , just remove the shuttle valve from inside the PWDA unit ?

Dave

As Jeroen says, removing the shuttle will allow the 2 circuits to effectively become 1 as fluid will flow across the space formerly occupied by the shuttle. Which kinda defeats the purpose of having dual circuit brakes!

There is also the fact that the silly PLASTIC switch will come under fluid pressure from the brake system (Around 2000psi) which will blow it out like a bullet from a gun and result in total brake failure.

A 3rd factor that I've only experienced on Bob's car, is that, even though the shuttle was stuck in place, there must have been some damage to the internal seals as I did find some fluid behind the switch where there shouldn't be any! This could result, as and when this internal leak got worse, in the situation above arising. A brown trouser moment in the making if ever I saw one!

So, in conclusion, better, safer, easier and cheaper to delete the PDWA. It's a complicated, unreliable and inefficient solution to a problem that doesn't really exist. The very fact that they were only fitted to ANY car for a handful of years in the late 70s and early 80s PROVES this beyond doubt, if they were any good, they'd still be in use!

A fluid level sensing cap on the master cylinder (which IS still used today) gives earlier warning of impending failure, cannot possibly affect brake performance by any failure within it, has NO effect on ease of servicing the braking system and doesn't need to be "set up" every time brakes are bled. Finally, in production terms, it's massively cheaper than the PDWA!

My personal opinion is that it was an early attempt by Girling to satisfy a piece of proposed legislation (possibly in the USA) that never actually got adopted. No other major brake company produced anything like it, though some ATE systems of the same period (Notably VW, who also invested heavily in the US market) had similar sorts of pressure switches built in to their dual circuit master cylinders. Again these were only fitted to vehicles built around the same time period when the PDWA was current.

Steve

[soe8m]

Lots of Japs and Yanks had similar devices. It's not just a few Brits. The thing is when in the UK most had still single systems the rest of the world had dual systems. In NL sprints never had single systems. My first series 1974 Allegro has dual also and such a pdwa.

A lot more cars had these or similar but just not in single system UK.

Jeroen

[sprint-revival]

The very fact that they were only fitted to ANY car for a handful of years in the late 70s and early 80s PROVES this beyond doubt, if they were any good, they'd still be in use!

Steve

Sorry Steve have to disagree with that one, as a Mini man. Can confidently say these valves were fitted from MK4 Mini's - 1976 ish right through to MK7 and end of production in 2000. Only ever had one leak/fail, and even then didn't loose all brakes. Brake fluid/dampness was visible around the end cap and dripping onto the front subframe turret. I do like the idea of the added peace of mind of the split/tandem system. I will say however the PDWA (FAM7821) on the Mini, does occasionally cause issue when brake bleeding, however if sticking to old fashioned two man system, avoiding pressure bleeders, usually ok.

Olie

[RichardHyde]

Steve, is there any specific brake master cylinder cap with sensor level that’s easy to fit ? Guess the thread, cap diameter and sensor depth are key…
Thanks, Richard

[new to this]

Steve, is there any specific brake master cylinder cap with sensor level that’s easy to fit ? Guess the thread, cap diameter and sensor depth are key…
Thanks, Richard

Richard

The cap ive got think it fits was from Saab 9-3