Re: Sprint Brakes
Posted: Fri Apr 08, 2022 8:41 pm
RESULT 
Well done...perseverance pays off in the end.
...but does the pedal drop when you start the engine now?
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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.
Glad you have it sorted now Bob.
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!sprint95m wrote: ↑Sat Apr 09, 2022 5:48 pmGlad 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
Check the wiring that runs through the gear stick, ive got to do mine10yearsafter wrote: ↑Tue Apr 12, 2022 10:28 am 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
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 ?Carledo wrote: ↑Sun Jan 23, 2022 4:11 pm 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
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.new to this wrote: ↑Mon Apr 25, 2022 9:46 pm
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
okay thankssoe8m wrote: ↑Tue Apr 26, 2022 12:58 amNo, 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.new to this wrote: ↑Mon Apr 25, 2022 9:46 pm
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
Jeroen
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!new to this wrote: ↑Mon Apr 25, 2022 9:46 pm
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
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.
RichardRichardHyde wrote: ↑Tue Apr 26, 2022 5:28 pm 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