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| Sprint Brakes http://forum.triumphdolomite.co.uk/viewtopic.php?t=37093 |
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| Author: | 10yearsafter [ Sat Jan 22, 2022 5:59 pm ] |
| Post subject: | Sprint Brakes |
as previously posted I have fitted an new servo to my rebuild sprint which has Tracker Jack conversion. but I still have virtually no brakes worthy of the name! I have twin circuit brakes with a new M/cyl all bled and working when jacked up with the engine off. I have also fitted a brake bias valve which may be a bad Idea so I intend to remove it. The supplier turns out not to be a fan of these things! NB the OE version was not serviceable. I suspect that the TJ conversion should make a bias valve redundant anyway. I have a Vac reading of about 8 at tick over and up to 25 on overrun. Running 2" SUs and a Lotus L14 cam. The discs are free of grease etc. Apart from removing the B/valve any Ideas as to what might be the cause? PS I have now found out what many will already know. If Your Tracking is out it plays havoc with the the camber! I live and learn. Bob |
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| Author: | GlenM [ Sat Jan 22, 2022 6:42 pm ] |
| Post subject: | Re: Sprint Brakes |
I think Jon does advocate getting rid of the LSV on the rear axle (a bone of contention with some on here). If you have fitted a bias valve (rather than a load sensing valve) I would get rid of that and then see what happens with the brakes. Although if it was incorrectly set you would expect either the front or rear brakes to lock prematurely. Is the pedal firm? Also, as it is a late system with the pressure differential valve on the bulkhead it would be worth checking that the shuttle is centred before bleeding. Ideally do away with it all together. |
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| Author: | cleverusername [ Sun Jan 23, 2022 11:12 am ] |
| Post subject: | Re: Sprint Brakes |
Why would a brake bias valve lead to poor brakes? Most of the braking force is at the front anyway, so I can't see how a valve designed to restrict braking force at the read could have such an effect. By no brakes, do you mean the brakes feel bad or the car literally won't stop? |
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| Author: | Carledo [ Sun Jan 23, 2022 4:11 pm ] |
| Post subject: | Re: Sprint Brakes |
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 |
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| Author: | 10yearsafter [ Sun Jan 23, 2022 6:33 pm ] |
| Post subject: | Re: Sprint Brakes |
Thanks for the responses To answer some of the questions; I have fitted a Screw type Brake proportioning Valve. In the Cab, in line with the rear brake line. The pedal is firm with very little travel. the Old LSV was junked. The stopping power is minimal even from 10 Mph. It does stop but very slowly! All parts are new and rear brakes adjusted well enough. Vin No VA22387DLO but this does not mean very much as it has been a nut and bolt rebuild. The twin circuit M/ cylinder is an upgrade. not sure about spindle being stuck. This would have been sorted in the recent seal replacement . No PDWA. H plates new. There is a potential problem; When the brake system was fitted (by others ) they failed to add brake fluid ! When I took on the work maybe 3 years after the fitting I had to replace rear wheel cylinder seals and master cylinder seals. I guess everything had set solid with no fluid. This might have effected the Proportioning Valve but all seems to bleed as you would expect and as I said the front brakes work when jacked up and turned by hand with the engine off. I will keep you posted. Thanks Bob |
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| Author: | GlenM [ Sun Jan 23, 2022 6:46 pm ] |
| Post subject: | Re: Sprint Brakes |
Bob, If the twin circuit system is an upgrade on a single circuit car, it might be worth checking that it is all piped correctly from the master cylinder. |
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| Author: | Carledo [ Sun Jan 23, 2022 10:36 pm ] |
| Post subject: | Re: Sprint Brakes |
Sounds like the servo isn't working, a high hard pedal and little or no stopping effort is a classic symptom. Possibly calipers sticky or seized. It doesn't take much to stop a hub turned by hand, but that doesn't necessarily translate to fully functioning brakes. Steve |
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| Author: | xvivalve [ Mon Jan 24, 2022 12:02 am ] |
| Post subject: | Re: Sprint Brakes |
Start the car with your foot on the brake pedal; if the servo is working you should feel the brake pedal drop. |
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| Author: | 10yearsafter [ Mon Jan 24, 2022 11:44 am ] |
| Post subject: | Re: Sprint Brakes |
Sounds like good advice. Thanks. Bob |
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| Author: | 10yearsafter [ Mon Jan 24, 2022 2:53 pm ] |
| Post subject: | Re: Sprint Brakes |
Despite a new Servo from our friends in Lincoln there appears to be NO pedal movement when doing the test described above. Does the panel think that this justifies removing the servo? I would guess so. Are there any tests that can be done with the servo in place or even once it is removed? I will speak to 'Lincoln' when Carl is back from Holiday. I feel there is proof that there is vacuum from the tests I have done. Who services the club Servos? DM if you think this might be of use. Bob |
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| Author: | cleverusername [ Mon Jan 24, 2022 5:14 pm ] |
| Post subject: | Re: Sprint Brakes |
Quote:
Despite a new Servo from our friends in Lincoln there appears to be NO pedal movement when doing the test described above.
Before condemning it, check for vacuum leaks. Always best to look for the cheap fixes like a split hose, before moving to expensive stuff.
Does the panel think that this justifies removing the servo? I would guess so. Are there any tests that can be done with the servo in place or even once it is removed? I will speak to 'Lincoln' when Carl is back from Holiday. I feel there is proof that there is vacuum from the tests I have done. Who services the club Servos? DM if you think this might be of use. Bob |
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| Author: | SprintV8 [ Mon Jan 24, 2022 6:52 pm ] |
| Post subject: | Re: Sprint Brakes |
Also worth checking you have vacuum After starting and running for a minute or so pull the vacuum line off the servo. It should hiss. If not check the one way valve is the correct way round. And you have vacuum from the manifold takeoff. |
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| Author: | 10yearsafter [ Fri Feb 25, 2022 5:40 pm ] |
| Post subject: | Re: Sprint Brakes |
2nd. servo from lincoln has not improved the job, so despite all the tests I think I have to look elsewhere. I plan to 1 ) remove a F.brake pad to check that the pistons are working. 2) Check the PDWA unit on bulkhead but I am not sure how this should be connected despite the parts book Showing 2 pipes (309760/759) coming to the top of the unit which I guess come from the Master cyl. another 2 pipes with in line flexi. connected to the L/H side and the underside leftof the PDWA which I take to be the front pipes. Leaving the 5th pipe for the rears. There is a lot of talk about centralising the shuttle. WHAT HAPPENS IF THE SHUTTLE IS NOT CENTRALISED, apart from the dash light coming on (not connected) , DO YOU HAVE EITHER FRONT OR ( GOD FORBID ) BACK BRAKES? Just having back brakes is maybe where I might be as they are not bedded in, test 1 should prove this? WHAT HAPPENS IF I REMOVE THE SHUTTLE ? there is no Dual circuit? I can live with that. I have read a lot of posts on this from over the years but can't help feeling I am missing something. Help Bob |
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| Author: | Carledo [ Fri Feb 25, 2022 9:24 pm ] |
| Post subject: | Re: Sprint Brakes |
You have a high, hard pedal that doesn't alter when you start the engine with pressure on it. This alone tells you that for whatever reason, the servo isn't working. The lack of stopping power can be entirely due to the servo not working. It's possible that if you had one duff servo from our friends in Cambridge you could have another. On balance of probability though, there is a good chance that the vacuum is not getting to the servo. Maybe the hose has collapsed internally or the valve on the servo end of the hose is duff. Sort this out FIRST! On the PDWA, the 2 pipes from the master go into the top of the PDWA, the one from the servo end of the master (rear circuit) goes to the outboard top inlet on the PDWA and the front circuit goes to the inboard top inlet. The pipe to the rear brakes goes in the outboard bottom exit hole, the pipe to the N/S/F wheel goes in the inboard central exit hole and the one to the O/S/F wheel goes in the inboard bottom exit hole. You must NOT delete the shuttle from the PDWA, as it would allow system pressure behind the plastic electrical switch which would blow it right out of the unit and result in a total brake failure! Even if you COULD do it, to do so would allow both circuits of the braking system to operate the entire system all together. Since the whole point of dual circuit is to separate the two circuits, this is madness! Either fix the PDWA and bleed it correctly or (my recommendation) delete it entirely. My delete kit is £30 including UK postage and comes with full instructions. Steve |
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| Author: | 10yearsafter [ Fri Apr 08, 2022 8:07 pm ] |
| Post subject: | Re: Sprint Brakes |
For anyone who wants to know. The story goes like this; having fitted the 2nd of 2 new servos, I decided that I had to look elsewhere. Found that the OSR wheel cyl. had seized-- stripped and cleaned= No rear brakes Consulted with Carledo/ Steve who advised that despite the parts book, it looked as if the PDWA was upside-down = removed and found that there was no airway/ brake fluid access from the M/cyl. connection to rear brake outlet.= Hot and Cold treatment seemed to cure this; with air going to all ports, so I pressumed shuttle was centralised. Reassemble= no improvement. Steve insists that the flexi pipes to the front brakes should be removed. The flexi to the OSF was too short when the PDWA was turned the right way up! Steve makes up a standard front brake system using a 3 way brake connector instead of the PDWA which showed signs of fluid where the switch wiring connector goes. The rear brakes ( Flexi ) are directly connected to the M/cyl.= gravity bleed and in a few minutes We have front brakes. But no rears- so conclude that there must be a problem with M/cyl. that was meant to have been re-sealed at the end of last year = lots of crud at the end of piston, so this hadn't been apart in the recent past- removed piston to find the rear most seal was fitted the wrong way round. carefully removed and replaced. To simplify things we decided to remove the proportioning valve that I have mentioned. RESULT = I NOW HAVE PUT YOU THROUGH THE WINDSCREEN BRAKES. Thanks to all those who have advised. Onwards and upwards Bob |
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