| Author | Message | ||
     Chris Buckenham Yet to post message Username: chris_buckenham Post Number: 1 Registered: 6-2012 |
Hello Everybody , I have been reading this excellent forum for some while now , it has been very helpful to me . Recently I acquired Turbo R 57843 1996 with 51,000 miles and a good service history . After exactly 1000 miles and one week the A bank head gasket went fortunately only a few miles from home . I live in north Essex and have had quite a bit of advice from P & A Wood on resolving the problem , which I tackled myself at home . After a fairly lengthy top end rebuild the car started and ran last weekend and at present I am happy with the outcome . My problem is that we can't seem to bleed the bloody brakes . Having followed the process in the manual and tried various other techniques as discussed with P & A Wood I cannot seem to get the system pressure to raise at all and certainly not to the point of extinguishing the "STOP" and "BRAKE" lights on the display . We have absolutely clean new fluid at all four front brake calipers and at the bleed point on the pressure switches . We have been bleeding the brake calipers with the pedal depressed / engine running using a syringe into the feed pipe to the pumps as suggested by the experts and achieve a good flow on applying pressure to the syringe . The fluid does not seem to issue under any form of pump pressure . When the pedal is released the lights stay on . So far we have only attempted the front calipers in terms of bleeding a system . We were expecting that at some point the pump would take over and fluid would begin to flow from the bleed screws on the calipers . We have bled the accumulators . The pumps were rebuilt using Crewe seal kits lubricated with the fluid but not filled prior to refitting . Any ideas on what is being done wrong would be greatly received . Thank you and best Regards , Chris. | ||
| James Feller Prolific User Username: james_feller Post Number: 222 Registered: 5-2008 |
Hey Chris, welcome from down under! Im sorry to hear that you have done a head gasket in such a low mileage car....this is not usual and I can only assume either the previous owner was not up to scratch with servcing or it just happened to be plain unlucky mate, shame too as you had only just got it....not a great start to Bentley really. As you would now know these cars, despite some people carrying on as if they are infallible, fail at times....anyway I trust all is going well now and your Zytec Turbo would I assume really move along!! make sure your knock sensors and boost solenoids are clean and working....long story in previous posts but you will thank me! OK back to your question, maybe an airlock in the system? odd you 'bleed the accumulators'? why....id just replace both the front ones on B Bank under the PAS pump(these accums power the brakes) and while you are at do the suspension damper ones in the boot for the rear struts. They are cheap items and are nothing to replace and make the world of differnce. Im no mechanic btw, but Im not sure other than the accumulators are stuffed thus not holding pressure, as to why your car would not be pressurising the braking system and suspension systems. There is not a pool of green HSMO in the engine valley? ie the pumps are not sealing properly? anyway Im sure you will get lots of sound advice. Good luck and get that fabulous Turbo storming along the motorways again, they love it! J | ||
| James Feller Prolific User Username: james_feller Post Number: 223 Registered: 5-2008 |
ohh btw, im not sure how familiar you are with these cars Chris but the brake pedal doesnt power anything on our cars, its not attached to a conventional master cylinder arrangement like that of other cars....its simply attached to a big spring in the 'rattrap' located under the floor about where your right foot normal is...the spring is what gives you the 'feel' of brake resistance and retardance. You can pump it all day long and it wont make a dick of difference in 'bleeding the system' or stopping the car for that matter if there is no pressure in the system. Its the 2 hydraulic pumps and spheres that provide presure to the whole system. Again no idea if you know how our brake systems work but its not like a conventional car. its all hydraulic actuation. again good luck it should not be too difficult to get working. Cheers J | ||
| Chris Buckenham New User Username: chris_buckenham Post Number: 2 Registered: 6-2012 |
Hello James , Thanks for the response . To be honest I/we now understand the system fairly well and so we are struggling to get to grips with why the pumps don't seem to be producing any pressure . Maybe I rebuilt them incorrectly , but I don't think so . I have been reading all about the Turbo issues and when the thing is back on the road again we will carry out some measurements and start checking the performance . There was a completely sheared - I know that sounds odd - hose from the turbo to one of the solenoids when the whole thing was dismantled which was replaced . Thanks again , Chris | ||
| Bill Coburn Moderator Username: bill_coburn Post Number: 1429 Registered: 4-2003 |
Did you check the pump bush rods that they haven't snapped? | ||
| Chris Buckenham New User Username: chris_buckenham Post Number: 3 Registered: 6-2012 |
Hello Bill , Yes - I did check the pump push rods when the valley cover was replaced , it was resealed as part of the process and they were fine . However we are beginning to consider that the pumps or the rods are not now working properly . But , what is your view on the following , when the syringe full of fluid is connected to the feed pipe of the rear pump / front brakes there is a visible pressure pulse in the syringe which can be clearly felt as well and is directly linked to engine speed . To us this suggests that the push rod is in contact with the cam side of things and that it is working as it should . We wondered if it had become bent whether it would still produce a marginal amount of movement resulting in the flutter but not providing enough travel to generate pressure ? I'm thinking about taking the intercooler off later and cracking the outlets from the pumps to see if fluid issues from them .Any views or suggestions welcome at this point . Regards Chris. | ||
| Chris Buckenham New User Username: chris_buckenham Post Number: 4 Registered: 6-2012 |
Hello Everybody , New information , we took the intercooler off this evening and cracked the outlet of the front pump and ran the engine briefly and fluid issued at some rate . Connected a hose to the outlet and ran the engine for about 30 seconds . It hunted around 1000 rpm and we collected about 150 - 200 ml of fluid , all clean new from the reservoir . Reattached the outlet on the top of the pump and ran the engine again with no effects whatsoever The rear suspension would not raise at all , it must be the accumulators ? Any thoughts on this greatly appreciated . Regards Chris Apologies for the way this is presented , I can't work this ipad | ||
| Omar M. Shams Prolific User Username: omar Post Number: 274 Registered: 4-2009 |
Dear Chris, Pull one pump out. This is not too hard to do. Put it on the bench and fill the inlet port with hydraulic oil. Activate the pump by pushing it against a drift of some kind to simulate its operation. with a full suction port, it would only take two or three actuations for you to get a significantly visible discharge come out of the top of the pump. I have previously rebuilt pumps incorrectly (in my youth) and they have not pumped as a consequence. if your pump works as intended, then my money would be on the accumulator body having a blockage of some kind. Good luck Omar | ||
| Michael Hicks Frequent User Username: bentleyman22 Post Number: 68 Registered: 12-2011 |
Hi I Have a RT and when we had a problem with valve push rods when it went back together she went and throw a tantrum with her brakes and fluid so we striped the top back off we striped and cleaned the both pumps and filled them up and then did the same with the pipes put it all back and it fired up ok and she slowly built up pressure and then used a litre glass bottle on a front Calliper B/Nipple and let it get rid of all the air and i did this on all Wheels but will admit she needed the Accumulator’s replaced and there good have you had a look at http://www.rrsilvershadow.com/ETechn/Hydr/Compaccum.htm | ||
| Chris Buckenham New User Username: chris_buckenham Post Number: 5 Registered: 6-2012 |
Thanks Very much Omar and Michael , I reckon that the accumulators must be done now to eliminate them as James said earlier . When the pipe was off the top of the pump the fluid would easily have travelled 5 or more feet in the air if not caught by a rag . | ||
| Omar M. Shams Prolific User Username: omar Post Number: 275 Registered: 4-2009 |
Dear Chris, I would look at the accumulator body not the accumulator itself. Thanks Omar | ||
| Chris Buckenham New User Username: chris_buckenham Post Number: 6 Registered: 6-2012 |
Thanks Omar , Are the pump bodies known to fail ? Chris | ||
| Omar M. Shams Prolific User Username: omar Post Number: 276 Registered: 4-2009 |
Dear Chris, Accumulator body not pump body. And yes the accumulator bodies have been known to fail. I had your exact symptoms on my friend's 96 Silver Spur and it was the accumulator body that was the culprit. By accumulator body I mean the block that the accumulator sphere screws into. | ||
| Chris Buckenham New User Username: chris_buckenham Post Number: 7 Registered: 6-2012 |
Hello again everybody , Things are not going too well . I have replaced the accumulator spheres and the bodies . There is good flow at the inlet pipe from the pump to the accumulator body . There is good flow at the outlet from the accumulator body . There is good flow at the inlet tYo the distribution bodies and a good outlet also with the pedal depressed . The leakage from the distribution body with the pedal up is barely perceptible and with the pedal down is zero . Absolutely nothing comes out from the return white and black pipes . There is not a good flow from the pipes , blue and purple I think as they go into the ABS unit . Is there anything in between ? According to the manual there is not . I have had good clean new fluid from all bleed nipples on the system but the pressure just will not rise . A great deal of air has come out but this has now stopped . So far I have not measured pressure but I can if necessary , I have assumed that as the pumps are delivering adequate flow then they must be working properly . I did think that I was going to fine a huge return flow at the distribution valves but as they seem perfect I am beginning to struggle with it . Any help Chaps would be greatly appreciated . Best regards , Chris | ||
| Chris Buckenham New User Username: chris_buckenham Post Number: 8 Registered: 6-2012 |
What an annoying weekend . We checked the flow again at the inlet to the accumulator bodies and it was good . Connected a pressure gauge and nothing . No pressure . Plenty of fluid delivered but no pressure . Did the same at the outlet of the pump and again no pressure displayed . So I reckon it must be out with the pumps . I am surprised at the amount of fluid delivered though . Best regards Chris | ||
| David Gore Moderator Username: david_gore Post Number: 1135 Registered: 4-2003 |
Chris, The following comments are based on my experience with Shadow pumps and I am assuming your pumps are the same. When you pull the pumps apart; check the washers for corrosion and if they are pitted, try wet cleaning them up using 800/1000 grit wet and dry sandpaper in sequence on a sheet of glass as backing. These washers act as a non-return valve so system pressurisation is achieved. The sequence of the washers is critical - if my memory is still reliable, one of the washers is slightly convex/concave and this washer lifts to allow the pump to pressurise the system and falls back on the suction stroke due to the suction and back pressure from the system. I have the washer sequence in my archives but I will not be able to access them till next week as I am away till then. Just use your finger in the centre to hold the washers lightly on the paper and use a circular motion to polish the washers. After you reassemble the pumps, bench test them by clamping them in a vice, filling them with methylated spirits [denatured alcohol], blocking the disharge port with your finger whilst pushing the piston in with a suitable rod. If the pump is properly assembled, you will feel the pressure and the pump will lock solid. If the piston continues to move and some pressure is felt, the washers need replacement/further rectification. If there is no pressure, the washers need replacement subject to the following information. If fluid runs out of the bore of the pump, replace the O-ring in the bore on the pushrod side of the pump and try again. If fluid continues to leak, the pump requires resleeving by a hydraulic workshop or replacement. My suspicions are the fault lies in the washers at the top of the pump. | ||
| Chris Buckenham New User Username: chris_buckenham Post Number: 9 Registered: 6-2012 |
Hello David and everybody else who has helped and looking at this thread . We took the front pump off tonight and disassembled it , cleaned everything , reversed the critical washer mentioned above so it was acting on what I believe to be its better face , reassembled and achieved 600 psi on the gauge pumping by hand against a soft drift in the vice . There was debris of varying types in the pump . Does anybody know of an easier way of removing the rear pump than taking off all the induction equipment ? Thanks Chris | ||
| Michael Hicks Frequent User Username: bentleyman22 Post Number: 71 Registered: 12-2011 |
Hi Chris good News getting the Throttle body of isn't that bad I can give you some tips if you like Michael but if your getting rubbish in there you need to get it all out Michael | ||
| Chris Buckenham New User Username: chris_buckenham Post Number: 10 Registered: 6-2012 |
Hello Everybody , Well , problem solved , brakes bled and full pressure restored . The problem was unbelievable . In both pumps the same issue . The aluminium sealing washers that came in the brake overhaul kits were both the same and oversize on their external diameter . Approx 0.45mm was removed on a mandrel on the lathe and as a result sat into their correct position in the pumps . They had been effectively allowing the valve face / non return valve to rise a small amount in the housing and fail to seal . It hadn't even occurred to me that the parts supplied to refurbish the pumps might have been at fault . Thanks to all of those who have helped . Regards Chris |
