Vexing Brake issue W460 - could it be the relined Master Cylinder?
Good day all
I have been rebuilding a 300GD over a number of years, when I got the car the brakes were poor so I replaced/rebuilt virtually everything on them. (including a master cylinder kit). After bleeding I still have a soft pedal.
- no external leaks, no bulging flexible lines
- a few pumps will bring the pedal up
- when disconnecting the pipe and blocking the front master cylinder outlet - the pedal is hard ie good
- doing the same for the rear outlet - pedal soft (This circuit goes to one of the two calipers on each front wheel)
I am unsure of the quality of the reconditioning job: the business which did the relining of the cylinder is no longer around. I do not have another cylinder to compare with, to check if the ports have been opened up correctly through the stainless steel liner now present. I see that there are 6 holes or ports down the length of the master cylinder:
- from the reservoir above there are 2 connections for the two circuits, each connection has 2 holes. One central and one drilled at an angle towards the rear. On my cylinder, the central holes are tiny, about 0.5mm in diameter! Is this correct? Can anyone confirm this size? The ones angled back are about 2.5mm in the case of the front connection and around 4mm for the rear.
- the 2 outlets to the pipework - these are drilled at about 1.5mm - looks to be the original outlet size.
Can anybody shed any light on this problem for me please? It is driving me up the wall!
Thanks in advance
Adrian
hi from Adrian to Adrian from the treffen 2012
Hi Adrian
Might be worth checking the vacuum lines. There is a vacuum pump mounted on the timing case cover. This is connected via a vacuum tube via a non return valve and accumulator to the brake booster. The brake booster has a vacuum connection but also a connection to atmospheric pressure. The pressure difference is the foot pedal pressure. Check these connections.
If you have a vacuum leak or defective non return valve the brake will still operate on hydraulic pressure but you will notice the difference at the pedal. Pumping the brake pedal restores brake pedal pressure and it will be maintained while engine in running.
It is difficult to find a small vacuum leak on these lines. They are prone to drying out and cracking at the t connectors.
Replacement vacuum lines are fairly cheap - I bought 11 meter length on ebay for 11 euro. I also replaced the non return valve as I found trace oil in the line a sure sign that the non return valve is passing.
Just a suggestion but worth checking..
Derek
You have mentioned some six ports or holes on your brake master cylinder (m/c), this confuses me for the pictures of m/c I have, show four ports. Two mounted top side for the reservoir and another two mounted on the side of m/c for the brake line feed.
Not knowing your chassis number I am working on the assumption of a W460 - 280GE model which shows four different m/c depending on chassis cut off's.
Two of which I have photos to support and the other two I have no image of.
Key points in m/c selection is knowing which side of the m/c body the ports are drilled - this determines a m/c for either a Left Hand Drive Vehicle or Right Hand Drive Vehicle.
Secondly, you need to know if the front calipers have three bleed screws or two or if the caliper is fed by one flexi hose or two?
But since you have repaired your original m/c, the above information is of no use to you.
Some newly build m/c can be difficult to bleed in which case you need to adopt a certain method of bleeding. Firstly be sure that the front calipers are freely moving, that being the case the rear brake shoes are properly adjusted and likewise, the brake cylinders are also freely moving.
Next, ensure all the bleed screws; front and rear are easy to undo and allow free flow of brake fluid through the bleed screw and either of the caliper bleed ports’ are not blocked as with the rear cylinder bleed ports.
Assuming you have a Right Hand Drive vehicle, use the following sequence to bleed.
We had better establish vehicle orientation and adhere to the Mercedes protocol which is by looking from the rear of the vehicle forwards we establish Left and Right hand sides.
So using the above protocol, bleed sequence is Left-rear, Right –rear, Left-front and finally Right-front wheels.
Before bleeding, clamp all flexi-hoses using hose clamp (Front brakes may or could have either a single flexi hose or twin hose per side but the rear brakes is a single flexi hose for both rear wheel cylinders) or very carefully using vise-grips or similar. Check the pedal pressure at the brake pedal. If firm and solid, the m/c is fine or else there is a problem with your newly build m/c.
Ordinarily, under normal bleeding, there would be no issues with the rear brake governor or limiter valve but since you are having problems it may be worthwhile to disconnect the bottom ball joint socket to the rear differential housing of the limiter valve connecting-rod. DO NOT excessively make up or down movements of the connecting rod as internal seal of the limiter can be damaged. Taking a 1/8th sized drill bit, insert this through the hole in the limiter’s lever (found at half the lever’s length) and feed this through - into a hole in the limiter’s body.
Keeping the hose clamps on all the flexi hoses except for the side or axle to be bled, bleed the first wheel side in the above mentioned sequence. If pumping at the brake pedal, bleed slowly and using the full pedal cycle. Do make sure the bleed screw is properly tightened before beginning the next pumping cycle. Do not rush this operation. After bleeding, when no air bubbles bleed out, move onto the second side and repeat as you did for the first side. The rear axle has one flexi hose which feeds both the rear wheel cylinders. After bleeding the second wheel, clamp the rear flexi hose and move to the fronts’.
Repeat the above procedure with the front wheel. I am no longer certain but my memory is confused if the front calipers have two flexi hoses per side in the case of split circuit brake feed but despite my confusion I will say take off one clamp at a time and bleed through all two or three bleed screws then repeat with the second flexi. In all this procedure, please have an assistant to keep the brake reservoir topped up at all times.
At the end all bleeding remove all clamps and check at the pedal. Hopeful you should be sorted. Remove the drill bit from the limiter valve and reconnect the link rod sock back onto the Diff housing.
If vacuum bleeding, wrap some PTFE tape on the thread screws of each bleed screw to avoid false air leaks or smear some copper clip on the threads.
Best result is you are able to pressure bleed
I am sorry I do not know or cannot paste my two photo images; would PM me your email and I can attach photos for your reference in that way.
If you any specific queries please do ask.
Adrian
I'm interested in the outcome / result if you could let us know. Also thanks for PDF article - very interesting.
Two points of note from what you have mentioned, either above or in your previous threads.
By blocking off the master cylinder outlet ports you have said there is a solid pedal, which suggests the master cylinder is fine.
If you clamp off front and rear flexi-hoses you should be getting a hard pedal. By removing the flexi-hoses clamps one side at a time will reveal which side is causing you a problem of a soft pedal. In my estimation, I feel that removing the rear flexi-hose clamp will give you the soft pedal; note: do clamp the front flexis' to isolate the fronts and as I have mentioned if the rears show soft pedal it can only be the rear brake shoes need adjust and assuming these are fine earlier as you mentioned not good enough.
Check your email as the document I want to send can not be posted from here.
Until my pipes were all replaced with braided pipes and the rear shoes replaced, my brakes were pretty naff. Good now.
1. So now master cylinder is OK .. previously you definitely had something wrong in one circuit.
2. I too do not/dislike hose clamps, I know they are used but having had inner hose lining delaminating and hence become one way check valves that hold pressure on in calipers etc .. it is not good practice (as an ex brake engineer). Saying that if I had old hoses I was going to bin or was in a corner I might still do it as lots of others do.
3. Brake shoe being unadjusted will make for a long pedal stroke
4. 460 brakes are not the best and are spongy for what they are.
5. If you change the master cylinder officially you probably need to adjust the servo output rod .. worse case you can get brakes to hold on .. otherwise a little longer pedal if the gap is too much.. but probably not a real issue.
6. Presume the ports you talk off are the little holes on the pistons in the master cylinders which stop the lip seals from sticking to the pistons and allow flow on the return stroke of the piston.. ultimately they are just hydraulic/pneumatic cylinders with spring between and one way lip seals.
Bleeding... the way I do it.
1. Assembly system
2. open bleed nipples fully i.e. about 1 turn
3. fill with fluid and allow gravity to push it down..
4. close off each caliper/piston/nipple as they start to dribble
5. then go to rear furtherest nipple (from master cylinder) and open 1/4 turn
6. pump 10 times, check fluid level in reservoir and that fluid is coming out, pump another 10 pedal strokes
7. Close nipple and work forward to next furtherest nipple.
8. Now thrash the pedal as fast as you can for 20 strokes. This will cause all the air pockets to become broken up into foam in the fluid .. note some ABS and valves will still have air pockets (and so the best is to Never allow fluid to drain).. so you may need to repeater after a pressure bleed
9. Pressure bleed = start at furthermost nipple from master cylinder again. Open nipple just an 1/8 or less. The idea is to get the foam/air compressed and then dragged out under high pressure through the nipples at emergency stop levels of pedal pressure. (air compresses quickly so at 10bar/150 stroke it occupies only 10% of the volume; an emergency stop is typically 100 bar/1500 psi). So each stroke should take 3 seconds at a high pedal force.
10. Do the next 3 nipples working towards the master cylinder.
11. Sometimes doing a low pressure /high volume bleed can help flush out foamed air (from the thrashing of pedal).
12. Flush everything with water to get rid of brake fluid .. it is nasty vegetable fluid which eats most things.
13. Repeat every 24 months.. and especially at the nipples as the standard black hoses actually let water through and into the fluid.
14. The black stuff in the fluid is "carbon black" which is leached out of the seals and also from seal wear .. the brake fluid will go dark brown at the calipers from heat too.. 100-120C for 200 hours will do that but that is a lot of heavy braking..
In a factory you have a £100k vacum rig which pulls 95% vacuum at the master cylinder filling point.. and this will boil off any liquids.. then it changes over to brake fluid and you get a perfect bleed. Actually you can get an even better bleed if you build everything under fluid (i.e. big tub of brake fluid and assemble everything "under water" i.e. below the fluid/air interface.. but the rest of the car does not like brake fluid and it would be a big tub of brake fluid.
.......................I will try pressure bleeding. Just one question: does one need to operate the pedal during pressure bleeding? .................................
Adrian
In pressure bleeding or vacuum bleeding, one does not have to do anything to the brake pedal at all.
One final suggestion from me, try bleeding with the engine running; sometimes the servo assistance of servo does help in bleeding.
Check your pedal shaft to the servo from the pedal to see that it is not bent. One thread from above has mentioned that checking of a length of shaft in the servo; I do not know what the length should be.- sorry.
Sounds feasible to me, you are already over the limit of minimum drum wear hence the pedal is effectively traveling a longer distance. The fact we are talking of a few millimeters is of insignificance - renew those drums without hesitation. The brake lining should be OK but if these are grooved, I would suggest a new set on your new drums or sand them so it comes with a flat surface.
Remember to slacken your hand brake cable to readjust the shoe adjustment and readjust the cable after the shoes have been adjusted.
If you need drums , i have just got a pair from these chaps....reasonable cost and quick delivery...
http://brakeparts.co.uk/#page=parts&pageSection=BDR&mancode=MERC&brand=M...
Steve
Nice of you Steve, but our matey is down under.
Oooops.....never was very observant. I'll try again
http://www.rdabrakes.com.au/page/Products-Brake-Drums.aspx
SK
Sorry to rub salt into a wound but..............................
http://www.ebay.co.uk/itm/BDR257-New-Pair-Rear-Brake-Drums-Mercedes-G-Wa...
steve
I tried stamping on the pedal and this produced no bubbles. I am pretty sure the secondary circuit is working as the pedal gets hard towards the bottom of the stroke. And when I took the car for a drive around the block, there was some braking action at that point of the brake pedal travel. The pedal gets harder after a few pumps, but this does not translate to much braking effort on the road.
I will try pressure bleeding. Just one question: does one need to operate the pedal during pressure bleeding?
OK.. proper pressure bleeding means putting a sealing cap on on the master cylinder reservior with a hole in it.. you attach that hole via a hose to a pressure vessel that has a hose out the bottom and pressurised air coming in the top and has brake fluid in it. This causes the air in the pressure vessel to push the brake fluid out into the master cylinder reservoir.. and when you open bleed nipple the fluid flows.
My method is a DIY pressure bleed which sometimes works better .. guess I should call it something else.. I create the pressure by pressing hard on the brake pedal while having one bleed nipple just cracked open. When you do that you will get foamy brake fluid as the fluid under pressure expands through the bleed nipple (due to expansion and partial vapour pressure) but that foam does not mean you have brought air out of the system; you are not looking for bubbles coming up through the reservoir.. you are looking to repeatly pressurise very quick the fluid to cause the air to foam internally to the valves (i.e thrash pedal with closed nipples).. and then as a second operation you are pulling that foam out through the nipples (with a long heavy pedal push).
The rear brake valve could have had air in it.. could be stroking out if not correctly fitted (it is a pressure reducing valve that will reduce pressure to the rear brakes dependant on the load (i.e. distance between body and axle which is related to suspension travel i.e. spring gets compressed under load). They are simply pressure reducing valves that start to operate at a certain pressure.. and then give a constant percentage reduction.
There must be 2 types of master cylinders .. one for your H-I setup (where one circuit does both front and rear, one circuit does half front) .. and one for my I-I setup (where one circuit does rear, one circuit front). These would need different volumes so the piston setup in the master cylinder would be different. I wonder if someone fitted an H-I setup to an I-I car .. so that even though you have a new master cylinder it is still wrong and so your are running out of volume.. and hence no pressure? Sorry to throw another unknown to you… but you are on the right track by isolating parts by parts.. and might as well clamp off the rear hose if you are replacing it to isolate the issue to the rear axle (or volume of fluid used there).
ARRGH.. this online editor is horrible .. keeps block deleting text as you write and catch the wrong key.. had to write this and paste it back.
Did he say he has 2 or 3 nipples on his front calipers? Correct sequence is from bottom inside to top outside nipples. No need to pump pedal as Rakesh says. Only open nipples a bit. You should not use too much fluid. Just work slowly watching the bubbles come out. Dont pump pedal in between Check all connections. Wetness= a leak=No good. I use a Mityvac bleeder to vacuum suck the fluid through. Set it to 20 for example and try to maintain. When it stays there and fluid fills the jar slowly( not too quickly as you will only have nipples open a bit remember). Air has been bled out and your sucking fluid. The line and caliper/ wheel cylinder is full of fluid which is what you want. Also are your calipers new? Check behind pads for fluid coming out if the seals. Not easy to see but you'll know when they dont work.
D
I will add..... When bleeding , once fluid coming thru the reading should stay constant once the nipple has been 'locked' shut. Use ptfe tape approx 5 times round each new bleed nipple. Pumping will introduce air into the system. Check the seal connection where the reservoir sits on the master cylinder. Did you say you changed the front flexy hoses. Pretty cheap to do. Braided ones are ok but wont add too much to the G stopping experience.
I will add..... When bleeding , once fluid coming thru the reading should stay constant once the nipple has been 'locked' shut. Use ptfe tape approx 5 times round each new bleed nipple. Pumping will introduce air into the system. Check the seal connection where the reservoir sits on the master cylinder. Did you say you changed the front flexy hoses. Pretty cheap to do. Braided ones are ok but wont add too much to the G stopping experience.
Well done on getting there.. well a "better" pedal. They are never the most solid of pedal IMHO and I have Goodridge hoses on all the way around. If you have had one busted up flexi hose .. then all the others should be regarded as suspect. They get busted up by folk using mole grips as clamps.. or I suspect clamp bars do not do anyone any favours as I said. They are known to break up on the inside after damage like this and then the hoses become one way check valves and hold the pressure/brakes on. No reason why if the fabric reinforcement has become damaged that they could not also swell under pressure like an accumulator. As I say.. Goodridge do a hose kit in UK with proper PFTE lining (so water cannot be absorbed unlike the rubber hoses) and stainless wire reinforcement so less swelling under pressure .. but then you cannot use hose clamps with them.
Montreal - the pumping is to break up air bubbles. Plain slow pumping or Vac sucking when you have air pockets (especially ABS) on dead end legs of the pipework/valves will never get that air pocket out. I used to do this for a living (designing and testing brakes) and you could get all sorts of air into the system once you allowed it to drain which nothing ever got out again (unless you have a deep vacuum from an industrial vacuum pump to boil the fluids off) .. the trick is to never allow the air into the system. The threads of the bleed nipple do not seal them.. it has a cone on the end but as an idea to make them more anti-sieze by using PTFE tape on it has merits as a good idea. I actually just use black/PTFE loaded grease (which could affect the brake seals.. but as the fluid does not go backwards ..it cannot get there), then water to wash, then blow out.. then Dinotrol ML over/into the nipple (all after tightening after final bleed.)
Hello
Seems that I've hit upon the same issue on my g300e.
After many months of restoration work, which included many new brake parts:
- Goodrich hoses
- New seals and pistons in front calipers
- New front pads
- New rear cylinders
- New brake shoes
- New drums
- New rear adjuster mechs
- new spring kit
- New pressure regulating valve for rear axle
- New brake line pieces
The brake pedal has the same problem of long travel, described in the above post. The rear shoes are adjusted to the point of slightly rubbing on the drum, but the brake pedal requires two or three pumps to begin to work and when it is hard, it maintains the pressure, so I don't think its an issue with the master cylinder being faulty.
I've been round the system several times to bleed any air and it think it's fully bled.
Does the 463 have the same pre-pressure retaining valve that was identified as the cause in the original post? If so where do I find it?
I am guessing this must also be the cause of my problem, since even a couple of mm movement on each side of the two rear wheel cylinders must equal a few cc of brake fluid that needs to be pumped before anything happens.
Thanks.
Hi Adrian
Lucky you, out there camping, and amoungst other G's too. I like your camper conversion, must be very comfortable!
Cheers !