MOT And rear brakes
I took my new to me 300GD SWB for it's first MOT today after being off the road for a few years.
Sadly, it failed on a couple of items. One is an exhaust leak on the silencer- nothing the welder can't put right.
Secondly is the poor brakes.
The rear brakes in particular, they were unbalanced and also had poor efficiency, but he also commented that he would expect a bit more from the fronts too, although they were in balance.
This is the printout from the testers brake machine.
https://drive.google.com/file/d/1hUVv3DhN1-JycrEcn5Oil_FRtU7QeR6Y/view?usp=sharing
A quick search brings me to the conclusion that it's likely an issue with the rear shoes not being adjusted properly.
I have replaced the cylinders, linings and drums, and followed the workshop manual procedure for pre setting the auto adjuster, but I suspect the adjuster isn't working right (even though it was free and greased), so this weekend i'll try to adjust them manually.
Am I right in saying that if the rear brakes aren't adjusted correctly, then the second circuit on the front calipers will also not be working very well? That would account for the lower than expected front braking force too.
Anybody with more experience on these brakes like to chime in please?
I am having the same work on my 230GE. Unbalanced brakes at the rear and a bit grabby.
When they were last overhauled, it was the auto-adjuster that was sticky. And if yours has been sitting a while, with hand brake on say, it was good to replace the drums in case of ovaling. I have drums coming today.
There is a balancer valve between the two rear brakes, but they don't generally fail and tbh I don't know how it equalises pressure in the brake fluid. I also can't see why front calliper pressure would be affected.
Assume by balancer valve you mean the load sensing valve that has the rod connected to the rear axle ?
This distributes more braking effect to the rear when more weight is in the back
These so often fail and will allow little rear effort so worth checking
The brakes should be bled with this rod disconnected and tied right up on full open
If the valve is seized however it need's replacing, from memory the early cars had a manual adjuster also and only later ones got the automatic type
Having said that rear adjuster as suspected could be the issue along with glazed / contaminated shoes if they are old or even glazed if new
Have you bled all 6 nipples on the fronts?
Rear drums could be glazed also or worn out of tolerance if old... we used to skim the drums and then fit oversized linings but new drums and linings is usual now
Ok, Well discovery today - I checked the auto adjusters and they had grown to 72mm, so they appear as if they have been working. I did, however, manually wind them out further, until the drums just had a bit of resistance.
This did not seem to make the brakes any better than they were, though the handbrake now needs another adjustment as I cant get it passed first click.
What I think is causing my low rear efficiency is the rear proportioning valve spring, it looks very stretched and not like the photos i've seen online, where the coils are all tight together. I tied the lever up, and tried the brakes again - much better, so I think this confirms that the spring is the issue.
In the short term, I'll extend the push rod from the rear axle using some M8 stud and a coupling nut, as I don't think i'll be able to get the new spring in time for the free MOT retest period. I doubt that squashing the spring in a vice will work, but I may give that A try first.
The other issue I found was that the MOT tester was using 58% as the required minimum efficiency of the brakes - I have since found out that he should have been using 50% as this vehicle is pre 2010. It still wouldn't have passed, but it's worth noting in case i'm very close next time.
Can I ask where you sourced the rear brake shoes?
I am replacing drums, and my rear brake adjuster looks fine. My problem was oil leaking into the drum from the OSR seal. So going new wheel bearing and seal and brake shoes both sides.
Several years ago, the brake shoes were available on an exchange basis from a brake re-lining company, but I can't find where. How were yours?
Note: I can find them on-line, but many routes lead back to autodoc, and as useful as they are, they ship everything from Germany and it takes 2 weeks (thanks Brexit).
I have a set that were donated to me by another member, which I didn't need, send me your details and I'll pass them on
I used the lining kit from..... Autodoc! I couldn't find shoes aready done, so I did it the old fashioned way.
It usually takes between 1 and 2 weeks for delivery from them. I have placed a few orders pre and post brexit, and haven't really noticed any difference.
Sounds like you've got a very generous offer anyway.
My retest is on Monday - Fingers crossed.
Find a company that re lines truck brake shoes, most of them are very helpful
Easy way to check rear brakes and the proportioning valve are working is to reverse as fast as you dare on a hard surface and slam on the brakes; the rears should leave evidence of locking up on both sides if all is well.
The proportioning valve does tend to seize up at the lever on the valve. I spent a few hours with it in my hands slowly removing corrision and then freeing it up. I then painted it up and packed with suitable red rubber grease on the bits inside boot and Dinotrol rust proofing (expensive waxoyl) on the outside. It has been fine for 12 years or so since.
Contaminated shoes can be cleaned up with petrol for a quick fix .. but really need replaced. 12 years ago you could certainly buy the shoes and retaining kits.
For MOTs my guy does it with the "dumpy tester" i.e puts a testing machine in front footwell and drives around the block with a couple of short stops. This is less "testing" but the brakes never were great on these. The argument for the dumpy tester is that the 4x4 system could be damaged by the brake tester; not true in our case as we do not have axle limited slip diffs... but MOT guys do not know this and mine is nice to me.. Before that I would struggle on rear efficency .. with manual adjusters just allowing the drums to turn and no more. I used to design and test brakes at Lucas Girling for 3 years many decades ago.. so like to think I know some things about setting up brakes.
This was an 1988 460GDS so I-H brake split.
https://www.brakesint.co.uk/about.html used to do everything?
Fitting Kit for rear brakes with Mercedes brakes for 1989 460 300 GD is MA601 421 00 92 for £8.90+Vat. from MB. The lower spring is too short and strong – reuse your old ones... hum are these ATE not MB make .. hence springs are wrong for Perrot?
Rear brakes .. .. they were fitted to the vans of same era. Ebay show Bonum_Ltd selling Bendix-Perrot type shoes for £98 today on a very quick search Ebay item number 174874412618. These are the most common ones say some..
The front brakes are also either Perrot or ATE - see here https://clubgwagen.com/forum/viewtopic.php?t=14528
The rears can be Perrot or ATE or Jurid - see here http://gwagenowners.com/forum/w460-back-plate and here https://clubgwagen.com/forum/viewtopic.php?f=18&p=200492
Not sure that helps but there will be local guys who can reline shoes for you if all else fails and then you know they are right! Ask at commercial motor factors or truck motor factors and search for brake friction suppliers locally.
I got replacement shoes, but they are not Perrot type, which mine are. So if anyone needs those... (thanks PRWALES)
I also got MB re-lining kit. They are available from MB, and also from Gav Helme who supplied these. Cheap and are pop-riveted onto the metal shoe when you have ground off the old contaminated ones. Gav informs me you don't need to cement or glue in addition to the rivets.
Thanks for the tip on the 'brake adjuster' mechanism. I think mine is OK.
@Ben - note that 460 rear brakes are never that great and your MOT tester may be being a little too 'by the book'. It sounds like you have replaced all you can. If they brake evenly, that's a result.
After adjusting the proportioning valve and setting the shoe adjusters as far out as I dare, I managed to scrape a braking force of just over 150Kgf on each of the rears and about 550Kgf on each of the fronts, so a vast improvement.
So it does indeed appear that a well adjusted rear set of brakes has an impact on the fronts too, noted by the increase in braking force over my original test, which was 54 and 26Kgf on the rears and just over 400Kgf on each of the fronts. I have the dual circuit front brakes, I don't think this will apply to single circuit fronts.
The pedal even starts doing something more or less right at the top of the travel too, so they even feel a lot more reassuring.
I have a feeling that if I was running the original 29" 205r16 tyres, the braking force would be even higher, but I have 32", so the additional outer diameter is bound to reduce things a bit.
This sounds a lot better. And balanced. But according to your post #4, shouldn't the rear brakes be 50% of the front? You are at about 30%
The more you dig, the more you find.
No, that isn't to do with front/rear bias, it's that the total braking force of all 4 wheels combined should be 50% of the vehicle weight for pre 2010 and 58% for post 2010.
So with the SWB W460 300GD being quoted at 1930Kg weight, I needed to have at least 965Kgf (50% of 1930) braking force combined.
In my first MOT test, he didn't enter the year into his brake test machine, so it assumed the 58% requirement, which came out at 1119Kgf. I exceeded this on my retest anyway, so at least I know that my brakes are reasonable and not just 'good enough'.
Here's some light reading for you:
https://www.gov.uk/guidance/mot-inspection-manual-for-private-passenger-...
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I have new front discs, pads and hoses, and all 6 nipples have been bled. I checked all four pistons on each side are free. Along with new drums, linings, cylinders, pipes and hose at the back.
The proportioning valve and linkage appears in good condition and all moves freely.
My thought was that the rears may affect the overall efficiency of the front brakes because the rear circuit is connected to one set of front pistons, so if the rear shoes are not adjusted up and have lots of travel before pressing the drums, then this shared circuit on the front will also see reduced pressure/efficiency in comparison to the other front circuit which shares nothing and can actuate instantly.
Am I making sence? It's early in the morning!
If the storm doesn't blow me away, i'll take the drums off later and see if the adjusters have moved at all on their own.