Mercedes-Benz Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
16 Posts
Discussion Starter #1
Does anybody know of any way to upgrade the brakes on a 460? After a few pumps, the pedal goes rock hard - it's a real problem in winter when you need more than engine braking and have to pump the brakes to stop a skid. It's either that or getting bigger bumpers.
 

·
Registered
1982 300gd
Joined
·
57 Posts
If you do a search under brake booster or brake hydraulics you may find some useful info. Also try purging the fluid from your calipers,new fluid does wonders.
scott
 

·
Registered
1980 LWB 280GE
Joined
·
3,504 Posts
The stock brake system will lock the factory tires into a skid on dry pavement when everything's in proper working order. If you have to pump the brakes, you need to repair the existing system, not upgrade it.

First do a full fluid flush and check everywhere for leaks (including inside cabin above pedals). Repair any leaking parts. Verify all linings are in good shape and not fouled with oil, past or present. Verify that the vacuum booster is in good working order with no leaks. If still having problems I'd replace the flex lines with new OEM, or else braided steel teflon hoses and look into potential internal leaks within the master cylinder.

-Dave G.
 

·
Registered
280ge
Joined
·
574 Posts
Ive had 3 460, 1 230 and 2 280's and the brakes have always been great, new fluid and vaccum pipes might be in order.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #5
Thanks for all the advice. I'll try these out. If no luck, the front bumpers are good enough.
 

·
Registered
85 300GD 83 300TD
Joined
·
978 Posts
To chime in with a couple of thoughts: if you have a GD (Diesel) the vacuum system is whimpy and if you pump the pedal multiple times you will run out of vacuum. The pump can't keep up with the vacuum volume required of the booster. Put on the brakes but don't do the pump pump pump thing and it should work fine. Petrol powered G's probably have better suction.
Also if the rear shoes are not in good adjustment your rig will not brake well because of too much wheel cylinder piston travel. If the shoes are in good adjustment the brakes work with authority on the initial pedal depression. There is a device that modulates the front to rear brake force that also needs to be in good adjustment. It lives above the rear axle and features a lever and spring arrangement that might be a contributor to poor performance if it is not set up correctly. That's three thoughts; I'll stop now.

-Dai
 

·
Registered
Joined
·
16 Posts
Discussion Starter #7
Yeah, it's a diesel - and I have just had the rear brake shoes checked and they are very worn. So you're right. By the way, as I have slightly longer springs than standard (about 1 coil more)I guess that means the brake distribution device needs to be adjusted to bring the drum brake shoes closer? Is it easy to adjust this thing?
 

·
Registered
1984 300GD 5 DOOR
Joined
·
130 Posts
re dai comments ,agree with comments .i am having same symptoms ,it is vacuum pumpin my case . adjustment of rear brakes and proportioning valve also makes a big difference .to adjust valve setting refer to manual but make sure pressure is applied to pedal as in instructions .good luck
 

·
Registered
230 G BGS 300G TDI
Joined
·
965 Posts
kerry460 - 5/11/2005 12:36 PM

re dai comments ,agree with comments .i am having same symptoms ,it is vacuum pumpin my case . adjustment of rear brakes and proportioning valve
------------------------------------------------------

The only comment I can add is the length of the load sensing valve rod is critical to a G, if you have moved the geonetry the rod will be too short, normaly you have to weld in as much as you have lifted the vehicle by.
 

·
Registered
1980 LWB 280GE
Joined
·
3,504 Posts
Rear brake proportioning and lift

If you change the distance between the rear axle housing and the chassis (like with a spring lift) You effect the brake proportioning valve.

A plain lift, like say by using a spacer block between the coil and the spring seat, that didn't change spring rate, would mean that you would have to increase the length of the actuator rod of the proportionng valve (the rod between the axle and the lever arm on the valve) by the same ammount that you lifted the chassis.

The spring that's on the proportioning valve is also matched to the springs that are on the rear axle. If you change the spring rate of the springs on the rear axle, then you need to change the spring that's on the brake proportioning valve too. The job of the valve is to INCREASE braking pressure at the rear wheels as the vehicle is loaded more heavily. The proportioning valve senses how heavily the rear is loaded by how much the chassis sags toward the axle. This means that the spring on the proportioning valve (which is the thing that actually changes brake pressure) has to be "in agreement" that is changing brake pressure an appropriate ammount, with the ammount that the chassis sags for a given weight, and that last is directly related to the spring rate of the rear springs.

The workshop manuals give a good description of how to set the actuator rod length and that much you can do at home to make sure you at least have close to the correct rear brake pressure when the vehicle is unloaded. If you decide not to change the spring on the proportioning valve, the worst thing that will happen is that you won't be taking fullest advantage of your rear brakes when the vehicle is loaded up.

In teh condition you have now (lifted with too-short actuator rod) you're getting less braking force from the rear wheels than you would if the rod was at the correct length.

The proportioning valve has nothing at all to do with how close the rear brake shoes are to the drum. That's a different adjustment, and if everything is working properly within the rear brake assembly, that adjustment is automatically maintained by the linkage inside the drum every time you press the brake pedal.

Sounds like you have lots of opportunities to get your brakes back to full functionality. When you do, you'll probably be amazed at how well it can stop, after being used to making due with the way it is now.

Good luck!

-Dave G.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #12
Thanks for all the comments here - I've learned more from just a couple posts on this website than I could have imagined. Cheers.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #14
Hi Harald!

It is the crazy Hun! You're the crazy Claifornian-German! (Or extremist, as I understand. I am still in Hungary - still doing the writing but will be employed from September.

Still remember your Rubicon course. I frequently am grateful to you when I off roading out here (you can off road anywhere in Hungary, it's great) - your 'let it stall and bump start in reverse' failed hill climb technique has saved me many times. As does the 'keep it straight' tip. I won't say more, as readers should pay to go on your course!

I've just got back from some great off roading, though managed to slit the sidewall on a BFG MT. Asd you may recall from your course, this is a specialty of mine!

Are you coming out to Graz area anytime?

Best,

Zoltan
 
1 - 14 of 14 Posts
Top