My racecar is an '87 Mercedes 190E Cosworth. Kind of an oddball. One of the weird issues on the car has always been the mushiness of the brake pedal. Now that we've swapped in dual Webers, it would be great to get rid of the gigantic brake booster. It gets in the way of the velocity stacks and air filters; and there really isn't a stable vacuum source any longer.
Anyway, let's say I scrap the stock booster and master cylinder in favor of an old-fashioned, dual-MC setup using Wilwood or Tilton components. Would I be able to retain the car's standalone ABS system?
As far as I can tell, the Bosch ABS system in this car is a totally indelendent circuit. Will it work with race-style MC's and no booster? Better to just scrap the whole thing maybe?
A 190E should be a front/rear split system. I have only ever seen diagonal split on front wheel drive vehicles, and vice-versa.
Of course, the outliers are the old Volvos that had two inlets on each front caliper, so each half of the braking system controlled one rear wheel and half of each front wheel.
The thing with manual brakes is the pedal ratio is generally a lot different. With my new RX-7, I am thinking of converting it to manual brakes with one of these dealies: http://www.ebay.com/itm/MAZDA-MX5-HYDRAULIC-BIAS-BOX-KIT-B-WITH-LINES-CMB6331-KIT-LINES-/282084767188 It's a neat little gizmo that combines a balance bar with a lever to change the total leverage against the masters. One of my friends in Michigan made/makes something very similar for Hondas and it works very well.
Ford used something similar in the 60s and early 70s to convert manual brake chassis to power brakes, the booster attached to a stamped steel bracket and there was a reduction lever between it and the pedal.
Sounds like it's an all-or-nothing type of deal then?
Pretty much. It's all about leverage. You can change it via the pedal ratio or piston sizes. The booster is basically a force multiplier in the system, if you remove that then you need to find some other way to get the line pressure back up to a reasonable point.
To go to the original question - as long as you have each master feeding one of the original circuits, I think the ABS should continue to work. That might not be the case for a modern system, but a 30 year old one is simpler.
A modern system with variable proportioning might wig out, but an older system should be fine. They aren't terribly sophisticated.
Not sure that ABS is worth keeping. That's a really crude system...
What doc said. Kiss it and be done!
get the right master cylinders and the right pedal ratio with adjustable brake bias, and you won't even want ABS in it..
No matter how good you are at threshold braking, you're limited by the tire with the least amount of traction. ABS does not have this problem. I'd keep it.
My home tracks are all in the northeastern USA and eastern Canada. Tremblant, Mosport, the Glen, LRP, and such. Rain is very common, so I'd like to keep ABS in the racecar of possible.
The big issue is the Weber carbs/stacks/filters and the stock booster/MC want to occupy the same space. If I could just swap the booster/MC for a an unboosted dual MC (plus proportioning valve) setup, I'd be golden
Can you move the booster/MC assembly forward/lower/etc.?
The Opel GT/Corvette lookalike had the Booster/MC mounted up by the radiator baffle.
Rog
Look into a hydroboost setup. It's the hot ticket for 944 LS swaps. Nice and compact and readily available.
Keith, with modern ABS, absolutely. With the system that 190E has? Not so much. I mean, it'll keep you for flat spotting a tire, but barely.
Be careful with the hydroboosts. When I put on into my LS swapped 944 it seriously messed things up on track. The brake bias was totally off as was the pedal stroke. It took years before an adapter was available so I could use my factory 944 master cylinder with it and that solved the issues.
So before I'd swap in a hydroboost I'd make sure there's an adapter for your factory master cylinder to bolt up to it...
Any ABS system can take greater advantage of available traction than a human with a single pedal, even if it is 30 years old. Sure, they got better, but as long as it prevents you from having to back off the pedal if you've got a low traction corner it's beneficial.
Doesn't have to be the factory master as long as it's the same size. I've driven a LS 944 with a Hydroboost setup, nothing was obviously off in a short drive. I never asked specifics as to the setup. Obviously, anything can be implemented well or done poorly.
How many channel abs is this old girl?
Keith Tanner wrote:
Any ABS system can take greater advantage of available traction than a human with a single pedal, even if it is 30 years old. Sure, they got better, but as long as it prevents you from having to back off the pedal if you've got a low traction corner it's beneficial.
The 2-channel diagonal systems that Chrysler used to use in the early 90s are something of an exception here. Put them on a FWD car, go autoxing, and as soon as it locks the outside rear tire, it releases the brake on the inside front. I'm a fan of ABS (enough so that I retrofitted it to my Miata), but those are bad enough I'd consider taking one out.
I doubt that's what the 190E has, though. Chrysler had a corporate mandate to put ABS in everything at that point, so they were using the absolute cheapest systems they could find.
Okay, a diagonal two channel system is pretty poor 
Three can work well, as it's the rears that share a channel and they're not working very hard anyhow. Each front wheel should have its own.
I'm thinking it might be fun to swap the left front and right front brake lines on one of those 2 channel systems.
Keith, that's the issue. Most of the LS 944 guys use the Mustang Cobra hydroboost setup. The MC for that isn't the right size for the 944. On the street it feels fine, well, with the exception of still having too short a pedal stroke.
On the track, that's a different story and it's rather frightening sometimes, even with a Tilton proportioning valve installed...
Does one of those cars have a staggered MC bore? It shouldn't mess with the proportioning otherwise.
In reply to Keith Tanner:
I don't think it's even possible to have staggered bores in a tandem master cylinder. The nature of lip seals means the bigger bore will push fluid into the smaller bore.
GM actually used this characteristic to make a "quick takeup" master cylinder. It had a third piston with a much larger diameter at the back, and a popoff valve. This was so they could run calipers that retracted extra-far (in theory). When there was little/no pressure in the lines, the big piston pushed fluid through past the main piston's seals, moving the calipers out extra-fast, and then when they made contact and pressure rose, it would pop off the valve and dump its contents to the reservoir, leaving brake pressure to be applied by the smaller main pistons (in theory).
In practice, the popoff valves would stick and you'd get a crummy pedal.
