Net Result Of Removing The Brake Servo From The 205 1.9 Gti Setup?

[rutlandguy 0]

Done a fair bit of searching on here and understand the basics around master cylinder (M/C) sizing with respect to calliper piston size. In that for a given calliper piston size making the M/C piston dia smaller will increase the travel of the pedal and increasing the M/C piston dia will reduce the travel and maybe remove some of the braking feedback from the pedal.

 

What I couldnt find anything about, was around the vacuum brake servo and what effect reducing or removing the vacuum assistance would have on brake feel/pedal travel/ability to lock the brakes up under hard braking.

 

The reason I ask is that cars like the lotus Elise run set-ups without brake servos and the pedal feel on those cars is really good. Given that the Elise isnt that much lighter than the 205 and runs discs which are I believe, comparable in diameter, could a non servo brake set-up be suitable for the 205.

 

I ask as Ive not had the car long but Im going through the car overhauling everything and as you would expect Ive started with the braking system. Ive replaced all the disks and pads front and rear and copper slipped all the moving brake part and the brake are now 100% better than they were. The next step is to look at the hydraulic side of the brakes and it occurred to me that if the servo was removed it would be one less part to overhaul and subsequently go wrong, would make the car lighter and the braking system simpler.

 

So has anyone experimented in this area Im guessing it would be those with more of a track/race car orientation. If so can you tell me about your experiences and the things Ill need to consider and the challenges I may face.

 

Thanks in advance for any help you can provide.

 

Cheers

 

Phil

[Sandy 189]

I ran my old 205 Rallye without a Servo for a while, but the set up was slightly different (306 266mm fronts, which have bigger pistons and 19mm MC, which is smaller), which would lend itself better to non assitance than yours. The pedal effort was quite hard but you could lock it, the feel is very different to servo'd brakes, but once you're used to it, it's very progressive. the flaw really is the bulkhead flexing, which is quite amazingly severe; a common problem with bias boxes on 205s too, bracing would be advisable. Rich that now owns the car took it to the Nurburgring like that and survived! I re-connected the servo after the MOT, because the tester made a note of it in the advisory and if (heaven forbid) Rich had an accident and the insurers were looking for a way out, i'd hate for them to pick that up.

[rutlandguy 0]

I ran my old 205 Rallye without a Servo for a while, but the set up was slightly different (306 266mm fronts, which have bigger pistons and 19mm MC, which is smaller), which would lend itself better to non assitance than yours. The pedal effort was quite hard but you could lock it, the feel is very different to servo'd brakes, but once you're used to it, it's very progressive. the flaw really is the bulkhead flexing, which is quite amazingly severe; a common problem with bias boxes on 205s too, bracing would be advisable. Rich that now owns the car took it to the Nurburgring like that and survived! I re-connected the servo after the MOT, because the tester made a note of it in the advisory and if (heaven forbid) Rich had an accident and the insurers were looking for a way out, i'd hate for them to pick that up.

 

Thanks Sandy

 

Taking your points into consideration. It looks as though the non servo'd 205's run 17.5mm dia. M/C's and latter GTI's run 20.6mm dia. M/C's. My fear that using a 17.5mm M/C in a otherwise std 1.9 GTI brake set-up may put the peddle on the floor without locking the wheels or do you think a 17.5mm M/C may well do the job?

 

Does anyone know what dia the 1.9 callipers pistons are?

Does anyone know what dia the unservo'd 205 callipers pistons are?

[jonah 1]

Front caliper pistons are 48mm on 1.6 and 1.9 GTI, and I'm pretty sure they are the same on all other 205s as well. IIRC the parts catalogue lists the same caliper seal kit for all 205s with the Bendix caliper, which includes the 1.6GTI and lower spec 205s. The pedal linkage has loads of travel in reserve anyway so I doubt that running out of travel would be a problem.

 

You should give it a try running without a servo to see if you can get on with it. Dead easy to do, just disconnect the servo vacuum hose and plug the stub on the manifold (use something that won't get sucked in by the vacuum!). I tried this at a gravel rally test day, and absolutely hated it. Just far too much difference in weighting between the pedals, I couldn't drive smoothly and there was no way I could heel & toe. A smaller m/c should improve that, but if your only reason to remove the servo is reliability, then I wouldn't bother - they seem to last forever.

[fxi1900 0]

I ran a group A pedal box (no servo) for a few years, I don't think it would be much good for road use but with proper pads and lots of heat you can't beat the feel of a non servo pedal

[pug_ham 241 3 Cars]

TBH I don't think it would be very good to use but its a very aquired taste only trying can decide for you imo.

 

When the servo vacuum pump died on an old 205 diesel I had (247mm disc & bendix calipers with 19mm mc) once up to any decent speed it felt like I was close to doing a flintstones impression to get it to slow at a decent rate & bracing my foot on the brake pedal by pulling down on the steering wheel. I certainly wouldn't recommend it for a road use car.

 

Best idea is to try the method above suggested by Jonah, blank the servo pipe off & see what you think before getting a 17.5mm mc & fitting it. The group A pedal box system use a 5/8"s front cylinder with either a 3/4" or 1" rear cylinder or twin 5/8"s system.

 

Graham.

[Grahamrally 0]

Just to add my experiences, I've had 205's with and without servos on. The first being a 954cc non servo 205 which didn't have a great feel to it and wasnt much fun. Then I had an XS with one which was fantastic. Then I got a rally car with a bias adjustable pedal box, but with a combination of the pads and calipers being knackered the brakes barely worked. Since then I've changed the whole brake system on the rally car to new wmms bias adjustable pedal box, 4 pot calipers and race pads etc and the feel is fantastic. A little more effort than servo'd but really good feel and response. For road use I wouldn't mind either to be honest. Just need the right matching of m/c to piston size to make the right pressures and pedal travel.

[rutlandguy 0]

Thanks for all your help so far,

 

I've researched some of the points made and confirmed (to myself that is) that all 205's have 48mm pistons as standard and the non servo'd models run 17.5mm M/C's. This is a similar calliper to M/C size ratio to the one Sandy refers to above where he is using 58mm calliper and 19mm M/C piston sizes.

 

Don't think I'll be disconnecting the servo to see if I get on with it or not though as the ratio appears to be wrong and the result I suspect will be a really hard pedal with no feel.

 

Don't suppose anyone has a 17.5mm M/C kicking around that they could let me have to try?