Bleeding Brakes

[GPF]

As you surmise, I don't think 5.1 generally has a high enough wet BP. I would try some ATE Racing/Super Blue or similar.

 

[robdimond]

I bought one of these (well a similar one) contrary to most of the advice I read on the forums and wouldn't really recommend it. I don't know if it was my own ineptness or that my calipers are knackered, but it kept sucking air from around the bleed nipples so it was quite hard to see if I'd got all the air out of the system. I think what you really want is something that applies positive pressure to the lid of the reservoir on the master cylinder. There is a great youtube video by irina25661 which shows him connecting an airline via a regulator to an old VW reservoir lid to bleed the clutch (it's a LHD car). Looked much easier!

 

[Cater_Racer]

Hi all, we've had problems all year with a long pedal in the second stint of our 40 min races.

We have done a bleed on the brakes but have never been totally convinced they are right.

I could be Dot 5.1 just ain't up to the job, or there has been some old stuff still in the system with either air or moisture in it.

We have taken out the front fogs, and have ducting through to the calipers on the front.

Now thinking about one of theses: http://www.minivac.co.uk/

To have one final try to clear out the old and put in brand new Dot 5.1

What's the consensus? Go to racing fluid? or give up and chuck it down to Kevin at EMC and spend Tom's inheritance?

Gerry

 

[zcacogp]

ORIGINAL: robdimond I think what you really want is something that applies positive pressure to the lid of the reservoir on the master cylinder.

I can't vouch for how good the fluid is when hot (dot 5.1 works fine for me, but I venture onto the track very rarely) but brakes with bubbles in will show sponginess in the pedal when they are cold and the car is stationary. And in terms of bleeding them, I'm with Rob - an eeze-bleed is the answer if you don't use one already (something like this: http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_productId_204645_langId_-1_categoryId_255216). I've never seen the suction type before but can certainly vouch for the positive-pressure types. (I am sure you could make something much more cheaply than the above with some old hosepipe and a lemonade bottle if you wished.) With these, you can simply open each nipple in turn and as long as you have run a litre or so of fluid through the system you will be very unlikely to have any old stuff left in. When bleeding them, it's worth giving the calipers a bit of a belt with a rubber hammer to dislodge any small air bubbles that may be lurking inside them. The smallest of bubble will make a huge difference to the pedal feel. Oli. ETA: Really stupid question (so stupid you'll have to forgive me asking it) but you are bleeding both of the nipples on each caliper aren't you? >Ahem< Best not ask me why I am asking this .... []

 

[944 man]

If you have concerns about contamination and air pockets, then Id suggest buying a flaring too and a roll of pipe, and spending an off-season weekend completely re-piping the car. Run the new lines inside the cabin and kill two birds with one stone. Thisd be a good time for a new or refurbed master cylinder too, as well as a move up to superior fluid. If youre still having problems then youll know that its air.

 

[zcacogp]

Interesting. What's to be gained by running the pipes inside the cabin? Oli.

 

[944 man]

Their being inside the cabin, principally. I wouldnt suggest this for the fuel pipes myself, prefering them to be protected with a length of Dexion, or similar.

 

[colin944]

Yep I'm with 944 man on this one.Roll of kunifer £12 new ends £2 and a simple brake bias valve £40 from Demmon Tweeks and your all good.

 

[Hilux]

Sounds like a fluid issue. Dot 5.1 is indeed better at high temps so if you are losing pressure via a long pedal in the second stint (is it a quick changeover) you may be getting excessive heat soak into the fluid as the car is stationery for a short period that its brake cooling then struggles to lose in the second for you would normally have a cool down lap at least after a race or track day session. Are the calipers standard, are the caliper bleed screws on the top? If not remove the calipers and invert them while bleeding. Any potential air pockets? ie: long curved pipes forming an arch where air can be trapped at the top? Ballooning rubber pipes can offer a long pedal but you have a solid pedal at the start. Braided lines are nice but hide damage/wear. People think you can only bleed at the bleed nipples but you can crack off any joint in a brake system as long as the fluid is under the slightest positive pressure (think the same for 944 clutch pipes) but its messier. Are you getting high pad wear rates? Low pads transfer more heat to the piston so as the race progresses you lose efficiency. Maybe harder pads? Do you run a servo? Check fluid isnt leaking into it and the seals are good as this would increase pedal effort. Old pipes? Then I agree with above. Roll of kunifer pipe, flaring tool, renew all pipes, inspect seals and cylinders and renew if dodgy, add a bias valve (if your rules allow) to balance in wet and dry conditions. PS: I`ve never used one but I am told the suction bleeders are a lot better than pressure bleeders as it attracts the air due to the vacuum

 

[zcacogp]

ORIGINAL: 944 man Their being inside the cabin, principally.

Why is that an advantage? Protecting them from damage? Keeping them warm? Shorter runs from servo to caliper? Gerry - just seen your bit about taking it down to EMC. I've never heard anyone saying that the brakes on a 944 are anything other than excellent when they are in good condition so I'd save Tom's inheritance for sure. Getting them right can't be that difficult and the cost of a couple of hours at EMC will pay for a lot of fluid and bleeding tools for you to experiment with!

 

[colin944]

You could also try taking the abs pump out.And running your lines direct from the master cylinder.There's only 2 lines out of the cylinder 1 for front and 1 for rear. Pop a bias/proportioning valve in the line to the rear and you can adjust the balance.

 

[Hilux]

Just a thought Exactly what 5.1 are you using? Standard 5.1 will be surpassed by many Dot 4 racing fluids

 

[os951]

I use Motive Power Bleeder. Works every time just great. If you have ABS system, turn ignition on, it helps bleeding process. Start from rear wheels and last front wheel which is closet to main cylinder. If ABS, bleed caliper closest main cylinder before the one which is nearest the ABS pump.

 

[Neil Haughey]

Caterracer even the ATE Blue race fluid will boil in my car. From talking to ppl over the years the only fluid that will not boil in these cars under race conditions is the Castrol SRF but it is very expensive. The EMC guys use the ATE fluid, I asked them before about it boiling over in the reservoir, they didn't see it as unusual but we all tend to bleed the fluid out with a load of fresh fluid on a fairly regular basis anyway.

 

[Cater_Racer]

Thanks all, useful stuff! We don't run the ABS system, and do have SS pipes, so I think we'll try ATE Blue and see if that helps. The brakes are fine cold, and I didn't have any issues at Donnington for the first 20 minutes but we had a slow change over (my fault being fussy about Tom's HANS) and it cost us about 5 places. Tom then had the long pedal problem. I think you're right Oli about the fact that cold it's fine, and after a 5 minute cooling off period all is fine again, so it's probably moisture rather than air. Or Dot5.1 boiling. Maybe the Castrol stuff would fix it.

 

[Hilux]

The brakes are fine cold, and I didn't have any issues at Donnington for the first 20 minutes but we had a slow change over (my fault being fussy about Tom's HANS) and it cost us about 5 places. Tom then had the long pedal problem.

" Dot 5.1 is indeed better at high temps so if you are losing pressure via a long pedal in the second stint (is it a quick changeover) you may be getting excessive heat soak into the fluid as the car is stationery for a short period that its brake cooling then struggles to lose in the second for you would normally have a cool down lap at least after a race or track day session." S`wat I thought, its heat soak from caliper piston to fluid) on a quick stop after spanking it. Titanium backing plates between pad and piston prevent this to a large degree I am told.

ORIGINAL: Cater_Racer Thanks all, useful stuff! We don't run the ABS system, and do have SS pipes, so I think we'll try ATE Blue and see if that helps. Maybe the Castrol stuff would fix it.

ATE Blue is not made any more I am pretty sure and what is for sale is old stock. It has a dry boiling point of 280 deg C and a wet boiling point of 198 deg C which is probably fine for lighter cars such as Cateringvans and Westfields etc but is a bit low in my view for heavier cars if being raced. I use Motul RBF 600 which has a dry boiling point of 312°C and a wet boiling point of 216°C (which is about the same as the new Castrol SRF to be honest) and if you search around is less than 1/3 the cost and readily available on the bay. Edited to confirm this data from Castrol................ Product Data Description Castrol React SRF Racing is a high performance brake fluid of special value in competitive motor sport where extreme braking conditions are encountered. It is an exclusive Castrol product registered under patents in many countries. Castrol React SRF Racing has an exceptionally high dry boiling point ( typically 320°C ) making it ideal for use under arduous braking conditions such as racing or rallying.

 

[Hilux]

ORIGINAL: Neil Haughey Caterracer even the ATE Blue race fluid will boil in my car. From talking to ppl over the years the only fluid that will not boil in these cars under race conditions is the Castrol SRF but it is very expensive. The EMC guys use the ATE fluid, I asked them before about it boiling over in the reservoir, they didn't see it as unusual but we all tend to bleed the fluid out with a load of fresh fluid on a fairly regular basis anyway.

Caterracer even the ATE Blue race fluid will boil in my car. From talking to ppl over the years the only fluid that will not boil in these cars under race conditions is the Castrol SRF but it is very expensive. The EMC guys use the ATE fluid, I asked them before about it boiling over in the reservoir, they didn't see it as unusual but we all tend to bleed the fluid out with a load of fresh fluid on a fairly regular basis anyway.

Hi Neil Look up the Motul RBF 600 as a cost effective alternative (improvement) over ATE []

 

[Cater_Racer]

Sounds sensible... Thanks. I'll definitely go the Titanium Plates route, anyone know a supplier? We never had problems with our R400 Catering Vehicle, but it was only 515Kgs but 230 BHP made it go quite well despite aerodynamics of a London cab. we will try a bleed and replace with RFB 600, using the eazi-bleed. Start front-right, front-left, rear-right, rear-left? Keeping going until the colour changes? Gerry

 

[Hilux]

We never had problems with our R400 Catering Vehicle, but it was only 515Kgs but 230 BHP made it go quite well despite aerodynamics of a London cab.

Exactly my point. When you brake you turn kinetic energy into heat and the more mass or weight you have to retard the more heat you generate. I dont know where you can get the titanium plates to be honest but it is to do with the fact that Titanium conducts heat at about half the rate of steel and I think they are used on Le Mans cars and endurance racers etc - basically like a posh anti squeal shim. EDITED: I found these.....................[link=http://www.racersedge-inc.com/racersedge/rehome.nsf/78c7bfeda53558a285257179006f75ff/94A91C2DB5584806852571FE0045DC6A?open&menu=menumodelbytype]here[/link] but I would imagine you could talk to a local fabricator and get a small sheet and make your own. Bleed the farthest away first on the rear, then the second rear, then the farthest front and finally the nearest front. Keep going until the colour changes (and there are no air bubbles) and dont let the reservoir run out. If you are changing the lot I`d buy a litre. You havent got ABS have you?

 

[Cater_Racer]

Thanks Paul, farthest first, OK will do. No we don't use the ABS, used to having the odd wheel lock up: