Clutch pedal fluid & brake fluid use same reservoir?
 

Hey guys,

Was running my car real hard the other day on a closed circuit to test out the new tune (amazing :) ). Ran her up to 140, then did a real hard brake stop to about 50mph. A few seconds later the clutch pedal went super soft and went almost to the floor. This had never happened before. I pumped the clutch a few times then pedal pressure came back and was back to normal 2 min later.

I made me realize that air bubbles some how got I to the clutch line from the hard braking I did which led me to believe the two share the same fluid/reservoir. Just wanted to confirm is this correct?

If so have any of you flushed out the stock fluid yet and put upgraded fluid in both the clutch and brake lines? I am thinking about putting in Castrol SRF (best brake fluid on the market). It usually provides much firmer pedal feel and never boils over or creates bubbles, so I want to put it in the clutch pedal lines as well to provide the same effect and improve clutch pedal efficiency. My stock brake fluid has probably never been replaced (90% of people always neglect this maintenance and yet it's the most important fluid to replace)... so I might as well replace it anyways because it is time.

Anybody tried this yet?

Thx,
007

remember, going to a racing fuid, only means you have to change it more often, as it can absorb water better than others. i would go middle of the road on the fluid. Im going to change mine as well and still up in the air on what fluid to use.

side note, the pads you are using, could have caused fluid boiling, as well as brakiing technique. I remember racing a guy with the same power to weight , big brembos and he was running 3 seconds a lap slower and boiling his fluid. technique in braking is huge! street pads next, and then fluid. :)

Hey XWGT,

You have it backwards, racing fluids are much LESS hydroscopic. Especially Castrol SRF. The reason Castrol SRF has the highest wet boiling point on the market is because it resist the absorbtion of water better than any other fluid on the market (which is why formula 1 ran Castrol SRF for almost a decade before switching to Endless750. The worst fluid you can is standard OEM DOT4 fluid that the dealer uses, but it's the cheapest and most readily available.

Hey guys,

Happened again today, Super hard breaking then clutch pedal went mushy almost all the way to the floor, I am almost convinced they share the same reservoir, the question is can you flush out the clutch line fluid as well as the brake fluid?

I really want to get the air out of the lines. Going to switch over to CASTROL SRF. It's pricey at $75 a liter but it's worth every penny, but I just want to make sure I can flush out the clutch line fluid first.

Anyone know how to dot hat or have a procedure on clutch fluid flush?

thanks... good to know. so, no downside for using the higher performance racing fluid?

Other than price there is zero negatives. All brake fluid should be flushes once a year but most people have never flushed their brake fluid for 3-4 years of not the life off their car (terrible). It is the #1 most overlooked maintenance item by far.

I bought the Castrol SRF today at $65 per 1Liter. It's actually not that much more expensive than Motul 600 when you factor that Motul comes in 500ml bottled which deceptively makes it look a lot cheaper until you realize you have to multiple 2x to get the same volume. It's about $20 more per liter, but performance is easily 200% better over the long run.

Going to have my shop do a full brake AND clutch fluid flush and will do a fully writeup on it.

Also, going to do a trnasmission flush (4.5 liters). I am choosing to do Mobil1 75w-90 Limited Slip formula for both cost reasons and to test to see if it is superior to Royal Purple in cold conditions. I have a feeling my previous owner did any transmission flush given how low the mileage is, and it was before they started putting the additive in to improve cold weather shifting. Should be interesting to see the results. Typically mobil1 is the thinnest which is why it's best for cold weather performance.

Will let you know how it turns out...

Thanks! where is the best place to buy SRF?


as far as transmission oil.. isn't their two segments, or are they shared like other transaxles? I thought it was 90/140 and 75/90 for the diff area.


any thoughts on redline NS transmission oil 75/90

Hey XW,

SRF can be bought online on Amazon.com or if you are local in Houston you can buy from Lamborghini Houston. On average it's about $65-70 per liter, it sounds pricey but trust me it's worth it, no other brake fluid repels moisture better than SRF, hence it's super high wet boiling raising and Formula 1 running it for over a decade. It lasts twice as long as other performance and OEM fluids, and if you aren't tracking the car it can easily last 2-3 years without replacement where as most have to be replaced 1 year max religiously (which nobody ever does of course unfortunately)

No, the transmission/differential/transaxle is all one piece and all shares the same fluid. It's all 75w-90, hence why it's 4.5quarts instead of the normal 1.5-2 quarts each as it is on most cars when they are separate.

I have used redline in the past twice both on European cars and I was never happy with the performance, others prefer to use it, but I wanted to try Mobil 1 bc it's only $10.99 a quart and is usually very good in cold weather shifting (it's the thinnest fully synthetic gear oil on the market pretty much). The "LS" version already has the limited slip modifiers in it already blended in. Royal purple by comparison is $18/quart.

I will report back with full writeup

thanks good information. I was using some SRF when racing last summer as i was getting some pedal softnss that i never had before. it seemed to help. (going from the very popular superBlue racing fluid which is cheap , but not that bad)

as far as the transaxle. i need to change that. its an '06, and only has 24000 miles on it, but its never been changed , so im thinking its not the mileage, its the 8 years! :) we dont get much heat into the transmission like a race car, but still, i think the impurities that are suspended in the oil after all these years should be changed. same with the brake fluid. at the track, its changed almost monthly, just by bleeding, but on my street cars, i fail to change it that often. I have to get that stuff out of there. :eek:

SRF should feel much firmer than stock, whoever did the flush probably did not use a pressure bleeder to get all the air bubbles out. To really flush ALL of the fluid out you need to use two full quarts. Some shops say you only need one but that's not true, make sure they flush out the fronts with 1liter and the rears with 1liter to ensure every last bit of the old fluid is gone. Clutch procedure requires a very specific procedure to flush the lines. Some people upgrade the clutch line to stainless steel in order to improve clutch pedal feedback, although not sure if ours is rubber or SS. I know for sure our brake lines are SS from the factory, but clutch line I never really looked at yet.

Yes transaxle fluid is definitely bad now. Recommended interval for tranny flush is typically 4-5 years tops regardless if it's low mileage or not (all fluids degrade over time, even if not driven on much). Especially as an 06 which lacked the additive to improve cold shifting, I would highly recommend replacing the fluid. Will let you know how the transaxle fluid swap goes after Wednesday when I take it in for the full service.

I was talking about my actual porsche race car, and the reason for the softness was boiling fluid during the race. the pedal feel wont really change once you have all the bubbles out of any fluid you use. (as fluid is in compressible), however, if the boiling point is higher, you dont have the chance of getting air in the lines which can give you a very soft pedal and reduce brake effectiveness for the amount of effort on the pedal.
the rubber brake lines, especially on porsches, are very thick and dont have any issues with causing a soft pedal. the stainless steel lines really only help with protecting the lines from bursting when they get old. ask me how i know. :eek: when i changed the blown line with the stainless. the pedal was the same, BUT, i have one less worry on the track now. :)

I think you are right about the transmission fluid. with the stiff cold shifting into 2nd gear issue i have (only when cold), im hoping that the transfluid change will fix that. Ill wait until you have posted your feedback on the mobil 1 to see if it works ok. Let me know if there are any tricks to changing the fluid, or if its just the usual drain and then using the pump to get the new fluid in through the filler hole.

I think I read that last post to say that 'getting the brake fluid to its boiling temperature will create air in the lines' which is correct. SRF, is my favorite choice as well, mainly because its wet boiling point is so high. You really don't have to change it near as often but I would still recommend yearly brake fluid flush. Soft peddle is also associated with brake fade, or heating the friction surface to the point that it can no longer create adequate speed reduction... and flex in the brake pressure lines, or rubber hoses as mentioned earlier. (Sorry for getting so elementary on this topic but I wanted to add those causes for the readers who may not be as familiar with their brakes as others).

IMHO, the transmission fluid is just as critical as the motor oil and should be change every 10k miles or every other year. The main reason to change the trans fluid often is because the transaxle box is basically comprised of gears rolling against each other quickly. The odds of metal shavings becoming part of the mix is pretty high. Those metal shaving are what wear out bearings, gears, ect...

Fresh fluids are a good thing.

Correct, most of the 06-08 Vantages probably have significant metal shavings in the gearboxes and you want to clean all of that out.

The procedure is very simple. Fill & drain plug, allow to drain completely, put drain plug back in and tighten, then fill up using a decent fluid pump to make the process much easier. Shouldn't take more than 30min-1hour tops.

The brakes take a little bit more time bc you have to allow the vacuum pressure slowly pull the new fluid through the lines to flush out all oft he old gunk out of the lines. Has to be done one corner at a time.

I am really curious to see how the clutch line flush benefits shifting performance and clutch pedal feedback, I hope it feels more positive.

Hey guys, lots of updates, going to do individual posts for both the transmission oil and the brake fluid... It will definitely be interesting to read. I did want to however add to this discussion specifically because I did more research on the web and (of course) the car that most exhibits these similar traits is the .... Ford Mustang (shocker). I have a feeling their may be some parts bin sharing relationship somehow between this phenomenon.

Posts coming soon

Found out the issue is the slave cylinder is starting to go on its way out. Needs to be replaced eventually. It's fine under normal drive but under heavy acceleration it performs less efficiently. Only way to replace it is during clutch replacement so I will just wait another 10k.

This is common issue on Ford Mustangs and Chevy Corvettes.