Bleeding / Flushing Brakes 308 GT4

I know it's pretty much standard practice to start your bleeding from the caliper that's furthest away from the master cylinder [in my RHD car it looks to be the drivers side rear caliper]. Has anybody noticed that in the workshop manual it specifically states to start at the front? Any reason you would do it this way rather than the usual standard procedure?

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Verry interesting. I look forward to the ensuing comments. One thing I can say though is not to bleed the brakes using the depressed pedal scenario. That causes the piston in the master cylinder to depress deeper than the usual motion. There are rubber seals in there and if they rub against the possibly pitted cylinder wall below it chews up the seals and means that a master cylinder rebuild/replacement is dead ahead. A vacuum bleeder or pressure bleeder is the best way to go.

 

Bleeding the farthest corner first is more applicable if the system is fully empty, i.e. get as much air out as soon as possible. With fluid already in the system it really doesn't make a lot of difference, but could be considered a best practice to minimize contaminating new fluid with the old. The the brakes are dual circuit (front on one, rear on the other) so the Ferrari recommendation of bleeding one 'axle' at a time makes sense. I usually start with the circuit closest to the pedal actuating rod then move the the other one, but again, probably doesn't make a difference. On my 308 the front circuit is closest to the actuating rod, btw. Also, after I've done all four corners, I go around them again. I like firm pedals

 

I flushed mine as part of resurrecting it after sitting from 1992 till 2018. The brake fluid was original (1978). While the brakes worked fine I thought it best to change the fluid. I started from the closest brake cylinder and worked my way around. Very simple, just rubber line to container to reduce mess, wife in seat and the old pump and hold while I worked the bleeders until the fluid came out clear. Old fluid was pretty dirty but no moisture or anything strange. As far as the seals all was good for a while then one of the E-brake seals started leaking. (all seals were original) prompting me to rebuild all four calipers. Total cost for full set of seals about $25.00. The E-brake mechanism is a little strange but not difficult. Even painted the calipers, not really apricated by my wife when I set the paint in her oven but turned out great with no further leaks.

Barry

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Egad! What have you done??? The Owner's Manual clearly shows that you are supposed to use a CHIANTI bottle to capture used brake fluid!!!
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Yep, as mentioned, a pressure bleeder makes this job relatively painless and much quicker than employing a helper in the car/pumping/releasing the brake pedal.

I don't like vacuum bleeders. The concept is, IMO, faulty because opening the bleed valve so the fluid can flow may also allow the vac bleeder to draw air in around the threads. Then, as you observe bubbles in the tube/drain bottle, you keep bleeding to get rid of the air "in the system" that isn't there...you keep sucking it around the threads into the drain tube.

Yes, you can put some grease around the bleed valve threads to stop that but it's just another finicky-A$$ thing to mess with.

 

Just finished this job on a 308 84 QV. Entire system was rebuilt. I rebuilt the master and discovered that there are three, not two, different seal sizes depending upon year and type of master. I am a fan of gravity bleeding first and then the pedal. If you have an old master, you do have to consider not pushing it too far. With a new or re-bored one, that is not a problem. I found that, since front and rear are separate to some extent, when I pedal bled the rear the pedal would only travel part way, since the front was apparently already firm. That might be why the manual recommends bleeding the front first, which is certainly contrary to normal procedure (farthest from the master first). I used speed bleeders this time. But if you keep the tube immersed in fluid and pump the pedal, I don't believe speed bleeders are necessary.

 

"But if you keep the tube immersed in fluid and pump the pedal, I don't believe speed bleeders are necessary."

Fluid can suck back UP from the bleed bottle when the pedal is released if you don't close the bleed valve before allowing the pedal to return.

 

Yep leaving the tube immersed works fine if your not flushing all the old fluid out.

 

Yes, but hopefully there is no air in it. I have used the speedbleeders, but know others who have had good results without. It's also nice if you have a helper to open and close the the valve.

 

Full fluid flush completed over the weekend with the old fashioned 2-person pump and bleed method. Started at the furthest point from the master cylinder and worked my way around as per standard practice. No issues encountered. I seriously thought about the pressure bleed method but have just read about one too many instances where they have sprayed brake fluid all over the place. Not a chance I'm willing to take on a concourse car. We were careful not to depress the brake pedal too far and worst case a master cylinder rebuild would be far cheaper and a better outcome than damage to the paint from splashed brake fluid.

 

Consider silicone brake fluid. It does not damage your paint and does not have to be changed every three years. It's amazing to me that it is still controversial. Obviously you can believe whatever stories you wish to believe. My experience: I have used it successfully in a number of 1960s, 1970s and 1980s vehicles starting in 1974 and never had a problem. On some cars I have simply flushed the old fluid and replaced with silicone. However, to err on the side of caution, it is arguably preferable to change to silicone when renewing the system.

 

I've had the opposite experience with silicone fluid. Not long ago I had a local shop do brake work on my wife's 2002 S500 MB. The car had excellent brakes as far as feel/stopping power going in but needed new pads and the rotors were replaced because they were too thin to be ground/re-used. I asked them to also drain/flush/refill the system. They did the work and the brakes sucked - long, mushy pedal travel.

I took it back and they checked it, said it was fine. I asked them what fluid they used - Dot 5. I said flush it and install Dot 4. They did. Brakes returned to their previous excellent feel/power. You wouldn't get me to put DOT 5 in any vehicle that did not specifically state in the owners manual to use DOT 5 in the brake system.

 

I do use Dot 4 in all my modern cars. After changing from 4 to 5 in my 308, I noticed no change in pedal travel.

 

Mike, what would be the technical reason DOT5 resulted in long/mushy pedal travel? I assume a 2002 MB has ABS - any chance the tech doing the work did not cycle the solenoids properly to remove air from the control module volume? Was it an independent shop or dealer? Weak pedal seems like a symptom of air in the circuit. I’m considering DOT5 so am genuinely curious about your experience, not trying to criticize or contradict you!

I’ve never worked on one myself, but a quick scan of the MB forums shows some of them have a hidden compartment in the reservoir that can run out of fluid and introduce air during bleeding while the main compartment still looks like it has some fluid.


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I see no reason to change to DOT5 brake fluid, simply because you're worried about fluid getting on the paint. Use a towel.

 

I was interested in DOT 5 because it doesn't absorb moisture. Some research led to a good article on the different types, and note that DOT 5.1 is backwards compatible with 3 and 4. Other sources indicated that when 5 is mixed with 3 or 4, gelling can occur which results in poor braking.

https://www.hemmings.com/stories/2013/12/06/tech-101-brake-fluids-whats-different-about-them-and-why-should-you-care

 

DOT 3, 4, and 5.1 are glycol-based. Generally speaking, the higher the number, the higher the boiling point (lowest around 400F, highest around 500F). Sans water contamination, DOT 3 tends to have the longest life. When water IS in the fluid, DOT 4/5.1 have much higher wet boiling points than DOT 3 (but overall boiling points are lowered).

DOT5 is silicone-based, and should never be mixed with the types above - it does indeed gel, so you have to run a ton of it through the old lines to get them completely flushed out. Also - while it doesn't absorb water, it tends to develop air bubbles when cycled rapidly (thus, is a poor choice for ABS systems.)

With proper maintenance, moisture shouldn't be an issue, as the fluid should be changed around every 3 years.

 

I used Amsoil Synthetic Dot 3 & 4 fluid. It exceeds the wet and dry boiling points of Dot 3, 4 and 5.1 specs. Specs are listed below.

Amsoil Specs
Dry boiling point - 271°C (520°F)
Wet boiling point - 187°C (368°F)

Dot 3 Specs
Minimum dry boiling point 205°C (401°F)
Minimum wet boiling point 140°C (284°F)

Dot 4 Specs
Minimum dry boiling point 230°C (446°F)
Minimum wet boiling point 155°C (311°F)

Dot 5.1 Specs
Minimum dry boiling point 260°C (500°F)
Minimum wet boiling point 180°C (356°F)

 

As I am over 70 years old, I should have learned my lesson by now. I have engaged in "discussions" regarding silicone brake fluid for nearly half a century. But I would like to be helpful to people considering silicone brake fluid for their 308's or GT4s. Since my BMW and Porsche do not recommend silicone, I use Dot 4. It may well be, as thorn suggests, that there are issues with ABS. Neither would I suggest it for racing.


However, having used it very successfully in an assortment of classic cars and motorcycles, over many years, I would recommend it to 308 owners. It is certainly preferable to introduce it into a renewed system. But reasonably thorough flushing has always been sufficient in my experience. I will admit to not changing silicone fluid for over a decade (because there was no need to) in garaged classic cars. I converted one car in 1974 and all was still well in 2005 without a change. I have personally changed fluid in scores of brake systems. While I change glycol fluid when the water content exceeds 3%, that may be after only two or three years. If you own a car for a long enough period of time, that is many opportunities for a wayward droplet, splash, contaminated towel or fingerprint, which you don't immediately detect, to mar your lovely paint job.

Just my actual experience; opinions indeed may differ.

 

The work was done by the local shop - they have a good reputation. Normally I do all that work myself but it needed tires/pads/rotors and I specifically asked them to flush/replace the brake fluid. I don't know what they did re the ABS module as far as purging. Since they do this sort of service constantly, I ASSUME they bled or cycled the ABS appropriately but I don't know that for sure.

I took the car back the next day, complaining of the soft pedal and insisted they re flush with Dot 4. The brakes were fine after that.

IT IS possible that the problem was incorrect (or no) bleeding of the ABS module the first time and proper bleeding the second time. IOW, if that was the case, the fluid may not have been the cause of the spongy pedal but they claimed they bled the system properly both times.

 

See my post above regarding DOT5 and ABS.

 

Yes, that was good info. Then the question becomes in that single day did Mike actuate the ABS while driving and froth up some DOT5 (or did the self-test do it when first turning on the ignition) enough to make a soft pedal. Who knows.

I also appreciate daynyc's comment about water content, and the 3% number. Reminds me to dig out my tester before spending money for a flush on my other car.

My conclusion, for me and my non-abs F car whose brake system is completely disassembled, is to go with DOT 5 or maybe 5.1.

 

"...Then the question becomes in that single day did Mike actuate the ABS while driving...'''

FWIW, I intentionally "activate" the ABS in our cars at least once on any day that I drive them. I do the same with our motorcycles. I activated the ABS on my wife's MB within 1/4 mile of leaving the shop. The way the pedal reacted - all the way to the floor before it provided sufficient stopping power - I would have immediately taken the car back but they were closing as I paid the bill so I brought it back the next day.