Reseal top of master cylinder

[CaptainK]

I was checking levels in my 1968 C3 the other day and decided to check the brake fluid level. Took the lid off it, all looked good. Put lid securely back on with the brackets etc.

Next drive out I noticed a small puddle under car and tracked it back to the brake master cylinder (the black thing on driver's side in front of the brake servo). It seems its weeping out of there. Topped up, and test drove. Again weeping out. Repeated again, each time jiggling the brake cover and checking the securing brackets, and cleaning the mating surfaces. Still weeps. The rubber seal on the "lid" looks good, and the brake setup itself isn't that old - 5 years I think.

Any suggestions on how to stop the weeping? It didn't do it until I decided to check the levels to see if it was low. Typical. . I did think about putting a bead of sealant around the top of it, but wasn't sure if that was a good idea or not, so thought I'd check with the club first for ideas.

Photo below is from before the leaks, and its the bit I've circled in red (not to be confused with the rest "circled" in red by the spark plug leads ):

 

[Emc]

Master Cylinders leak from ,either the cap seal, or the internal seals, which leak from the rear .this gets on the booster then drips onto the floor, both are replaceable

 

[CaptainK]

Master Cylinders leak from ,either the cap seal, or the internal seals, which leak from the rear .this gets on the booster then drips onto the floor, both are replaceable

Mine is leaking from the top - from the lid you remove to see how much fluid you have left. You can see "wetness" coming out from under the lid. Amusingly, it was all fine before I first decided to take the lid off and have a look.

If you have a spare seal going free, I'll probably get one from you - I've been meaning to put in an order with you for a gearbox speed sensor when I know what colour one I currently have (my speedo under-reads, so I'm actually going faster than what the speedo says). Probably due to the previous USA owner swapping the rear diff from whatever the standard 1968 327/300hp rear diff was to a 3.08 LSD diff it now has.

 

[Roscobbc]

This has always been an issue with my '68 non PB car. Even with a new cap and rubber seal if you top-up to within a half inch of the reservoir it would leak out of the rear section after brake application, the fluid trickling down the master cylinder and removing paint etc untill getting on the the headers and smoking-off. If you apply the brakes with the master cylinder cap off.... you'll see why this happens. A vertical 'squirt' from inside the reservoir. I believe this pressurised the reservoir, causing the leaks. I deliberately run a far lower fluid level to prevent this occurring.

 

[CaptainK]

This has always been an issue with my '68 non PB car. Even with a new cap and rubber seal if you top-up to within a half inch of the reservoir it would leak out of the rear section after brake application, the fluid trickling down the master cylinder and removing paint etc untill getting on the the headers and smoking-off. If you apply the brakes with the master cylinder cap off.... you'll see why this happens. A vertical 'squirt' from inside the reservoir. I believe this pressurised the reservoir, causing the leaks. I deliberately run a far lower fluid level to prevent this occurring.

Yeah, the rear does seem to be the worst like you said, but I also get bits leaking out of the side of the fronts. The rear fluid definitely got much lower than the front section. Front hardly moved at all.

Its just annoying as when I originally checked it (after 5 odd years since install), it had been fine and the levels looked good without any leaks. Then after that it has been leaking. I should have never checked it. Grr !

 

[teamzr1]

Mine is leaking from the top - from the lid you remove to see how much fluid you have left. You can see "wetness" coming out from under the lid. Amusingly, it was all fine before I first decided to take the lid off and have a look.

If you have a spare seal going free, I'll probably get one from you - I've been meaning to put in an order with you for a gearbox speed sensor when I know what colour one I currently have (my speedo under-reads, so I'm actually going faster than what the speedo says). Probably due to the previous USA owner swapping the rear diff from whatever the standard 1968 327/300hp rear diff was to a 3.08 LSD diff it now has.

Gears as to size and teeth to color

 

[CaptainK]

Nice one thanks. I think from my rough calculation I need the 19 teeth natural one for my 4 speed manual with 3.08 rear diff. Problem is, I don't know what the DRIVE gear teeth count is on the bit inside the gearbox (I'm assuming my 1968 Corvette has its standard 4 speed gearbox). So I was gonna look at the colour of the DRIVEN removal plastic speedo gear to then see about changing the plastic gear.

But that's a minor issue.... the leaking brake fluid is more annoying. Almost tempted to put a bit of "plumber's mate" around the sealing edges to stop it leaking

 

[Chuffer]

Has the cap become distorted by prizing off the two clamp bars ? You say it was ok until you removed it after 5 years . As I am sure you found out , those clamps are a bugger to flick off and spring back on again whilst still keeping the sealing gasket in place.

 

[Roscobbc]

Yeah, the rear does seem to be the worst like you said, but I also get bits leaking out of the side of the fronts. The rear fluid definitely got much lower than the front section. Front hardly moved at all.

Its just annoying as when I originally checked it (after 5 odd years since install), it had been fine and the levels looked good without any leaks. Then after that it has been leaking. I should have never checked it. Grr !

Much the same as mine Capt - don't like having the levels (certainly the rear one) so low......but it hasn't proved to be an issue. I wondered if it was something to do with being manual brakes.......but yours is power brakes.

 

[CaptainK]

Much the same as mine Capt - don't like having the levels (certainly the rear one) so low......but it hasn't proved to be an issue. I wondered if it was something to do with being manual brakes.......but yours is power brakes.

Mine is reproduction power brakes from a kit. Originally manual brakes. All worked fine with no leaks until I disturbed it. Grrr....

I've had some PMs with ideas, so I'm gonna give them a go when I get chance. Then find the time to take Vette out for a spin to see what happens.

 

[Waynio]

If you dont get it sorted then no reason why you cant try a differarnt seal. I have had made seals before using EPDM and adhesive on one side. Use the A262 Adhesive from here and the seal of choice. stick it down one side
First time i used it was 10 years ago while fitting boat windows and still water tight.

Solve Your Sealing Problems | Seals+Direct Ltd

Seals Direct specialise in the manufacture and supply of rubber seals, trims and gaskets within the marine, industrial, caravan and automotive industries.

www.bing.com

This place could be good for other sealsd aswell maybe.

 

[Mad4slalom]

Mine is reproduction power brakes from a kit. Originally manual brakes. All worked fine with no leaks until I disturbed it. Grrr....

I've had some PMs with ideas, so I'm gonna give them a go when I get chance. Then find the time to take Vette out for a spin to see what happens.

Just as well buy a new seal from gavin for peace of mind , job done, the plumbers mate route sounds a bit “bubba”

 

[CaptainK]

Just as well buy a new seal from gavin for peace of mind , job done, the plumbers mate route sounds a bit “bubba”

Haha. Yeah, I wasn't really going to put plumbers mate on it due to possible contamination of the fluid in that rather serious bit of safety gear called the brakes. Its just those kind of thoughts that pop in your head from sealing other fluids (but know its silly because this is a brake system)

But, one thing I have tried is making the top clips "stiffer". By that I mean make them a bit more thicker so that they produce a greater downforce on the lid. Mine seemed very slightly loose, so I've wrapped metal around the clips to make them thicker. Not been out in the C3 yet to see if it helps. Ultimately I'll probably get a new seal once I've got around to looking at my gearbox sensor (posted in different thread), so I can buy lots of stuff at once. I rarely drive the C3, only short distances when I do, and its loss of brake fluid is very minimal when I drive it anyway, so I'm not in urgent need to do it.

 

[Mad4slalom]

Haha. Yeah, I wasn't really going to put plumbers mate on it due to possible contamination of the fluid in that rather serious bit of safety gear called the brakes. Its just those kind of thoughts that pop in your head from sealing other fluids (but know its silly because this is a brake system)

But, one thing I have tried is making the top clips "stiffer". By that I mean make them a bit more thicker so that they produce a greater downforce on the lid. Mine seemed very slightly loose, so I've wrapped metal around the clips to make them thicker. Not been out in the C3 yet to see if it helps. Ultimately I'll probably get a new seal once I've got around to looking at my gearbox sensor (posted in different thread), so I can buy lots of stuff at once. I rarely drive the C3, only short distances when I do, and its loss of brake fluid is very minimal when I drive it anyway, so I'm not in urgent need to do it.

Phew !good one with the plumbers mate

 

[CaptainK]

I took the speedo bullet out over the weekend to see what I have, and its a white / natural looking driven gear. So 19 tooth. It all looked ok, and the speedo itself turns fine with no lag or anything - it just reads slower than your actual speed - e.g. from memory an indicated 64 mph is a real GPS speed of 70mph. I'll take it for another test drive during the week when I have time, and double check the calibration before ordering a new speedo gear. Gavin will know best. The missus' is also using the "daily" car tomorrow, which currently blocks the garage to the Vette - so she can put it back on the other side of the drive so I can easily get the Vette out. Yes, I can shift the "daily" out of the way to get the Vette, but I don't like doing it often as the "daily" doesn't get used much either (both work from home) and thus little stop start shuffle on the drive would just flatten batteries over time.

 

[CaptainK]

Took the Vette out for a quick spin up and down the 60mph road out of town. Testing my speedo against two GPS speedometer programs on my phone. Needless to say at a speedo indicated 60mph, I am doing a GPS speed of 63mph. So the car is travelling faster than indicated, with the gap getting bigger the faster I go. I guess a new speedo gear is needed then.

Also whilst out meant I could see if any leaks from brakes after I tightened it up. Deffo seems to be better now and I couldn't see any fluid like last time. I'll order a new seal anyway, but keep an eye on it for now too.

 

[teamzr1]

There are times when the speedo is incorrect is the gear on cable side is changed
Other times it is the inner gear that sits inside the tranny and sometimes both

Here is speedo gear calculators to find out which would be required to calibrate VSS output to your speedo

Speedometer Gear Calculator | GTSparkplugs

Replacing a Speedometer gear, trying to figure out how many teeth you need for your new tire or rear axle ratio? This tool will help with the calculations.

www.gtsparkplugs.com

Speedometer Driven Gear Calculator

 

[CaptainK]

Here is speedo gear calculators to find out which would be required to calibrate VSS output to your speedo

Thanks Team, I've used a few speedo gear calculators before on the internet, including the GT spark plug one. Sadly the "STL" one doesn't work for me, no certificate on web site and when I proceed anyway it just says its broken.

The minor issue is I'm not sure what my DRIVE (not driveN) gear is in my gearbox. I'm assuming its the standard one for a 1968 4 speed gearbox, but the internet tells me it can vary a bit. But from my playings around on calculators, its either a 19 tooth driveN gear I need for my car if my DRIVE gear is a 8 tooth, or a 18 tooth driveN gear if my car is a 7 tooth DRIVE gear. As I have a white / natural driveN gear in my car currently and the speedo is wrong, then I have to assume my gearbox has a 7 tooth DRIVE gear. Thus I think I need a 18 tooth (brown) driveN gear according to the calculators. This also fits with my observations of my speedo on the road, and how different it is compared to different GPS devices.

Then the other compounded problem is which 18 tooth driveN gear do I get? As you noted above, there is the option of 1.76" and 1.84" DRIVE gears in the gearbox, and my research so far hasn't given a conclusion as to which I have. When I pulled my white / natural one out to check it, I did measure it's diameter at the very widest (from the peak of a tooth on one side, to the peak of the tooth on the opposite side) and that was 1.9 cm (0.748 inches).

I've messaged Gavin @ EMC to see what he thinks, then I can get it ordered too.

 

[Roscobbc]

Capt - yopu are experiencing the same conundrum that I had long long after buying my Vette. Both the drive and driven gears were the correct colours/no. of teeth for the rear axle ratio of my car. Yet it shows a good 20 mph less than what it is really doing. TBH I gave up on it yeaers ago and worked-off indicted RPM.....I had the speed/rpm combo's inplanted in my brain.......eventually I fitted a redundant TomTom unit in the car which gave me the indicated speed for 90% of the time (not in tunnels or city centres with tall buildings though)

 

[CaptainK]

Capt - yopu are experiencing the same conundrum that I had long long after buying my Vette. Both the drive and driven gears were the correct colours/no. of teeth for the rear axle ratio of my car. Yet it shows a good 20 mph less than what it is really doing. TBH I gave up on it yeaers ago and worked-off indicted RPM.....I had the speed/rpm combo's inplanted in my brain.......eventually I fitted a redundant TomTom unit in the car which gave me the indicated speed for 90% of the time (not in tunnels or city centres with tall buildings though)

Yeah, that's what I currently do, and to be fine I'm happy doing that. But I fancied tinkering and having a play with the car to see if I can improve the situation. I'm not great with car mechanics, but I like to tinker.