TR2/3/3A another brake master cylinder question

[tomnanney]

Recently I replaced the brake MC with a new Moss unit. I also replaced several brake lines etc. I didn't bench bleed, but did take the push rod loose from the car connection and have someone manually push it in as far as it would go to repel any excess air. I've now bleed the brakes probably five times and the pedal will pump up,but then goes soft again. I'm not sure what to do next or is the MC possibly bad? I have heard that Moss did have some MC problems a while back?
tom
61 TR 3a

 

[bobhustead]

Unless you are using DOT5 fluid, not bench testing was a mistake. What bleeding procedure are you using?
Bob

 

[TR3driver]

The TR3 MC is a lot simpler than the later cars, it's hard to have much wrong with it. Do you get more air when you re-bleed the brakes? Have you checked the soft lines, rear brake adjustment, no stuck caliper pistons, etc?

Not sure I understand your comment about the pushrod. The "car connection" is just the top of the pedal, which should move easily. IOW there is no need to disconnect it. In fact, that's a good point, the pedal needs to return fully and easily. If it binds due to rust in the pivot or whatever, and doesn't let the MC return that last little bit, you'll have problems. There also needs to be some free play at the pivot. Not usually a problem with the later cars, unless perhaps someone has added a pedal stop. (Earlier TR3/A came with a pedal stop from the factory, but it was deleted later on.)

Also, the residual pressure valve on top of the 5-way connector can sometimes cause problems if it gets gunked up inside. If all else fails, you might try cleaning it. Or just leave the plunger out entirely as I do. It's actually supposed to help prevent a low pedal after hard cornering, but I would rather deal with the low pedal than have the brakes drag a bit all the time.

 

[tomnanney]

I usually bleed the brakes the old fashion way with two people, one in the car and one at the bleeder screws. By "car connection" I mean the top of the pedal. Also, All the soft lines are braided and the the 5 way connector has been gutted! I haven't check each wheel cylinder,however, it doesn't appear they are leaking.
(Bob, I see your summer address is Robbinsville, NC.? Are you on Lake Santeetlah? I have a place their in Cross Creek)

 

[CJD]

I rarely have the luxury of 2 people to help. Once a brake system is primed, if you just open a bleeder at any wheel gravity will bleed the lines for you. I connect a clear hose to the bleeder and just crack it open a bit. Then I watch the fluid drain all on it's own into a cup. Of course, keep an eye on the reservoir so you don't suck it dry. The clear hose gives you an idea of how much air you are venting, so you know when to stop. The rule of thumb is farthest cylinder from the MC first, and then work your way closer.

I have used this system dozens of times on a dozen vehicles, including ABS cars and the TR3A. I like it better than pumping, because when you pump, at some point you induce a suction that can draw air into the bleeder if your helper is not following instructions properly.

 

[bnw]

I ran almost 2 quarts of brake fluid through a 72 mini Clubman with 4 wheel drums with a pedal similar to yours until I adjusted all four corners. DUMB

 

[Chuck Murphy]

Do check the rear brake adjustment as Randall said. I had a problem similiar to yours and believe it was caused by too loose a rear brake adjustment. I fixed my problem by adjusting the rear brake properly.

Chuck

 

[bobhustead]

Sometimes different techniques need to be tried. Furious pumping, hold pedal down and crack the longest line's bleeder; crack a bleeder with no pedal pressure, push down once and hold, close bleeder, repeat; clear hose on a bleeder, other end in a clear glass of fluid, pump it, and watch the bubbles; drip bleeding as described by CJD.
We are on Franks Creek east of town.
Bob

 

[tdskip]

I doubt the issue is the new Moss MC at this point, I'd focus on what the guys are suggesting above.

 

[tomnanney]

Well, I adjusted the rear wheels and bleed the brakes again and so far the pedal is holding fairly firm. Thanks for all the help!
Tom

 

[Crankshaft]

I hope this is not an act of piracy upon this thread but I have a related question. Due to a new paint job, I am considering converting to Dot 5 fluid. Do I need to just make room in the reservoir and fill with Dot 5 then bleed system to purge the old fluid, or is there more to it than that?

 

[Geo Hahn]

Theories and opinions abound on both the merits (or drawbacks) of DOT 5 and the steps involved in the conversion.

My experience on 3 cars: I just sucked all the old stuff out of the reservoir that I could, filled with DOT 5, then bled in the usual fashion until the fluid came out purple.

I think it is a good idea to let the newly filled reservoir sit awhile (e.g. over night) before starting the bleed as DOT 5 holds the tiny air bubbles in suspension longer than the other stuff.

After a few months you may notice that your new fluid has lost its color - I think that means the remaining DOT3/4 in the system sucked the dye out of it. Possibly not necessary, but at that point I do another full bleed to get a more pure content. After all these years mine stays purple all the time.

I've used said cars for 14 years since I did this and observed no ill effects. I have had to do a brake master rebuild and a clutch master rebuild and a slave rebuild (among the 3 cars) along the way but have no reason to blame that on the DOT 5 -- simply worn out seals.

 

[TR3driver]

I'm with Geo: I've done it that way several times and it worked out well for me. Although I think there is something to be said for doing a full rebuild of the hydraulic system, it does not appear to be required.

But it does seem to me that new components last longer with DOT 5 than old, worn components do. Seals and hoses are pretty cheap IMO, compared to the potential consequences of a failure and the mess & effort of changing them later.

Just one example, to illustrate my point : When I got Stag #1, the brakes appeared to work OK but the fluid was old and dark. Obviously DOT 3 or 4 and obviously not changed recently. So I switched to DOT 5 by just bleeding through. Worked great at first, but a year or so later the brake pedal started sometimes sinking slowly while sitting stopped with my foot lightly on the pedal (like at a stop light). Didn't seem too serious, as I always got good pedal with one pump; so I ordered a MC rebuild kit (from the UK) and eventually tried to drive the Stag to a shop to have the MC rebuilt. (Had a lot of other things going on in my life at that point and didn't want to do the work myself.) On the way to the shop, the MC quit working entirely! No hydraulic brakes at all! Postmortem on the old MC showed that both pressure cups had become much too soft and literally tore where the pistons pressed against them. Obviously I think, the cups were on their last legs (very likely original to the car) but I suspect the DOT 5 hastened their demise.

OTOH in many cases the old seals have continued to last very well. I never did have to do any of the wheel cylinders on that car, and they are still holding today. (although it's been off the road since 2005 or so). So it's a gamble IMO.

 

[Crankshaft]

Thanks for the input Randall & Geo. I'm going to try this. I think I might try in about a year to re-bleed. I do have new hoses to install, and I'll probably gut the valve before the conversion.
I guess at my age (since I rarely buy green bananas) I shouldn't talk about what I'm going to do next year should I.
Thanks again, I'm always glad to get your insights.

 

[TR3driver]

I guess at my age (since I rarely buy green bananas) I shouldn't talk about what I'm going to do next year should I.

Seems like the wrong attitude, to me. It's always good to have something to look forward to, no matter what the odds are of actually getting there to do it. Much better than the other way around, running out of things that interest you before you run out of ability to do them. I've got way more projects planned than I will ever find time to actually do.

I love that scene in "Little Big Man", where Chief Dan George decides "It is a good day to die." and lays himself down to pass with dignity. "Sometimes the magic works, and sometimes it doesn't."

 

[Geo Hahn]

I planted 3 Saguaros this past week. If you don't know them -- they take 50 to 75 years to reach maturity and can then press on for another 50.

Sometimes you have to take the long view even when the end is out of your range.

 

[Crankshaft]

Thanks for the motivation guys. I'm going to bleed fresh fluid into the systems (mine and the brakes) next year for sure.