AISIN Brake M/C Rubber Cap

[middlecalf]

This is the second AISIN TEQ brake master cylinder rubber cap that‘s gotten soft and is disintegrating. When you handle it your hands get readily black. Had this happen on my 40 a couple of years ago (it was a ~10yr old m/c) and is now happening on my 45 (m/c is a few years old). Only happened with the brake m/c‘s, not the clutch, both using DOT 3 fluid.

Here’s the AISIN brake m/c cap (cleaned up a bit):

This is the clutch m/c cap, it’s still good and solid:

Thoughts? @ToyotaMatt heard any issues about this from AISIN?

 

[ToyotaMatt]

This is the second AISIN TEQ brake master cylinder rubber cap that‘s gotten soft and is disintegrating. When you handle it your hands get readily black. Had this happen on my 40 a couple of years ago (it was a ~10yr old m/c) and is now happening on my 45 (m/c is a few years old). Only happened with the brake m/c‘s, not the clutch, both using DOT 3 fluid.

Here’s the AISIN brake m/c cap (cleaned up a bit):
View attachment 3251577

This is the clutch m/c cap, it’s still good and solid:
View attachment 3251578

Thoughts? @ToyotaMatt heard any issues about this from AISIN?

- You NOT using Fully Synthetic DOT 3 brake fluid for starters ....

- that older RETRO AISIN cap above is either older then the TITANIC or aftermarket , because i have NEVER seen one with AISIN koolness factor logo on it like that before ?

- maybe a fresh young tender OEM JAPAN Spec. one here is all you need , see below , ..

- and FLUSH 100% of all old fluid out and install the prescribed above , i use the VALVOLINE DOT 3 SYNTHTIC with excellent results for well over a decade ,,,





- ill mail you one out as a professional sample if ...................

- you swear to use FULLY SYNTHETIC DOT 3 ......

 

[pbgbottle]

ive. Ever seen one say Aisin either

 

[middlecalf]

Interesting. Assumed AISIN was the manufacturer. Brake fluid doesn‘t harm rubber, so must be some other environmental issue with their rubber (e,g ozone).

Matt @ToyotaMatt send me a cap, those look like the good one I have on my clutch m/c. PM me with payment details. Thanks.

 

[middlecalf]

Actually I need two Matt @ToyotaMatt. PM payment details.

Here’s my logic and conclusion. Prior to my engine rebuild, this thing had a lot of combustion (blowby) products entering the engine compartment. I think that is not too friendly to rubber. Also carb fuel venting after shutoff probably contributes. The m/c’s are close to the carbs. The brake m/c cap is further along in deterioration compared to the clutch m/c cap, but there are early indications of deterioration in it as well. Distance and some structural shielding could be in play as well as to difference. The deterioration I had in the cap in my 40 a while back can also be explained by engine combustion byproducts, its late 50s-vintage 283 motor has been a bit like… an old engine for the time I’ve had it. And a 4bbl carb so fuel venting issue as well.

 

[pb4ugo]

Over time all rubber deteriorates.. I've seen many caps do the samething as mentioned previously. Ive noticed the rubber exposed to the fluid is ok, but the external portion exposed to air is not. Maybe thats why the cap deforms. With minimal research you'll find all dot 3 and 4 brake fluids are synthetic. It's lab based and not petroleum based. Evidently, some manufacturers blend their fluid to be more resistance to moisture. Dot 5 and 5.1 are silicone based and shouldn't be used in dot 3 and 4 applications.

 

[rex in bama]

Just got my later model cap from @ToyotaMatt. Fits tight and now have the sensor working again (wires a had been cut earlier in its life)! Don’t know how you tracked it down, but thanks!

 

[middlecalf]

I hate this crap.

Here’s the underside of the above cap with AISIN on it:

Don’t know what the NRC is, and a search of the part number 47225-12012 only ends up in some Jakarta website .

Here’s the underside of the clutch m/c cap shown above:

It‘s an AISIN also!

This is what I need.

It’d be nice if Toyota repro’d the tin cups. You can see how close the brake m/c is to the carb due to the offenhauser dual-carb setup. I bet offenhauser never thought of this issue. Of course, tin cups were the standard back then. So here’s my pathetic tech tip from this thread: be aware of shortened useful life of rubberized brake m/c cap when employing an offenhauser dual carb setup.

I crack myself up.