Which brake fluid?

[Dayla]

1983 with a 305, original paperwork told me use DOT 5. Bought it, added about 1/4 cup only to read on the master cylinder to use DOT 3! What?! (The cap was rusty enough to be nearly unreadable til i took some flitz to it.) So does anyone know if that master cylinder is original? think someone replaced it with the wrong one?  or the paperwork is wrong? Not cool.  That was AFTER spending way too much on new brakes too 😳😰

[Gunslinger]

Since you don't know for sure what fluid was in the car, you should get the entire brake fluid system completely flushed.  DOT 5 and DOT 3 do not mix and can create an unsafe situation.  If you see any cloudiness in the fluid that's a sure sign you have DOT 3 and 5 mixed.

I know in 1970 Avanti Motors was specifying silicone fluid (it became DOT 5 later) regardless of what the master cylinder was marked.  If Avanti Motors changed that specification I don't when or if that occurred.  I believe but again am not sure, that Avanti Motors placed a sticker on the master cylinder or near it specifying the brake fluid to use...but decals under the hood wear away and peel off with time.

After you have your system flushed fill with one or the other but make sure you keep it that way.  

[mfg]

Hi Dayla,  I'd speak with the mechanic who overhauled the brakes on your '83 Avanti to get his thoughts on this....He should be able to tell you the type of fluid which was used.

Although Avanti Motors specified silicone brake fluid for their '83's, I have found (and this is only my opinion) that silicone (Dot 5) brake fluid is somewhat problematic......I use Dot 3 brake fluid in all my Studes, including my 'everyday driver' 1983 Avanti.....Best of luck!

[Dayla]

On 8/19/2019 at 7:48 AM, Gunslinger said:

Since you don't know for sure what fluid was in the car, you should get the entire brake fluid system completely flushed.  DOT 5 and DOT 3 do not mix and can create an unsafe situation.  If you see any cloudiness in the fluid that's a sure sign you have DOT 3 and 5 mixed.

I know in 1970 Avanti Motors was specifying silicone fluid (it became DOT 5 later) regardless of what the master cylinder was marked.  If Avanti Motors changed that specification I don't when or if that occurred.  I believe but again am not sure, that Avanti Motors placed a sticker on the master cylinder or near it specifying the brake fluid to use...but decals under the hood wear away and peel off with time.

After you have your system flushed fill with one or the other but make sure you keep it that way.  

Thank you! 

[Dayla]

20 hours ago, mfg said:

Hi Dayla,  I'd speak with the mechanic who overhauled the brakes on your '83 Avanti to get his thoughts on this....He should be able to tell you the type of fluid which was used.

Although Avanti Motors specified silicone brake fluid for their '83's, I have found (and this is only my opinion) that silicone (Dot 5) brake fluid is somewhat problematic......I use Dot 3 brake fluid in all my Studes, including my 'everyday driver' 1983 Avanti.....Best of luck!

Thanks!