Rodney Dickman early master cylinders. (Page 1/1)
1985 Fiero GT JUL 25, 02:50 PM
I just bought myself most of the major Rodney Dickman clutch hydraulics, master cylinder, slave cylinder and clutch release lever. All of this is for the Muncie 4 speed, early version (specifically 1985 Fiero GT). I love the quality of all of the parts, it is obvious that they were made and designed with care, but the master cylinder seems to be out of spec. I do not know any official GM specs that he might have used to design this, but I do know that my original OEM master cylinder has a throw of 1 1/4", whereas Rodney's master has a throw of 1 1/8". To further complicate things, Rodney's late series master has a throw of 1 1/2", as does the $35 cad aluminum master I got off of rock auto. You may be asking what the difference is between 1 1/8" and the OEM 1 1/4", but that is on a lever, so the maximum throw of the clutch is noticeably less. With the original and the cheapo replacement, the clutch would travel from the top bump stop all the way down to the carpet, with the Rodney Dickman replacement, the clutch stops about 1/4" from the bump stop, as high as it will go, and stops about 1/2" from the carpet. So I either have to choose to have my clutch at the same level or lower then the brake pedal, or have it stop before it hits the floor, and therefore risk bending the clutch pedal or damaging the master cylinder by reaching the end of its travel. The other thing is that by the specifications, to fully disengage the clutch, the slave must move 1 1/8". That means that if there are any inefficiencies in the system at all, like even the smallest air bubble, expansion of the flexible hose, the tiniest bit of give between the slave and release arm, or anything else, it will not give the required 1 1/8" travel at the slave, because the master simply cannot overcome those inefficiencies. Don't get me wrong, I love the products that Rodney makes, and respect the amount of effort that goes into them, but if he has sold thousands of products that are off by 10% from the factory original, and over 20% from his later version and other aftermarket solutions, then that is something I don't quite understand, and wonder why it isn't mentioned more often.
Patrick JUL 25, 04:21 PM
Paragraphs man, use paragraphs.

Does Rodney's clutch master not have an adjustable banjo?

I have both a 5-spd Isuzu and a 5-spd Getrag. I adjust the banjos on my clutch masters to allow the clutch pedal to come within maybe 1/16"-1/8" of the pedal return stop. This ensures that the master is at the end of its return travel, and I get full stroke of the master when I push the pedal towards the floor.

Make sure any switch located at the pedal return stop is not misadjusted and interfering with the pedal's full return.

[This message has been edited by Patrick (edited 07-25-2023).]

1985 Fiero GT JUL 25, 05:36 PM
Yes, it does have an adjustable banjo, but any adjustment does not add effective travel, just modifies how high or low that travel is, with the other masters, the pedal would travel all the way from its stop to the floor, with this one, it travels less, so I can pick to either have a lower pedal, with its travel ending at the floor, or to have a higher pedal that doesn't go all the way to the floor.
Patrick JUL 25, 05:49 PM

quote
Originally posted by 1985 Fiero GT:

Yes, it does have an adjustable banjo, but any adjustment does not add effective travel...



It most certainly makes a difference if the banjo length is too short. The clutch pedal would hit the floor before the master reaches the end of its travel.
1985 Fiero GT JUL 25, 05:54 PM
Yes, I understand that, what I am saying is that it never gets the chance to get anywhere near the floor, because the master bottoms out early. If I had the banjo adjusted so the pedal is at the right height, it will be about 1" from the floor when fully pressed, all the others go right to the floor, and start at the right height, this never truly bottoming out the master cylinder, the limiting factor is always the floor, not the cylinder
Patrick JUL 25, 06:32 PM

quote
Originally posted by 1985 Fiero GT:

... my original OEM master cylinder has a throw of 1 1/4", whereas Rodney's master has a throw of 1 1/8"...to fully disengage the clutch, the slave must move 1 1/8". That means that if there are any inefficiencies in the system at all, like even the smallest air bubble, expansion of the flexible hose, the tiniest bit of give between the slave and release arm, or anything else, it will not give the required 1 1/8" travel at the slave...



That's not necessarily true... you haven't made any mention of bore size and therefore volume of fluid being moved. For example, if the bore size of the master was greater than the slave, then 1-1/8" travel at the master would translate to more than 1-1/8" travel at the slave. There were threads years ago regarding the use of slaves for Isuzu 5-spds being used with Muncie 4-spds in order to get more slave travel. The Isuzu slaves have smaller bores, and therefore, the travel is increased.

Both of my manual transmission Fieros are 5-spds, an Isuzu in my '84 and a Getrag in my Formula. I have zero experience with 4-spds and any associated clutch issues.
1985 Fiero GT JUL 25, 06:58 PM
I am not sure as to the bore size but my main concern here is that 1: it feels different, and inconsistent with the rest of the car, it feels too delicate with the short travel, I also have worries of bending the clutch pedal and sanding the master cylinder, as before, you couldn't press on the clutch hard enough to bend the pedal, because when it was fully down, the pedal was resting on the floor, so any more force would be supported by the floor, and not by the master cylinder, now at the end of its travel, it is stopped by the master cylinder, so if any more pressure is accidentally applied, it could bend the pedal or damage the master cylinder. Rodney's late style master, which my dad has, like you would have if you have one, is done correctly, so that the pedal rests on the floor when fully depressed, therefore not transmitting any extra force through the weak pedal
Patrick JUL 25, 07:04 PM

Rodney Dickman is quite approachable. Have you addressed your concerns about his clutch master cylinder with him?
1985 Fiero GT JUL 25, 07:27 PM
Yes. I have, his customer support is very good, he has confirmed that the throw of his early master cylinder is 1 1/8", which is at variance with the other examples I compared to above. He says that no one has brought this up before and he doesn't know what the problem is

[This message has been edited by 1985 Fiero GT (edited 07-25-2023).]