You're first an third options are the same did you intend that? And the step bore on them is 40mm, not the 44mm that you state.

To get the pushrod length, I'd have to go out in the snowdrift and remove the MC. I will be traveling to Florida between Christmas and New Years. Should be there by 1st or second week of January. Can you wait until then?

I think there is a high probability that the pushrod length would be the same between the 40mm, 1-1/8" bore MC, and the 40mm, 1-1/4" bore. But would highly advise doing the adjustment procedure on both and measuring the two to verify. The last thing you want is for the MC piston to not retract all of the way holding the brakes on. JMHO

In reading these brake postings, including pushrod comments, I kept
thinking Y'All could use my "Pushrod Gauge", so here's a link to it:
http://www.gmcmhphotos.com/photos/g6289-master-cylinder-pushrod-gauge.html

Like many of my postings on the photo site, you need to go through the
photos backward -- last one first. Wish there was an easy way to correct
those, but I don't know how.

Ken H.

Larry,

Thank you for the reply. I did get the P30 with the filter screen that Ken H. had mentioned. I specifically sought out the one with the screens on the inlet port.

I am very interested in the new master cylinder. I had a discussion with Dave L. about 2 weeks ago and we were talking about it. He said he was waiting for test results. I would like to rid myself of the "O" rings in the p30 for the cup piston seals found in the new master cylinder in question. It would be nice if I didn't have to buy another Vacuum Booster.

Thanks again and Oki and I hope you and Lucy have a wonderful Christmas.

Take care,
Tom K.

Bill Van Vlack wrote on Sat, 18 December 2021 19:48

Quote:

Randy said...." this MC works better than the OEM MC I was using previously. I had plenty of stopping power before but now I have reduced my stopping distance significantly."

Then you said.... "It left me confused about which MC you are using now and what kind of braking you have, and what has reduced stopping power."

So, Randy now has reduced stopping distance, therefore more stopping power, so nothing has reduced stopping power. Au contraire.

I think he's using the 1-1/8" with

I have the Dave Lenzi two-port booster; I assume it's metric but I'll have to check; I didn't have to send a core. I understood that you have the same and have fitted the 1-1/4" MC. I'm asking if
1. You can share the length of the pushrod to save me some time if I go that way as well.
2. You think the 1-1/8" MC can use a pushrod of the same length. (I think you answered that they look the same but haven't installed to be sure.)

It seems like there's three options...
NAPA NMC M2580 ......44mm, 1-1/4" bore for metric
Cardone 13-1870......44mm, 1-1/8" bore for OEM
NAPA NMC M2580 ......44mm, 1-1/4" bore for metric

Did I get that right?

You're first an third options are the same did you intend that? And the step bore on them is 40mm, not the 44mm that you state.

One more option is of coarse the OEM MC which does not have the 40mm step bore.

Still not sure what Randy is using. Would have to confirm that with him.

To get the pushrod length, I'd have to go out in the snowdrift and remove the MC. I will be traveling to Florida between Christmas and New Years. Should be there by 1st or second week of January. Can you wait until then?

I think there is a high probability that the pushrod length would be the same between the 40mm, 1-1/8" bore MC, and the 40mm, 1-1/4" bore. But would highly advise doing the adjustment procedure on both and measuring the two to verify. The last thing you want is for the MC piston to not retract all of the way holding the brakes on. JMHO

Not saying this is the right thing to do, but when my MC was failing and I had just seen an alternative MC from 85-96 Chevy G30, P20, and GMC, G3500, P2500, P3500 Vans and trucks, I decided to just try it. Saw it at the last GMCMI convention. It is a MC that is two stage. Kinda like the principal behind the two stage floor jacks that pump up quick until they meet resistance. This MC has two bores. The initial is a 40MM bore supplying a lot of fluid initially to bring the calipers and/or wheel cylinders fluid to get the pads/shoes out to contact. Then reverts to the main bore which is 1 1/4", the same size as the OEM MC. Brings the pedal up and keeps the MC from bottoming out with 80mm front and bigger calipers in rear. I like the feel of this with better brakes. Down side is one will have to be careful to watch the fluid level as the fluid reservoir is somewhat smaller. Also, installation must be with a metric sensitized booster as the OEM booster will not accommodate this MC. Also, needs a adjustable pushrod and some time adjusting it so it is not dragging the brakes when pedal is let up. The shape of it accommodates the shape of our hood. Again, this is just an experiment on my part that seems to be working. Also available through other parts houses. Just what I'm trying. No guarantees, not endorsing. Got information from another GMC'r who will remain silent for now. Here is the NAPA part#.

https://www.napaonline.com/en/p/NMCM2580

Pic installed

http://www.gmcmhphotos.com/photos/new-style-master-cylinder/p68374-mc-from-late-model-gm-trucks.html

[quote
> As a data point Bob Stone did a output volume test on a NAPA NMCM2580 MC
> and he got 22cc's on the primary and 10cc's on the secondary. This is the MC
> Larry posted about and Walt pioneered.[/quote]
>
> Wally, could you translate the " he got 22cc's on the primary and 10cc's
> on the secondary" to how it relates to our situation.
>

I believe it was Wally who was thinking outside the box in his development of the split reservoir system. How is that working out? Is it a viable solution?

Tom K.

Tom Katzenberger wrote on Mon, 20 December 2021 18:12

I believe it was Wally who was thinking outside the box in his development of the split reservoir system. How is that working out? Is it a viable solution?

Tom K.

Tom I only messed with reservoirs to get things to fit under the hood. So far so good with those parts. The objective was to get a MC under there that had more volume per stroke.

wally wrote on Mon, 20 December 2021 19:42

Tom Katzenberger wrote on Mon, 20 December 2021 18:12

I believe it was Wally who was thinking outside the box in his development of the split reservoir system. How is that working out? Is it a viable solution?

Tom K.

Tom I only messed with reservoirs to get things to fit under the hood. So far so good with those parts. The objective was to get a MC under there that had more volume per stroke.

AND....maintain or increase pressure of the OEM MC?