GM hydroboost pushrod length

[jeffahart]

Glad you got it figured out!

[Bama57]

I saw this thread while searching for hydroboost pushrod length.............


Just a warning !!

I ordered a new GM reman hydroboost from Rock Auto and had to use my old pushrod
( 3.45 in length ) It stuck out oh-so-little ( almost flush with the front flange of the new hydroboost ) It locked the front rotors.

Put the pushrod back in the bad hydroboost ( it ws leaking steering fluid )
and the pushrod is inside the front flange by the depth of the notch that is under the bore of the hydroboost.

Looking at my master cylinder, it inserts about a half inch inside the hydroboost before the flanges mate. It looks like there must have been some pre-load on the master cylinder all the time ( ?? ) Gotta get my digital calipers to measure, but should there be ANY preload ? If so, I have a bunch of grinding or making a spacer to correct this .

Any Suggestions ?


Thanks. Don in Huntsville

btw ...... Hello everybody !!

[racecougar]

Yes, as shown in post #24.

[Bama57]

Originally Posted by racecougar

Yes, as shown in post #24.

Does that mean we need some MC preload ?

Thanks


Don

[racecougar]

Originally Posted by Bama57

Does that mean we need some MC preload ?

Thanks


Don

The pushrod should contact the master cylinder piston ~1/16" before the master cylinder and hydroboost flanges mate up.

[Bama57]

Originally Posted by racecougar

The pushrod should contact the master cylinder piston ~1/16" before the master cylinder and hydroboost flanges mate up.

Thanks, Racecougar.

I'm pretty sure my old hydroboost had more like 1/4 to 3/8 pre-load.

I had to back off the nuts on the master cylinder quite a bit before the front calipers released.

I'll try to make more accurate measurements when I have a chance.


Don

[racecougar]

That certainly sounds like you have the wrong combination of parts. brownge did a good job of illustrating the differences in post #3 of this thread.

[Bama57]

OK.... I bought this truck off the showroom, so there hasn't been any non Chevy parts installed until last week when I had to replace the hydroboost.

Using digital measuring calipers and depth gauges, I got the following measurements
off a stock Chevy 3500 crewcab.

Distance between the bottom of the hole on the hydroboost to the bottom of the hole
on the master cylinder = 3.500 and the pushrod length = 3.450 inches.

The pushrod might not bottom out in the holes, so maybe the pushrod is snug when the master cylinder is bolted up.

The new Rock Auto hydroboost has a "Genuine GM rebuilt" sticker and it's for my specific truck.... 454 and not four wheel drive.

My 3.45 inch pushrod sticks out past the NEW hydroboost flange, so tomorrow its put the master cylinder on the studs and only tighten the nuts tight enough to find the resistance, measure the gap between the hydroboost and the master cylinder and then see if I can build a spacer.

Sorry for the long read, but I hope this helps someone.

Don in Huntsville



Don

[racecougar]

Originally Posted by Bama57

The pushrod might not bottom out in the holes, so maybe the pushrod is snug when the master cylinder is bolted up.

That is correct; the pushrod does not seat all the way to the tip of the pockets.

[Bama57]

Originally Posted by Bama57

My 3.45 inch pushrod sticks out past the NEW hydroboost flange, so tomorrow its put the master cylinder on the studs and only tighten the nuts tight enough to find the resistance, measure the gap between the hydroboost and the master cylinder and then see if I can build a spacer.
Don

The spacer is a bad idea..... the hydroboost has a spring that is held in place by a thin star mount.

Too thin to hold all the spring pressure when the pedal is pressed.

The Master Cylinder slides up inside the Hydroboost and the Master Cylinder wide front flange
takes over the duties of supporting the hydroboost spring by a couple of thousandths. ( measured )

So .... shortening the pushrod is the only correct option.

Don in Huntsville

[jeffahart]

Originally Posted by Bama57

So .... shortening the pushrod is the only correct option.

Don in Huntsville

I personally wouldn't modify anything. If you get the correct master for the booster it will work as designed. Mix and match then you may never know if your paired setup is working correctly... you will always have that little tic in your head... could it be better!

[Bama57]

Originally Posted by jeffahart

I personally wouldn't modify anything. If you get the correct master for the booster it will work as designed. Mix and match then you may never know if your paired setup is working correctly... you will always have that little tic in your head... could it be better!

Jeff, I agree with you 100%.

This was supposed to be a correct GM hydroboost replacement.

Part numbers look correct for my truck.

Obviously ( Now ) it is different .....

I suppose I could send the hydroboost back to Rock Auto, ( more $$ shipping )or try to find a master cylinder to match at Advance or the Zone.

Thanks !!

Don in Huntsville

[novice]

Originally Posted by racecougar

By the way, if anyone runs into this same issue in the future (needing a pushrod, spring, and retainer for a refurb'd unit), shoot me a PM and I'll hook you up.

I am currently in need of one. PM sent.

[Bama57]

Just make sure that the new pushrod isn't pushing on the master cylinder.
If the master cylinder piston is being pushed in, there is no way for the brake line pressure to return to the master cylinder, and the brakes WILL drag and overheat. Use modeling clay or similar on the exposed end of the pushrod to check for clearance. I set mine for five thousandths.

[novice]

If anyone knows where I could purchase a rod, retainer, and spring please let me know. Everything I read says the parts are no longer available unless you get them from a junk yard.

[bs46488]

I bought my replacement rod, retainer, and spring from these guys:

http://www.tallonhydraulics.com

[novice]

Originally Posted by bs46488

I bought my replacement rod, retainer, and spring from these guys:

http://www.tallonhydraulics.com

I'll give them a shot.

[novice]

They have them as you said. Thank you sir. My order is on the way.

[racecougar]

Originally Posted by novice

I am currently in need of one. PM sent.

PM replied, but it looks like you already ordered a set elsewhere.

[novice]

Originally Posted by racecougar

PM replied, but it looks like you already ordered a set elsewhere.

Moneys sent. Thank you sir. Yours may fit better.

[forcedinduction]

I looking for the same parts (pushrod, spring retainer, spring, etc) and it seems that Tallon is out of business... at least the phone number listed is not connected.

Can anyone please assist me with a supplier for these? Thanks!