Help - MH Brakes Locked Up!

[chriscraw]

Originally Posted by PeterH-Airstreamer

http://www.airforums.com/forums/f311...ml#post1927046
Slowly and evenly unbolting the master cyl and using a feeler gauge, when it is pre loaded, will give you a start point for correcting the length of the pushrod.

2 components can cause your problem, in your case its probably the push rod. The other is the master cylinder. The distance of the red bar (at the black arrow) needs to match your existing system.

Peter..always a pleasure to receive you advice and expertise..thanks for the subsequent phone conversation
Note to Nick..purchase a "matched set" of hyrobooster and master cylinder..keep your old ones until you can measure the two alongside the other. Peter had given me this advise earlier but by buying separate re-manufactured units to save $$$..!!

[Boom Sounds]

I will do that Peter.

I've already got my Delco Master Cylinder. I've just had a look at the matching hydroboost and it's $450 bucks. Yikes.

Nick

[chriscraw]

Originally Posted by Boom Sounds

I will do that Peter.

I've already got my Delco Master Cylinder. I've just had a look at the matching hydroboost and it's $450 bucks. Yikes.

Nick

Nick..Ouch. Great news however..see my following posting. After what I discovered, not sure if the "matching" is all that critical particularly when you can get a re-manufactured Bendix hydroboost here in the States for $US150.
Could not find any "new" version of the old Bendix unit..here are the re-man units from O' Reilly's
http://www.oreillyauto.com/site/c/se...P30&vi=1059500
Similar prices from other sources.
bloody heavy to ship
Nor sure if you could get the old hydroboost reconditioned in the UK?
As you will see below, it's all a mater of "mating feel" and having a the ability to access the required push-rod length which you can but from Tallon for $US15.
whatever you do, keep the original and ALL parts until you are ready to fit.

[chriscraw]

Ah...the sweet smell of success. Today, after digesting and reviewing all the above and other on-line bumph, decided to unbolt and just let the master cylinder move back to a point where the MC flange was freely visible and not "pre-loading" the booster push-rod. (All this was done without undoing the MC brake lines so as to avoid a re-bleed!)
Using a caliper, I measured the distance between the MC and booster mating faces at .296". Essentially, this meant that when I bolted the two components together, I was "pre-loading the push-rod by over 7 mm! I measured the push-rod length at 3.446". Subtracting the .296 from this rod length, I calculated 3.146 as being ideal before pre-load and ..guess what I had collected in my foray to the local "chop-shop"..a push-rod measuring 3.146. Being really careful to reset the retaining washer, spring and clip, I installed the shorter rod, tightened-up the MC bolts and chassis mounting plate.
Brake pressure pumped-up and when the engine was started, the hydroboost was immediately felt to push-back. The subsequent road test was spectacular to say the least and after repeated panic braking tests, declared time to pop the champagne!
So seems to me that although the original Bendix/GM spec for push-rod length was 3.446", actually this (on some installs anyway) was reduced to 3.146. Fortunately, when I was grabbing 3 rods from the chop-shop, I ended-up with the 3.146" version. Unfortunately, I also pocketed a 3.446 version! The Gods were indeed smiling that day.
Thanks to all my fellow Forum Members for advice and consolation. Please let me know if I can embellish my success any further!

[PeterH-350LE]

Originally Posted by chriscraw

.....Please let me know if I can embellish my success any further!

[Isuzusweet]

If I were you I'd create a medal out of an unused rod. The hydroboost braking order of merit with rivet clusters.

Well done Chris, although after what you've been through my choice of refreshment would be a bit stiffer than the bubbly.

Cheers
Tony

[Boom Sounds]

There's no stopping him.

Nice one Chris!

PS Did you just buy the hydroboost or were there other bits e.g. seal repair kit which you purchased at the same time?


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[Boom Sounds]

Chris - which one of those hydro boosts was the one you actually purchased? Would you mind sharing the part number?

Many thanks
Nick


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[chriscraw]

Originally Posted by Boom Sounds

Chris - which one of those hydro boosts was the one you actually purchased? Would you mind sharing the part number?

Many thanks
Nick


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Nick..the re-man hydroboost I purchased is the O'Reilly part number BHH 52-9383. This cost $US166.99 with a return core deposit of $44 (given the weight, a core return from the UK might not be worth it!). The O'Reilly compatibility check is VITAL. In my case the above booster was the only entry that stated correctly "P30 Base V8 - 7.4L vin N 454ci - TBI GAS OHV, 1990-1994. When you select a specific hydroboost from their web site, check the tab makrked "Compatibility" and make sure your specific Chevrolet P30 model, VIN designation (in my case the "N"digit ) and year are listed.
The hydroboost I selected was exactly the same (mounting, bolt holes, brake pedal shaft, PS pump pressure and return-line connections etc) as my old version. It comes fully ready to mount BUT does not include the push-rod, spring, washer and retainer clip which you will need to recover from your current booster (as you see, I did not keep my bits which resulted in 6-8 extra hours of labour and sheer luck at finding the 3.14 push-rod.
Chris
http://www.oreillyauto.com/site/c/de...patibilityTab_

[chriscraw]

Originally Posted by Boom Sounds

There's no stopping him.

Nice one Chris!

PS Did you just buy the hydroboost or were there other bits e.g. seal repair kit which you purchased at the same time?


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Nick..see below..all included in re-manufactured unit (except bloody push=-rod).Apparently DIYing a hydroboost seal repair is not work the effort as you really need a new spool valve and the chamber honed.
Maybe other Members can comment on the DIY approach?

[chriscraw]

Originally Posted by Isuzusweet

If I were you I'd create a medal out of an unused rod. The hydroboost braking order of merit with rivet clusters.

Well done Chris, although after what you've been through my choice of refreshment would be a bit stiffer than the bubbly.

Cheers
Tony

Tony..I was being polite in not offending the more "effete" Forum Members with my celebratory tipple! Thanks for the vote for "Hyroboost Order of Merit"

[chriscraw]

Originally Posted by PeterH-Airstreamer

Peter..coming from the Master Himself..praise indeed and appreciated!
chris

[Boom Sounds]

Thanks Chris......I might be reviving this thread in the not too distant future.


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[Boom Sounds]

Interesting, the Cardone 52-9383 Hydroboost does not show as a fit for my coach. My coach came with the RPO JB8 brake code (I have smaller size 16" wheels)

https://www.stockwiseauto.com/a1-car...MC&Model=P3500

The one which shows as a fit for my 1991 250 classic is the following. I shall give this one a go and report back to this thread on whether it worked!

Cardone Reman Brake Power Booster
Part Number: 52-7257
Application: With rear drum brakes
With hydroboost
Notes: W/o master cylinder
Motorhome chassis. With JB8

[martin300662]

Originally Posted by Boom Sounds

Interesting, the Cardone 52-9383 Hydroboost does not show as a fit for my coach. My coach came with the RPO JB8 brake code (I have smaller size 16" wheels)

https://www.stockwiseauto.com/a1-car...MC&Model=P3500

The one which shows as a fit for my 1991 250 classic is the following. I shall give this one a go and report back to this thread on whether it worked!

Cardone Reman Brake Power Booster
Part Number: 52-7257
Application: With rear drum brakes
With hydroboost
Notes: W/o master cylinder
Motorhome chassis. With JB8

The JB9 code covers the units with rear discs (which I believe necessitates the larger wheels), which also has a different combination valve.

[Boom Sounds]

Martin - I am not going mad here, am I? The 16" wheels have front disc and rear drum brakes.


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[martin300662]

Originally Posted by Boom Sounds

Martin - I am not going mad here, am I? The 16" wheels have front disc and rear drum brakes.


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Certainly the earlier Argosy were disc front/drum rear JB8 code and had 16.5"/8 stud rims. Most folks change to the more modern 16"/8 stud. They cannot be converted to rear disc using the JB9 code parts because they wont fit inside the wheel. There are other rear disc parts (totally from memory) from an El Dorado????) which do fit, or after market kits(based on those parts).

I believe all the 19.5 wheel/rear disc models are JB9 code.

To be honest I am really surprised you have the 16" wheels, I thought everything after 1978 was 19.5" and either 8 or 10 stud, and didn't know 16" was ever stock.

[Boom Sounds]

I think only on the 240 and 250 had the 7.50 R16 stock. 270s upwards went to 19.5.


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[Boom Sounds]

Just to say, so far, so good. The Cardone unit 52-7257 seems to work alongside the new Master Cylinder Part Number: 18M230. I've done 50 miles with no loss of braking, power steering or seizing up of brakes. I'll check for leads today.

Note this is for a 1991 coach with 16" wheels and brake code JB8. It's a different set up on the longer coaches.

Product Notes:
Brake Master Cylinder
All; w/13in x 3-1/2in Brakes; Rear Drum*
Per Vehicle: 1; Years: 1990-1992

[chriscraw]

Originally Posted by Boom Sounds

Just to say, so far, so good. The Cardone unit 52-7257 seems to work alongside the new Master Cylinder Part Number: 18M230. I've done 50 miles with no loss of braking, power steering or seizing up of brakes. I'll check for leads today.

Note this is for a 1991 coach with 16" wheels and brake code JB8. It's a different set up on the longer coaches.

Product Notes:
Brake Master Cylinder
All; w/13in x 3-1/2in Brakes; Rear Drum*
Per Vehicle: 1; Years: 1990-1992

Nick..nice piece of sleuth work particularly as all my postings referred to a different configuration