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New Proportioning Valve and large rear Brake Cylinders on my '99 Burb

Big T

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On the advice of THEFERMANATOR, I went ahead and installed the Service Bulletin recommended upgraded proportioning valve (Part #12548265) on my '99 Suburban. This proportion valve is supposed to cut off pressure to the rear wheels at 800 psi, versus the 600 psi of the original valve. At the same time, I followed THEFERMANATOR's advice and installed a set of larger rear brake cylinders from the K3500 dually of the same era trucks. At $4.95 per cylinder might as well because I'd be bleeding the entire system anyway.

The job was not that hard. The proportioning valve is held in place by 3 torx bolts and of course I stripped one. I ended up pulling the entire ABS pump and just grinding through the old proportioning valve behind the bolt head. Got a replacement torx bolt free from the local bone yard.

Getting the rear brakes back together was a bit of a bear. The parking brake cable had slipped out of the driver's side and you really need 3 hands to hold the end of the cable in a pair of vice grips, while pulling the spring back with another pair of vice grips and then installing the parking brake lever assembly. Got it? Eventually I did.

I have forever had problems with the ABS on this truck. On, off, mostly off with the ABS dash light on. I'll note that the PO had it disconnected when I bought it. I've replace the front bearings. I've replaced the sensors. I recently had the right front bearing fail and that is new. Well the ABS light turned off last Sunday and it has stayed off since this work. Not sure if it had anything to do with removal of all the wire plugs on the pump or what, but the light has stayed off for at least 20+ starts now and that has never happened. The ABS actually works. I've done some testing with the brakes yesterday and today. Even had my son independently test them to verify that the brakes stop better and they do. Today, with no traffic I did some two footed stops from 60 mph and the brakes performed substantially better. I can honestly say that this was definitely an improvement and a worthwhile modification.

So on a day we give thanks, I would like to thank THEFERMANATOR for all of his advice and encouragement on this matter. That said, I still plan on doing the conversion to get the later model dual piston calipers on the front. You can never go wrong with bigger and better brakes.:Justwait2:
 

THEFERMANATOR

FRANKENBURBAN
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The proportioning valve is for BURBS only with the 14 bolt 10.5" rear axle. Teh wheel cylinders is an upgrade that can be done to the 9.5", and 10.5" single rear wheel trucks. The wheel cylinders are teh ones that go in the 3500 duallys and are 1 3/16" VS teh 1 1/16" for the single rear wheel with a 10.5", or the 1" for the 9.5".
 

Big T

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Here's a link to an article on implementing the TSB:

http://www.mightyautoparts.com/pdf/articles/gb0602.pdf

And here's the link to the TSB:

http://aplsweb.com/Topics/TopicPix/TSB99-05.gif

Like THEFERMANATOR said, changing the proportioning valve applies to the Suburban. That said, it does say that changing the proportioning valve IS NOT REQUIRED ON OTHER VEHICLES. Knowing how bad these brake systems were, I would think there is no harm in changing the proportioning valve on the trucks. Certainly the rear wheel cylinders can be changed and that is a very cheap and easy job.
 

THEFERMANATOR

FRANKENBURBAN
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Here's a link to an article on implementing the TSB:

http://www.mightyautoparts.com/pdf/articles/gb0602.pdf

And here's the link to the TSB:

http://aplsweb.com/Topics/TopicPix/TSB99-05.gif

Like THEFERMANATOR said, changing the proportioning valve applies to the Suburban. That said, it does say that changing the proportioning valve IS NOT REQUIRED ON OTHER VEHICLES. Knowing how bad these brake systems were, I would think there is no harm in changing the proportioning valve on the trucks. Certainly the rear wheel cylinders can be changed and that is a very cheap and easy job.

The updated proportining valve for the BURBS is basically a truck proportioning valve. GM felt the bURB needed less rear brakes than teh truck did, and is why they capped them at 600PSI instead of 800PSI like the trucks had.
 

Big T

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Here is the picture (from RockAuto) of the backside (side up against the ABS Pump) of the AC Delco Part # 1254865:



I looked for the differences and they are in the casting on the right hand side of the picture (left when looking at it on the ABS pump).

Here's the photo of the front side of the wrong part AC Delco Part 1254879:



I think the left side of the casting is smaller on this part. Hopefully it can be seen between the two photos.
 
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