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| | | | Joined: Nov 2010 Posts: 123 'Bolter | | 'Bolter Joined: Nov 2010 Posts: 123 | In wet or dry conditions, if I slam the brakes hard enough, the truck stops very well, but the rear tends to drift almost turning the truck sideways sometimes when I come to a stop. Is this normal for old bolts or should I look into another proportion valve? Im running a 40mm master cyl. With a combination valve and front and rear discs. I'm guessing the rear is locking up slightly more than the front?
Thanks
Last edited by diseasel; 11/30/2016 11:56 PM.
| | | | | Joined: Dec 2015 Posts: 2,063 Big Bolt Forum Moderator | | Big Bolt Forum Moderator Joined: Dec 2015 Posts: 2,063 | since your brakes are not stock, whatever may or may not be "normal for old bolts" does not apply. I would imagine that with an adjustable proportioning valve, you could get it to stop straighter and put a bit more pressure on the fronts.
All that said, bigger trucks are different than passenger cars. Passenger cars and lighter duty trucks, front brakes do most of your braking, larger trucks, the rears do. | | | | | Joined: Apr 2005 Posts: 7,441 Bolter | | Bolter Joined: Apr 2005 Posts: 7,441 | As Mike suggested above, you need to take some of the rear braking away. About a 60/40 ratio should help your sideways drift. Play with the adjustable proportioning valve til you get it to your liking.
Martin
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| | | | | Joined: Jun 2011 Posts: 5,096 Crusing in the Passing Lane | | Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | Many 1 ton or so trucks have a prop. valve hooked to the rear axle height with a vertical rod from the axle to the valve, Toyota trucks also, might be wise to look at one.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
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| | | | | Joined: Mar 2002 Posts: 9,115 'Bolter | | 'Bolter Joined: Mar 2002 Posts: 9,115 | I had this problem with my 1 Ton. Since I don't carry loads with my truck, the solution for me was a proportioning valve. The adjustment only allows you to adjust the point at which the valve comes into play, not the ratio.
Some modern light trucks and minivans used the arrangement with the suspension linked to the valve, very successfully. I had a Dodge minivan years ago that had one. The braking didn't seem to change whether the van was full or not.
Last edited by truckernix; 12/01/2016 2:53 PM.
| | | | | Joined: Feb 2000 Posts: 5,224 'Bolter | | 'Bolter Joined: Feb 2000 Posts: 5,224 | I bought an adjustable valve from Speedway Motors similar to this one, http://www.speedwaymotors.com/Speedway-Purple-Proportioning-Valve,23498.html . Its installed at the back of the truck.
Mine did the same as yours, so I took it to the local open parking lot and after about five, 40 mph stops, I had it dialed in. It does make for a heavier brake pedal, but the truck stops straight and I know what it's going to do if I ever really have to stand on the brakes.
Joe | | | | | Joined: Jan 2000 Posts: 734 'Bolter | | 'Bolter Joined: Jan 2000 Posts: 734 | Waaay back in college, cruisin' through town not paying attention...ugh!!...light turned RED, panic stop but the rears lock up (LEAKY AXLE SEAL!!)  truck pitched around, sliding sideways through intersection, off the brakes yanked 'er straight and rocketed on through. No cops, no ticket, no collision. Thank God. Ah, the negligence of youth. Glad to have lived through it!
Matthew 6:33 1952 Chevy 1/2-ton 3100 Late '55 235/SM420/torque tube 3.55 Dalton Highway survivor (using original 216) www.truckwithaheart.com | | | | | Joined: Jul 2000 Posts: 2,195 Insomniac | | Insomniac Joined: Jul 2000 Posts: 2,195 | I had a similar experience - spreader bar "somehow" fell off and only one of the rear brakes was working. Going sideways down a major highway is not type of experience I care to repeat.
I would check that both rear brakes are working properly before plumbing in a new proportioning valve!
Gord 🇨🇦
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1954 1/2 ton 235 4 speed
| | | | | Joined: May 2005 Posts: 8,878 . | | . Joined: May 2005 Posts: 8,878 | I've had a 1 ton with front and rear disc brakes and no troubles as you describe.
I used the common longish brass GM proportioning valve/distribution block.
I believe they make them for trucks with disc and drums as well as a different one for disc and disc.
Perhaps if you have one already it's not the right one? | | | | | Joined: Nov 2010 Posts: 123 'Bolter | | 'Bolter Joined: Nov 2010 Posts: 123 | The one I have is a disc/disc combination vavle. The only factor I can think of is that most older 1tons ive seen with a disc rear were associated with a dually axle, maybe that's whats causing the rear to lock up? . Between 35-45 mph It'll track fairly straight when coming to a hard stop, so its very minute. Ill try a proportion vavle and see if it helps | | |
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