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Old 02-07-2020, 09:32 PM   #1
Curt C
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Wheel hop under braking

Tried search. Most posts are about wheel hop under acceleration. I get some pretty good hop under hard braking: 1956 Studebaker (I know not a Chevy but suspension dynamics should be similar). Ford nine inch out of an older Mustang with original leaf springs and drum brakes. Front clip is from a 1977 AMC Matador (nutty) with disc brakes. Chevy 350 with Turbo 350. New shocks front and rear and brakes have been gone through and are in good working order. Leaf shackles and bushings look good.

I assume most of the weight is shifting forward and unloading the rear. Tires thus can lock up easier and start hopping. Without having to completely re-engineer the suspension, what are some basic fixes? I have read a bit about clamping the leafs and using sliders in lieu of shackles. Thoughts? Some say add weight to rear but it needs to be a good bit. How much and how? I would prefer not having to stiffen up the front.

The truck drives and stops reasonably well. But if it needs to stop quickly at highway speeds its going to go for a ride. Thanks for the responses.
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Old 02-07-2020, 09:52 PM   #2
MiraclePieCo
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Re: Wheel hop under braking

Some possibilities:

Springs wrapping up on braking just as they would on acceleration?

Differential front-rear braking bias - rears locking up first while fronts still rolling?

Rear drums out of round, or grabbing?

Worn suspension components causing movement?
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Old 02-07-2020, 10:03 PM   #3
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Re: Wheel hop under braking

It's common for bit-o-this brake systems to be so far out of balance they're dangerous. It sounds like yours is one of them. Due to the weight distribution of the chassis the front brakes are responsible for most of the stopping effort while the rear brakes are contributing far more than they should.


I'd start by calculating a rough estimate of the brake bias. Get the weight on the front and rear wheels to figure out static weight distribution. Then make a crude calculation to estimate front brake contribution vs rear brake contribution. You'll need exciting numbers such as caliper piston diameter, # of caliper pistons, rotor diameter, wheel cylinder diameter, drum diameter, duo-servo or single-acting shoes (most likely single acting), and mater cylinder diameter(s). From there you can find online calculators that help calculate the force applied at front and rear wheels. Set the percentage of front to rear brake bias slightly higher than the percentage of static front to rear weight bias and you'll be close. If you'd like to collect the numbers I can help with the calculations.

Even without the numbers work you can make a big improvement if you buy an adjustable proportioning valve to "turn down" the rear brakes.

If you really want to work with suspension start looking for higher rate front springs. Keeping the weight from rising off the rear springs should be done by reducing front end deflection rather than limiting rear travel. The crudest approach would be to install bump stops of some kind. You will still have substantial pressure on the front brakes but it may reduce lifint of the tires as the car stops.
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Old 02-08-2020, 12:12 AM   #4
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Re: Wheel hop under braking

or try backing off the rear brakes about 2-3 clicks. I found my rears would lock up under hard braking and just had to play with the adjustment. took tightening the front drums and loosing the rear drums. I know you have front discs so just play with the rear adjustment. doesn't cost anything but some time.
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Old 02-08-2020, 05:44 AM   #5
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Re: Wheel hop under braking

some of those rear ends came with 10 x 2.5 rear brake shoes an I'd think that the original may have been 10 X 1.75 or 2. If that is the case the braking power of the shoes might be overpowering the springs.

Same as wheel hop on acceleration Wheel hop on braking would be the springs winding up and snapping back.
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Old 02-08-2020, 11:25 AM   #6
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Re: Wheel hop under braking

Wrong proportioning valve. I went through hell on dodge where it took forever to stop. Finally figured out it was the ABS unit. I bypassed it with running a chevy portioning valve and the brakes never worked so good. Even running larger wheel cylinders in the back giving it almost 50 percent more braking I had a hard time locking the rear. It took high speed, wet roads, and a bump to make it lock up and skip the rear. This was on a diesel truck so worst case scenario. Heavy engine, stiff springs and no wieght over the drives and huge rear drums. The braking system has to move more fluid to the front quickly when you start to brake.
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Old 02-08-2020, 01:42 PM   #7
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Re: Wheel hop under braking

check rear springs and shocks for being worn out. possibly the springs are just weak and susceptible to wrap
install an adjustable prop valve
install traction bar with eyelets on both ends, so it is attached to the frame near the spring mount bolt and also the spring near the axle pad, to eliminate wheel hop in both directions. won't fix rear wheel bias but may help the hop.

go for a ride with a few buddies driving behind/next to you and get some video of the actual occurrence so you understand whats going on. then decide what you need to do to fix it.
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Old 02-08-2020, 05:41 PM   #8
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Re: Wheel hop under braking

I had a Dodge that had bad wheel hop when braking, after I installed Rancho shocks. Reinstalling OE style shocks, problem went away.
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Old 02-08-2020, 07:37 PM   #9
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Re: Wheel hop under braking

I'm thinking he has the Original springs.

The Ford rear axle most likely has a lot more brake lining surface than the original Studebaker rear shoes did.

Front rear bias depends a lot on how he plumbed the brakes as a lot of guys don't use the combination valve or factory proportioning valve and just plumb straight to the master cylinder with lines running to a T on each side. An adjustable proportioning valve for the rear is usually under 50 bucks for a good one and is easy to plumb in the line.

Still I would want to know if the rear is wanting to come around when you lock up the brakes? On most trucks where the rear brakes lock up first the rear end wants to come around. I totaled one truck when that happened (70 long bed) and spun my 71 out in a violent spin when I locked up the brakes when a Geo Metro pulled out in front of me and I would have killed everyone in the car if I had been distracted. The truck spun so violently it broke the alternator bracket. That was at 55 mph.
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My ongoing truck projects:
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77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.
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Old 02-09-2020, 12:02 AM   #10
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Re: Wheel hop under braking

maybe wanna check if the brake lines are connected to the correct ports on the master cyl as well. also balancing the whole brake system, master cyl size, booster size, pedal mechanical advantage, correct master cyl for disc/drum or drum/drum-whichever, residual valves in correct places-some masters have the residual valves still in after a rebuild, even though they are supposed to be disc/drum.
anyway, a complete check would be a good idea. ensure the system you have is actually what you need. master, prop valve, residual valve, brake bias with lining sizes front rear, etc.
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Old 02-09-2020, 01:10 PM   #11
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Re: Wheel hop under braking

Does that truck by chance have lowering blocks on it? Sitting here watching Fourwheeler on the Motor Trend network and he is saying that lift blocks can cause axle wrap and lowering blocks would have the same effect if they were maybe three or four inches.

OR just as bad, has it had several leaves removed to lower it?
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My ongoing truck projects:
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71 GMC 2500 that is getting a Cad 500 transplant.
77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.
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Old 02-09-2020, 05:01 PM   #12
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Re: Wheel hop under braking

this is what I was thinking.

https://www.summitracing.com/parts/c...xoChGQQAvD_BwE
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Old 02-09-2020, 09:16 PM   #13
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Re: Wheel hop under braking

I never had problems with lift blocks. Heck my old dodge had something like 4 inches from the factory. The theory is sound but you would have to have some serious wet noodles for springs. I actually had more problems with the overloads feeling like bouncing on the end of a diving board. So far I think the best suggestion has been to ride behind and watch it. There has been alot of good ideas but the visual will que him in alot more.
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Old 02-09-2020, 09:43 PM   #14
Curt C
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Re: Wheel hop under braking

Thanks for all the responses. I forgot to note that I do have a proportioning valve on order. That is the easy way to crutch it but if I can get some of the axle wrap to abate braking would further improve.

This truck is new to me but here goes with the questions:
.

Yes the rear wants to come around under lockup. I am just in the testing phase so I get off the brakes quick.

It does have 3 inch blocks between the axle and spring. And the truck is pretty low with those.

There are 4 leafs in the spring package and they look old for what it’s worth. Shocks are new and they have little coil over helpers on them.

I believe the master and distribution block are from a 77 AMC matador like the front disc brakes. We will find out soon enough. The MC is leaking and I ordered a new one. I’ll measure bore etc. The rear brakes are plumbed to the rear of the MC which is the larger compartment. Is that right?

I will have to measure the rear drum linings and report back.

So traction bars will help with axle wrap going the other direction? Braking versus acceleration?

Appreciate the help folk. I can get pics if needed.
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Old 02-09-2020, 11:06 PM   #15
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Re: Wheel hop under braking

I'm thinking you are going to have to do more than a little bit of sorting out on that one.
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My ongoing truck projects:
48 Chev 3100 that will run a 292 Six.
71 GMC 2500 that is getting a Cad 500 transplant.
77 C 30 dualie, 454, 4 speed with a 10 foot flatbed and hoist. It does the heavy work and hauls the projects around.
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Old 02-09-2020, 11:43 PM   #16
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Re: Wheel hop under braking

Hehe. I can appreciate that comment. But the truck really does drive, turn and brake (other than highway speed threshold) good. It’s far, far better than the completely stock 53 GMC I had. I will turn the rear bias down and get the MC swapped and properly plumbed if that is not the case and go from there.
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Old 02-10-2020, 12:31 AM   #17
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Re: Wheel hop under braking

I think your lines are reversed. The discs should take more fluid to actuate than the drums.
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Old 02-10-2020, 11:52 AM   #18
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Re: Wheel hop under braking

Quote:
The rear brakes are plumbed to the rear of the MC which is the larger compartment. Is that right?
Quote:
I think your lines are reversed. The discs should take more fluid to actuate than the drums.
Yes, the lines are probably reversed. The larger reservoir is fluid storage for the front calipers. It may not make a difference in how the vehicle stops but it does help ensure you have plenty of fluid to actuate the brakes.
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Old 02-10-2020, 05:37 PM   #19
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Re: Wheel hop under braking

on traction bars, only the ones connected to something at BOTH ends will possibly help with brake wheel hop.
with the block between the axle and springs the force developed when the brakes are applied is multiplied because of the lever action of the spacer block. if the springs are old they will wave easier. rather than install new springs you could install the traction bar idea instead. new springs will need to be "set" so the ride height is going to change after a bit as they break in to being used. I would say with the coil springs over the shocks that who ever set up the rear suspension was having trouble getting the ride height they wanted. one more leaf in the rear spring pack must have been to high and then without it the truck sat lower then desired, that's why the coil springs were added. personally I'm not a fan of the coils because they put a lot of necessary strain on the shock mounts. I would rather dial in the proper springs and/or shackles/blocks etc.
one other thing to check, since the suspension has been altered, is the driveline angles. the output of the trans needs to be roughly the same but opposite of the pinion on the rear axle. usually 3 deg down on the engine, because that's what the factory used so intake manifolds and oil pans/pick up tubes etc are made so the carb sits level on the intake when the engine is in the chassis. so, 3 deg down on the engine and trans would mean 3 deg up on the pinion. having an adjustable length traction bar set up will also keep the diff from turning under acceleration so the set pinion angle will stay ,more like what it should be. with the blocks installed and no traction bar the pinion angle will change easier, just like it does under braking. something like I posted in post 12 above will help keep the angles correct under accell or braking. without buying a new set of springs. you can easily fab one of your own but maybe check for a prefab one first because the threaded tubing and tube ends add up fast.
these guys have lots of misc brackets and kits for things. they are Canadian dollars so USD goes further.

https://welderseries.com/?_vsrefdom=...EaApWuEALw_wcB
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Old 02-10-2020, 06:59 PM   #20
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Re: Wheel hop under braking

Ill check the Caltracs out dsraven. Like you say, easier than trying to get a new spring package in place. Thanks for the detailed write-up. I made a little progress today. Measured the brake pads and they are 1.75 with the shorter lining in front. Rear proportion valve is now in place but I have not had a chance to test it. Ill measure the pinion angle shortly. I eyed it the other day and it looked okay but I need to measure for sure. Took a couple of pics.
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Old 02-10-2020, 08:07 PM   #21
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Re: Wheel hop under braking

rubber snubber behind front hanger on leafs looks like it is constantly bumping the frame, like there is a lot of spring wrap up. a traction bar of some sort may help with that or maybe the leafs have been modded (some removed) to the point of them being too weak. either way, a traction bar isn't gonna hurt anything and it's something easier and cheaper than a new set of springs. especially if you fab it yourself. (make it adjustable for length).
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Old 02-10-2020, 09:55 PM   #22
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Re: Wheel hop under braking

Quote:
rather than install new springs you could install the traction bar idea instead.
An "axle damper" made from a steering damper would also be effective. Ford used them in Fox body cars and you can tell when one is worn out. I'd still work to balance the brakes...
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Old 02-10-2020, 11:34 PM   #23
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Re: Wheel hop under braking

years ago I made up some traction bars to control wheel hop on launch. I did add a cross bar at the front end of the bar with a U bolt to keep the bar from angling down. I did use a pinion snubber that mounts with a bolt that fastened to the lead end of the bar. They seem to work well.
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Old 02-11-2020, 08:41 PM   #24
Curt C
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Re: Wheel hop under braking

Quote:
Originally Posted by 1project2many View Post
An "axle damper" made from a steering damper would also be effective. Ford used them in Fox body cars and you can tell when one is worn out. I'd still work to balance the brakes...
Ha! The infamous quad shocks on the even more infamous Ford 4 link (aka Quadrabind) I road race / auto cross an 86 Mustang so I am very familiar with 3,4,5 links, torque arms and panhard / watt links. That is a great idea - grafting a quad shock on. And there are a million takeoffs out there to get wider wheels on.

I am absolutely going to dial in the brake balance but if I can get rid of some of the axle wrap I should be able to employ more bias and thus better braking.

Pinion angle is good at 2. Tranny is 3 and Diff is 1

What do you think about this traction bar setup?

http://www.tractionmaster.com/

It doesn't have the tunability of the Caltracs but I dont really need that I dont think. I called them / sent pics and they are evaluating. Much cheaper
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Last edited by Curt C; 02-11-2020 at 09:50 PM.
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Old 02-11-2020, 10:58 PM   #25
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Re: Wheel hop under braking

Looks good but you could easily make it adjustble with a bit of work and a few parts. Either way it would be better than nothing.
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