Rear rotors clunking after drum/disc brake conversion

[Guanfy]

16's are even more common than 15's now. Might as well jump on up to 16" Ford has been using 16" rims since the mid 90's, so they are out there.
Here is a very common Ranger wheel in 16"
View attachment 50054
I like these
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Already bought the rims and tires tonight in 15 inch. I was going to do this anyway once the existing tires wore out but this axle business accelerated my schedule. Now to find somebody who needs 5 14 inch rims with tires... get some money back.

 

[don4331]

You threw me as your profile says 15" rims and 15" rims would have the 2.8" center bore (versus the 14" with 2.5" centers).

And I believe you also failed to mention that you had replaced the rear axle.

Glad you were able to resolve your issues.

 

[Guanfy]

You threw me as your profile says 15" rims and 15" rims would have the 2.8" center bore (versus the 14" with 2.5" centers).

And I believe you also failed to mention that you had replaced the rear axle.

Glad you were able to resolve your issues.

It's all the little things that you don't read in the swap guides that wind up biting you in the butt. From what I read the center bore changed size in '98, becoming larger. The 15x7 rims I bought should fix it and they should also fit up front too.

 

[Guanfy]

It's a RABS/Check valve; it isn't really a proportioning valve. It's probably best to "shorten" the spring a little than to remove completely - rear wheels locking 1st is bad...

Is it the long spring that you see in his picture of the proportioning valve that you are talking about? I'm getting conflicting information on the location of the residual brake valve. Some sources are saying it should be located on the master cylinder, others on the proportioning valve.

 

[don4331]

Yes, there's a couple additional items which could probably be added to the axle detail so all the information was there....

15" rims came with the 4x4s once the Dana 35 was introduced and center hole had to be larger to clear the locking hubs - they weren't tight even on the rear axle of pre '98 trucks.

We're actually concerned with the residual pressure - which is controlled by the long spring in the RABS switch. And remember you are only wanting to decrease pressure by couple psi, so minor trimming is all that is needed (1/2 coil maybe). You don't want to shorten so much it no longer has any pressure, or RABS won't work.

 

[Guanfy]

We're actually concerned with the residual pressure - which is controlled by the long spring in the RABS switch. And remember you are only wanting to decrease pressure by couple psi, so minor trimming is all that is needed (1/2 coil maybe). You don't want to shorten so much it no longer has any pressure, or RABS won't work.

My RABS currently doesn't work due to what I think is an electrical issue behind the dash so no worries there. However, it sort of works when I get on the brakes so I will try to preserve it... By 1/2 coil you mean cut the spring in half right? I was thinking something like that. If a full spring is supposed to be around 10lbs of force, then knocking it down to 5 would be enough. 2lbs is what I read for a full disc system but I imagine 5lbs would work as well.

 

[don4331]

My RABS currently doesn't work due to what I think is an electrical issue behind the dash so no worries there. However, it sort of works when I get on the brakes so I will try to preserve it... By 1/2 coil you mean cut the spring in half right? I was thinking something like that. If a full spring is supposed to be around 10lbs of force, then knocking it down to 5 would be enough. 2lbs is what I read for a full disc system but I imagine 5lbs would work as well.

If you look that the picture in Gacknar's thread, the spring has ~18 coils. Full pressure for drums is probably in 1,000 psi range = full compression on spring (piston is only fraction of inch square, so spring won't be pushing with 1,000lbs). You want to reduce it just the slighted amount and test (1/2 coil might be too much).

 

[Guanfy]

If you look that the picture in Gacknar's thread, the spring has ~18 coils. Full pressure for drums is probably in 1,000 psi range = full compression on spring (piston is only fraction of inch square, so spring won't be pushing with 1,000lbs). You want to reduce it just the slighted amount and test (1/2 coil might be too much).

Ok. I that's what I thought you meant. Some folks when talking about springs will say coil meaning the entire spring versus one winding on the spring. I'll try to get this modded over the weekend if I have time.

 

[Guanfy]

Another update. I've got the new tires and rims on and they fine perfectly. Clunking rotor issue gone. As don4331 mentioned I cut around 2.5 coils off the brake valve spring and that feels pretty good. Truck no longer feels like the back is grabbing and rolls well in neutral while the brakes still grab very nicely. If anyone out there has my era truck you can adjust the the brake valve spring without needing to remove the proportioning valve. All you have to do is unplug the electrical from the proportioning valve and move it out of the way. Then a 7/16 socket will allow you access to the spring. Be mindful that you are working around the starter so unplugging the battery whilst you work is not a bad idea.