8.8 Axle/Rotor Issue - Chevelle Tech
Transmission & Driveline Transmissions and Differentials

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post #1 of 10 (permalink) Old Feb 24th, 20, 6:32 PM Thread Starter
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Ray
 
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8.8 Axle/Rotor Issue

Working on a Ford 8.8 rear axle swap for a buddy of mine into a GM chassis.

All went well till I went to install the rotor. The rotor hits the caliper mount just slightly.

As to the specifics. It was a complete rear, including the brake system, from a local dismantler. I Disassembled it. Gave him the axles to have them redrilled to 5 on 4 3/4 and new studs installed. He also purchased a new set of Ford Rotors and had them redrilled. Same shop, that he found, did the axles and the rotors at the same time.

On reassembly everything went together as it should. The rear caliper mounts on these are stationary and bolt on at the backing plate. The rotor seems to hit the bottom of the mount by about 1/16" or so.

Could there be an issue w/ where the lug holes were drilled? Because using a caliper the distance from the edge of the center hole to the leading edge of each lug hole is not consistent.

Any solution here that anyone can think of sort of a new set of axles and rotors?

Thanks and I knew I shouldn't have agreed to swap a ford rear into a chevy!
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post #2 of 10 (permalink) Old Feb 24th, 20, 10:29 PM
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Re: 8.8 Axle/Rotor Issue

Are you sure you don't have the left and right mounts on the wrong side? Take the caliper mounts off, rotate the axle and see if the rotor has any run-out radially or in & out.
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post #3 of 10 (permalink) Old Feb 24th, 20, 11:50 PM
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Re: 8.8 Axle/Rotor Issue

Quote:
Originally Posted by rortwein View Post
Working on a Ford 8.8 rear axle swap for a buddy of mine into a GM chassis.

All went well till I went to install the rotor. The rotor hits the caliper mount just slightly.

As to the specifics. It was a complete rear, including the brake system, from a local dismantler. I Disassembled it. Gave him the axles to have them redrilled to 5 on 4 3/4 and new studs installed. He also purchased a new set of Ford Rotors and had them redrilled. Same shop, that he found, did the axles and the rotors at the same time.

On reassembly everything went together as it should. The rear caliper mounts on these are stationary and bolt on at the backing plate. The rotor seems to hit the bottom of the mount by about 1/16" or so.

Could there be an issue w/ where the lug holes were drilled? Because using a caliper the distance from the edge of the center hole to the leading edge of each lug hole is not consistent.
YES
Any solution here that anyone can think of sort of a new set of axles and rotors?

Thanks and I knew I shouldn't have agreed to swap a ford rear into a chevy!
Well that would be a stop sign for me.If the 4 3/4 bolt circle was drilled correctly it should be the same from edge of bolt hole to edge of rotor consistently.They may have winged the 4 3/4 bolt circle.Do you have anything to measure the bolt circle with ? maybe an old rotor with lugs ?
They sell a bolt circle measuring template tool that is cheap if that will help,it's made of carbboard or plastic.
here is one from Summit racing

https://www.summitracing.com/parts/mfy-8021392

What does it look like when you spin it ? wobbly ? if the drilling is off center it will affect how it spins
You could also use a compass or a machinist compass.The thing about the bolt circle being off is that shouldn't affect the caliper bridge location ? Maybe a picture will help.
How will that 8.8 rear attach to the upper control arms ? some pictures really would help.
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post #4 of 10 (permalink) Old Feb 25th, 20, 6:21 PM Thread Starter
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Re: 8.8 Axle/Rotor Issue

Thanks guys. I believe the mounts are on the correct side. On the ford the mount and backing plate is all one piece. So the caliper is in correct location of about 2-3 o'clock looking at the axle. So both calipers rear of center. With the parking brake adjuster on the bottom on both sides.

I can't get the rotor on far enough to spin it. So I will try and flip it a see if that gives me enough to get it on enough to see how it turns.

Matching the lugs up to a stock GM rotor the spacing looks correct. The lugs in the axle will also match up to a GM wheel. I have tried each rotor on each side too thinking maybe there was a difference. Nope.

So I am still at a loss. Naturally I have the center section all back together with a new gasket. Thankfully I have not put the gear on in it yet so if I need to pull the axles and/or backing plates I am only out a cover gasket at worst.

I'm going to try and check it out again tomorrow after work. I'll try to snap a picture or two of it then.

The suspension doesn't require the upper control arm mounts. So no worries there. It's all installed. Was down to rotors and calipers to call job done. I'm sure I am just overlooking something minor but I haven't seen it yet.
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post #5 of 10 (permalink) Old Feb 26th, 20, 5:44 PM Thread Starter
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Re: 8.8 Axle/Rotor Issue

Here is a picture of what it looks like w/ the rotor on as far as it will go.

I did spin the rotor on the axle and using where it hits the caliper mount as a gauge it does spin true.

If you look in the center of the rotor, hopefully it is clear in the picture, the center of the axle does not appear to be centered in the opening of the rotor.

At this point I am considering pulling an axle back out and pressing out the studs. Put in 2 or 3 ford studs and then putting it back and trying the ford pattern.

If that works then at least I have isolated the problem.

Again thanks for the help and ideas.
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post #6 of 10 (permalink) Old Feb 26th, 20, 5:52 PM
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Re: 8.8 Axle/Rotor Issue

If the rotors are hitting on the OD, why not turn the OD down until they clear?

Do you still have the original rotors so that you can compare both diameters?

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post #7 of 10 (permalink) Old Feb 26th, 20, 6:14 PM
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Re: 8.8 Axle/Rotor Issue

Have you flipped the rotor to see if it seats onto the axle?
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post #8 of 10 (permalink) Old Feb 26th, 20, 10:33 PM
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Re: 8.8 Axle/Rotor Issue

Those Explorer inside parking brakes are a major PIA,you could try turning the adjustment all the way back in just in case those shoes are what is holding the rotor out there.
If not then I like the idea of knocking the lugs out and trying the ford pattern out.

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post #9 of 10 (permalink) Old Feb 27th, 20, 6:49 PM Thread Starter
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Re: 8.8 Axle/Rotor Issue

Unfortunately the old rotors went to the scrap yard a few months ago. Yup already have the parking brakes turned all the way in as I thought that was what was hitting it at first. Nope.

I think i'm going to pop one side axle out and verify the rotor fits on the axle as it should. I did flip it and it seems to fit fine.

That's an idea on turning the rotor down on the the OD. Just can't imagine it should be necessary if everything else is correct as it's all stock replacement ford parts except for the bolt pattern.

I told the guy to just run 5 on 4.5 bolt patterns wheels on the back when we started this project. lol.

Thanks guys for responses. I will make sure to post up what i find this weekend when i dig into it some more.
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post #10 of 10 (permalink) Old Mar 12th, 20, 6:44 PM Thread Starter
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Re: 8.8 Axle/Rotor Issue

Problem solved. Owner originally bought rotors for a 2008 Explorer. Rear is out of a 1998 Explorer. Rotors are different. He did not mention this or even remember the mistake. I measured the rotors and they were off. Checked on RockAuto for pics and quickly realized his mistake. He got a set for a 1998 and had them drilled to Chevy pattern. They got here today and slipped right on as they should. Again thanks for all the ideas guys.
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