C4 Dropmember and Trailing Arm Conversion Install

[Wild83C10]

So for the last 4 years I have been waiting for the right time to convert my leaf spring suspension to the the trailing arms. I finally got to it in the past few months. I used the CPP 73-87 conversion crossmember, original arms from an older C10 (welded seams), CPP adjustable track bar and some QA1 coilovers.
I have also been building up the parts for the C4 dropmemeber install over the last year + and I finally started the install in December. I upgraded to the C5 Z06 brake setup. I am also upgrading to all new hard lines and SS braided lines as well as the CPP MCPV-1 Master Cylinder.
The main intent of the C4 DM and trailing arm conversion wasn't to get the truck on the ground but for performance as that is my #1 goal.

Next up on the to do list is the CPP rear disc kit and an extra couple hundred horsepower from a Borg Warner Turbo

Check it out:

[BIG KRIS]

[JW76]

super nice job... i put off doing the trailing arms on my long bed til i can weld good enough to make my crossmember... nice to see a 73-87 with trailing arms... i had a talk with jeff at CPP the other day and he is talking to the engineer about designing a crossmember and kit that will work with a long bed. hopefully they will think it is worth it. again awesome job!

[nastyc10]

Nice job! It should perform great!

[bluex]

Would a stock 67-72 crossmember not work? I'm planning on running stock arms and crossmember on mine with the rest of the CPP kit.


Vette stuff looks killer!

[Wild83C10]

Originally Posted by bluex

Would a stock 67-72 crossmember not work? I'm planning on running stock arms and crossmember on mine with the rest of the CPP kit.

I don't think the 67-72 crossmember will work. You will have intereferance with the cab floor. I was working on my own crossmember using 2x6 tubing but it hit the floor. The CPP crossmember is S shaped for that reason. I would have had to mod the floor if I wanted to use my 2x6 crossmember. The CPP crossmember was a nice piece. The only thing I would have liked is the ability to adjust the trailing arms. The CPP piece was worth it, call up Jeff and he will hook you up.

[SCOTI]

Originally Posted by Wild83C10

I don't think the 67-72 crossmember will work. You will have intereferance with the cab floor. I was working on my own crossmember using 2x6 tubing but it hit the floor. The CPP crossmember is S shaped for that reason. I would have had to mod the floor if I wanted to use my 2x6 crossmember. The CPP crossmember was a nice piece. The only thing I would have liked is the ability to adjust the trailing arms. The CPP piece was worth it, call up Jeff and he will hook you up.

Bolt hole alignment of the CPP piece vs. an OE c.member where it bolts to the frame similar? You have PM.....

[aggie91]

Looks good. What sway bar did you use for the front? What was required to do the C5 brake upgrade with the C4 suspension parts?

[DKN]

We have a different track bar mount that we use on the 73-87 trailing arm conversion to get the track bar up closer to the frame. Call Jeff and tell him what you need.

Danny Nix
CPP

[Wild83C10]

Originally Posted by aggie91

Looks good. What sway bar did you use for the front? What was required to do the C5 brake upgrade with the C4 suspension parts?

That is a stock C4 sway bar (24mm) with some energy suspension mounts. I plan to upgrade to at least a 1.25" later. I put together the end links from parts that I ordered from McMaster-Carr.
You can buy a C4-C5 adapter bracket and hardware. This will also allow you to bolt up the C6 brakes as well, which I will most likely upgrade to at some point if I end up taking it to a track once and a while. The C6 brakes are still a bit expensive though.

[Wild83C10]

Originally Posted by SCOTI

Bolt hole alignment of the CPP piece vs. an OE c.member where it bolts to the frame similar? You have PM.....

Took some measurements, I can move the x-member back about 1.75" and forward maybe an inch. My install was about 1.5" forward of where CPP had placed their x-member on their '79 build. The rear cab mount and the cab floor are the two limiters. See pictures.

Kind of hard to see but the cab floor does go below the frame/x-member.


Here is the rear of the x-member and the rear cab mount.

[bluex]

Originally Posted by Wild83C10

I don't think the 67-72 crossmember will work. You will have intereferance with the cab floor. I was working on my own crossmember using 2x6 tubing but it hit the floor. The CPP crossmember is S shaped for that reason. I would have had to mod the floor if I wanted to use my 2x6 crossmember. The CPP crossmember was a nice piece. The only thing I would have liked is the ability to adjust the trailing arms. The CPP piece was worth it, call up Jeff and he will hook you up.

Thanks for the Info. I'll cancel my search for the stock xmember and put that $$ towards the CPP kit. Its just taking me a while to save up my lunch money.

When you going to get that beast on the road? What was the reason you had to move it forward from CPP's location?

[Wild83C10]

Originally Posted by bluex

Thanks for the Info. I'll cancel my search for the stock xmember and put that $$ towards the CPP kit. Its just taking me a while to save up my lunch money.

When you going to get that beast on the road? What was the reason you had to move it forward from CPP's location?

I am shooting for the end of March but not sure I will make it, but shouldn't take me much longer then that.
I placed the c-member based on the location of the rear. I measure the location when the leafs where on and made sure it was centered on the wheel wells.
Good luck with your conversion.

[djracer]

Sweet lookin setup I'll have to watch this one.

[68 TT]

Originally Posted by bluex

Would a stock 67-72 crossmember not work?

With a long bed the 67-72 crossmember might work. The crossmember stops just in front of the bed. It might tuck into the raised section of the cab right behind the seat.

[smashingchuck]

I'm really diggin the whole concept. However, the tabs for the rear coil overs don't look like much. Is there a way you can touchen up the upper and lower mounts?

[Wild83C10]

Originally Posted by smashingchuck

I'm really diggin the whole concept. However, the tabs for the rear coil overs don't look like much. Is there a way you can touchen up the upper and lower mounts?

If the rest of the rear suspension does it's job then there shouldn't be too much stress on the brackets. Just the vertical forces from the weight/g-forces under hard acceleration. The brackets are made for drag racing setups by QA1 and Comp. engineering. As long as the welds are good they should be fine. I may add a gusset from the upper bar to frame just because it's cantelivered a lot.
I plan on testing them plenty with my 650-700hp turbo motor which will eventually be 1000+hp turbo motor.

[tomtuna1978]

i like how you put the rear coil over outside the frame on that tube you put threw the frame ! what wall thickness is that tube ? and od ? thats what i wanted to do on my 4x4(shocks only) 79 c10.

[Wild83C10]

Originally Posted by tomtuna1978

i like how you put the rear coil over outside the frame on that tube you put threw the frame ! what wall thickness is that tube ? and od ? thats what i wanted to do on my 4x4(shocks only) 79 c10.

The wall thickness looks like .120, the OD is 1-5/8.

[N2TRUX]

This thread will answer a lot of questions on this conversion. I see members ask about Dropmembers with coil overs. Your install should I show the feasabilty of the application.

I also see the questions about converting 73-87 to trailing arms. This is encouraging to those that are considering the conversion.

[72BlckButy]

Nice looking install!

[Wild83C10]

Heres a picture of a 67-72 chevy truck frame. The light blue line is the x-member location. The red lines are the 73-87 frame profile. Obviously the lines aren't exact but just to give you an idea of how the frames are different.

[SCOTI]

Originally Posted by Wild83C10

Heres a picture of a 67-72 chevy truck frame. The light blue line is the x-member location. The red lines are the 73-87 frame profile. Obviously the lines aren't exact but just to give you an idea of how the frames are different.

Yeah, we looked under the frame & I could see where the 'initial' kick-up is vs how the 67-72 frame is (I have a 68 swb frame sitting on my trailer). The CPP dropped center is still higher than the bottom lower plane of the frame rail.

[aggie91]

I also looked at a LWB mid 80's truck. There is a kick up in the frame rail about 1/2 way between the front cab mount and the rear cab mount. after that it is straight until just past the front spring hanger where it kicks up again to go over the rearend housing.

Does the SWB frame have the same kick up under the cab? I do not have one handy for a visual inspection...

[JW76]

yes it does and the crossmember goes in where the kick up is on the shortbed. that is part of the issue why it wont work on the longbed because the longbed calls for a crossmember to be located on the straight part of the frame which is higher than in the kickup