C3 Rear Suspension Upgrade Roadmap

phantomjock

phantomjock

Well-known member
Joined
Sep 2, 2009
Messages
1,851
Location
Retired Again!
The chassis is disassembled. All componets are off. I am in the middle of POR-15 painting, so what next? (Suddenly, I feel like my sig)

Goal -- improve performance (Think -- Drag and Autocross). Do it incrementally to help distribute the costs over time.

The members of this forum have done a heap of work -- and I am building on their kind experience and sharing.

So - here is what I am thinking as a plan for the rear end on my C3:

A Multi-bar system, that will;

minimize camber change,
have adjustable toe-in,
improve opportunity to use wider tires/deeper offset wheels, and,
have adjustablity to ride response and ride height.​
​

OBJECTIVES:

1. Keep the original Trailing Arms -- but modify:
1a. Do the Johnny Joint mod to them found here:
thum_12694aad7135636f5.jpg

1b. Do the Twin Turbo Coil Over mod (the strut with shock mount as described here:

thum_12694aad7135b8e2d.jpg

2. Add an upper link mount to the Trailing Arms similar to:

thum_12694aad71364d7ae.jpg


2a. Fabricate an upper Diff Mount - similar to the "Smart Struts" I have on the bottom of the Diff (or follow Stroker427s lead)
thum_12694aad7137a7ccf.jpg

thum_12694aad7136859ea.jpg


2b. Build the Links - 5/8 inch Heim Joints with jamnuts and tubes sized to get close to parallel:


thum_12694aad71373c60a.jpg

3. Add a rear (Toe-Adjust) mount to the Trailing Arms (a la Stroker427):

3a. Fabricate a diff mount aft of the diff - maybe using the Upper Diff mount in 2a above:
thum_12694aad7138106ef.jpg



3b. Build Toe adjust Arms

thum_12694aad7138af208.jpg



4. Relocate E-brake mount to top of Trailing Arms:

5. Design, build, and install half shaft safety loops

6. Design, build, and install drive shaft safety loop

Now, the incremental part:

7. Add a drag strut (optional) Not too expensive - may do the welding now and add bar later

8. Continue to use the monoleaf fiberglass spring, but mount shocks to new mounts

9. As time and money permits - upgrade to adjustable (single - or dual?) coil overs on the new shock mounts and ditch the Monoleaf

10. I don't think it will make a very good Boat Anchor - but might make a good spring for a DIY CROSSBOW!

I'm certain I'll have questions to add to this thread as I move along too.

Meanwhile, I anxiously await everyone's thoughts and comments before I take too wrong a turn!

As I have time I'll try and sketch up a pic or 2.
Also load some of the POR-15 progress/effort.

Cheers - Jim
 
Last edited:
Lots to digest here but I kinda went through the same thought process as you. I added an upper control rod to the trailing arm and installed johnny joints. I don't like the shim adjustment for toe control so I intend to use fixed mounting of the pivot with toe and camber adjustments done with the upper and lower control rods. This means that I will have to use splined/slip half shafts.

44aabbf1f45f45.jpg


44aabc0576b58b.jpg


44aabbf9e63976.jpg
 
BBShark --

Yeah, it is a Muther to read through that way -- so I did a pdf with pics from the urls -- but left the refs in so its easier to follow the plan. I find with a plan I can keep from muddling through .:skeptic:

BUT, its 777Kb and exceedes the attachment limit. SO, If anyone wants a copy PM me you email, I'll send it to you -- Just ask. -- or we can put in Downloads if warrented.

You have offset TAs is that right? Was considering those, but for now will opt for modifying the originals.
I am thinking with the johnny joints - you can get by without the shims as long as the toe/trail is set with the control arms. Seems like you can sorta line the TAs up to close enough, then fine tune with the arms. Have I got that right? I'll be using the aft Toe Adjust Arm for that and leave the upper and lower fixed.

Will your upper control arm mounting be similar to the lower? Or in the vertical plane with the half shafts? I plan on the Shafts and upper and lower arms all in the same vertical plane. That way as I adjust toe in/out, the 3 will all move fore and aft in concert. My toe adjust will be in the horizontal plane of the half shafts.

You gotta good source and price on those slip half shafts? I finally found where the C Clips are. That took a lot of research -- but GTR1999(?) did a nice review of a Diff rebuild and had some great pics.

Thanks for the good pics! I'll figure out how to do that soon!
Cheers - Jim
 
Last edited:
phantomjock said:
BBShark --

Yeah, it is a Muther to read through that way -- so I did a pdf with pics from the urls -- but left the refs in so its easier to follow the plan. I find with a plan I can keep from muddling through .:skeptic:

BUT, its 777Kb and exceedes the attachment limit. SO, If anyone wants a copy PM me you email, I'll send it to you -- Just ask. -- or we can put in Downloads if warrented.

You have offset TAs is that right? Yes Was considering those, but for now will opt for modifying the originals.
I am thinking with the johnny joints - you can get by without the shims as long as the toe/trail is set with the control arms. Seems like you can sorta line the TAs up to close enough, then fine tune with the arms. Have I got that right? I'll be using the aft Toe Adjust Arm for that and leave the upper and lower fixed. Are you going to use slip shafts or remove the retainer clip from the stub axles?

Will your upper control arm mounting be similar to the lower? Or in the vertical plane with the half shafts? I plan on the Shafts and upper and lower arms all in the same vertical plane. That way as I adjust toe in/out, the 3 will all move fore and aft in concert. My toe adjust will be in the horizontal plane of the half shafts. I'm not following this, are you going the have upper and lower control rods and a toe control rod? I'm not sure how you would do this with modified stock arms.

You gotta good source and price on those slip half shafts? The half shafts I have are modified Viper shafts. I guess I have about $350 in them. I finally found where the C Clips are. That took a lot of research -- but GTR1999(?) did a nice review of a Diff rebuild and had some great pics.

Thanks for the good pics! I'll figure out how to do that soon!
Cheers - Jim
Click to expand...

I'm interested to find out if the guys who have removed the C-clip for modded rear setups have had any problems. Seems like the lip seals wouldn't like that?

VetteMOD has it's owm picture hosting. Put your pictures in there and just copy the IMG tag into your post.
 
BBShark --
Thanks for the tips and hints -- I've uppdated the orginal post - so the pics are there too.
So, As I understand it, some folks have elminated the C Clips - but not a preferable solution. As I understan it - from inside the Diff - so the splined shaft has some in and out play to ccomodate variation i nthe set up. TT would have the best thinking on that-- I believe he has worked taht before. Yu bring up a good point too -- Lip Seal wear is a good consideration.

Re the stock TA's and Toe adjust: I'll hang a clip/bracket/fitting for the heims on the inside of the aftmost extension - the one the monoleaf spring mounts through -- BUT, facing the mount inwards. That way I can still use the monoleaf and its through bolt config while setting up the rest of the system. Image 4 in Post 1 above ought to be clear enough -- I'll leave it in my gallery too.

BUT HMMMM thinking out loud again here -- if the aft toe adjust is mounted there, and you (to the very extreme) tighten the toe adjust arms -- the monoleaf will automatically be flexed too. May have to be an itterative process -- or send me shopping for coilvers sooner!

Cheers - Jim
 
BBShark -- Thanks for the tip -- FIXED!

RE: The C Clips -- TT is proly the expert on that issue. But, I have seen a few references to leaving them out of the DIFF with a multi-link system as the system does the job -- until something lets go!

Regarding the AFT TOE adjust and the Upper and Lower on modified TAs:

thum_12694aad7137a7ccf.jpg

Upper and Lower + toe -- yes . Image #4 I think showes 2/3 of it clearly. Butt HMM I am thinking out loud again...
IF (IMAGINE) the toe is really cranked in - and mounted at the position I show (same point as the Monoleaf Spring), we'll tighten the monoleaf and raise the body height, now, needing a LONGER bolt AGAIN! Well, it will be itterative until the cost equals a new set of coilovers -- RIGHT?

Cheers - Jim
 
BBShark -- Vansteel question OFFSET TRAILING ARMS?

BBShark said:
I added an upper control rod to the trailing arm and installed johnny joints. I don't like the shim adjustment for toe control so I intend to use fixed mounting of the pivot with toe and camber adjustments done with the upper and lower control rods.

44aabbf1f45f45.jpg

44aabbf9e63976.jpg
Click to expand...

Those trailing arms look very much like the Vansteel offset arms.
ARE they?


Did you press out the original poly bushings - and press in the johnny joints? Does the long pin assembly:
1. Hold the Johnny Joint in place, or
2. Only add some control of angluar movement?
3. Looks like a challenge to drill and tap. Didi you drill through from the outside?

Here's what I'm now thinking - save some time and fabrication/complication and use your approach with the johnny joints I have (2 inchers) on the following kit Vansteel has:

It isan offset system that includes coil overs and offset TAs:
thum_12694ad9bed3c1146.jpg


Solves a lot of potential headaches for my planned DIY mod to do the same thing:
1. Shock Strut on Trailing Arm is done -- CHECK
2. Includes Frame Mount for Shocks -- CHECK
3. Brake line mount is moved -- CCHECK
4. Offset TAs -- CHECK
5. Coil-Overs included - and sized for the Shock Strut -- CHECK
6. Already painted/coated -- CHECK.

I'll need to; Sort out the how to on the BBShark Johnny Joint mod you did, add an upper mount for the upper cross links, fabricate something for the aft most arms (toe in control), AND write a CHECK!
Cheers - Jim
 
Not sure who originally made my arms. They could be Van Steel.

If I had known then what I know now, I would have made them myself! The upper control bracket was added to the arm, made from 1/4 inch plate. The shell of the poly joint that was originally in there was machined out for the Johnny Joint. The tube that is on the inside channel of the arm is a grease fitting extension. I don't like the hollow bolt option for greasing and there is no way to get to the standard fitting with the JJ inside the pocket.

Looks like the VS coilover setup will get you most of the way there. What do those cost?
 
BBShark
Yeah -- they'll get me to 75-80 percent there- gotta insert the Johnny Joints, and the upper control bracket --
BUT, it includes the coil over shocks, etc, etc.
"There's a price to pay - oh oh oh a price to pay..." (apologies to the BOSS):
$1300 bucks for single adjustable shocks QA1s, For the dual adjustable -- 1600 Bucks!

But it skips a lot of fiddling. You're right it would very do-able for the DIYer, with a bit of welding skills.
Thanks for the inputs!
Cheers - Jim
 
I guess its time to make a revision to my "ROADMAP"!

Well, during a bit of some spare time, I've been doing some more research on rear end approaches for the C3.
Here's an approach an AUSSIE made to adding upper struts to a semi-stock rear-end.
The pic is a paint-over I did to show the points of his work I like and things I'll do - and there is a lot of bling!
thum_12694af97c72a284f.jpg

12694af97c72a284f.jpg

He used a bracket that was left-over from a Smart Strut install.
Now, what I like about his approach, is that he also kept the Stock Shock mount location!
I was considering using Coil-overs in a Twin-Turbo-like trailing arm mount -- but, now am on a different vector. Bump da Bump - gone off the map!

I have an existing monoleaf spring. I'll still make the johnny-joint mod to the TAs and move the parking brake mounts, but will forego the extra strut for the shocks.

Naturally, I'll add the tabs for Toe-In, and strut-rods, heims, etc.

As I understand the advantage of using the monosprings, they will let you adjust ride height - somethig a bit more difficult with coil-overs. And to adjust spring rate, I'd need to move to a dual mount monoleaf, but that can happen later -- If I'm careful in placing the mounts for the Toe-in!

AND - This is way less than the VanSteel mod shown earlier!

thum_12694ad9bed3c1146.jpg

12694ad9bed3c1146.jpg
The difference in costs - will pay for double adjust shocks all around. Also the front will now also move to a monospring - agaiin concern over ride height adjustment.


Cheers - Jim
BTW -- How do I make the pics look bigger in the postings? Is there a trick to that? DISREGARD -- I Figured it out!
 
Last edited:
Moving along...

Well continuing along the "secondary roads..."

Had a look at the VB&P rear monospring mount for the dual mount setup.

12694af99d6d366c2.jpg

Looks like it will accomodate a rear toe-in adjust strut with a little mod or two to the mounting brackets.

The Vette Brakes set up uses the rear crossmember (diff mount) to locate the monoleaf mounts. I propose making new mounting brackets that could easily accomodate the monoleaf spring - and the struts.
Also, it looks like if you added some larger plates to the fabrication -- more adjustability to the spring rates as well.

12694af99d6e35f99.jpg


This will require me to call them to make sure I don't excede the springs ultimate strength.
That would suck!

Enough thinking and playing with the crayons. Its time to make some calls and place an order -- or two.

ANY cross talk - or thoughts appreciated!

Cheers - Jim
 
I think there is a plate on the inside of the VBP dual mounts that would make it difficult to mount a rod end on the inside. Are you going to run upper and lower control rods and a toe link? If you do this, are you planning on floating the trailing arm pivot?
 
BBShark -
Yeah - You're Spot-On!
As I looked closer at the catalog (on line) -- there is a web that seperates the forward and aft plates. "Bugger!"

Thats why I'd consider making totally new plates/mounts - that way I could get the space opened for the toe-in adjust. The red box construction (upside down and backwards 4H look) that I've drawn over the left (end-view) in the VB&P diagram is an endview of the new mount drawn over the original. No web to keep the sturt out, and spacers to improve rigidity.
Maybe this will help explain:
12694af9d671c4335.jpg
I talked to VB&P today and they didn't quite have a good response on my question regarding the spring max load question -- but maybe my question was a bit öbtuse -- or esoteric. I'd need to think that through before buying the dual mount, and making the modified mount.
The plan is YES - Upper and Lower links, and YES - the trailing arms should float with the Johnny Joint mod planned -- and I'll say goodbye to the shims!

Working out the half shafts and C-Clips will remain an issue and a concern.

I did order bits and pieces for the front end - so will work that as I go too. Gives me some more thinking time on the rearend before - writing a check!
 
Great info in this thread guys :thumbs:

Just wondering what the use of a toe control rod would be if you have an upper control rod that you could use in conjunction with the lower control rod for toe.
Also...
What do you mean by making the johnny joint a floating design after putting in a toe control rod?
Lastly... is there no definitive answer about the reliability of removing the C-clip when adding an upper link (shaft seals/cross shaft etc..)?
 
vette427sbc --
sorry to send you off to another post -- but here is the complete Johnny Joint info:

http://www.vettemod.com/forum/showthread.php?t=2315


The TOE -IN Strut will make up for the lack of shims and locate/support the Johnny Joint and trailing arm in the inward/outward position.

The location (I believe) of the TOE-IN should be in the same horizontal plane that includes the half shafts and the TA to Frame joint (the Johnny Joint). To that end -- I believe that the inner and outer joint locations of the TOE_IN Struts should match (as closely as possible) the inner and outer U-Joints on the Half Shafts.
That seems like the right geometry -- I could be wrong -- HELP anybody!

I'll post pics similar to the previous postings as I do mine too -- I have the bits and may start this weekend - we'll see what happens!

And - YES -- I suspect that the upper and lower "could" serve as the TOE-IN Control -- but kinda wonder -- why all the other 5/6/multi-link rearend systems have a seperate link for that. I suppose if, Well Designed and Carefully Installed -- the Uppers and Lowers could have a resultant vector and interaction that looks/acts like a seperate TOE-IN strut.

HMMM, that may take some specific CAD modeling -- oops more time less movement to get complete, or..

TWIN-TURBO -- Your ideas here please!!!

And I gotta defer to TT for inputs on the C-Clip mod (removal) or using a slip joint half shaft. That will be a bankbook killer I'm sure --- ahh but what a passion!

ANd I hope this is usefull information! So much good stuff on this site --Thanks to all!

Cheers - Jim
 
Last edited:
So when using a toe control rod, you still dont use shims to position the T/A in the pocket? So hypothetically, if you had this setup and took the toe control out, the T/A would be free to slide inward and outward in the pocket? Im having a hard time figuring out what you are referring to by free floating johnny joint. Or am I over thinking this and you are just referring to the johnny joint assembly itself as free floating :confused:

Also, have any of you looked at the Global West T/A's? They are a tubular design and you can get them with spherical joints. A little Pricey though...
http://www.globalwest.net/1963-82_Corvette_tubular_rear_swing_arm_and_adjustable_strut_rods..htm
 
Maybe I have confused my build plan ...I'll try and clarify (if anyone outta be accused of over thinking-- Its me!) :bonkers:

First, the Johnny Joints are spherical joints. They replace the stock Trailing Arm Bushings -- with some work -- that is the post I listed. They are welded in postition and then are more or less üniversal, and need some "containment." Hense, the Toe-In Strut.

And -- YEP, the Global West TAs are nice - -and pricey. AND --DOWNSIDE -- they keep the Parking/E-Brake mount bracket in the stock position! This should be moved to the top of the TA if you want deeper/offset rims!

Thats what I think I'm replicating -- using my existing TAs and 2x $39.99 for the (Currie 2 inch) Johnny Joints! (Well, I'll hire a welder too...so a little cost there (equals postage and tax on the GW set )

Yes, there may need to be permenant spacers (shim-like) set in the pockets -- but not changed for suspension geomerty adjustments -- That will be the Toe -In Struts!

Any help there?

And the rest of the build outta get me:

1. Ride height adjust, shock compression and rebound adjustments too
2. Toe -In adjust, and,
3. NEAR ZERO camber change!-- the BEST! :yahoo:
4. Lowest possible costs... we'll see.

Cheers - Jim
 
Last edited:
Thanks Jim, that was my question- the permanent shims to locate the T/A's.

Now you've got me pricing out parts to build a similar setup. :waxer: It seems like if you do the R&D on your own, a pretty nice setup can be had for a few hundred $$ (minus the fancy shocks). Here comes another winter project....

About the Global West arms- The advantage I see with them is that they could be lighter than the vansteel ones. The parking brake cable mount shouldnt interfere as long as you use 17" or 18" wheels.
 
You must log in or register to reply here.

Latest posts

Back
Top