Steering, Suspension, & Brakes

tips, technology, tools and techniques related to non-driveline mechanical components

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tr8todd
Todd Kishbach

(326 posts)

Registered:
12/04/2009 07:42AM

Main British Car:


IRS in a TR8
Posted by: tr8todd
Date: July 07, 2017 07:23AM

Starting a journey down a road I've never been on and I'm looking for a little guidance. Plan is to install parts from the 2010 Camaro IRS under my LS3 powered TR8. Figure the engine and tranny are already in there so why not try and figure out the rear end as well. The Camaro has a wheel mounting face to face measurement of 64". Thats huge compared to the TR8s 57.25", so installing the thing as a unit is out the window. So far I have come up with using the center section, hubs redrilled to 5X4.5" and the bearing carriers. Driveshaft can be shortened, and new shorter axle shafts can be made no problem. I will need to make a tubular carrier for the center section with mounts for tubular arms with rod ends. Also need to come up with a plan for brakes because Camaro came with 14.4" rotors and Brembos that have a 120mm mount spacing. Working on that issue so no advice needed there. What I need is general pitfalls to look out for with geometry on the custom arms/brackets. Plan is to set the center section ride height at a position just above the center line of the wheels. That will put the arms at a slight downward angle at rest, and under compression they will end up at a slight upward angle. Figure that will minimize the change in camber the least, but I have no idea if thats correct or not. Also plan on making said arms as long as possible. Any advice before I start welding things is greatly appreciated. Fall back is to just install one of the narrowed 8.8s I have.


Dan B
Dan Blackwood
South Charleston, WV
(903 posts)

Registered:
11/06/2007 01:55PM

Main British Car:
1966 TR4A, 1980 TR7 Multiport EFI MegaSquirt on the TR4A. Lexus V8 pl

authors avatar
Re: IRS in a TR8
Posted by: Dan B
Date: July 07, 2017 08:52AM

Have you seen this: [www.triumphroverspares.com.au]

Seems like several have swapped in a Jag IRS.


tr8todd
Todd Kishbach

(326 posts)

Registered:
12/04/2009 07:42AM

Main British Car:


Re: IRS in a TR8
Posted by: tr8todd
Date: July 07, 2017 10:00AM

Sticking with the Camaro stuff because I have it. Don't like the bearing carrier layout, but whatever. I'll work with it. Found out the Camaro uses the same hubs front and rear, so right off the bat I have 4 hubs to play with.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5342 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: IRS in a TR8
Posted by: BlownMGB-V8
Date: July 07, 2017 11:19AM

"Sticking with the Camaro stuff because I have it."

Well, right there you have the best possible basis for any sort of conversion, right? ;)

How about some photos so we know what you are working with? I'm just guessing, but UCA, LCA, tubular half shafts, and lateral links of some sort? Most GM IRS seem to be pretty straightforward and do not require complex analysis of torque transfer. How much room between the tube axle and the frame rails? Need space for that top link.

Overall the TR has lots of room to work with so it shouldn't be too difficult I wouldn't think. Devil's in the details of course. Your thought on pumkin position is good, in general you will want it up high and half-shafts near level at loaded ride height, maybe angled down just a bit. Watch your compression distance and do all you can to maximize it.

Control arm geometry can be complex but can be dealt with. A model is useful. The biggest factor is the length of the control arms but the relative positions of the pivots give a lot of variability in what motions result from them. You will probably remove the same proportional amount of length from UCA and LCA but if you move the inner pivots that might change. Outer pivots will be harder to move.

I think the newer IRS designs have some built in geometry changes based on loading such as braking forces and cornering loads so you'll want to be aware of any of that and decide if you want to keep it that way.

Jim


Scott68B
Scott Costanzo
Columbus, Ohio
(495 posts)

Registered:
10/25/2007 11:30AM

Main British Car:
1968 MGB GM 5.3 LS4 V8

authors avatar
Re: IRS in a TR8
Posted by: Scott68B
Date: July 07, 2017 11:52AM

Have you ever visited this site?

[vsusp.com]

You could input measurements of the stock GM rear suspension and then modify the parameters to fit your TR. It would give you a rough idea how your changes compare to the original design. Of course there is better software out there but this might be a starting point.


tr8todd
Todd Kishbach

(326 posts)

Registered:
12/04/2009 07:42AM

Main British Car:


Re: IRS in a TR8
Posted by: tr8todd
Date: July 07, 2017 12:58PM

The V8 Miata guys and the Cobra kit car guys actually prefer the GM 8.6 aluminum center rear end over the Ford 8.8 aluminum centers. They are 12lbs lighter than the Ford as well. Gear selection choices are decent, and the limited slip is a better design. The one I have is a 3.45 and has limited slip. The Camaro only had 11,000 miles before I parted it out, so unless I run into something that is insurmountable, the Camaro/CTSV rear end is the one I'm going with. Completely ditching all of the Camaro control arms. I have seen it called a 4.5 link system. Images abound on the internet and you can easily find an image with any angle you could possibly want. I'll snap some photos later of just the stuff I plan on using. My driveline guy said he can shorten the driveshaft for me no problem, and put me in touch with a place less than 100 miles from here that will make custom heavy duty splined shafts for way less than I thought possible. I'll reuse the existing inner and outer CV joints, just use shorter spend shafts between them. Need to get the hubs back from my machinist buddy with the new bolt pattern so I can mock things up. Preliminary mock up shows I will need at least a 17" wheel to clear the two LCA mounts on the carrier. I mocked up with a 16X8 wheel and it was just too close to call. Looks like 17X9 or 17X10 wheels will be needed for the back. Once the hubs are back I can look at what I need to do for brake hat offset and caliper brackets. Looks like the minimum size rotor is going to have to be 12.19", which is the same size I already have on the fronts.

There is all kinds of room back there now that I removed the gas tank, and built a fuel cell box where the spare tire well was. I will have to make an upper control arm with a curve to it to clear the frame rails. If the rails look like they will still be in the way, I can always cut them out and remake them higher up. Need to figure out where the coilover is going to mount and the frame rails look to be in the way as it is, so they may have to go anyway. No worries. Most of the body has been cut, chopped, flared, removed, replaced anyway. The extensive roll cage is keeping everything together.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5342 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: IRS in a TR8
Posted by: BlownMGB-V8
Date: July 07, 2017 01:42PM

Be aware that your coil-over shocks are going to be a weakness. Specifically the mounts. Yes, I know they are light and compact, but they carry the entire static and dynamic load. So if there is any one area you'd like to beef up that will be it. Not really designed for durability and long life. Of course if it's a race car that's different.

Jim



tr8todd
Todd Kishbach

(326 posts)

Registered:
12/04/2009 07:42AM

Main British Car:


Re: IRS in a TR8
Posted by: tr8todd
Date: July 10, 2017 06:46AM

Can't really agree with your statement on the coilovers. I have run them for many years on my TR8s. Most of my friends run them on their TR8s. Have them front and rear on the BMW 2002 race car. My TVR 280i had them on the rears. Never had any issues with durability. Just a spring located over a shock or strut for minimal packaging space. No different than a shock in one place with a spring in a different one.

Pretty much given up hope on using these Camaro rear uprights. They are just too big. Going to have to crawl under some Ford products in the junkyard and have a look at the Explorer, T bird, Lincoln MK VIII systems. I know they all run wheels and brakes that could be considered in the realm of normal. The Camaro's 20" wheels, 14.4" rotors and gigantic 4 piston Brembos are not what I call normal. Might keep the center section and adapt ford axles/uprights. Don't know yet. Did spend some time under the rear of the car over the weekend cleaning things up. Lots of room under there now because of the oversized tunnel and lack of fuel tank.


mgb260
Jim Nichols
Sequim,WA
(1802 posts)

Registered:
02/29/2008 08:29PM

Main British Car:
1973 MGB roadster 260 Ford V8

Re: IRS in a TR8
Posted by: mgb260
Date: July 10, 2017 09:57AM

Todd, Look at TR6, Datsun 510, RX7 and BMW Trailng Arm IRS. Normally need twice the spring rate because of distance/leverage of coil spring but some have used coil overs closer to wheel for more normal spring rate.


BlownMGB-V8
Jim Blackwood
9406 Gunpowder Rd., Florence, KY 41042
(5342 posts)

Registered:
10/23/2007 12:59PM

Main British Car:
1971 MGB Blown,Injected,Intercooled Buick 340/AA80E/JagIRS

authors avatar
Re: IRS in a TR8
Posted by: BlownMGB-V8
Date: July 10, 2017 01:20PM

Feel free to disagree, lots of coil-overs out there. But the attachment points are heavily loaded. I don't believe there is a compliant bushing made which can sustain that sort of load indefinitely, and spherical ball ends are subject to grit and wear. I've seen the ball fall out of the race and the race fall out of the housing. Just sayin...

Jim


tr8todd
Todd Kishbach

(326 posts)

Registered:
12/04/2009 07:42AM

Main British Car:


Re: IRS in a TR8
Posted by: tr8todd
Date: July 10, 2017 04:14PM

The 4000 pound Camaro I just pulled all of this suspension out of has stock coilovers. So do some of the Fords I crawled under today. I like the way the Explorer is set up. Found an 02 with an aluminum center section and a 3.73 LS. Might end up picking that up. The kit car guys seem to like the thunderbird stuff and there is a whole running 5 speed thunderbird with IRS on craigslist now for $500. Could not find any Tbirds or MK VIIIs in the yard to look at.


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