Differentials

[ROBBMAG]

Just as a note, there is a gravel road near my parents farm that I used to time myself on in that old Celica. After I did the IRS swap, the traction and control difference was incredible. BTW Those IRS rears have a canted swing arm with LOTS of travel.

[4wdchico]

Petros,
The Celica ST, and GT had a solid axle, the GTS has IRS. The earlier ones, '82? to '84 had drums, the '85 had discs. '82 - '86 Supras also shared the exact same rear suspension. I talked to my brother last night and confirmed the location of the SEVERAL complete sets of rear suspensions with LSDs from the Supras we used to road race. Game on.

Very interesting. So you are contemplating an IRS swap? Pretty cool! At first I was thinking that the Supra/Celica had a wider wheel track. But then I remembered that those cars use a zero offset wheel where the terc uses a very negative offset wheel and this might compensate for the wider spaced hubs. Wonder how much it costs to have those hubs drilled for the 100mm bcd lugs?

Another benefit would be that a terc with an IRS would be able to run a one piece drives shaft and eliminate the center support bearing and a couple of u-joints from the stock setup.

[Petros]

I was aware of the Supra IRS, it was the same one put in the Celica? That seems like it might be real heavy, too heavy perhaps for the Tercel? The Supras are way more common than the Celica GTS (I just saw one this morning on the freeway, I wanted to flag the girl over that was driving it and crawl underneath it, but I thought better of it).

Might be worth it the extra weight, especially if you have a more powerful 4age engine swap. The rear hubs on the MR2 use the same 4 x 100mm bolt pattern, and they are likely much lighter too. That might swap into the Supra IRS system to make the wheels match. I might be looking under some Supras this Saturday at the local pull-a-part.

Now if we can find a heavier 4 wd trans to fit our cars we would have everything we need. An early 4x4 truck trans perhaps? too heavy again.

[ROBBMAG]

I already looked into the truck drivetrain swap. I've had a complete drivetrain sitting in the garage for years just waiting for a project but the transfer case is WAY too big and slings off to the lower left of the whole shebang. One would have to put a 6 inch lift on the car to accommodate the case, and would need an entirely different front drive axle. I'm pretty smooth with fabricating but, that's way too much work for a car I paid 300 bucks to get. As far as the weight goes. the early trannys are cast iron, or steel, but you get the idea. Although the Supra 5M-GE engine DOES bolt right up to the 4 cyl truck bell housing. That's just crazy talk though. Saturday I'm hauling my kids up to the storage shed to dig out an IRS or two to toy with.
I need to replace the CV joint boot on the rt front inner joint. Anyone know if there is a quick way to do this little trick? I have lots of duct tape!

[Petros]

I was afraid of something like that. As I recall, even the older 4cyl truck trans was a pretty large and heavy installation that raises even the truck quite a lot over the 2wd version.

On the CV joint, I have thought about this but I have not tried it yet (I have two other cars that need the same thing). With it still on the car, clean off all the grease and grime, maybe even flush out all the old grease and put new clean stuff in through the split (this is special high pressure lube not normal wheel bearing grease BTW). Than clean off the outside of the damaged boot and stitch it closed with heavy synthetic thread. Use a baseball type stitch with two needles, space the stitches fairly far apart (like 3/8") so you do not tear the rubber boot further. Than clean off any remaining outside grease from the surface of the boot. Use contact cement to glue over the stitches a strip of nylon fabric or a thin layer of rubber (like tire patch material, or a piece from another old CV boot), make sure you cover over all the stitching holes. If you wrap the strip of cloth over so it overlaps on itself it should hold up pretty well. You might also use some kind of strong vinyl repair tape too, but it must be flexible and stretchy or it will work its way off.

That would make a good temp fix (or maybe permanent), and it should be a lot less work than pulling the axle and the CV joint apart. If I do this soon I will report back on the results.

On the IRS issue, I had visited relatives over the holidays and my sister has a 2001 Toyota RAV4. I spent some time laying on the driveway under the rear end admiring the IRS in that too. I was thinking how nice that would be to have. I wonder if that is the same set-up as the Supra, or perhaps not since it is a taller vehicle. The trans is no good since it has the transverse engine and trans set-up similar to the all-trac. It does have a pretty nice 2L 4cyl engine too. Hmmm....

[SynthDesign]

I already looked into the truck drivetrain swap. I've had a complete drivetrain sitting in the garage for years just waiting for a project but the transfer case is WAY too big and slings off to the lower left of the whole shebang. One would have to put a 6 inch lift on the car to accommodate the case, and would need an entirely different front drive axle. I'm pretty smooth with fabricating but, that's way too much work for a car

I think you'd be better of just putting the Tercel Unibody on a 4x4 pick up or 4runner frame. YES way tooo much work!


As for IRS, I see benefits but I beleive a solid axle rear is far superior for offroading and 4wheeling. Especially in the rear end.
What's you reasoning, besides you can, which is good enough for me?

[Petros]

You bring up an interesting point about the rear axle vs. IRS. When I worked for the race shop we built both IRS cars (the old Dastun 510, and the 280z and 300ZX) and live axle rwd cars (the B210, pick-up). And we could make them both have very similar skid pad results, about 1+g lateral acceleration. But on road racing tracks the irs put in better times. Likely on a pure drag race the live axle would be better (tires stay perpendicular to the road surface).

The issue is unsprung weight, the less the better. Unsprung weight is that of the wheels, tires, brakes and the suspension components not supported by the springs (as is the weight in the rest of the car). the higher the unsprung weight, the harder it is for the tire to stay in contact with the surface. With a live axle you also have the problem that a large bump or disruption with one wheel will affect the grip on the other. So IRS has much lower unsprung weight and allows the wheels to move independently to keep better contact with the road surface. This is true off road as well as on road, the better contact with the ground, the better control, handling, and braking. It will add weight and complexity to the car.

IRS should improve handling, traction, braking and ride comfort over the live axle. If it is enough better to make all the messing around with parts, welders, drilling, etc. and sorting out all the unforeseen problems that will likely turn up, is another question. It would just be an expensive hobby to make something fun and different, that most who start will likely never finish.

[SynthDesign]

IRS should improve handling, traction, braking and ride comfort over the live axle. If it is enough better to make all the messing around with parts, welders, drilling, etc. and sorting out all the unforeseen problems that will likely turn up, is another question. It would just be an expensive hobby to make something fun and different, that most who start will likely never finish.

I agree, but than why do 80% of the truck manufactures feature a solid live axle in the rear(yes I know some still use leaf springs too)? I think clearance and drag-over-things-ability is ideal for off-roading and 4x4 with the solid axle, especially considering our vehicles limited suspension design. I know many vehicles in rally racing can be taken out in a matter of seconds if a small branch catches up in an independent suspension system. Then again, I have yet to see a solid axle front wheel drive only consumer car or truck. Is there one in Finland or Iceland or something?

[Petros]

But you are missing the most important point: the fastest road and off-road racing cars all have 4-wheel independent suspension. All of the most costly luxury cars all have 4-wheel independent suspension. There must be a reason for that too. I think the reason most trucks still use shitty leaf springs (the WORST way to locate an axle!) is simple cost. It is cheap, durable and reasonably reliable, but everything else about it SUCKS.

Back to LSD: I have been thinking about this a lot, and since the rear axle only is powered during 4wd in the Tercel, if only it has an LSD it would only be engaged when in 4wd. So would this give the best of both worlds by keeping the front an open differential, with LSD rear. I like the idea: Smooth and economical driving in 2wd on paved road, with the extra traction in 4wd with an LSD in the rear. I have heard the LSD affects fuel economy on paved roads.

Or would it behave strange in 4wd with the open diff in the front and LSD rear?

[ROBBMAG]

As far as I know, anything that is 4wd and is equipped with or has an LSD as an option has an open front diff. I may be wrong about that, but, all the Chevy trucks at my shop are LSD rear and open front. All of my brother's Tacomas are the same even with the factory rear lockers.

[Petros]

I was at the local Pull-a-part this afternoon, and low and behold there was a mid '80s Celica GTS with IRS and rear wheel disks. It appears the wheel bolt pattern is a bit larger dia, and it uses a semitrailing arm type IRS. The cross member bolts to "hard points" in the floor with vertical bolts. It appears a swap over would be a pretty involved project, a lot of cutting and welding I would say, if only for the mounting points.

I think the whole rear axle assembly could be bought for about $100-150. or so from Pull-a-Part. So, should I grab it for a future project? It will soon end up in the crusher, the engine and trans from this car are already gone and the body is rusty. Or is this too much work? Wish I could drive one of these to see how the rear end behaves before I commit to it. It looks like it would be a hot custom rear end for a Tercel! Paint and chrome all the parts and than raise the rear end so everyone could see it under your little Tercel wagon.

I happen to have my camera and got some pics. The whole picture does not show, right click to see it better.



From the side, it appears the upper spring seat and upper shock mount could still be used on the T4wd.


The cross member with the drive shaft runing through it, you would have to have the front of the T4wd drive shaft spliced to the Celica drive shaft, the Celica drive shaft appears much larger. You can see the bottom of the diff housing below the cross member.


The body mounted center diff. There are LSDavailable for this diff, and you can put in a Supra rear end for extra strength.

Probably the best way to mount this rear end would be to get a whole car and cut out the whole rear floor, and than weld it into the rear of the Tercel. A big job.

[4wdchico]

Cool idea. But too much work. The Corolla All-Trac rear axle swap sounds like the way go if the total width is compatible.

[ARCHINSTL]

Off-topic a bit, but...
I note the pictured GTS's diff case is finned - did these get that hot?
Tom M.

[Petros]

If you have an LSD and you use it to compete in slalom or autocross events, it would get hot. I doubt on daily driving it would get hot enough to matter (pulling very heavy trailer up a long steep hill? Not normal us on a sport sedan). I think on this car it is more like a performance feature put on the GTS just to make it look racy. When I worked for Nissan racing USA, even on a 900 hp turbo 300zx full race car w/LSD did we feel the need to cool the diff. Even on the 500 mile endurance races. But they do make auxiliary diff coolers, mostly used on 4x4 racing, I have seen them.

I know this would be a lot of work, and likely not worth it, but darn it, now I know this is available I keep thinking how I might make this rear end fit in my Tercel4wd. Think how cool those cooling fins on the diff housing would look under a T4wd. Stop thinking about it, stop thinking about it, you do not want to go there....