Front strut coilover project to allow taller tires

[mountainhick]

Edit/update August 4 2015; This is a real project now. f you want to skip to the actual project/solution, skip to Post #10. I am picking things up there and will document the work as it happens.


Previously edited this entire thread. I started it before getting into the idea of building a set of lifted front struts and coil over springs, but that looks like where this going. This is pretty long winded so I'll breakit up into sections

The goal: 2” front lift and ability to use 29”-ish tires. Preferred size 235 75r15 just because they are super common in LT.

Transmission gearing and diff ratios are already accounted for. If I swap the diffs back to 4.3 it will give me essentially the same engine RPM to ground end ratio that I have now, with extra ground clearance. I realize I will need to trim wheel wells, Can possibly get away with just trimming the plastic that wraps from side trim panels, but we'll see.

Already tried:

-I did the 2” lift using Tim's method of building lift blocks for the top mounts. But, it doesn't raise the spring perch, so I can't run larger tires. In actual use I have caught oil pan, transfer case, exhaust and diff mounts when on dirt roads and really could use that extra clearance. If I am taking it apart again, rather than just replacing tired front springs, may as well really do it up.

- I tried to find other struts that would take care of it. I referenced Zenseeker's suspension page with possible strut replacements, and referenced to Monroe's dimension chart. I looked at mount type and stock tire size on the other models of cars. The one that came out the winner dimensionally was the model for Ford Escape/ Mercury mariner/Mazda Tribute, with the model for Hyundai Sante Fe runner up. So I went to the pick n pull and found these. Neither had bottom mounts that would bolt to the previa steering knuckle. I consider the one for the sante fe as completely incompatible. It is for a 1” thick steering knuckle and the Previa's is 1 7/16” The one for the Ford/Merc/Mazda is kind of closer, it is 1 7/16”, proper thickness, but hole spacing and holes themselves are smaller, and there is not enough metal in that part of the strut to mod without welding on extra metal and completely re drilling. May as well weld extensions on the bottom of stock Previa struts, but I don't think anyone around here will do any welding on a charged strut.

I also had a quick look at an earlier model Sienna strut and the spring perch was not high enough, so I didn't even take other measurements on it.

I still want to see the strut for the Mazda MPV before launching into a coil over project, but I have my doubts.

[mountainhick]

So in the meantime I am trying to piece together design data for possible DIY coilovers:

The original springs are probably progressive rate, coil overs are generally constant rate. There is the possibility of adding tender/helper type springs in a coil over, to make them more like progressive rates (really more of a double rate setup) but to keep it simple I'd try constant rate first.

So here is the proposed strut set up:

-Use spent set of previa strut bodies

-cut top of cylinder, and remove guts

-Option 1 (preferred): remove bulk of spring perch leaving just a bit of it still attached to strut tube as collar/ base for coil over adjustable tube. Threaded tube with bottom spring height adjuster nut(s) slides over upper strut tube and sits on this collar.

-Option 2 that I don't think will be necessary unless a threaded tube's diameter is too big; remove spring perch entirely and weld a collar on a couple inches higher on the strut tube to support threaded coilover tube. No problem to weld once the guts and pressure are no longer a concern.

-use shock/strut insert inside the cored out strut body. This is also something I'd have to spec out. Relevant parameters are size, travel and valving. Many of these have adjustable valving, but adjustment at the top of the shaft, and would be a nightmare to access under the dash. It would have to be a set it and forget it option, but these cartridges have the benefit of several adjustment levels rather than an insert with fixed valving which if not selected properly may just not work well.



So, to spec out the springs themselves, I need:

-Corner weights of front wheels. If anyone has this please let me know, or one way or the other I'll weigh mine

-Stock spring rate: I think I found a reference for stock spring rates based on Tein springs in Japan for Estima 1990-99 (thoughTR11-21 independent rear)

https://www.tein.co.jp/srch/eng_sear...ype=1&allvch=0

Front 3.2 kg/mm (179 lb/in)
Rear 7.6 kg/mm (425 lb/in)

Front 3.2 kg/mm (179 lb/in)
Rear 7.6 kg/mm (425 lb/in)

-Spring height measurement from top hat down to spring perch, measured with vehicle on level ground. I can't get a useful spring height measurement here. My own van's spring height measurement is wrong (low) due to worn out springs,



SO...

[mountainhick]

Question for anyone who can grab a quick measurement.

I need the measurement from top hat down to spring perch on good front springs, with the vehicle level.

And actually, the more the merrier. With Previas being older cars, I reckon many have tired springs, so the tallest measurement found with stock parts would be the closest most useful measurement to new spring height.

Please help me out!

[mountainhick]

It's the weekend and it'll take all of a couple minutes, please can anyone help me with this measurement?

Measurement with vehicle on the ground, front spring from top hat to spring perch. Mine is at 7" and I am sure much lower than it should be.

Thanks

[timsrv]

I'd do it for you, but my Previa (the only one I have left) is also lifted and I have rubber "H" blocks between the coils. My coils are also original and have been overloaded and abused. Good luck. Tim

[mountainhick]

Thanks for the consideration Tim,

The lift doesn't affect it. It is the same vehicle weight compressing the spring regardless. It would be different measuring "ride height" from the ground, but I am looking for spring height measurement only within the strut assembly. But with the spacer blocks and sag, yeah wouldn't be a useful case.

[mountainhick]

Please, is there anyone else that can take this measurement?

I really need the best info I can round up in order to spec out coil overs. Without it, it could be a lot of investment for mediocre or worse results.

Thanks

[mountainhick]

Update; another day at the junkyard yesterday. Struts from Mazda MPV do not have compatible bottom mounts for Previa. Too narrow gap for steering knuckle and holes spaced closer and smaller diameter.

[mountainhick]

Another update. I got my hands on Toyota Highlander front struts, 2 different versions from 2008 and 2012. Both have the correct bolt spacing and hole size on the bottom bracket, but much slimmer fit to the steering knuckle. No go.

So, I found 2" strut bodies with threaded retainers for strut inserts on a Volvo 240 and cut them off to splice to my old set of bad Previa struts. Looks like I am heading down the road of rebuilding them as coilovers.

I am finding the spring rate and shock damping issue quite challenging however. Older model years of the Toyota Rav4 used strut inserts that are about the right size with adequate travel. I checked with KYB. Previa struts have 110/40 front shock damping and the Rav4 has 105/55. That's about 5% softer rebound, but 37 % harder compression. A little stiffer ride would be good, but 37% could be a significantly more unforgiving ride.

[mountainhick]

After trying to find replacement struts to bolt in, I found nothing compatible. After trying to find inserts with correct damping, found nothing compatible in a reasonable price range. It seems Koni has some adjustables for other model cars that would have compatible range, but would add another $340 to the cost, more than double than if I use the stock struts.

So, Plan B is in motion:

-Use current struts which were just replaced 2 years and less than 12K miles ago.
-Remove old worn out coil springs, replace with coilovers
-Cut spring perches off current stock struts, but leave a small rim at the weld to support a coilover sleeve.
-After all the measuring and calculating, a 14" 200lb/in coilover spring seems best for maintaining close to oem rate, setting ride height and maintaining excellent suspension travel while allowing extra clearance for taller tires.
-Redo lift strategy, remove 2" lift spacer (Tim's version) at top mount. I think the passenger side top mount is stuffed anyway, so I am replacing the strut mounts and will fashion 1" spacers from solid material that are not welded to the top mounts, and gain 1" more lift from coilover height adjustment.

All of this will accommodate bigger wheels and tires. I plan on 28.5-29" tires. I will be going back to the 4.3 differentials to regain the torque, with a resulting 3.5-4% reduction in top highway speed, (currently optimised for about 75 mph in 5th gear at 3100rpm , that will drop to about 72 mph), but gain same percentage in low end torque. As is, acceleration is pitiful, so this is helpful. I am sure I'll need to mod the wheel well trim, and possibly the wheel wells themselves.

Here's the parts list linked to where I got them:

Allstar ALL64160 5" coilover sleeves
Allstar ALL 64180 coilover adjuster nuts
Coilover top hat for 2 1/2" ID coilover springs, 22mm bore matches stock Previa/KYB strut shaft
Hypercoil 14" 200 lb/in UHT coilover spings
KYB SM5095 Top strut mounts
shock boot/bumpers (my old bump stops are shot)

Total cost of these parts shipped: $313.63

Next is to decide on which size tire. Maybe keep the original rims and go for 235/75R15, but they are a bit wide. Could cause rubbing on the shock tube itself. Might have to go up to 16-17 rims.

[Ian R.]

Hey MountainHick,

I saw a post you made on MP with regards to climbing rigs. I thought to myself, wonder if they are on TVT. Sure enough.. Your ride sounds pretty stellar!

[timsrv]

This is awesome! Pictures?

[mountainhick]

Hey MountainHick,

I saw a post you made on MP with regards to climbing rigs. I thought to myself, wonder if they are on TVT. Sure enough.. Your ride sounds pretty stellar!

Cheers Ian, yes I am at Mountain Project

[mountainhick]

This is awesome! Pictures?

Thanks Tim,

Just ordered the parts yesterday. Pics will be coming once work starts.

[timsrv]

Cool! FYI, the picture hosting feature on the site is now FIXED!!!

[mountainhick]

That's great Tim!

So I had to add another $32 to the cost. For the upper spacers: http://www.ebay.com/itm/231632712528

[zepedrorusso]

You're awesome! Any idea to build a special shield for the oil pan ? I have been knocking it in my hard trips !

That's great Tim!

So I had to add another $32 to the cost. For the upper spacers: http://www.ebay.com/itm/231632712528

[mountainhick]

We'll see about a skid plate, I don't know.

Work has commenced. I started working the aluminium plate for the spacers. Metalwork with woodworker's tools!

Unfortunately, my bandsaw tires crapped the bed. New set is on order, going to have to wait until I get them to cut the plate to fit the mount footprints. I'll update this post once I can complete the work and have usable spacers.

For now, here's what I have been up to:


Laying out for mount:

spacer-1.jpg



Without a mill, how I do the circular cutouts... Drill first:

spacer-2.jpg



Cut out with jigsaw:

spacer-3.jpg


Oscillating drum sander to sand to line:

spacer-4.jpg



Mount fitted, I chamfered the inside edge to ease the fit. Bolt holes located and initial drilling done. I doubt I'll be able to get the same kind of press in bolts 1" longer, so I'll probably tap the aluminium so I can bolt the strut mount to the plate and the bolts will protrude through to mount into the vehicle.

spacer-5.jpg



More work, finishing the spacers:

Tapping the holes:

spacer-6.jpg



Cutting out the shapes on the bandsaw:

spacer-7.jpg



From there I filed/sanded them smooth and painted them. You'll see them in the next post with the struts...

[mountainhick]

The work on the strut and putting it all together:


Cutting off spring perch with cutting wheel on angle grinder:

strut-1.jpg

strut-2.jpg




Then I ground off most of the perch and wanted to try the fit of the sleeve, but the upper flange was too big in diameter, so I ground down the flange so the sleeve would fit over it. (Note, I kept cooling the metal with water as I worked, I didn't want any chance of a pressurized strut heating up).

strut-3.jpg

strut-4.jpg



After spending considerable time with a hand file, trying to make the remnant of the perch and it's weld provide a good seat for the sleeve, I wasn't happy with the result, and wanted a better platform for the sleeve. The solution was to use one of the pieces of aluminum I cored out from the spacer billet, and turned it on my lathe into a pair of collars.

Here's the strut with perch ground/filed down, the sleeve and the collar.

strut-5.jpg



The sleeve was a bit of a loose fit on the shock tube, so I built it up with a few layers of electrical tape to where it went on very snugly. Then I packed the gap at the top of the sleeve with RTV sealant.

Here are the parts ready to assemble (minus the dust boot/bumper). Note that the spring compressors are only on the top half of the spring. There is not enough room between the coil and the sleeve for them to fit down lower.:

strut-6.jpg




Top cap and conical washer. This washer is necessary so it bears in the inner bearing race of the upper strut mount. Without it, the spring top cap would not be able to pivot correctly when steering. This part is from Subaru, and is a standard part on pretty much all their struts since at least the 1990's. Blessedly it is a perfect fit!

strut-8.jpg



Top mount and spacer attached

strut-9.jpg



Assembled coilover strut:

coilover-1.jpg



I will be installing tomorrow. More to come on installation and setup.

[timsrv]

Much better way to do this! My method sucks compared to this. Looking forward to seeing this with monster tires on it . Tim