Suspension Seat modifications.

[Hilife]

I have a hzj73 with suspension seats. My understanding these are good to around 80kg.

Can these be modified to increase the capacity? Has anyone tried replacing the cylinder or springs with something a little stiffer?

 

[Sundowner]

I have a hzj73 with suspension seats.

Me too! So, congrats on your good taste.

My understanding these are good to around 80kg.

Mine are pretty stiff at 80K, even though that should be a pretty balanced setting for me. A lot of that system's performance is going to depend on how much cyclic usage the springs and shocks have seen in your particular rig, and whether or not they're fatigued.

Can these be modified to increase the capacity?

Sure: just add resistance.

Has anyone tried replacing the cylinder or springs with something a little stiffer?

I haven't, but that something like that would be the method that I would use...but "something a little stiffer" would be an OEM part or known-good-takeoff. If you want custom stuff of any sort, it would be good to know the values of the stock parts in new condition before you look for replacements.

 

[LDowney]

Based on my experience with the suspension seats in my BJ70, they have significantly better performance than a limitation of 176 lbsf (vrs 80 kgm).

As Sundowner identified, ride comfort/performance can be complicated. For example; when I first got my BJ70, the springs were flat so the ride was rigid except for what I realized from my suspension seats. After replacing the leaf springs, the combination of a good leaf spring suspension and suspension seats provides me with a very comfortable ride ... on- and off-road. And it does so even with a fat boy like me at the wheel.

If you are realizing an uncomfortable ride in your 73, reviewing your entire Cruiser might be helpful in identifying what actions to take.
Good luck.

 

[Hilife]

Thanks for the feedback.

I guess I should have led with I am 6’7” and pushing over 300lbs. My first thought was I am well past any safety factor on the suspension seats. So I bottom my seat out immediately. I was hoping to get something to soften the ride a bit.

I didn’t think a ton about the suspension. I have about 145k miles and the suspension looks ok, but perhaps I should do a deeper dive. The truck has a decent size lift that was on it when it was imported so I am assuming that makes for a rougher ride.

how would I inspect the leaf springs. I don’t see any type of sagging or anything I would expect to see in a coiled suspension. This is the first truck I have had with leafs.

 

[FJ73Texas]

Better suspension and locking the suspension seats does it for me but then I am not very happy with the suspension kit I have on the 77 now. I liked the tough dog set up that trail tailor used to offer and had that on the FJ73 but he stopped selling tough dog years back.

 

[Sundowner]

I guess I should have led with I am 6’7” and pushing over 300lbs.

I mean absolutely no offense by this, but I'm not even sure how you fit in the driver's seat comfortably. Two people that I know whom are pushing your size basically don't ride anywhere with me because it's so tight in the cockpit; I'm only 5'-10" and I push the seat almost all the way back on the factory sliders.

My first thought was I am well past any safety factor on the suspension seats. So I bottom my seat out immediately. I was hoping to get something to soften the ride a bit.

Safety factor: no. Those seats are tested to FAR higher forces than you can generate during normal driving. Even back in the day with lower crash-test standards, they were put through the wringer; you're not making them unsafe... you're just overtaxing the spring and shock because you're a larger hominid, and those are two different issues. That being said...

I didn’t think a ton about the suspension. I have about 145k miles and the suspension looks ok, but perhaps I should do a deeper dive. The truck has a decent size lift that was on it when it was imported so I am assuming that makes for a rougher ride.

Most of the ride quality issues I've ever faced have been due to stiff springs and overinflated tires; I'd check those first.

how would I inspect the leaf springs. I don’t see any type of sagging or anything I would expect to see in a coiled suspension. This is the first truck I have had with leafs.

You'll have to measure them...and that means pulling them loose, inspecting them, measuring the free arch (look that up) and the overall length, checking how much force it takes to flex them a given amount, and then comparing all of that data to known measurements when new...and that's where it all gets difficult. You have to get the as-new data, or you're working in the dark in terms of whether or not the suspension is fatigued, sagging, etc.

That being said: usually, when there's a question of roughness in a suspension, it's because the springs are just too stiff for the normal load, and they're not moving correctly. Either that, or there's a physical problem with the suspension: seized bushings, over-tightened shackle bolts, etc. Might be good to check those easy things - and the tire pressure - before you start pulling leaves.

 

[Guyute]

Better suspension and locking the suspension seats does it for me but then I am not very happy with the suspension kit I have on the 77 now. I liked the tough dog set up that trail tailor used to offer and had that on the FJ73 but he stopped selling tough dog years back.

I resemble this remark. 6'3" and over 200#. Locked them seats and installed Dobinson suspension. Helped. You mention importing and a tall lift... Are the shackles comically long on your 73? Both my imported JDM rigs had crazy extendo shackles and they don't help any with ride quality.

B

 

[Hilife]

Thanks for all the info.

As for fit. I have sat in, driven and seen exactly one 70 series. And I bought it. So I have limited comparison.

A buddy has a fj43, and I couldn’t fit in that all.
I originally was looking for a 60series and I could drive that, albeit tight. I had an 80 before this one and I could fit fine but not a ton of extra room. The 100 I have now and this 70 I have no problem fitting. I also have a pre Tacoma pick up and fit in that with no issue and that is a tiny truck. I am all torso. So that helps.


I do not have factory seats. I replaced the drive side seat that came from Japan ( it was a sea marine boat seat) with a seat out of an old wrangler and biased it back a little. Temporary solution until I ungraded to new seats. There is no room in the back seat but I have plenty of leg room.

my suspension does have long very long shackles. Tire pressure is fine. Assuming the leafs are very firm creating the rough ride. I am unclear if the ride is rougher then normal or is what should be expected as again, I have riden in or driven one 70 series. Feels rough, but maybe I just need to toughen up.

As for safety factor, what I meant was the safety factor n the design. So if they design the seat to work at 80kg, it will probably work to 100kg. Me pushing well over that, I think I would bury out a brand new suspension seat.

Why are you guys locking your seat? Doesn’t a locked seat offer the same ride quality I get from bottoming out the suspension seat?

( coincidentally I tried locked the seat tonight and found that with the seat all the way up my head occasionally bounces off the front top when going over speed bumps…….

 

[FJ73Texas]

I resemble this remark. 6'3" and over 200#. Locked them seats and installed Dobinson suspension. Helped. You mention importing and a tall lift... Are the shackles comically long on your 73? Both my imported JDM rigs had crazy extendo shackles and they don't help any with ride quality.

B

It was just a 2" inch lift but in reality it felt maybe a little less than that. Maybe I need to drop it back down to OEM height? The suspension was original prior to the OME lift kit install so no crazy JDM lift like I have seen on other rigs.

 

[JuanJ]

Hello,

70 Series suspension seats' weight range goes up to 100 kg or 220 lb. I think they can handle 120 kg or 265 lb. Check the adjustment crank: it has a scale to adjust the user's weight.

The suspension mechanism's parts are not user-serviceable, at least not with Toyota parts. However, it is possible to replace the shock absorber and the springs. The shock absorber is the same size as the ones used in suspension seats for big rigs such as Mack or Kenworth.

You can check suppliers for these big rig suspension seats and look for parts there. I remember reading that a 'Mud user repaired his suspension seats using these supplies.

Regarding your leaf spring suspension, you can measure the clearance between the front and rear frame rails and the ground. Measure the clearance 2 in. from each bumper. The values are below:

1. Front: 471 mm to 499 mm or 18 1/2 in. to 19 5/8 in.
2. Rear: 473 mm to 501 mm or 18 5/8 in. to 19 3/4 in.

Add 2 in. or 50 mm for a typical suspension lift.

If your measured values are below, your leaf springs are sagged and need replacement. If your values are above, you have a suspension lift.

Hope this helps.





Juan








Juan

 

[Sundowner]

If your measured values are below, your leaf springs are sagged and need replacement. If your values are above, you have a suspension lift.

What tire diameter/pressure/etc. does the equation assume? There is quite a bit of room for variance, depending on those specifics. Same goes for fuel and other things; full tank or empty? Winch, no winch, factory bumper, aftermarket stuff?

I'm not trying to discredit the method, but a frame-to-ground measurement depends on a lot more than the spring arch. On a fresh, bone-stock rig it will have some validity, but it gets more difficult with every variance from that factory-fresh ideal.

 

[LDowney]

... However, it is possible to replace the shock absorber and the springs. The shock absorber is the same size as the ones used in suspension seats for big rigs such as Mack or Kenworth.

You can check suppliers for these big rig suspension seats and look for parts there. I remember reading that a 'Mud user repaired his suspension seats using these supplies.

...

I researched that a couple of years back (I want to use my suspension seats for many years and it is likely that the shocks will merit replacement but Toyota does not support spares) and could not find a match. I approached it via the shock absorber manufacturers databases that supply the seat manufacturers. The motion/stroke of the semi seats was significantly longer than what our Toyotas use. To your point, maybe restarting my research by approaching the seat manufacturers directly yield different results.

Thanks for the inspiration.

 

[Hilife]

Thanks for the feedback,

I def have a suspension lift. I believe a rather large one.

@LDowney - if you make any progress on your research do you mind reaching out to me. I will do the same to you if I figure anything out.

I will pull my seat this weekend and see if I can find the manufacturers part number for the cylinder.

 

[Sundowner]

I will pull my seat this weekend and see if I can find the manufacturers part number for the cylinder.

Should be in the FSM, or on an online diagram.

 

[JuanJ]

What tire diameter/pressure/etc. does the equation assume? There is quite a bit of room for variance, depending on those specifics. Same goes for fuel and other things; full tank or empty? Winch, no winch, factory bumper, aftermarket stuff?

I'm not trying to discredit the method, but a frame-to-ground measurement depends on a lot more than the spring arch. On a fresh, bone-stock rig it will have some validity, but it gets more difficult with every variance from that factory-fresh ideal.

Hello,

Procedure and data are from the FSM.

The measuring points are in the illustration below.

The range I posted is due to tire size. The list of tire sizes and corresponding clearances is below.

There is no mention of accessories such as a winch, though.

On a personal note, this measurement guide helped me with suspension maintenance in my 73 Series last year. By the way, I run 31 x 10.5 x 15 tires on it, with a 2 in. suspension lift.

My clearance is 20 3/4 in. or 527 mm in the front and 21 in. or 533 mm in the rear. Substracting 2 in., my values are close to the specification. My truck has a stock bumper and does not have a winch.







Juan

 

[JuanJ]

Should be in the FSM, or on an online diagram.

Hello,

There is no part number, at least none that I could find. I may be wrong on this. Perhaps it is worth a look in, say, Tokico or Koni's catalog.

The parts catalog lists the suspension mechanism as a whole, with no user serviceable parts inside.





Juan

 

[Sundowner]

There is no part number, at least none that I could find. I may be wrong on this. Perhaps it is worth a look in, say, Tokico or Koni's catalog.

Or pull and measure the shock.

The parts catalog lists the suspension mechanism as a whole, with no user serviceable parts inside.

Ugh, that makes it a pain. They have part numbers for single washers, but not an entire shock...? Of course they don't.

Also, thanks for posting the chart: that does help calculate the offsets. Personally, I'd still go by free arch of the spring and eliminate all other variables, but that definitely takes more work.