Coil Spring Rear Suspension

[620slodat]

I am wondering about a 1995 Mitsubishi Montero LS rear suspension. I picked up the Montero for parts for my 620/720 Datsun diesel pickup build, and got to looking at the rear coil spring suspension and wondered if it could be used also (my Datsun pickup will be used mostly for transportation). From what I read coil spring suspension apparently is considered to be much better than leaf suspension. It is a three link suspension, and appears to be stock. I have spent a little bit of time measuring and thinking about the rear suspension on the Montero, and have come to the conclusion that it may be possible. I know how to stick weld but I don't do enough to keep in practice, so If I do this I will tack it in place and get a relative who was a professional welder to do the final welding.

 

The specifications for the springs are: 1992-1995, .56 -.62" wire diameter, 6.3 - 6.4" spring diameter, 15.9" free length, progressive, and 151-218 lbs/inch. If I do this it will be going into a 1982 long wheelbase frame, diesel motor and 5 speed transmission, and 1973 body extended to a king cab so it will fit me (and the standard bed on the lwb frame). I'm not real tall (almost 6'), but I like to be able to stretch out at times.

 

 The suspension up front is similar to the 620 and 720 with torsion bars. I have no experience with knowing how the Montero rode with torsions up front and coils in the rear, but I am assuming that it rode good as the Montero is considered (from what I read online) to be an upgraded vehicle. What I am needing to know is what I am needing to look at/measure to make sure that no mistakes will be made IF I decide to use that rear suspension. One of the items I am planning to use is the rear axle. Primarily because of   1) the E-brake should be real easy to hook up with stock Montero parts, no u-bolt clamps or other mickey mouse items.   2) though not important, it does have disc rear brakes.  3) the wms to wms rear dimension is close to the Datsun, 4-5" wider only. I looked at a 2000 or 2001 Isuzu Rodeo and came to the conclusion it was too wide at almost 10" wider than the Datsun.

 

Don

Edited July 6, 2020 by 620slodat

[datzenmike]

If coil were clearly better everyone would use it. Generally coils for cars and leaf for trucks but this is absolutely not carved in stone. You can do more with a leaf spring. Add or subtract leaves even re-arch them and a leaf spring positions and resists side to side movement of the axle where a coil needs links and/or a panhard bar.

 

The '84 720 spring constant is 109 to 310 lb/in.This is the lightest spring available.

 

4-5" is not close to a Datsun. 2"a side wider will move the tires outward and under the fender lip. Nothing sadder than fenders or tires messed up from contact at speed.

[620slodat]

The outside width of the tires is an area that I forgot to measure. What you did here is just exactly what I needed, and why I started this thread. I don't understand how I missed that measurement, but I did. Thank you for pointing that out. You are correct that the tires will be close to the fender, if not under it. I now need to take more detailed measurements to be exactly sure of my initial measurements.

 

As far as the spring rate is concerned, I knew that the coils were a bit on the light side compared to the Datsun leaf. But, as I remember riding In Dad's Datsun pickup it rode harsher than  what I thought my wife would like. I'm laying things out so that my wife will enjoy riding in the pickup also. I was not sure of the leaf spring rate, but the Montero had three rows of seating as an option. I'm not sure if this vehicle had the third row or not. The interior looks to me like it may have had the third row, but it is torn up enough that I am not sure about it. Anyway, this third row option (weight), and the possibility of adding air bags to the springs is why I thought about it. 

 

Fortunately for me the Montero is still drive-able, although my impression is that the motor is an oil burner.

 

Don

[canon3383]

Let me get this straight, you want to put coils on this so your wife will ride with you? First of all, its a small TRUCK, not a car. You want to take away the purpose of the truck, which is Hauling things, so you'll have a 2 door ride with a unusable box on the back? OK? I bought mine just because it rides like a Truck. It hauls trees, furniture, and anything a truck is supposed to.I have a car, if i take the wife, we just get in the car, UNLESS she wants the truck ride and we have a great time in the Truck bouncing around.

[Stinky]

Coils, IMHO, are not better than leafs.

 

Cut the pads off the axle and weld on perches and go from there.

 

If you cant do it, it will be easy to find a shop that can.

[datzenmike]

Nothing wrong with a comfortable ride. My 620 had F-150 leaf springs on all four corners if you want to talk about stiff!!! You could remove a leaf from your spring pack to reduce the rate. The short one(s) at the bottom. Problem is you may lower the ride height doing this. Truck springs only feel comfortable with 400+ pounds in the back.

[620slodat]

Canon, you don't have all the facts. I didn't give all the facts because I didn't think it was needed. The fact is that I have a Chevy K2500 that I use for all my heavy work. I use it a lot for hauling firewood, and other very heavy stuff. But, it is expensive to drive all the time.  I don't need something to haul heavy stuff. If I wanted/needed something to haul stuff I wouldn't choose a small pickup as I already have that covered.

 

The Datsun I have is one my Dad bought brand new, and until he retired he drove it up to 50 miles a day, mostly on the freeway. I am interested in the same thing he was, mileage. That is why I bought a diesel motor for it, and am in the process of putting it in the pickup. I don't need a heavy hauler, I need to honor my Dad's needs, and to use as a mileage maker.

 

What I am needing is something that rides real good (not like the American balloons of yesteryear). Something my wife will ride in, not harsh like the pickup when it was newer. My wife is dealing with fibromyalgia, which means that she feel things that most people don't even think about. That is why I am seriously considering adding things that were not even thought about when the pickup was new. And, I'm needing input from others (not criticism) as I may not be able to think of everything. Datsunmike has already proven that point with his first post.

 

Stinky, thank you for that opinion. Do you have any facts to back up what you said? I need facts and links to read stuff. Adding leaf spring perches is what I was originally planning.

 

Don

[wayno]

The 720 2wd truck is not like the trucks that came before it, even using 4wd leafs in the rear of my 520 and 521 kingcab the ride is smooth, I even notched my rear frame in both trucks because I lowered both of them, the 520 is lowered a lot, the recently lowered(3" maybe) 521 kingcab was notched because it kept hitting the frame over the rear axle because of drop blocks.

That frame/chassis you have is a 1981 or 1982, it only has a couple arched leafs, it will ride like a car more than a truck when compared to a 521 or early 620(kingpin truck), I do not know if the late 620 balljoint trucks had earlier rear leaf packs(very firm) or later leaf packs like the 720(soft), in my opinion the 2wd 720s ride like cars, but everyone has to keep in mind that my work truck that I drive a lot has a 521 leaf pack with 2 extra leafs(2&4 positions), that truck rides like rough/very firm, if empty with no trailer I prefer smooth roads.

Personally I think you will be surprised how smooth that truck is once you can drive it.

Edited July 8, 2020 by wayno

[620slodat]

Wayno, what you say is important to me because you have experience with a pickup on a diesel frame, (the frame I got from you is a 1982 according to Oregon DMV). It sounds to me like you used 4wd leafs in your diesel pickups. The pickup I have is a 1973, and as my memory tells me it rode very firm/rough. Because of what my wife is dealing with I don't want her to have to deal with that ride. Simply put, she won't ride in it very often, if at all, with the stock 1973 rear suspension in it. I want it to be comfortable enough for her that she will enjoy riding in it as I want it to become my daily driver. That is why when you say "even using 4wd leafs in the rear of my 520 and 521 kingcab the ride is smooth, I even notched my rear frame in both trucks because I lowered both of them," I will very carefully consider it.

 

I had to lift the cab 2" to get the radiator/condenser package out of a 2000 Nissan Altima in there. For this reason I'm considering eventually using a 2" drop spindle, and maybe lowering the rear end also.

 

Don

[datzenmike]

18 hours ago, 620slodat said:

  And, I'm needing input from others (not criticism) as I may not be able to think of everything. Datsunmike has already proven that point with his first post.

 

 

 

Don, did I come across as critical? I do apologize. I prefer leaf springs is all, mostly because I've worked with them and not any coils though I have had a few GMs. Your first post doesn't really mention the end result you are looking for.

 

Not sure what the L520 and L521 spring rate was but the load carrying was 1,000Kg that's 2,200 pounds !!!!!!

 

Later PL521s may have kept the earlier stiff springs and  just changed the paperwork to 1,102 pounds limit. Ask any 521 owner what's the most weight you have ever loaded on your truck and almost always it will be over 1,500 pounds. Mine was 1,700 of produce.

 

FSM...

The '73 620 spring rate maxes out at 560 lb/in.*

The '78 620 spring rate maxes out at 308 lb/in.

The '84 720 spring rate maxes out at 310 lb/in. US 2wd

.............................................................. 442 lb/in, optional US and Canadian 2wd and all 4wd

.............................................................. 649 lb/in. HD/Cab/Chassis

 

*Only used on the '73 BUT was an optional spring for Campers through '76, so that says something about the stiffness and load carrying.

 

 

[620slodat]

DM, no you didn't come across as critical. That was meant for another person. As far as the first post not mentioning an end result, my apologies. The first post was put together real quick, for me (I usually take a bit of time to write something). All I was looking for was information, both for, and against, both leafs and coils for rear suspension. I just need information about them, and if that is a link to information on this site, or another, I will definitely read it. 

 

Wayno gave me good information that 620 leaf suspension for the early years of 620 was harsher than the early 720 suspension. Good information as my experience was with a 1973 620, and it was harsh enough that I think my wife would have problems with it. What I'm really wanting is a front and rear suspension that my wife will accept as good for her, and the fibromyalgia she is dealing with. The front suspension I think is good enough, except for the restriction that the torsion bar gives for exhaust systems.

 

That spring rate information is real good as that will give me something to compare to the Montero. I'm real surprised that the 1973 max spring rate was close to double the 1982 2wd rate. I realize that was maximum, but the lighter end of the spring rate must have been close to double for the 620 over the 720. That says a lot to me. I just looked at my Dad's 620, and it was made in July of 1973. He had a 1967 pickup (I was in high school then) before the 1973, and as I remember it, they rode very similar. He usually used it for freeway driving, so I never saw it loaded very heavy, but he did haul some gravel with it. He used passenger car tires (4 ply rated), so they would show the weight before any springs did. 

 

Don

[datzenmike]

All clear. Usually changing something is to gain a clear advantage, a rare time it's just to be different.

[Stoffregen Motorsports]

First off, great idea to utilize original components to build something custom. That's a great way to save money, but also a great way to get the design right, Simply copy all the widths, heights, angles, lengths of the Montero control arms, bracket locations, etc.

 

Second, others here have mentioned it - coils vs leafs. Leaf springs are more suited to carrying loads than coil springs are. The multiple leafs act as variable rate springs, getting firmer as the suspension compresses. So if you want to use your truck as a truck, stick with the leaf springs.

 

Third, the spring rate of the original Montero coils is probably a lot firmer than you think. The Montero weighs considerably more than a 720 and is a SUV so the rear body is heavier. I bet the Montero springs are more than enough for the 720.

 

Fourth, axle width. Be specific. Is it 4" or 5" wider? Datsuns already have a problem with wider tires, so if you go 2" to 2.5" wider per side, you may not only look goofy, but have a tire clearance issue.

 

Last, fabrication. While the job may look easy on paper, you need to be exacting in your measurements when doing custom suspension work. You need to start off with a perfectly level frame. I have some custom jack stands that I built especially for this purpose. They are made with 1" Acme thread and adjust up to 24" height. I use them when doing custom frame/chassis work. You can do this with regular jack stands and shims or also on a two post lift with shims. I also use a plumb bob to mark the critical locations on the floor of the shop. Take your axle centerline and mark it on the floor, your body mount locations, the suspension pickup points, etc. Anything that is critical to building a square chassis needs to be mapped out before you get started and as new components are added. The vehicle can not move at all during this process unless you want to keep taking measurements over and over again. As far as the plan goes, there are many old sayings about plans - man plans, God laughs. The best laid plans of mice and men. Etc. So learn to be flexible in your design to make sure all the vital components end up where they need to be.

 

These pics show the stands I built and use to level everything out.

 

 

 

 

[Charlie69]

Years ago I own aI think it was a 70 that had the stock rear coil springs.  I replaced all the bushings in the rear and installed new springs and shocks all around.  The reason for the bushing replace was they were shot and the rear end in corners (remember I drive my trucks like I stole them) felt like it shifted positions under the truck.  This was worse with a load in the bed.  After all the work on the truck it was better but still felt like the rear end shifted position in the corners.  I ended up taking measurements  of the rear end and went to the wrecking yard and found a swabar off I think it was an old Cadilac.  I made brackets to install it on the rear end and this made cornering much better.

 

Had a Blazer with rear coil springs also for a short time.  It was lifted and I did not like it so I sold it.  I made a profit on that one because I did not fix any thing on it prior to sale.

[620slodat]

Some very good information there Stoffregen. Thank you!!! If I use the rear suspension I am planning to use all that the Montero had for suspension, including the sway bar. Also, needing to start with a totally level frame is good info. I spent several years installing cabinets in expensive homes (stone countertops) so I know for sure what level means. 

 

I am aware that the Montero is a lot heavier than the 720, and the Montero coils vs the 720 leafs is also good information. I have never rode in a Montero, I have rode in a diesel 720 just once so I don't remember it, and many times a 1973 620 (which was stiff). The Montero had a third row of seats as an option, but the Montero that I got didn't have the third row in it, and the second row was setting in there loose and sideways. However, the interior is torn up just enough that just by a quick look at it I am not sure if it had the third row or not, and I have not spent any time looking through the stuff in there yet. At the moment I don't know if the third row came with a heavier spring or not, and I haven't come across any information that says that a heavier spring was used.

 

I was recently able to take the rear tires off the Montero and get some accurate measurements. The rear axle is 5" wider than the 720 axle. The Montero wheels are inset deeper than most rear wheel drive vehicles, almost as much as newer front wheel drive vehicles, but I don't remember at the moment what the back set is. What I am planning is to soon put the Montero rear wheels on the 720 rear axle/frame and see what the width is, and compare that measurement to the 1973 rear axle and bed.

 

Thank you for the pictures, especially the jack stands, as I am a visual person. Your first pic looks to me like you are working on a modified Toyota FJ40 frame, and the second pic is of a Toyota FJ40 cowl and front seat area, maybe the same frame as the first pic. 

 

Charlie, thank you for the info about bushings. I am planning to replace bushings, whether for coils or leafs. Replacing the front bushings is still up in the air. It all depends on the condition they are in compared to the difficulty of replacing them. Other items will probably be changed, ball joints, tie rod ends, etc.

 

Don

[wayno]

I wish you were closer, we would take a ride in my 520 and 521 kingcab and my 1980 Datsun 720, the 520 is smooth, the 521 kingcab is slightly firmer as the back of that truck doesn't weigh a lot with that stepside box that has fiberglass fenders, the 720 rides like a car without the overload helper springs

The 1980s 720 leafs are different animals than the early Datsun trucks, the 521 has 5 arched leafs and I expect the 1973 Datsun 620 was the same, the 2wd 720 has 2 arched leafs and 2 flat overload leafs, the 4wd 720 leafs are slightly firmer but it is not really that noticeable until one loads them up, but that may be due to the 2 flat overloads they have also.

My only vehicle I have with the 521 leaf pack is the work truck and it has had 2 extra leafs in each pack, I tried using the HD/CAB/CHASSIS 720 leaf packs Mike mentioned but it would not take the weight and it felt weird, especially when towing the trailer, so I switched to my original modified 521 packs after I did the chassis conversion and I got my truck back, it felt exactly the same as before, it is what that truck needs for how I use it.

Edited July 10, 2020 by wayno

[620slodat]

I just checked the 1973 620, and it has a total of 5 leafs. The first has the eyes on it, the second and third are slightly progressively shorter and about the same thickness of the first leaf, the fourth is a little bit shorter than the third leaf but it is probably about three times the thickness of the first three, and the fifth leaf is thinner like the first three but much shorter than any of the first four. 

 

I just might take you up on the ride comparison if I ever get up your way. Riding in an early years 720 would be a clincher for me. I was just up there at the airport (twice) a week and a half ago. Our son and daughter paid for themselves and my wife to fly to the southern tip of Texas for a wedding. Otherwise I don't get up there very often, but if I do get up close then I will contact you and see if you have the time when I plan to be up there.

 

Don

[wayno]

Just contact me if your coming to the area, we can likely figure something out, or maybe someone else you know that lives closer to you has a 2wd  Datsun/Nissan 720 that you can hitch a ride in, all the 2wd trucks ride like cars unless they have been messed with, well except the heavy duty dually cab/chassis trucks.

Edited July 11, 2020 by wayno

[canon3383]

I apologize you didn't get my humor. I have seen many people around here destroy great little trucks, I hope you get great advice as the people on this site are great, especially datzenmike

wayno and charlie69, I hope your wife enjoys it when you are done. 🙂

[620slodat]

As far as advice is concerned, I did get great advice. Wayno, datzenmike, charlie69, Stoffregen, and even you, all gave me sound advice. I probably didn't initially give all that I was looking for. But, since I already have a heavy hauler, and many parts of the 620 will be from my Dad's pickup, I am wanting something that will haul only lighter stuff. And, my experience is only with the early 620. What I am looking for is a mileage maker that might haul a few tools on rare occasions, but mostly a mileage maker that will allow me to have a DD that I can afford to drive, and take my wife when she wants to go.

 

One thing I really want to do is take up wayno's offer and know first hand what a 720 longbed diesel rides like. He lives probably 80 miles away, which is not very far for many people, but on my income it will take a bit of planning to do more than one thing per trip. If his pickup rides good enough with leaf spring suspension that I think my wife can take the ride it will save me a lot of work. But, I am ready to use the coils if need be. I already have a plan of attack for the leafs if needed. I just need an actual leaf spring vehicle comparison to see what it should ride like.

 

Don

[Charlie69]

Swap to early 720 2wd leaf springs they are a softer ride than the early 620.  Wayno might have a pair.

Edited July 22, 2020 by Charlie69

[wayno]

He already has an early diesel chassis with early leaf springs Charlie, he just needs a ride in an early 720 to know how soft they are, in my opinion they ride like a car.

 

55 minutes ago, Charlie69 said:

Swap to early 720 2wd leaf springs they are a softer ride than the early 620.  Wayno might have a pair.

 

[powderfinger]

I drive an 85 720 to work everyday, 55 mile round trip, and I think the suspension is too soft so it's probably exactly what you are looking for. I will say however, that I have never ridden in any older model Datsun trucks so I can't compare the ride quality/smoothnesss.

[620slodat]

The ride in my Dad's 1973 620, and his 1967 Datsun pickup, was a bit rough as I remember. When he got the 1967 pickup it was broken in with a trip to Crater Lake, and this was with a home made camper shell on it. Home made is almost always heavier than what can be purchased commercially.

 

Wayno, the 1994 Chevy 3/4 ton K2500 that I have is one of the better riding 3/4 ton pickups that I have ever had. My wife will ride in it occasionally, but she does complain about how it rides. I am hoping that before the winter rains start I will be able to take your offer. I just need something else to make the trip up there pay for itself.

 

Don

[Stoffregen Motorsports]

A '90s Chevy K2500 does have a nice ride.