Getting my vintage mini truck ready for towing

[chuyler1]

We made it to our first camp site. I think for the next trip I may install a WD hitch just to get some more weight on the front of the truck. Now that it is fully loaded the front is too high for my comfort level. I didn't weigh the tongue but since we were only driving an hour I did fill up the rear water tank before departing. Acceleration was about what I expected. Braking was good. 60 mph was about as fast as I felt comfortable going. We weren't holding up traffic or anything until we reached the campground road where I took it a little slower than I normally would.

The brake controller has a nice feature where it holds the brakes momentarily after I release them. This helps for hill starts but it means I need to slip the clutch more than usual during any start because I'm working against the brakes. First couple times I thought I was never going to get the truck moving...but after a moment it released and the truck had plenty of power to start.

Oh and did I mention is was 90 degrees and 100% humidity? My wife overheated in the truck (no a/c) but the cooling system did not.

[LeonardS]

Nice photo. Looks like a happy dog, too!

So, just wondering, are you set up in a tent spot?

[chuyler1]

It's a "standard" spot. The image on reserveamerica.com was an RV instead of a tent. I could have parked closer to the road but I was able to back it up to the rear of the site. Could probably fit two more campers on this site. This park has no hookups so we're just using the campground showers and bathrooms. Fantastic fan was fantastic last night!

[chuyler1]

One more update...



The ride home was fine. With less traffic on the road I felt fine at 65 mph but whenever I noticed my speed creep up I brought it back down to 60 just to be safe. Getting lots of looks and thumbs up on the road. When we got home I grabbed the bathroom scale and placed it on a cinder block about the same height as the hitch. 280 lbs at the tongue with everything still packed, 6 gal of water left, and full propane tanks. After taking everything out of the front cabinets and bathroom and placing it on the back bed I got it down to 205 lbs. Scamp claims the trailer is 1700 lbs with a 165 lb tongue but that's unloaded with no options (I can only assume). Judging from other forum posts my version is between 2400-2500lbs loaded so I should shoot for 240-250. I think I can manage that by putting some stuff back where it belongs. I also spent some time last night relocating the air shock valve so I could easily reach it. That should allow me to fine tune the ride height a little easier.

However I may still need a WD hitch to get some weight on the front of the truck. Not sure if I mentioned before but I have rather stiff/tall springs up front from a later model Ford Courier and they only leave about 1/2" between the top control arm bump stop. When the trailer mounts up, I basically don't have any upward travel. I may need to take the springs out again and cut off a coil, but I don't want to do that if I don't have to. They were a nightmare to install the first time. I'll have to research how most truck lift-kits work to see if there are some tricks I can pull to keep my ride height and improve the handling.

[gmw photos]

Chris,
Nice looking setup for sure. I agree with your assessment that a WD hitch is likely the proper course of action. With 250 to 280 pounds of tongue weight, you are likely removing close to 200 pounds from the steer axle. On a vehicle with a lightweight engine especially, this could certainly make for the potential for understeer, especially on wet pavement. WD would also get the front end back down into the spring travel.
Although I am not generally a fan of the Andersen, this "might" be a good application for it.
More likely I think I would look at a EZ lift or one of the other simple spring bar hitches.
Cool setup. Love the trucks from that era. While out driving yesterday, I saw a very clean example of my old '92 Toyota truck. Kinda brought back memories. Those trucks from that era made good tow vehicles for small trailers, for sure.

[MC1]

Originally Posted by chuyler1

One more update...

With less traffic on the road I felt fine at 65 mph but whenever I noticed my speed creep up I brought it back down to 60 just to be safe. Getting lots of looks and thumbs up on the road.

Yes it really does look great and very unique. Can appreciate all the work you have put into the project.

Although we prefer and use quality P rated tires front to back we too find our speed can creep up but always bring it back to the 60 to be safe.

When my dad had his RV dealership back in the 60's most of the trailers were 13 to 17' in length. Almost all went off the lot with a WDH. They work and once you try one you understand the value. It just makes the combination drive and feel better.

[Brian B-P]

Originally Posted by gmw photos

With 250 to 280 pounds of tongue weight, you are likely removing close to 200 pounds from the steer axle.

For 280 pounds of tongue weight to pry 200 pounds off of the front axle, the distance from ball to rear axle would need to be 200/280 or 71% of the wheelbase... it's a teeter-totter thing.

If, for instance, the wheelbase is 104.3" (what I found for a 1974 Courier with 6' box), the ball would need to be 74" behind the rear axle to transfer that much load off the front axle... it looks like four feet, not six, so 115 to 130 pounds transferred (due to 250 to 280 lb on the hitch) is more likely. That's well under 10% of the front axle load.

[chuyler1]

I'd have to dust off some of my old physics to number crunch and confirm that.

This isn't my truck but it's a good shot of the front suspension.


You can see in this photo that with no load, the top bump stop directly under the upper control arm rests on a platform. When my truck sits under its own wait, the stiffness and height of the later model springs cause the bump stops to rest only 1/2" from this platform. They provide a nice lift. It corners great and handles most road bumps fine. I have to go slow over speed bumps or I can feel it smack the bump stops when the truck rebounds. With the trailer mounted (no WD hitch) I glanced underneath and the bump stops touch the platform. This means if the trailer were to dip the tongue it could lift the front wheels off the ground instead of the suspension catching some of that action. I didn't feel any of that while driving (and I was only performing a visual inspection without anyone in the truck (that's about 320 lbs not in the cab between my wife and I). I'm a little nervous that under hard braking the trailer could push down on the back and lift the front of the truck up high enough to cause the front tires to lose grip.

I'm wondering if a) I could put smaller bump stops in or take them out b) cut the platform off, c) remove the springs and cut a coil off, d) install a WD hitch to add more weight to the front and pull it down away from the upper bump stops.

Keep in mind this is my second set of springs. I cut the first set and it made them too soft so I'd have cut less and hope it works. It takes several hours to pull the springs because they don't make compressors that will fit the small space. It's a painstaking job of jacking up the control arm and moving it into place. So option c is something I'd rather not do.

[MC1]

I understand. You have very limited suspension travel when the front of the truck rises for whatever reason. A WDH would tend to firm up the connection which would prevent excessive hinging at the connection point.

No sure what kind of issues you would run into by taking out the bump stop.

We also know that considerable damage can occur if the suspension bottoms out (on the up or down) so you need to be care full about that issue.

[gmw photos]

And Brian may be right on the amount of weight removed from the front axle. I reckon the most accurate was to find out would be to load up to go camping, then stop at the CAT scale on the way.
It is at least somewhat troubling to hear the suspension is near topped out when loaded and hitched, and a WD would help in this issue.

I'd be interested to hear what the weight distribution percentages are for this truck empty compared to the same truck with a piston engine.

[Brian B-P]

Originally Posted by chuyler1

... this is my second set of springs. I cut the first set and it made them too soft so I'd have cut less and hope it works.

Cutting a spring shorter makes it stiffer, not softer, but I think I understand what Chris is saying.

What seems to be going on is that the long springs are highly pre-loaded so they don't compress further until there's a high force on them, and that causes the problem of riding against the rebound bumpstop. Cutting them shorter reduces the preload (they are not so highly compressed during installation), but stiffens the spring. If they are cut too short they may sit too low under load (which you see as "soft"), but the spring rate (change of length with force) will be higher (a "stiffer" spring) than before the cutting.

Just to complicate things a bit more, those control arms might be at a significant angle when near the upper stop. Bringing the ride height down might change the geometry and make the same stiffness of spring effectively softer (for the techies: the wheel rate is not a constant fraction of the wheel rate).

I realize that this is not easy to resolve, but it seems to me that if a load reduction of less than 10% of the truck's empty load takes the suspension out of its properly operating range, it would be advisable to fix it.

Regarding the amount of weight removed from the front axle:

Originally Posted by gmw photos

I reckon the most accurate was to find out would be to load up to go camping, then stop at the CAT scale on the way.

I agree. The calculation provides decently accurate numbers for the change in axle loads, and the scale confirms those numbers, plus provides the total load on the axle. Of course, the truck scale need not be a CAT Scale.

Originally Posted by gmw photos

I'd be interested to hear what the weight distribution percentages are for this truck empty compared to the same truck with a piston engine.

I would, too, but I doubt there's a big difference. The Mazda/Wankel rotary is very compact, and decently short, but not very light... it has a lot of cast iron in it, especially compared to the small four-cylinder engines which otherwise occupy that space.

[Brian B-P]

Wild idea: it may seem overly complex and out of place on a simple classic truck, but the front coils could be completely replaced by air springs, and adjusted to suit the load.

[chuyler1]

That is a wild idea Brian. I've seen a few slammed B1600-B2000 pickups that obviously had airbags but couldn't find photos of the suspension and what was done.

As for spring cutting, I've never quite understood it. Here's what I did in detail so maybe you can explain it...

The springs I found that fit are MOOG CC250. Which have a rate of 412 and a load of 786. Free height is 13.44" and installed height is 11.50". The only info I have on the OEM REPU springs is that they are 11 7/8" tall with a spring rate of 512 lbs.

When I couldn't get the first set in, I cut them down from 13.44" to 12". This produced an acceptable ride height but very soft front end that would dip around corners and there wasn't enough clearance to turn the wheel full lock without rubbing the fenders. I thought like you that cutting the spring would increase the rate and make it closer to the OEM rate but that's not how it felt.

I bought another set (they were only about $80 so it wasn't a huge investment) and spent an entire day getting them in. The front was lifted about 2" higher and the truck corners flat and is much more enjoyable to drive.

A few other stats can be grabbed from the Road and Track review. Curb weight of 2800 lbs and a weight ratio of 53/47 puts about 1500 lbs on the front axle. Their test weight was 3200 lbs which would be 1700 lbs up front.

So I could pull a goldielocks and maybe cut the springs down to 12.75" and see how the feel...or I can figure out something else. I'm thinking the WD hitch will pull the front down to a safe height.

[gmw photos]

Brian, Chris,
I think I may want to disagree with the idea that cutting a spring changes it spring rate. I believe that is incorrect. Cutting it makes it shorter, but the remaining coils are the same rate, and therfore require the same force to compress them a given distance.

EDIT.....CORRECTION: I mis-spoke. You are correct, the number of free coils is part of what determines rate. I found a good reference here:

http://www.bluecoilspring.com/rate.htm

[Brian B-P]

Originally Posted by gmw photos

... the number of free coils is part of what determines rate. I found a good reference here:

Suspension Spring Specialist, Inc.

I started a reply with an explanation before George's update, and looked for a good web reference... and I was disappointed to find that a good ready-to -use explanation is not easily found. It's not surprising that so many people misunderstand this subject.

(My follow-up to the detailed spring info from Chris is in progress)

[chuyler1]

Everything I've ever read says the rate increases if you cut it. That should be fine for me since they are rated at 417 and I should be shooting for 512. Perhaps the stiffness I feel right now is really due to the proximity of the upper bump stops which prevents excessive body roll. I'm really dreading this but I think I need to pull them out and cut 1/2" at a time until I find a happy medium between ride height and suspension travel. I think the WD hitch will help...but it's just a bandaid.

[MC1]

Originally Posted by chuyler1

Everything I've ever read says the rate increases if you cut it. I think the WD hitch will help...but it's just a bandaid.

I too have cut coils to lower a vehicle. It did firm up the ride which I wanted. An AMC Pacer with cut Olds coils.......
http://img.photobucket.com/albums/v2...05/pacer11.jpg

I don't think I would call the WDH a bandaid. It really is an upgrade to your combination. It is the way I would go first. Then see where you are at.

[Brian B-P]

Originally Posted by chuyler1

The springs I found that fit are MOOG CC250. Which have a rate of 412 and a load of 786. Free height is 13.44" and installed height is 11.50". The only info I have on the OEM REPU springs is that they are 11 7/8" tall with a spring rate of 512 lbs.

Excellent info, Chris.

First, for those not familiar with springs...

• The rate of 412 will be in pounds per inch, so each 412 pounds of load causes an inch of additional compression in length.
• The free length/height is with no force on them.
• The installed height is the length when carrying the designed load (the truck, sitting empty and stationary).
• Compressing a 412 lb/in spring from the free height of 13.44" to the installed height of 11.50" (1.94 inches difference) should take 799 pounds... but the "load" value is the force at the installed height, and is slightly lower (786 lb) - explanation to follow. The total load for two springs as installed (1572 lb) should be substantially more than the empty weight on the pickup's front axle, because the suspension arms are levers and the spring location is only partway out them.

Originally Posted by chuyler1

When I couldn't get the first set in, I cut them down from 13.44" to 12". This produced an acceptable ride height but very soft front end that would dip around corners and there wasn't enough clearance to turn the wheel full lock without rubbing the fenders. I thought like you that cutting the spring would increase the rate and make it closer to the OEM rate but that's not how it felt.

If the Moog springs were constant-rate, then cutting one down from the original free length of 13.44" to 12" would make it 1.12 times as stiff (12% stiffer, 11% shorter). That's 461 lb/in, still softer than the stock 512 lb/in spring. So cutting did make them stiffer, but apparently not enough.

The complication is that the Moog springs are not constant-rate - they're variable-rate. This is also called "rising rate" because as the spring compresses the more closely spaced turns at one end close up solid so it is as if they are no longer spring, but just a rigid spacer, leaving a shorter effective spring and thus a higher rate (stiffer spring). If the wider-spaced end was cut off, 11% of the length would be less than 11% of the spring. If the photo on the linked page is correct (it is actual part, not just a typical example) it has 6.5 free turns of coil, and cutting one off has the same effect on the starting spring rate whether it comes from the wider-spaced end or the tighter-spaced end... one turn would make it 18% stiffer than stock (487 lb/in). Also, the quoted rate is probably an average, so the actual rate at full length is lower (see the load value note above), and at the installed height the first coil might already be closing up.

The Moog springs were probably good before cutting, because they are intended for use at higher loads, and in that case they would be compressed enough to be in their stiffer range... they are probably supposed to carry a heavier load at stock height, not a stock load at raised height... or a reduced load at raised height. Of course, Moog doesn't list them for the REPU at all - they're for the Courier and other Mazdas, so they fit the suspension but maybe are not appropriate for the loading.

Also, those springs are square on the low-rate end and the spec says tangential on the other end (square means the last turn is closed up so that it meets the next turn - hard to see in the photo). Some coils have ends ground flat so they work on flat mounts, but these are the more typical version that needs a seat shaped to hold the coil end. If the square end is just cut off it becomes tangential, and some force will be required to collapse that first turn down to match what the factory-prepared end always looks like.

The way to change height without changing the rate of the springs is with spacers... but they take up space and thus may limit compression travel. Would the stock spring fit with a spacer, or would it close up entire and block further movement before it should?

Originally Posted by chuyler1

I'm thinking the WD hitch will pull the front down to a safe height.

WD would work, but it just seems like a lot of hardware and operational hassle to fix a problem with wouldn't even exist with the front suspension at its stock height.

Back to the fundamental nature of the situation...
The longer springs are in there to raise the ride height moderately from stock. Doing this solely by a spring change - any kind of spring change - means moving the normal ride point higher in the same range of travel, and that means giving up droop travel - that's a problematic combination with reduced front axle load, even though the load is still above that of an empty truck.

The solution for raised trucks is to not just extend the spring, but relocate the suspension mounting points downward - or from the other perspective, lifting the truck off of the suspension. I doubt that's worthwhile in this case. The slickest systems lower the bottom control arm, leave the top control arm where it was, and connect them with a longer spindle carrier;however, there is not going to be an extended spindle carrier for a REPU... or anything from Mazda, or anything from 1975.

Next not-as-wild idea: use the stock springs, add cheap air bags (Airlift 1000 or Firestone Coil-Rite) inside them, and pump them up to add just an inch or so of ride height. These bags are not intended for lifting, but presumably by staying within the stock suspension travel range they would be acceptable. They can be let down (to low but not zero pressure) to correct ride height when towing without WD (or for the original "low rider" attitude). Firestone doesn't list applications this old and obscure, so a suitable match would need to be found based on spring inner diameter and length.

One last techie note: the solution in oval-track "stock" cars to adjusting coil-spring rear suspension is to put the top mount on a screw jack, and turn to desired height. This doesn't change the rate, but does change the height for a given load... it's like a quickly adjustable spacer. I don't think I would try to fit one those into that spring mount area, especially with the droop stop for the upper arm.

[Brian B-P]

Originally Posted by MC1

An AMC Pacer with cut Olds coils.......
http://img.photobucket.com/albums/v2...05/pacer11.jpg

Wow - a chopped Pacer! It doesn't look chopped, it looks like it was designed to be that low.

Back to the REPU as trailer tug...

[chuyler1]

Awesome info Brian.

Unfortunately I don't have the stock springs and I can't seem to find anyone willing to sell them to me. The truck came with a set of coilovers that a guy on the mazdarepu forum sells. Even at their highest height they provide a 2" drop from stock. Here they are next to the MOOG springs (before I cut the MOOGs)...



You are correct about them being progressive instead of linear. They also don't have the tangental top coil like they are supposed to.

There was an intermediate step I took after cutting but before purchasing a new set of coils. I installed a spring rubber. Although it claimed to offer up to 2" of height, it only lifted the truck 1/2" more than it was with the cut springs. I wasn't able to install it near the bottom where the coils are closer. I could only get it in the top where the springs don't really compress that much. The ride got a little firmer but I was still rubbing the fenders when I turned.



So it comes back to my only real option being cutting the spring...but not as much as I did before. The rate won't be right...but I'm not sure what other options I have. Maybe if there was a business that could make affordable springs to spec...and I knew exactly what specs I wanted.