Getting my vintage mini truck ready for towing - Page 4 - Fiberglass RV


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Old 07-04-2013, 01:52 PM   #43
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Name: Chris
Trailer: Scamp 16
New Hampshire
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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!
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Old 07-08-2013, 11:30 PM   #44
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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.
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Old 07-09-2013, 06:55 AM   #45
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Name: george
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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.
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Old 07-09-2013, 08:11 AM   #46
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Originally Posted by chuyler1 View Post
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.
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Old 07-09-2013, 03:24 PM   #47
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Originally Posted by gmw photos View Post
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.
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Old 07-09-2013, 04:04 PM   #48
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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.
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Old 07-09-2013, 04:29 PM   #49
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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.
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Old 07-09-2013, 05:36 PM   #50
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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.
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Old 07-09-2013, 07:23 PM   #51
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... 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:
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Originally Posted by gmw photos View Post
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.

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Originally Posted by gmw photos View Post
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.
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Old 07-09-2013, 07:26 PM   #52
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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.
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Old 07-09-2013, 09:56 PM   #53
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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.
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Old 07-10-2013, 02:01 PM   #54
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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
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Old 07-10-2013, 02:47 PM   #55
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Originally Posted by gmw photos View Post
... 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)
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Old 07-10-2013, 03:25 PM   #56
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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.
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