1986 R686ST value

[Bjt]

I’m thinking of purchasing a 1986 R686ST from a private owner and know very little about a Mack or any other truck really. What is known- previously a tractor for a small trucking company but a 14’ dump bed has been installed,  cab and  brown interior in really good condition with no visible rust, it’s has a/c controls but not sure if works, the odometer says like 100,000 but it’s probably like 1.1 mil, hour meter 1900, tires is old but no dry rot, 10speed tranny, with Jacob brake, owner says it’s a 350econodyne engine and I wouldn’t know the difference lol. The bad is it has been setting for 12 years but started occasionally, i moved it  up  and down the driveway, brakes released and went into and out of fwd and rev smoothly. Appearance is good it could use a paint job though. The price is 12,000 firm and would like advice if it’s a ok deal or I need to run. Thanks. 

[yarnall]

Seems pricey to me for a truck that needs paint and not being able to confirm the milage.  What are you looking for?   Do you want a dump truck?  Will i be a hobby truck or a work truck?  Where are you located?  There are a lot of R models for sale.  Mike. 

[Bjt]

Looking for a cab n chassis to put log bed/bunks on not really a dump. Will only use 20-25 times a year and I’m located in Kentucky. I’ve looked at some r models and what made this one stand out to me was the good condition of the interior and lack of rust in the cab the owner says it’s a galvanized cab. Thanks 

[hatcity]

• What kind of shape is the frame? double rail? rust?
  if you are planning to do some logging, the frame will take a beating, so be sure that is all good

[Bjt]

Single rail frame with no rust but I think it’s been painted in the past. I forgot to mention that I think it’s an air ride cab because they’re 2 small air bags and 2 shocks at the rear of the cab. It also has a air dryer. Any ideas what type of suspension this is? It has 3 leafs and 2 shocks per side. 

[terry]

not a good suspension for heavy hauling, that is only a 34,000 bogie, and can break leaves real regular with any heavy weight.    terry

[j hancock]

Great specs to be put back as a tractor.

[Bjt]

Hancock. A tractor and trailer would be very nice but the terrain here at my place would make it very difficult,  which is why a small truck will be more convenient. Do u think the suspension would be ok as long as the load is at or below the 34,000lbs? Any Ideas on engine size? Oh yeah if it makes a difference the  truck has only hauled 4 loads of dirt with the dump bed and that was the only times it was off the highway. 

[mowerman]

Nice looking ride ... bob

[mowerman]

It doesn’t look beat to death I would go for it I think price is fair and it’s probably a 350... great strong engine I used to have one.. good luck... bob

[Quickfarms]

My 688 is a 350 hp, I thought the 686 was 300 hp

[Red Horse]

For sure as Terry said-Not a rear end/suspension you would use in any kind of off road application.  Will it work? I'm sure it would as long as you remember that you are asking it to do something it was not built to do- and load and drive accordingly when you are in the woods.

Now I'm sure there are plenty of talented posters here who would have no trouble taking that truck at the right price and getting a heavy tandem cut off and converting it.  Next question is, if it was built as  a lighter weight tractor, will the frame hold up to the task?   Today single channel frames with a deep section modulus are preferred to the double channel frames of the old days.  But if its a single channel, again  probably built for highway serviced.

[Vladislav]

I agree with what was said above. Too probably basic 1/4 thick R-600 single rail frame and rear suspension of the same ballpark of capacity used. A good (and light) combo for on-highway use. If plan to offroad with sufficient loads it seems better to look either for a RD or DM which would have basically heavier chassis than many of R-models.

[j hancock]

18 hours ago, Bjt said:

Any Ideas on engine size? Oh yeah if it makes a difference the  truck has only hauled 4 loads of dirt with the dump bed and that was the only times it was off the highway. 

I think it is probably a 300 engine.  To be sure, check the stamped engine number off of the top of the timing gear casting in front of the injection pump.  For example, E6300 or EM6300L or ???

Be aware of what you have for a combo and use accordingly.  If you were going into the dump truck business, it isn't the correct truck.  If you are doing projects at your home or farm, could last a long time. 

[hicrop10]

I have a 1979 r model and I m the original owner.My dad brought 20 of them along with 10 u models,15 dm600 triaxles,all at once.The specs of the r models were 169 WBA’s,endt676-300 series 285 hp,trxl107 low hold 5 speed,12,000 front,38,000 rear,4.17 rear ratio.When it was new it pulled a dump trailer and it was never loaded less then 80,000-90,000,except on Saturday when it was loaded at 90,000-100,000 or more.The point I am making is that we never had a problem with these trucks,carrying that weight.I think that it was in the trans with the low hold.We also used them to pull the lowboys.The most we would load them with were cat d8’s.

[Bjt]

Thanks everyone for the comments. I'll think a few days on it make a decision and post what was decided. Thx again

[Red Horse]

2 hours ago, hicrop10 said:

I have a 1979 r model and I m the original owner.My dad brought 20 of them along with 10 u models,15 dm600 triaxles,all at once.The specs of the r models were 169 WBA’s,endt676-300 series 285 hp,trxl107 low hold 5 speed,12,000 front,38,000 rear,4.17 rear ratio.When it was new it pulled a dump trailer and it was never loaded less then 80,000-90,000,except on Saturday when it was loaded at 90,000-100,000 or more.The point I am making is that we never had a problem with these trucks,carrying that weight.I think that it was in the trans with the low hold.We also used them to pull the lowboys.The most we would load them with were cat d8’s.

But the truck in question is a rubber bushed 34 right?

[Phase 1]

On 2/1/2020 at 6:53 AM, Bjt said:

Looking for a cab n chassis to put log bed/bunks on not really a dump. Will only use 20-25 times a year and I’m located in Kentucky. I’ve looked at some r models and what made this one stand out to me was the good condition of the interior and lack of rust in the cab the owner says it’s a galvanized cab. Thanks 

That wheelbase isn't long enough to put any kind of a bed on it. It is too short for the dump box that is on it. Of course it could be lengthened if you want to do that.

[Bjt]

Not for sure if the the truck has 34 rears and rubber bushed red horse, and the owner doesn’t know either lol. I’ll try n get some pics tonight then post them. Thx 

[terry]

19 minutes ago, Bjt said:

Not for sure if the the truck has 34 rears and rubber bushed red horse, and the owner doesn’t know either lol. I’ll try n get some pics tonight then post them. Thx 

In a prior post there was a picture of the suspension, if that is it, is a rubber bushed 34,000 bogie.   terry

[Bjt]

10-4 on the rubber bushed 34. The tag behind the fuel pump is gone, this is the # on the passenger side of the block. Any indicators on motor size? And it’s a 9 or 10 speed Mack transmission, looked under it today. 

239GB5410A-P2

[Lmackattack]

that 3 leaf suspension was for on road use. the springs were known to brake in the off road. they also would brake the shock mounts due to excessive travel. will it work for you. im sure it will.. is it set up right for a dump truck. not really.  price should be the deciding factor here in my opinion. that being said a exporter would pay about that much for it.

[Bjt]

Well fellas just wanted to post that  I’m a owner of an r model Mack. The Mack dealer said the motor it came out with was an E6 300 the transmission was a T2090 9 speed OD and the gear ratio was 464. Transmission has a tag that confirms it is a T2090 Mack reman on September of 1990. Looking to get started on a complete fluids change and service.  It runs great and is really fast. The rpms at wide open throttle are at 2350-2400  I read somewhere that it should be 2100. Is that an indicator of a air leak or a turned up fuel pump and do I need to be concerned and have it set back? Thx

 

Edited February 7, 2020 by Bjt

[Ditchdiggerjcf]

Nice truck. No pusher axle so shouldn't see weights heavy enough to damage suspension or frame. It's worth 12-14k all day long.

[terry]

1 hour ago, Bjt said:

Well fellas just wanted to post that  I’m a owner of an r model Mack. The Mack dealer said the motor it came out with was an E6 300 the transmission was a T2090 9 speed OD and the gear ratio was 464. Transmission has a tag that confirms it is a T2090 Mack reman on September of 1990. Looking to get started on a complete fluids change and service.  It runs great and is really fast. The rpms at wide open throttle are at 2350-2400  I read somewhere that it should be 2100. Is that an indicator of a air leak or a turned up fuel pump and do I need to be concerned and have it set back? Thx

 

Did you buy the one in the photos? As far as the RPMs, somebody probably turned the pump up a little, nothing to worry about, just would not run at them RPMs very much.    terry