Ditchdiggerjcf Posted July 8, 2020 Share Posted July 8, 2020 RD685S6855 Anybody run a vin? How was this bulldog configured when it was born? Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/ Share on other sites More sharing options...
j hancock Posted July 8, 2020 Share Posted July 8, 2020 RD model, 600 series chassis with a 237 HP engine. S six wheel straight chassis (3 axle truck) 6855 unit production number. 1 Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455298 Share on other sites More sharing options...
Ditchdiggerjcf Posted July 8, 2020 Author Share Posted July 8, 2020 1 hour ago, j hancock said: RD model, 600 series chassis with a 237 HP engine. S six wheel straight chassis (3 axle truck) 6855 unit production number. 2 drives and a steer, or 2 drives and a pusher + steer? I was curious about the front axle weight rating. It must be an old truck. It has the tan interior and juice brakes on the front axle. Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455306 Share on other sites More sharing options...
j hancock Posted July 8, 2020 Share Posted July 8, 2020 RD685S6855 left the factory as 1 front steer axle and 2 drive axle tandem. Early VINs (such as this) or the modern 17 digit VIN will not give as built axle ratings. Have to run the number with a Mack dealer or the Mack Museum or find the axle numbers currently on the truck. Couldn't answer why it has hydraulic brakes on the front axle. Either special order or changed in the field? The RD model was introduced by Mack in 1970. 1 Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455315 Share on other sites More sharing options...
Ditchdiggerjcf Posted July 8, 2020 Author Share Posted July 8, 2020 Fronts are an FAW616D? That mean anything to anybody? 16k fronts? Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455333 Share on other sites More sharing options...
j hancock Posted July 8, 2020 Share Posted July 8, 2020 A FAW616D front axle is rated at 18,000. Quote JimIt doesn't cost anything to pay attention. Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455336 Share on other sites More sharing options...
Ditchdiggerjcf Posted July 8, 2020 Author Share Posted July 8, 2020 The truck does not have two steering boxes, or a slave cylinder on the passenger side. The other ones have always had that if the were 18/20k fronts. Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455339 Share on other sites More sharing options...
terry Posted July 8, 2020 Share Posted July 8, 2020 9 hours ago, j hancock said: RD685S6855 left the factory as 1 front steer axle and 2 drive axle tandem. Early VINs (such as this) or the modern 17 digit VIN will not give as built axle ratings. Have to run the number with a Mack dealer or the Mack Museum or find the axle numbers currently on the truck. Couldn't answer why it has hydraulic brakes on the front axle. Either special order or changed in the field? The RD model was introduced by Mack in 1970. i have seen hydraulic disc brakes on the front, but not very common. terry 1 Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455371 Share on other sites More sharing options...
Ditchdiggerjcf Posted July 8, 2020 Author Share Posted July 8, 2020 Can they be swapped with a hub change, or do I need to swap an entire axle? Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455373 Share on other sites More sharing options...
JoeH Posted July 8, 2020 Share Posted July 8, 2020 I have an '88 Rd with 20k steer and only one gearbox; a 1980 DM686SX with 20k steer and one gearbox; and a 1995 RD with an 18k steer and one gearbox. Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455377 Share on other sites More sharing options...
Ditchdiggerjcf Posted July 8, 2020 Author Share Posted July 8, 2020 All mine have a slave cylinder on the passenger side. Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455379 Share on other sites More sharing options...
Ditchdiggerjcf Posted July 12, 2020 Author Share Posted July 12, 2020 Can the square fuel tanks on this unit be swapped out for the round ones? They are in rough shape and I have spare round ones. Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455726 Share on other sites More sharing options...
Vladislav Posted July 13, 2020 Share Posted July 13, 2020 20 hours ago, Ditchdiggerjcf said: Can the square fuel tanks on this unit be swapped out for the round ones? They are in rough shape and I have spare round ones. Yes if you also swap the brackets. Quote Никогда не бывает слишком много грузовиков! leversole 11.2012 Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455774 Share on other sites More sharing options...
Ditchdiggerjcf Posted July 13, 2020 Author Share Posted July 13, 2020 The front brackets too? Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455777 Share on other sites More sharing options...
Ditchdiggerjcf Posted July 13, 2020 Author Share Posted July 13, 2020 I guess if I make this swap I might as well take the entire air ride cab system from the donor truck and do it all at the same time. Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-455778 Share on other sites More sharing options...
JoeH Posted July 17, 2020 Share Posted July 17, 2020 You'll need to ensure that the radiator is not attached to the firewall via support arms. And the hood stoppers on the firewall need to be rollers, not the donut style sometimes used. Radiator needs support rods that go diagonally to the shock absorber brackets on the frame. But air ride cabs are a beautiful thing. We bought an '88 RD690S last year that we're still fabricating the body for before putting into full-time service. We converted it to air ride cab mount,which is a must with a 20k steer axle. 1 Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-456027 Share on other sites More sharing options...
Ditchdiggerjcf Posted August 2, 2020 Author Share Posted August 2, 2020 Spring pads on axles vary on the R models, or are they the same? Will the air brake axle from a DM fit this truck? Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-457403 Share on other sites More sharing options...
Ditchdiggerjcf Posted August 16, 2020 Author Share Posted August 16, 2020 A little tlc and she has a job to do. 2 Quote Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-458717 Share on other sites More sharing options...
Vladislav Posted August 22, 2020 Share Posted August 22, 2020 On 8/2/2020 at 4:05 AM, Ditchdiggerjcf said: Spring pads on axles vary on the R models, or are they the same? Will the air brake axle from a DM fit this truck? Seems like all R-model axles fit the springs similar. But you can not use a beam off a DM because the U-bolt drillings located different. The same story with MH/RW2 axle beams. It looks like the casting is basically the same with wide spring fitting areas but then they're drilled specially to different chassis types. Quote Никогда не бывает слишком много грузовиков! leversole 11.2012 Link to comment https://www.bigmacktrucks.com/topic/63212-rd685/#findComment-459261 Share on other sites More sharing options...
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