question Any tricks to increase a Diamond T's top speed by a few miles?

While still in the midst of the restoration of a 981 (DXFE engine) we are now seeking a way to increase this transporter's top speed.

Reason for this is that we plan to drive the "T" from Holland to Normandy in June 2014 for the D-day commemorations. However, with other vehicles in the same convoy and the T's max. speed of only 35mph, it is going to be an extra long haul.

We do not want to make any irreversible changes to this 100% original vehicle, therefore does anyone know of a more sophisticated trick in the book? I am then thinking along the lines of making changes to the final drive for instance. Esp. since we will not be pulling out any stranded Shermans nor do we plan to take it offroad at any time. Maybe by adjusting pignon and/or crown wheel? Or swapping any of these out with a specimen from a different truck like GMC, Mack etc.? Or perhaps there are other ways to just add a few extra miles per hour?

Any help or hint is greatly appreciated!

Thanks,

Marco

Marco;

I would be surprised at a top speed of 32 mph, it would be closer to 22 mph flat out on level ground. You would be hard pressed to find any gears that would work in trying to change out the reduction unit. These trucks were built to pull heavy loads SLOW, wether they were laden or unladen. The ideal oparating rpms of the Hercules diesel is 900 to 1100 rpms. Many operators in theater and post war found out the hard way whats happens when you overspeed the Hercules diesel. If you are going to drive it, go slow and enjoy the countryside. You should be commended for driving it that distance.

John G

did you meen 35k,?. i have a 981 and 22mph is spot on for top speed, i can average about 18mph on a run. it also will be in normandy june 2014 so hopefully we will bump in to each other, not literally i hope!!!!

Marco;

 

I would be surprised at a top speed of 32 mph, it would be closer to 22 mph flat out on level ground. You would be hard pressed to find any gears that would work in trying to change out the reduction unit. These trucks were built to pull heavy loads SLOW, wether they were laden or unladen. The ideal oparating rpms of the Hercules diesel is 900 to 1100 rpms. Many operators in theater and post war found out the hard way whats happens when you overspeed the Hercules diesel. If you are going to drive it, go slow and enjoy the countryside. You should be commended for driving it that distance.

 

 

John G

I do agree, I wish that I was coming along with you, enjoy the trip, and like John has stated, enjoy the countryside along the way.......... the slowest vehicles should be at the front of the convoy, setting the pace.

I dont know much about these things but I do remember talking to the owner of the 'Dewsbury Diamond T's' a few years ago and I seem to remember he said he had fitted a Fuller 9 speed box (does that sound right?), which considerably increased the top speed, but resulted in frequently broken halfshafts...

Tim

There are trucks from the 50ies with almost identical double reduction axles , these diffs should be possible to adapt to the Diamond axles .Problem is that you have to go to the States to find them on an old truck . if you increase the speed more than 33 mph , than the engine won`t pull uphill anymore . gearbox modification also only can increase speed a bit , otherwise prop shafts revs. are getting to high . And oil in axles starts to foam .

There were always these talks over here from the heavy haulage companies that they turned over the transfer case gears , but again the prop shafts would spin to fast.

I'd suggest about the only thing you could do that would avoid the problems associated with speeding up the actual drive train would be to fit bigger tyres for the journey .....

..that way everything is still going at the same speed in the drive train but your road speed would increase ......and seeing as you got plenty of low gears I would think as long as she's not being asked to tow anything that she'd manage any hills you came to?.... just a suggestion

PS: you could I suppose, even take the original size wheels / tyres with you to put on her for trundling around when you're 'on show' and keep the others for the main part of the run on the highway.......bit of a faddle I know to change them... but....

Like I said........just a suggestion if her top speed really bothers you that much ...otherwise I'd agree with the above...

.sit back and enjoy the countryside going by

PS : a further thought....

you're still not going to be doing any kind of roadspeed to have steering issues so you only really need to fit the big wheels on the back axles (yeah ok she might have a slight 'jacked up hot rod' appearance ) ...more or less any tyres off a modern tractor unit would be much bigger outside diameter than her standard tyres and I'm sure someone on here can soon work out what difference 'X' amount would make to your final speed.....and any truck wheel outfit could fit your 'new' wheels out with new wheel centres to match the old trucks studs too simples gotta be a lot easier than messing about with the gearbox or the diffs ???

hi freeland, i find it difficult to understand why you need to increase the speed of your diamond, i have been dealing with diamonds for nearly forty years and have heard of horrendous tales of changeing engines that are not compatible with the way the diamond 980 981 was designed, a good friend of mine ran dawes recovery at swanley and they fitted a nine speed fuller gear box to the original transfer box to increase speed, as you probably know every turn of the wheel the propshaft turns eleven times, so every 50 miles or so the intermediate propshaft would fly off in all directions, i have a friend who has a set of high speed diffs, ok on the flat but useless on the gradients. personally i would leave well alone or if you still want more speed i suggest you change vehicles, hope of some help, tony g.

Tony graves is the king of the DIAMOND T :drive:

I would tend to agree with what's been said about leaving it alone. I have a Diamond T 969 Wrecker, its fitted with a Ford Cargo/D Series 6 cylinder Turbo engine by a previous owner. Its been well fitted and goes great, a 969 normally goes about 30-32 but I've opened this one up and due to the power & higher revs I've had it up to about 40-45mph.

I'll only ever do it the once, it was all moving far too fast, the props and diffs were spinning round quicker than was healthy and although the air brakes are great I wouldn't have liked too had to change direction at that speed. Maybe slightly larger tyres are a good compromise.

Regards Andy

 

I'll only ever do it the once, it was all moving far too fast, the props and diffs were spinning round quicker than was healthy and although the air brakes are great I wouldn't have liked too had to change direction at that speed. Maybe slightly larger tyres are a good compromise.

 

Regards Andy

STOP PRESS - I am going to say something!

I kind of thought the same as Andy when I read this. I think anything you are in or on going at a speed that it isn't built for is more than scary. I done this once in my GMC on the motorway - nearly hit 60mph and it wasn't a nice experience. A DT at speed would be a lot to handle as previous members have stated.

Just enjoy the ride, less stress, less wear. You aren't going to gain a great deal really unless you really tune it up.

- can't believe I just made a half sensible post

I agree with Jack, I once too hit a high speed in my truck, and it was really a new underpants experience. Especially after in developed a death wobble too.

Then there's the question of stopping all that weight at a speed it wasnt designed for in an emergency (possibly in the wet )

I agree with Jack, I once too hit a high speed in my truck, and it was really a new underpants experience. Especially after in developed a death wobble too.

 

 

Then there's the question of stopping all that weight at a speed it wasnt designed for in an emergency (possibly in the wet )

now...to be fair there speaks some good sense...

I once built a Series 1 Landrover (albeit with up rated brakes) with a seriously tuned high compression V8 Rover lump in her.......she turned 168 HP at the back wheels and would do 100 mph ( gauged very accurately with a mate following me one day in his Audi sporty job ) ..at about 70 MPH she would hit a sort of 'critical point' where everything seemed to let go and wobble and shake...the steering wheel would need vigorous twists to keep her vaguely straight and it honestly felt like she was coming apart at the seams ..but then....at about 80 MPH everything calmed down and she would run as sweet as a nut up to her peak at, as I said , about 100MPH..

.the worrying thing was you knew you had to come back down through the 'critical' point as you slowed down again .... worth thinking about I reckons

Last evening I drove my Ward LaFrance series 5, 25 miles from where it is stored to my house for a car show on Sunday. The Mrs was following behind with the 4 way flashers on for safety and to run "blocker" if needed. Truck ran fine with no issues at all.

A few points to relay about road speed, as I was thinking about this thread as I was driving.

It took a couple of miles for the flat spots in the tires to "round out " so ride went from lumpy to smooth.

The max rpm's on a Continental 22R is 2400 rpms with a max speed of 45 mph.

The trucks "comfort zone" was 1800 rpm's at about 33-35 mph. As you drive, the truck "talks" to you, as you listen to the transmission and transfer sing there whine.

I was driving on a relatively flat road so I was in 5 th gear and had to drop down to 4th on the slight hills. You plan your shifts and road speed as you approach a hill. It took me 1 hour to go 25 miles. The front end had no shimmy, as I am not using NDT's.

I had to stop one time to crack the windshield open and open the cowl vent as my feet were getting roasted by the engine heat, mind you it was dusk and the temperature was 72 degrees. I can only imagine how brutal it would be on a sunny warm/hot day.

Drive these trucks as they were intended to be driven, you won't get anywhere fast, but you will enjoy the drive.

John G

Surely any modifications can have serious implications for insurance ?????? Best left alone and enjoy the drive.

The axles wont have been made by Diamond T but to a spec by Fuller Spicer Rockwell or Eaton. The spec will have been very deep reduction on the crown wheel ratio. Of hand i believe the opening where the diff fits is in front of the diff not on top so it will be a standard axle casing of one of the above makes. So in theory there will be axle sets kicking about from all sorts of vehicles british american even Eindhoven produced trucks that will have different ratio diffs that can fit into your casings. from vehicles right up to the 90s. That will give greater overall speed. I doubt though the gain would ever out wiegh the financial cost. No as every one has said sit back relax and watch the world go by and enjoy the ride out.

DT 980 series diffs are a double reduction unit that drops in from the top.

Sorry i thought they had standard front casing even so they will have been out sourced and differrent gear ratios will have been available but the out comes the same not worth expence of puting into casing.

.... The Mrs was following behind with the 4 way flashers on for safety ....

You do know that that is illegal, don't you (having the hazards on that is, not being followed by the wife)?

Is that a UK law, not aware about in the state of Maryland in the US.

John G

hi, in response to the previous letter the hercules engine revved at a maximum of 1600 which at normal road speed ie 23 miles an hour gave an output of 201 bhp, the army introduced in the fifties the rolls royce c6 143 series direct injection engine which pushed the road speed up to 29 miles an hour but kept the same amount of torque for the differentials, as was quoted quite rightly by the previous letter be happy to plod along at 23 miles an hour and enjoy it, all the best tony g.

I appologise for my typo regarding the max revs,

it was 4am.

:yawn::yawn::yawn::yawn::yawn:

Good job you pointed that out Tony.

STOP PRESS - I am going to say something!

 

I kind of thought the same as Andy when I read this. I think anything you are in or on going at a speed that it isn't built for is more than scary. I done this once in my GMC on the motorway - nearly hit 60mph and it wasn't a nice experience. A DT at speed would be a lot to handle as previous members have stated.

 

Just enjoy the ride, less stress, less wear. You aren't going to gain a great deal really unless you really tune it up.

 

 

- can't believe I just made a half sensible post

JACK.....we want our money back you told us YOUR truck had NEVER been raced or rallied you fibbed....no wonder you were always running out of petrol......

Hi all,

Just found this thread. It is of interest to me as I wish to speed up a Diamond T 969 to 50mph when it is finished. Due to the relationship between the 980 and 969, I wish to add some comment.

Diamond-T-Steve, are you sure the 980 diffs are a double reduction worm drive unit? Worm drives have tremendous reduction (eg. 25+:1) compared to conventional gears and it would also be impossible to tow as a 'worm wheel' will not drive a 'worm' at all (theoretically).

My Diamond T (and a Federal 606 tank transporter) has 8.43?:1 double reduction Timken diffs, consisting of a crown wheel/pinion in the top section and a 'bull'gear/pinion in the lower section. My M1A1 is the same design Timken and is 8.27:1.

Also, why would the rear-most diff be reversed? They both need to turn in the same direction. Am I missing something?

The top section, I have been told, is not that well lubricated and is prone to bearing failure at higher rpms. This is quite believable after seeing the design of the top section of the diff innards.

The best answer I came up with is a combination of slightly higher rpm and much larger tyres. I could have replacement bull/pinion gears made at around $1000 each x 2 per diff x 3 diffs :blush:. Fortunately, the 969 almost looks as if it was designed for 11/12.00 tyres but ended up with 9.00's, which I expect will make for easy experimentation when the time comes.

Also, I know of two repowered M1A1's that were said to do 100kmph. No accompanying comments about unsuitable drivability. But words are cheap.

Does anyone actually know of later model diff gears of higher ratio that will go into 980/969/M1A1/606/etc trucks?

BTW, I am looking for 969 and M1A1 hardware bits and pieces, eg gas tanks/wrecker crane accessories/suchlike. Email to schosa@optusnet.com.au

Have a nice day.

Sam.

Is that a UK law, not aware about in the state of Maryland in the US.

 

John G

Oops! Yes, UK law. Sorry, I didn't spot that you were across the pond!