Hi,
New to the classics forum. recently purchased a 1965 Daimler 250 "basket case". Missing the engine but pretty much everything else is there.... i think. I'm putting an old school chevy 283 bored 60 over to 292 in it with a tremec t5 behind it. I have the front mounts fabricated and am moving on to the transmission mount. I want to set the trans angle equal to the rear diff pinion angle but have not been able to find that specification. Does any one have that spec?

thanks,

Steve

 

hi again,

I got my hands on a digital angle finder and measured my pinion angle. With the chassis rails set at 0 degrees, my pinion angle is 2 degrees. The angle finder is accurate to 2 tenths of a degree. The rear springs, and spring perches, referred to as "longitudinal members"in my parts book, are new. Measurements were made with the weight of the vehicle on the suspension. I am not sure this is to specification as i could not find one.

Next question is... Does the rear axle "wrap" upwards during acceleration in similar fashion to conventional leaf spring suspensions? Or is the wrap some how limited by this unconventional leaf spring/torque arm setup?

Thanks, steve

 

I don't have a spec for the pinion angle and my car isn't in a condition where I can measure it. I'd guess that 2deg up is about right. You could eliminate the whole alignment question by swapping to CV joints. I've a vague memory of Cobra builders using Rover SD1 CVs with Jaguar flanges, but I may be wrong.

For a 1950s design, the Mk2 rear axle is well located, but the leaf spring still leaves a lot to be desired. As I recall, my car didn't suffer from severe squat or axle roll up (about it's own axis). There was twist about a longitudinal axis, but nothing too extreme. However, the effective arm radius of the cantilever leaf is too short for good geometry in cornering. There is a rear suspension upgrade to coils and long trailing arms in place of the leaf springs. It's available from the usual suspects at about ten times what it should cost (I.e. a lot more than similar conversions for Fords or MGs). The best accessible sources on locating live rear axles are various articles by Arthur Mallock - you can find them with Google.

 

Peter,

thanks,

Eventually I would like to graft in an IRS from a 420... but until then Im just trying to put together a reliable driveline....so I have 4 degrees down at the transmission and 2 degrees up at the pinion... that leaves 2 degrees for wrap.... my concern is will that be enough for a 283 making around 250 to 300 ft lbs of torque. The 455 diff gears might have a tendency to climb quite a bit in first gear..

cv joints might be necessary... but i would prefer u joints for ease of maintenance ....


Steve

 

You want the angles equal at normal ride height, otherwise you'll have vibration at highway speed. That can crack the transmission housing and other nasty things.

Ideally, the angles need to be within ½° at each end of the shaft. So if the diff angle is 2°, the angle at the transmission should be in the range of 1½° to 2½°.

 

Is the SD1 shaft a double carden type joint or a Rzeppa type joint?

 

​​​​​​No, they're not Cardan shafts, they have CV joints presumably GKN Rzeppa type.

I can guarantee that a drive shaft vibration can damage the transmission housing. I had a vibration in my Mk2 that I eventually traced to a bulge on a rear tyre. It caused the spool piece section of the overdrive housing to fracture right through. Surprisingly, the car ran fine apart from leaking some gearbox oil.

​​I can't imagine it's possible to adjust the engine and transmission by even 1° as that would require lowering the front of the engine or raising the tail of the transmission by about an inch. How much freedom is there to lower the engine mounts?

 

I have been reading alot about this and the number of varying opinions on this is as various as the number of opinions.... but, it seems everyone agrees that 3 degrees or less is the starting point. That's to say if your trans is 3 deg down then the diff should be 3 degrees up and nothing more than 3 degrees...Also, everyone seems to agree that a driveshaft slope equal to the trans/diff angle deg is a no because the u joints caps wont spin on the brngs wearing them out.... As far as wrap (with leaf springs) is concerned, I have read to add any where from nothing to 7 degrees down for wrap.... at 7 degrees it seems they are guarding against u joint failure on hard launch with disregard to drivability. Mostly, a small increment downward of a half degree or so is recommended. So I think i need to look hard at lowering the front of the engine as Peter suggested... Im using a cradle type front mount which i can modify but there is only so much room to go before bottoming to the suspension cross member. My goal at this point is to have the motor at 2.5 degrees down, with the diff at 2 degrees up.

Steve

 

Rather than opinions, here is a good guide from Spicer on how to layout a driveline: https://media.spicerparts.com/cfs/fi...store=original

Don't forget that you have angles in 2 planes: looking from the side of the car, and from the top of the car. You need to calculate the total angle between those 2 planes. I honestly wouldn't worry about the axle moving and building in a permanent misalignment based on that. Instead I'd focus energy on better restraining the axle.

That being said, CV joints will solve the problem completely.