Salisbury diff over-heated

[Thunderbold]

After driving with elevated speed on the German highway the Salisbury diff of my Mk IV 427 (>400 HP) produces terrible cracking in narrow corners particularly when I am starting. I assume that the diff is then over-heated. Is there an suitable way for cooling the diff ?
   Are there maybe finned diff covers available?
   KInd regards from Frankfurt Germany

[Flyinghorse]

Barrie Bird just had a Salisbury diff fail-splines.
   So he has just been through the rebuild procedure, and also has diff cooling on another of his cars. (Think one was offered up recently on this forum).
   
   You say on starting,suggesting the high speed  driving has caused some damage as you say the noise is now on "starting" -not consistent with over heating.
   
   I think you need to start by eliminating al the potential back end sources of the problem --UJ's could be worn, Diff fluid level etc
   Its a big job to take out the diff on your own,if that's not the issue.
   However it may be that your diff friction plates are worn. There was also some additive recommended to be added to the newly rebuilt Salisbury in certain circumstances.
   
   Perhaps Barrie/others may be along with a better insight than my ramble.
   Graham

[B.P.Bird]

Hermann, Further to Graham's thoughts: Sounds like the LSD clutches are snatching. This is not uncommon, but as it was after your high speed run maybe the elevated temperatures have 'cooked' the oil. I use Mobil SHC 75W-90 and this in itself is the best cooling modification you can make. A98 has a temperature gauge for the diff. and with ordinary mineral hypoid oil the temperature quickly exceeds 150 degrees C. Using the Mobil synthetic drops this to 75 or 80 degrees C. I would drain your diff. and check for metal debris. I would also check for oil leaks at the pinion (input shaft)oil seal which seems to be the first thing that fails with high temperatures. Then try it again using the synthetic oil.
   There were oil cooler modifications done in period and the simplest were driven by a Bendix (Facet) fuel pump. Two unions were brazed into the rear cover pressing - one half way up and one near the base and the oil circulated through a small oil radiator positioned just ahead of the rear propshaft flange. Be careful of ground clearance if you add this modification.
   If you still have a jerky, noisy LSD action on tight corners then try the Jaguar LSD additive. The part number is on my post in the Cobra Forum reference my Salisbury diff. failure http://www.acownersclub.co.uk/forum/topic.asp?TOPIC_ID=2756
   Finally I would just observe that possibly not all Mk. IVs have the Salisbury diff. and the Hydratrack alternative uses a viscous fluid to achieve a limited slip action. I hear that these do not like hard driving, but I have never used one.

[cobham cobra]

Having trashed the diff back in March, the car was recovered by Thunder Road who set about removing it and had it rebuilt by their specialist.
   FYI – it's never a good sign when the drain plug is removed and lumps diff fall out.
   
   Many new parts were used in the rebuild and while the diff was out I took the opportunity to have Al and Alec rebuild and refurb the rear suspension. Apart from normal weekend duties the car is used for European trips each year and had often developed a really annoying squeak when being driven for four or five hours at a time. The strip-down revealed a few worn bearings and the lower shock absorber bearing on one side had all but dissapered. Since the rebuild the squeaking has not returned – but I've yet to do a long drive.
   
   Anyway, back to the diff, the first time it was fixed and refitted we were off to France within days for the Laon Historique
   http://www.continentalcartours.co.uk/documents/f-LHupdateApril.12_001.pdf
   
   By the time we got to Northern France the problem started.  The problem was the LSD was locking on slow corners and also when driving out of junctions. This resulted in either the inner rear wheel hopping, spinning or some very unhappy sounds coming from the drive train. On returning to the UK T-R worked incredibly quickly to remove the diff (out in one day!) and sent it back to their diff man.
   
   Turns out the diff was set to "race spec" ie it was too enthusiastic at locking up for road use. The diff was re-set and re filled with what T-R described as the "most expensive oil in the world" and refitted. I think they also used the recommended additive and the problem was instantly solved.
   
   Hope this helps

[Thunderbold]

Thank you very much for that plenty of helpful information. Following your recommendations I ordered  Mobil SHC 75W-90 oil and the Jaguar additive and it arrived today. So, I will chance the diff oil within the days and replace it by a mixture of SHC 75W-90 plus additive. Will let you know whether it worked. Kind regards from Hermann and AK1240 (Frankfurt, Germany)

[westcott]

Sorry for highjacking your post Hermann,
   
   @ cobham cobra,
   
   John,
   
   do you have the part# or a source for the lower ball bearing on the koni shocks ??
   
   Mine are in bad condition and need to be replaced soon.
   
   The only information i got out of the net is that they are aircraft replacement parts.
   
   I want to get rid of this annoying sqeeks I have while driving on uneven roads, it drives my grazy...
   
   Thanks, Uwe

[MkIV Lux]

quote:Originally posted by westcott
   
....
   
   
   I want to get rid of this annoying sqeeks I have while driving on uneven roads, it drives my grazy...
   
   Thanks, Uwe
   
   
   

   
   same with me....... only when freshly greased or when it rains there is no sqeek [:)]
    Constant

[SJ351]

Thunder Road sourced and fitted some lower bearings for my rear Konis. They are not cheap parts!

[cobham cobra]

Hi Uwe / Hermann,
   I can't help with part numbers – sorry. I suggest you have a word with either Big Al or Alec at ThurnderRoad as they may be able to tell you how to get the parts locally or source them for you. http://www.thunderroadspeedshop.co.uk/2.html
   
   FYI – we've had some very hot weather in the UK so far this summer and it's typically in hot weather that rear suspension would develop the really irritating squeak. So far this summer, since the back-end rebuild, I've not had a squeak out of it and the diff is working fine #61514;

[Thunderbold]

By the way, how much is the oil capacity of the Salisbury diff? According to the manual it is 3.12 litres. Flyinghorse / Graham states here in the forum that it only takes 1.5 litres. Actually, I ordered 2 litres .....

[Flyinghorse]

My comment was for the BTR Hydratrak unit.  I think its 3 pints which is about 1.7 litres for a Salisbury, but others will be along soon to let you know.
   
   Graham

[Thunderbold]

Thanks for all the excellent recommendations. In the meantime I changed the diff oil (about 1.4 liters) and replaced it by Mobilube 1 SHC 75W-90 plus around 100 ml Jaguar LSD additive.
   So far no single strange noise anymore in narrow corners even after high speed on the "Autobahn". Have a nice day, Gentleman!
   Hermann and AK1240 from Frankfurt, Germany

[jbottini]

Hope you found the refil and drain access plug in boot....I found it after doing it from below the car on jackstands with a siphon pump.

[French Frie]

+1 [:o)] ... and I put a message about that when I did it few months ago !
   
   PS: Jim, no Florida for us this year [B)] ... socialist government and increasing taxes (+14%!) killed us !