Rear Diff max BHP

[215m3]

I have a standard diff in my car. What is the maximum these diffs can handle? Is it the diff or the driveshafts that are weak for 400+ BHP

[nrubenstein]

Medium case diffs will take plenty of power. People generally run into halfshaft issues before anything else.

[Ron ///Man]

Medium case diffs will take plenty of power. People generally run into halfshaft issues before anything else.

Def agree that half shafts are the next weakest link, esp if you're not nice with the clutch... As HP goes up, you should monitor diff (and trans) temp esp if a track car and add coolers to help them live longer.

[215m3]

Def agree that half shafts are the next weakest link, esp if you're not nice with the clutch... As HP goes up, you should monitor diff (and trans) temp esp if a track car and add coolers to help them live longer.

Hi Ron

Thanks for your reply.

I am running a different cooler and have a temp sensor fitted. What is the max temp the oil should not exceed?

So if the driveshzfts, or halfshafts as you call them, are the weak link, what upgrade options are there? Which part fails?

[Ron ///Man]

Hi Ron

Thanks for your reply.

I am running a different cooler and have a temp sensor fitted. What is the max temp the oil should not exceed?

So if the driveshzfts, or halfshafts as you call them, are the weak link, what upgrade options are there? Which part fails?

Hi Toby

My pleasure. My personal opinion is that I don't like to see any temps above 250F or thereabouts in the engine, trans or diff, even with synthetic oil. In my own race car, I monitor diff and trans temp and when they reach 235F, I have my MoTec start cycling the trans and diff coolers. I found it better to start cooling before you reach critical temp rather than starting to cool when you hit it. When I started cooling at 235F, it was easier to maintain 250F max. At first when I started at 250F, it would often go to 260F before it began to drop. Just an FYI, shorter tracks and tracks with lots of corners can really work the trans and diff harshly. The more up and down shifting you do causes trans temps to rise. The more corners cause the diff temp to rise from the diff clutches slipping in the corners.

I've never experienced half shaft failures myself, but I've seen many of them. The part that usually fails is the CV joint itself. Usually the cage breaks. There are companies out there that will make you new half shafts with stronger cages. As a side note, be careful using rebuilt half shafts. As half shafts age, the cages get worn, and where the balls sit is no longer round. When they are rebuilt, the cages are often re-ground in an attempt to make the holes round again, and larger balls are fitted. The issue is the cages are now thinner and are much more prone to breaking. Whenever possible, I try to replace with new, but, they have gotten very difficult to find. .

[215m3]

Hi Toby

My pleasure. My personal opinion is that I don't like to see any temps above 250F or thereabouts in the engine, trans or diff, even with synthetic oil. In my own race car, I monitor diff and trans temp and when they reach 235F, I have my MoTec start cycling the trans and diff coolers. I found it better to start cooling before you reach critical temp rather than starting to cool when you hit it. When I started cooling at 235F, it was easier to maintain 250F max. At first when I started at 250F, it would often go to 260F before it began to drop. Just an FYI, shorter tracks and tracks with lots of corners can really work the trans and diff harshly. The more up and down shifting you do causes trans temps to rise. The more corners cause the diff temp to rise from the diff clutches slipping in the corners.

I've never experienced half shaft failures myself, but I've seen many of them. The part that usually fails is the CV joint itself. Usually the cage breaks. There are companies out there that will make you new half shafts with stronger cages. As a side note, be careful using rebuilt half shafts. As half shafts age, the cages get worn, and where the balls sit is no longer round. When they are rebuilt, the cages are often re-ground in an attempt to make the holes round again, and larger balls are fitted. The issue is the cages are now thinner and are much more prone to breaking. Whenever possible, I try to replace with new, but, they have gotten very difficult to find. .

Thanks for reply Ron.

I am pretty sure with my electronic setup i could get the diff cooler to cut in if it goes above a certain temp. Or even get a warning on my display. I have ditched the old harness in favour of the latest can bus wiring system.

My half shifts are the original ones, never been rebuilt, so if/when they need replacing will probably get uprated parts.

[JS154]

halfshaft angle on lowered cars will increase wear rate. the shafts themselves are quite strong, like Ron said, it's the CV joint that goes.

If you need stronger halfshafts Metalore can make you a set. Or Pankl. Probably a little (!) expensive and unnecessary for an S14 engine, but they are options.