E21 Differentials and Driveshafts (The weak Point?)

[Duracel79]

Thought I start this thread seperate from the M42 one as its taking it a bit off topic.

Lets try and get the real info on how strong the E21 drivetrain is?

E21s had a reputation for weak rear axles before people started welding diffs up, it might be true they are more prone to implode with a welder though.

I have always been told that "the diffs are weak and can't cope with big power, 200bhp is the limit"
Now my problem with this comment is I've never experenced one breaking or seen a report of one breaking on this forum since I've been a member.

There have been two or three reports of broken CV's not the driveshafts (Tommi, Wiz0r & Murran that I can think of). I generally looked at these failures as more due to age and wear issues over 20 years use, they are then asked to cope with a much more violent pursuit (Drifting with a welded diff).

My own experiences with the small case diff has been good. No breakages when running a tuned 2.3 M20 (180bhp), a std 2.5 M20 (185bhp) and a tuned 2.7 (209bhp). There was abuse due to circuit work with curb bouncing etc. The only thing that went wrong for me was a split CV boot.

So my experience is the diff, CV's and driveshafts can cope with 200-210bhp when using an LSD.

What are other peoples real experiences with the std driveshafts and diffs when running higher power outputs?
M10 / M20 / M30 / M50 / M52 / S14 ? What you got?

Cheers

Ben

[DC]

on my 320i Turbo I have 323i rear axle with 75% LSD and it is still working without problems even after 2 years of drifting and racing with 228hp and 340Nm of torque

now I have diff temperature sensor and oil never exceeded 70°C

[TopCat]

On Herman running a full Alpina 3.5 M30 whilst doing full Power upshifts- not sure of HP reckon around 240-260 bhp

see:http://www.bmwe21.net/forum/viewtopic.p ... &start=765

one cv joint sorted of exploded damaging one driveshaft- interesting what the ball bearings did- Steve will post a picture when he gets back to island next week

set out below pix of the exploded rear driveshaft bearings etc!
see:
Look at the bearing damage
-
and the explosion!:


Now all sorted with the new ones - interesting- how good the quality is on the standard ones (I suppose I shouldn't be surprised as they are BMW - I suppose I am just used to Chevrolet stuff from 20 years earlier (which all needs improving in this area!)

[E21meister]

The question to ask is: do people rebuild their driveshafts and diff, or do they expect items that have 30+ years and thousands of miles under their belt to work like they're new?
Anyone that doesn't treat these items like an engine and rebuild them after lots of running hours must expect them to fail, period. That's why my small case LSD and driveshafts are being rebuilt to handle the power of an ITB-equipped, 200bhp+ 2.7 lump. It's folly not to.

[Jason_323i]

On the track car i have rebuilt and uprated gear box & diff, recon driveshafts, new wheel bearings all round. The down side is that soons adds up to a lot of ££ as much as yout typical engine swap.

[e21-Mark]

I think the way some folks drive (with a lack of mechanical sympathy) can have an effect, along with wider, grippier tyres. I never had a problem with either a 2.5, 2.7 or M52 with normal street use. Mind you, I have since converted to an e12 sidewinder LSD.

I'm sure I have read that it was the minimal oil capacity, of a standard e21 diff, that was the problem? Isn't that why the Alpina cover was developed?

How hard would it be to engineer an oil cooler system? I'm guessing it would need a thermostat and some sort of pump to circulate the oil?

[nige21]

Interesting thread. I had run my m50'd e21 for about 14 months with no driveline issues, however induced wheelspin was mostly in damp/wet conditions. In dry conditions the car would get run hard (wheelspin on hard 1st-2nd changes etc) and using all available rpm and torque about 3-4 times a week. As the car was my daily driver at the time, it was driven sensibly most other times it was on the road.

It seems like CV's are what will break first, but im curious as to whether anyone has had and diff centre failures, bearings/crownwheels etc?
I am looking at fitting a medium case diff soon with custom halfshafts, but if centres are not failing then custom halfshafts with a small case centre might be an option.

Heres a video of an e21 race car with i believe a small case welded centre.

[TopCat]

I
I'm sure I have read that it was the minimal oil capacity, of a standard e21 diff, that was the problem? Isn't that why the Alpina cover was developed?

How hard would it be to engineer an oil cooler system? I'm guessing it would need a thermostat and some sort of pump to circulate the oil?

I believe oil capacity is the key- and that is why Alpina fitted the larger diff cover- I see they are advertised on EBAy in US/Australia ......

The Racing CSL E9s all ran with diff oil coolers
We had the same issue with Chev gearbox= insufficient oil capacity and fitted a small Mocal electric pump to a separate oil cooler plumbed to gearbox- I have a temp gauge and when things get hot (6-8 laps) I switch on pump- Rally Design sell them wwwrallydesign.co.uk
Best avoid a thermostat - one more thing to go wrong- that is why we use a switch.

[nas80]

It was jimmy who told me that the stock diff was weak because he'd broken two..

I've destroyed a euro car parts guibo and a center prop bearing. But no driveshafts or diff.

I run an m50 with a quaife atb. My drivetrain has done 80k.

The stock diff is rated to 280lbs ft

The reason why welded diffs snap cv joints is because when they turn corners there are opposing forces. This weakens as it adds stress the joint isn't designed for.

[e21-Mark]

A quick Google search gives 101 reasons why welding a diff is a bad idea. I'm sure it's fine for drifting or loose surfaces but diffs exist for a reason and apart from the mechanical problems, you'll also be blessed with terminal understeer.

[rob0r]

I've never experienced terminal understeer in the 4-5 years I've been running welders, they really are made out to be terrible for handling... People who make such statements have either not driven a car with a welder or driven one that had very bad tracking/alignment issues. I've done grip trackdays with a welder with no hint of understeer and I used to commute 110 miles a day with one rain, snow or shine. The only slight understeer I get is when I initiate a drift wrong and it pushes the car on instead of sideways, and only when I try to drift. Also I believe the 80's Sierra touring cars had spool diffs which are the same in locked functionality.

I don't disagree that welders do cause more problems mechanically and I accept that, but I'm not confident that the rear axle is strong enough that it won't cause me any more trouble going forwards. The only problem with driveshafts have been on the E21, all my E30s including my M30 3.5 touring have been fine. This maybe age/wear related and a brand new E21 CV joint maybe just as strong as a new E30 CV joint, but personally for me, it's more hassle that I don't get with other BMWs.

If the E21 axle is so strong then why are people swapping in E12/E28/E30 diffs/axles? Including people in this thread stating the E21 axle is fine.

As for the diffs, I'm not worried about the small case diff. E36 owners deliberately fit small case diffs to their 328i for better gear ratios and they hold up just fine.

The M50 is currently out of the E21 and is going back in with a new sump and paddle clutch in the next month or so, then I will be drifting it at every possible opportunity and I'll let you know how I get on... I'll be bringing spare driveshafts to each event!

[Jason_323i]

I guess the purpose of this thread is to find some definitive information

Torque tends to brake things not BHP, in any drive train it is good to have a bit of slip normally tyres but as we use modern tyres that are more sticky and drive the car side ways you are going to increase the load on the diff. Unless you doing hard launches, drifting etc I think a good condition diff is okay.

The only period upgrades where alpina with the dual mount large capacity diff cover all the way up to a 2.8m30 and Hartge who did the e12 conversion for the H3.5. A think the hartge conversion spawned the e12 upgrade as a must have for big power.

The other reasons for upgrading the rear axle is more diff choice, and going five stud or even weight distribution (have you felt the weight of a e28 m5 diff)

So far the facts are drift guys blow cv joints, Herman took out a CV joint

Jimmy blew 2 diffs with a tuned m20, but all the other tunned m20/m52’s so far are okay on a stock diff

J

[e21-Mark]

People who make such statements have either not driven a car with a welder or driven one that had very bad tracking/alignment issues.

Erm, not entirely true but only my experience/opinion anyway. The e30 we had with a welded diff was OK on larger corners (or less noticeable anyway) but physics dictate they'll always struggle on tighter turns. You're also more likely to get snap oversteer on lift-off and the ultimate amount of grip available is less. All that is acedemic when it comes to drifting I guess anyway where they obviously suit their purpose and work well. It's been a while but didn't Cossies use air lockers?

Either way, you pays your money and takes your chances.

I pinched the bit below off of a drift site.

Initial Understeer (fact).
Below is a picture of the understeer moment on turn in with a welded differential. The size of the circles are directly proportional to the load on the tire. The arrows are pointing in the direction of movement of the tire.

the front tires are creating a slight braking force but pointing the car in the appropriate direction for the corner. The outside rear tire is actually creating a significant braking force due to rolling resistance. The inside rear is giving us the forward appropriate momentum. Again, the inside rear tire has less load on it and can break loose easier. This is the "fighting" force that tries to right the car to go straight that causes understeer.

[Duracel79]

It was jimmy who told me that the stock diff was weak because he'd broken two..

I've destroyed a euro car parts guibo and a center prop bearing. But no driveshafts or diff.

I run an m50 with a quaife atb. My drivetrain has done 80k.

The stock diff is rated to 280lbs ft

The reason why welded diffs snap cv joints is because when they turn corners there are opposing forces. This weakens as it adds stress the joint isn't designed for.

Nas,

Where does this figure come from? I've not seen it quoted for a 168 diff before. Having said that its just reminded me of this bit of info from metric mechanic's website:
http://www.metricmechanic.com/pdf/Differentials.pdf



Ben

[nas80]

That's where I got it from - metric mechanic..

I usually go by personal experience. Normally if you drift out of every junction / drift roundabouts / burnouts / donuts.. You will snap something. Its wear and tear.

I am putting an e12 diff in my car at one point soon with hardened driveshafts but that's because Im going to be near the limit with my new engine.

The e12 diff is a nice easy solution because it weighs lots it might help with weight transfer. And its capable of holding big torque.

Btw I've driven with a welded diff. Its banging makes your car sound like its broken and you have to approach bends in a completely different manner. Didn't suit me driving style.

Jimmy... He was adamant tat the stock diff was extremely weak. He did say he had gone through two diffs one that had been rebuilt and it was the crown wheel and pinion that went each time. Id be pointing the finger at who built the diff tbh.