Lotus Elan

Diff Seals

PostPost by: toomspj » Thu Jul 09, 2009 9:51 am

My diff gets sooooo hot that it melts the tie rod rubbers! And the roadsports regs in HSCC do not allow an oil cooler to be fitted. I've sorted out the side seals using Viton material but currently I'm having no success with the nose seals - they leak after 15 minutes of work. In fact leak is too nice a word for it - they let go.

Does anyone know a source for top quality seals? Are they a Ford item or a generic seal?

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PostPost by: john.p.clegg » Thu Jul 09, 2009 10:11 am

Paul

Have you tried cooling it via an air-scoop fitted underneath (if allowed?).

John :wink:
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PostPost by: msd1107 » Thu Jul 09, 2009 2:19 pm

Get your ring and pinion treated with REM (http://www.remchem.com) or RF85 (http://www.rf85.com).

Both of these reduce the coefficient of friction and thus the heat generated.

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PostPost by: Davidb » Thu Jul 09, 2009 3:14 pm

That is really fascinating! Thanks :mrgreen:
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PostPost by: msd1107 » Thu Jul 09, 2009 4:11 pm

To blather on a bit.

REM stands for isotropic superfinishing. Even though the surface of the gear, bearing, crank, etc appears smooth, it is actually rough when measured on the scale of 50 u" or so. It is this roughness that contributes to friction, heat, and detracts from strength.

The REM process takes, for instance, the R&P. It is coated with some material to a very nominal depth that coats both the low and high parts, then placed in a vibratory drum where special material gradually wears away the high parts of the coating and the high parts of the R&P. The process stops when the surface is smooth to within 1-2 u". The original coating that remains in the low portions of the gear is removed.

Under high loads, the coefficient of friction is reduced by around half and the strength of the gear is increased a nominal amount. For our R&P, its mesh loss is probably above 3-4%, so this results in a useful increase in power at the rear wheels. Oil temperature is reduced due to less friction.

REM will treat virtually anything that rolls or slides. The process is licensed to numerous places, mostly in the US but there is at least one in the UK. precisionbearing.net claims they will do our roller bearings. REM will handle small orders like 1 R&P at a somewhat reasonable price.

RF85 is a newer process. They are closed mouth about the details of the technology, but apparantly use some calcium based compound to modify the surface of the piece in question. This supposedly results in a reduction of 85% in friction.

The pricing structure for RF85 is interesting, with the stated intention of modest pricing for the small guy, and higher pricing for the big successful teams. However, their price for a R&P gives one pause. However, if you disassemble your engine, transmission, R&P and ship the whole lot of pieces, the job lot is reasonable on a per piece basis.

Supposedly, you can apply RF85 after REM.

As far as Paul's overheating goes, check the oil level - too high can lead to over heating. Check the adjustment of the ring and pinion. Unless these are precisely adjusted, they will generate excess heat. And finally, rotate the pinion and check for variation in drag. You may have a strange ring or pinion. Overheating is an indication of some other problem.

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PostPost by: Davidb » Thu Jul 09, 2009 5:23 pm

Thanks for the extra info.
I wondered about doing the two processes but, it we do the REM process first the RF85 process will (supposedly) reduce the remaining friction by 85%. However, we have already reduced friction considerably so the result would be 85% reduction in not much.... I wonder what Colin would have done? :roll:
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PostPost by: rgh0 » Thu Jul 09, 2009 10:27 pm

Interesting problem as i have not heard of others without diff coolers having this problem.

I presume you are using a modern synthetic GL 5 gear oil such as Redline.

THe fact that you get to such high temperatures after 15 minutes of racing says you have high losses in the diff gears due to roughness or misalignment or gears or bearings.

Also what sort of limited slip diff centre are you running as that may be contriibuting to the heat generation also.

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PostPost by: Dag-Henning » Fri Jul 10, 2009 6:12 am

Agree there, never heard of it.....Changing seals to something else is attacking from wrong direction......Get the temp down first....! " Melts the tie rod rubbers.." - if you mean the torque rod rubbers, you really have a heat-problem that you have to cure from the inside......Ventilation will not help.

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PostPost by: toomspj » Fri Jul 10, 2009 11:22 pm

Thanks for all the helpful responses. I must admit I assumed that diff heat was a common problem since most racing elans used scoops and coolers. I have had the heat issue with 3 different diffs. I use Millers 80w/140 synthetic oil and change it every 3 races. LSD's are not allowed in HSCC. I have used a Quaife ATB in other events.

The rules in HSCC roadsports are a bit strange. We are allowed almost complete freedom with the engine other than carbs and capacity and so can get around 170 bhp. But we aren't allowed to strengthen the chassis, change the brakes (other than pads) or add any cooling for the diff (scoops specifically excluded). We can use Yokohama tyres which just adds to the problem. The result is a car that pretty much keeps pace with a 26R, or a TVR Griffith but weighs 100kg more (than a 26R) and runs outrageously stressed in certain areas - brake & diff temperature + chassis fatigue.

In terms of setting up the diffs, do you run with extra backlash and low pre-load on the pinion bearings?

It's only recently that the nose seals have really started to let go, although I have been trashing the polybush type torque rod rubbers for some time!
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PostPost by: rgh0 » Sat Jul 11, 2009 3:41 am

I run under similar rules in Australia for the groups S production sports historic class. I currently use Yoko tyres and have around 175hp. We are allowed LSD and I run a quaiffe but no cooling scoops. Do you spin the inside rear wheel a lot coming out of corners like I used to with no LSD, this may be generating extra heat? Stiffening up the front and softening the rear suspension can help reduce it

I set my diff up as standard but have not touched it in almost 15 years of racing - no problems with seals or torque rod bushes and I use the standard components. I change the diff oil about every 5 years using synthetic, approx 5000 miles of racing. You are using a very heavy weight oil at 80w /140 which will also generate more heat, the orginal spec was 90EP I use Redline 75w/90 GL5 gear oil


Chassis fatigue is not much of a problem. I have a standard Lotsu chasis and only few little around the engine mounts after 30 years of racing.

Brake temperatures used to be an issue with the standard brakes. I use standard size disks from Powerbrake in South Africa, Mintex F6R rear pads from TTR and Hawk 9012 Blue front pads, DOT 5.1 racing fluid and now have no problems and very good life of all components despite reaching 610C on the front disks hard use tracks. I used to go through a set of disks in a couple of weekends and a set of pads in 100 miles on a hard braking track now the disks dont wear and the front pads last 2000 miles

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PostPost by: toomspj » Sun Jul 12, 2009 8:30 am

Rohan
That's encouraging.
As for brakes, I've used F6R but now use Performance Friction front and rear (I found a shop in California that will cut the rears for me). I use Castrol SRF fluid, bleed the brakes every outing and never have a problem - but they get hot to the point that the dust shields just become brittle crumbly things. I change discs roughly once a season at the front and less at the back.

Chassis issues at the front is down to a couple of things I think. I had a big collision at the start of last season and straghtened the front out - so I think that metal is a little tired. I also run the front a little too hard I think with 350 # springs. I'm planning to go back a notch.

This is my third season, and this year I have the suspension working phenomenally well (slightly too well at the front) - last year I couldn't get the tyres working hard enough, this year I'm driving round much lighter cars in the twisty bits.
The diff is a bit strange though - it hasn't really changed during the last 3 seasons (other than I've tried a Quaife too), has always seemingly run hot. But it's only this last batch of seals that seem to let go. And I should be clear that the standard rubber bushes for the torque rods dont melt, just the poly ones that TTR sell.

Paul
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PostPost by: Frank Howard » Sun Jul 12, 2009 2:54 pm

Davidb wrote:I wonder what Colin would have done? :roll:

He would have added sawdust to the diff, driven the car for 50 miles, emptied the diff, and re-filled with fresh lubricant.
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PostPost by: msd1107 » Sun Jul 12, 2009 4:37 pm

A similar technique has been used for decades.

Assemble the diff carefully. Instead of oil, use very fine lapping compound. Use a motor to spin the pinion until the gears are finely polished. Disassemble the diff. Install new bearings - the old ones are trashed. Re-assemble and you are good to go.

Conceptually, this technique has a family resemblance to the REM process using technology from a century ago and with old time craftsman skills.

How did ACBC keep the bearings from being trashed?

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PostPost by: GrUmPyBoDgEr » Sun Jul 12, 2009 6:37 pm

msd1107 wrote:A similar technique has been used for decades.

Assemble the diff carefully. Instead of oil, use very fine lapping compound. Use a motor to spin the pinion until the gears are finely polished. Disassemble the diff. Install new bearings - the old ones are trashed. Re-assemble and you are good to go.

Conceptually, this technique has a family resemblance to the REM process using technology from a century ago and with old time craftsman skills.

How did ACBC keep the bearings from being trashed?

David
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I think the story goes that ACBC needed a special back axle ratio & did it by pairing a miss match of crownwheel & pinnion.
Similarly, he used a liquid metal polish & drove the formentioned odd few miles & then did a clean & rebuild.
With his reputation, he may have or maybe not have used fresh bearings.
My money's on not :roll:
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PostPost by: twincamman » Fri Jul 17, 2009 2:44 am

in F.V. CARS we polished the diff gears with tooth past and cleaned and rebuilt the unit --ed
dont close your eyes --you will miss the crash
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