Differential Removal

[sltous]

Hello All,

 

Looking for differential removal tips and tricks.  While installing my differential bracing I discovered that one of my lower differential bolts had sheared so I think I need to remove the diff, use a bolt extractor on the half of the bolt still in the diff, and get it all back together.  Planning to use:

https://web.archive.org/web/20190416085218/http://alcester-racing-sevens.com/prop_-_step_1.htm

https://www.pistonheads.com/gassing/topic.asp?h=0&f=101&t=1670013

but any other guidance is appreciated.  Supposed to be going to the track on Monday so it'll be a bit of a race against time.

 

 

[MV8]

I suggest you take the removed diff to an automotive machine shop so they can remove the broken bolt and clean/chase all the threaded holes while they have it, verify the thread size and pitch. It is easy to make the problem worse by breaking off hardened extractors in the hole. Use copper anti-seize on the new grade 10.9 bolts and shanks. Make sure the new bolts are not too long and bottom out in the diff. Adjust with washers if needed. I'd add a split lock washer and regular flat washer. Mcmastercarr is a good source for hardware.

[sltous]

Thanks MV8.  

 

Removal was pretty straightforward, followed the pistonheads process and took my time.  Now to get the bolt end out and then 'refitting is the reverse of removal' 

[sltous]

This might be a long shot, Rich @ Kampena informs me that the lower differential bolts are M12 threads, 1/2" shank, does anyone in the Bay Area of California have a spare lower differential mounting bolt?  I think they are the 85mm long bolts, my good bolt is at the mechanic so I can't easily measure. https://caterhamparts.co.uk/differentials/1559-bolt-m12x85mm-with-1-2-shank.html

[MV8]

I think you'd be much better off with a common m12-1.75x85 in 10.9 or 12.9. The oversize shank doesn't make the m12 threads any stronger. It is essentially a shoulder bolt like this: https://www.mcmaster.com/97713A124/

 

Versus something much stronger like this: https://www.mcmaster.com/91502A253/

 

The bolt is just a clamp for the inner bush sleeve. 

 

No need to be super tight if you have lock washers, serrated step washers, lock tabs or safety wire to prevent loosening.

 

If the threads get damaged, you might consider taping for 1/2 inch instead of a m12 helicoil.

[CarlB]

You might want to consider replacing the U joints. To remove the driveshaft, you have to pull the differential. 

[sltous]

29 minutes ago, CarlB said:

You might want to consider replacing the U joints. To remove the driveshaft, you have to pull the differential. 

Thanks CarlB, if I didn't have a hard deadline where I needed to be reassembled and on the track 8am Monday morning I would have considered that.  By the time I realized I had a problem with the differential it was too late to get any shipments in from Caterham so anything that could not be corrected with McMaster or locally sourced parts is going to have to wait.

[sltous]

49 minutes ago, MV8 said:

I think you'd be much better off with a common m12-1.75x85 in 10.9 or 12.9. The oversize shank doesn't make the m12 threads any stronger. It is essentially a shoulder bolt like this: https://www.mcmaster.com/97713A124/

 

Versus something much stronger like this: https://www.mcmaster.com/91502A253/

 

The bolt is just a clamp for the inner bush sleeve. 

 

No need to be super tight if you have lock washers, serrated step washers, lock tabs or safety wire to prevent loosening.

 

If the threads get damaged, you might consider taping for 1/2 inch instead of a m12 helicoil.

Not worried about strength of the bolt, does the shank of the bolt not need to be a close fit to the bore of the bushing to prevent rattling/torquing?

[CarlB]

I had my dif out this year for the first time and I didn't measure the hole. The places I have, Caterham used a metric hole were the part being attached used metric bolts. The difference between 1/2 inch and 12 MM is 28 thousands of an inch. The hole clearance would be 14 thousands around. I do not believe you have a problem.

[MV8]

Ditto. It is just a clamp for the bush inner steel sleeve bonded into the bush and will not move around if the bolt is tight.

 

Had the bolt been a stronger grade (no head marking?) and/or had rolled versus cut threads (a possibility with specialty hardware along with softer material easier/less costly to machine) then you probably would not have a diff out right now. I see no other reason for the bolt failure with such a corrosion-free diff.

[sltous]

3 hours ago, CarlB said:

I had my dif out this year for the first time and I didn't measure the hole. The places I have, Caterham used a metric hole were the part being attached used metric bolts. The difference between 1/2 inch and 12 MM is 28 thousands of an inch. The hole clearance would be 14 thousands around. I do not believe you have a problem.

 

13 minutes ago, MV8 said:

Ditto. It is just a clamp for the bush inner steel sleeve bonded into the bush and will not move around if the bolt is tight.

 

Had the bolt been a stronger grade (no head marking?) and/or had rolled versus cut threads (a possibility with specialty hardware along with softer material easier/less costly to machine) then you probably would not have a diff out right now. I see no other reason for the bolt failure with such a corrosion-free diff.

Understood. I believe (to be verified) I have two grade 12 M12x1.25 bolts with appropriate shoulder length ready to go in once the helicoil is delivered and I can get everything reinstalled tonight after work and tomorrow. 

[MV8]

Is it 1.25? I would expect 1.75 or 1.5 in aluminum but I don't know.

[MV8]

I'm sure you will figured it out.

[sltous]

2 minutes ago, MV8 said:

Is it 1.25? I would expect 1.75 or 1.5 in aluminum but I don't know.

Oops. Yes standard M12 so 1.75, I got mixed up with the 1/2-20 bolts that are in a lot of the A Frame

[sltous]

Tried to get all the bolts where threadlocker is appropriate, or that are a prerequisite for a threadlocked bolt, installed and torqued last night.  Safety wire on the two lower bolts on the differential (I used one original and one M12 grade 12) to avoid pulling the helicoil if the differential has to be removed again.

 

One question that came up during the re-assebmly process: I added a small amount of grease to the bearing seals to ensure that they didn't run dry, and I added a small amount also to the differential seals to ensure that they don't run dry, is this OK?

[sltous]

After a little artisanal engineering my boot floor can fit again with the additional braces.  Pending bleeding the rear brakes and filling the differential, I should be able to put some test miles on this afternoon.

[sltous]

Differential is filled and brakes are bled, completed 10 miles of testing, so far so good.  Thanks to all providing feedback and advice.