Broken Bolts in Gearbox

Blarge · Post by **Blarge** » Fri Jul 17, 2015 9:31 pm

Hi All,

Anyone got any advice on removing a broken bolt out of the gearbox. Last weekend the master and slave cylinder were being replaced, we were unable to remove the bolts holding the slave cylinder and after several hours of trying one of the bolts snapped and the other seemed to have lost its thread. They had never been removed by the looks of it and it was original Master and slave.

To remove the bolt I have a few options:

Left handed drill bits hope the wind out the stud, colbolt bits to drill the stud out then re-tap or try getting the stud out using an easy out?

The bolt is currently an M8 and was wondering if its safe to heli-coil it to M10?

Has anyone got any advice or experienced the same problem?

Its on a 93 Mk4 Si Vtec

Thanks,

Ben

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Fri Jul 17, 2015 10:44 pm

Argh, hate when this sort of jobby happens! Feel for you man

I never have any success with easy outs, but obviously they must work sometimes...

My favoured approach is filing the top of the bolt flat, centre punching properly in the middle and then carefully drilling out with ever increasing diameter drill bits.

When you get a hole diameter up near the ID of the thread, often that has taken so much pressure off the thread that it will either then start screwing in as you drill (depending on thread depth) or unscrew by hand (grab it with GOOD mole grips if you have an end, or use the end of a screwdriver as a drift with a hammer to try and 'knock' it in the unscrewing direction if not) or, also using a screw driver and hammer on the edge of the bolt remains, you can 'collapse' it in like a roll pin and then pull it out.

As this is on the front of a gearbox though, access with all the tooling paraphernalia will be a complete arse/impossible!

Also as it will be a blind hole, you need to be very careful about drilling depth...

Or...
You could just swap the gearbox

W1ggz · Post by **W1ggz** » Fri Jul 17, 2015 11:53 pm

Is it in a position to weld a nut onto the broken bolt?

Blarge · Post by **Blarge** » Sun Jul 19, 2015 12:11 pm

@wurlycorner Thanks Iain, Yes was thinking about drilling out the bolts there is very little room and have removed the rad and think I'm going to need to remove the aircon or drop the unit. I bought some colbolt bits and some drilling oil as I didn't want any mistakes and don't want to have to replace the Gearbox. Do you reckon I should heli-coil it to M8 or just re-tap the thread?

I have got some left handed drill bits that are supposed to grip and back out the bolt but never used them before. I'm sure others will have a similar problems but thought I would share my experience. I'll add some pics after today on the car and the before and after and what I found was the best method.

@W1ggz I did think about this method but don't have my welder at the moment its being borrowed and was a bit reluctant where its located. Would I drill a small hole in the thread to help it weld to the bolt?

Thanks,

Ben

106pete · Post by **106pete** » Sun Jul 19, 2015 12:35 pm

If the bolts are so seized that they snapped any ezout isn't goin to work, they have there uses but it's very limiting.

If you get the bolt spot on with drilling you can just retap the thread to clean it up, always aim to do this as helicoil is more of a last chance option. The most likely thing to happen is because of access the drill will wonder off course and leave half the thread behind, it's should come lose enough to pull out with pliers.

I wish you all the best with this one!!

Blarge · Post by **Blarge** » Sun Jul 19, 2015 9:16 pm

@wurlycorner@106pete @W1ggzThanks for your help I was able to successfully get the bolt out. I didn't have the clearance for a drill in the end and was reluctant to remove aircon and bumper to do it. But I did find another way to get it out that might help others.

I used a diamond disc fitted to a Dremel to cut a line in the top of the bolt as there wasn't a lot there but it was worth a try. Then I used a screwdriver with a ratchet end and socket wrench and was able to back it out with a bit of patience moving back and forth and spraying it as I went.

I then re-tapped the holes with some cutting oil to remove the broken thread and fitted new bolts with a bit of anti-seize.

Thanks for your help, hope this thread might be of use to someone in my situation in the future,

Ben

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Sun Jul 19, 2015 11:46 pm

Nice one, well done

Lude Generation

Broken Bolts in Gearbox

Broken Bolts in Gearbox

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