# rear drum to disc swap--worth it?



## shoebear (Nov 22, 2009)

I'm trying to decide whether it's worth the hassle to do a rear drum to disc brake swap on my '98 Jetta TDI. Most of my driving is my 132 mi round trip commute on 75mph interstate highway. About once a month traffic will come to a dead stop from 75mph, requiring hard braking. I generally keep a reasonable following distance, so I haven't come close to rear-ending anyone yet. But stops like that tend to warp my front rotors, and I never know when I might need to stop just a bit shorter some day.
I would appreciate any thoughts pro or con, especially from folks who have done this swap. My local brake shop wouldn't give me a straight answer about how much (or even if) this swap would help.
Thanks!


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## akid420 (Apr 23, 2009)

sounds like u really want to which is always a good reason. but i have driven both and don't find much if any difference.


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## shoebear (Nov 22, 2009)

*Re: (akid420)*

Thanks, akid. The only reason I'm considering it is to make sure my brakes are up for the job. If it doesn't add to brake performance or longevity, I don't want to do it.


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## teutoned (Jul 29, 2008)

*Re: (shoebear)*

don't waste your money


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## germancarnut51 (Mar 23, 2008)

*Re: rear drum to disc swap--worth it? (shoebear)*

In the case of a single hard stop on dry pavement, a switch to rear disc brakes is not going to make a difference vs properly maintained rear drum brakes.
But, disc brakes are more fade resistant, and dry quicker when wet. Meaning if you needed to make mulitple consecutive hard stops, or a hard stop in wet conditions, rear disc brakes would have an advantage. Also, while rear VW disc brakes have some problems with the parking brake, I find it easier to service rear disc brakes.
If you want more braking, without that much of a hassle, I'd suggest a front brake upgrade. You can upgrade to 11" front brakes from a Corrado G60. This is a simple calipers with caliper carriers and brake pads with front 11" rotors bolt-on job. You should be able to do this for $200 or less, and you will see a bigger braking improvement than adding rear disc brakes.
Of course if you do the rear disc brakes and the 11" front brakes, then you will see even a greater braking improvement. 

11" brake calipers need 15" or larger wheels to clear the calipers.



_Modified by germancarnut51 at 11:27 PM 4-30-2010_


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## shoebear (Nov 22, 2009)

*Re: rear drum to disc swap--worth it? (germancarnut51)*

Thanks, carnut -- very thoughtful and helpful answer.
My primary problem is front rotor warpage. Colorado is semi-arid, so wet conditions are rare but do happen (primarily in the winter). Likewise, repeated hard stops do happen, but are rare. Current braking performance is adequate; I would be happy to have better performance in these areas, but they are not my primary focus now.
I was already thinking that bigger front rotors might be a better investment for what I want. My main problem seems to be that a hard stop dumps too much heat in the rotors and warps them. Bigger disks should be able to soak up the same amount of energy but not get as hot (theoretically).
But I have 14" alloy wheels x8 (winter & summer) with good tires on all, so upgrading to 15" wheels would be pretty expensive. I just checked, and it looks like I have about 12mm clearance between my current calipers and the wheel, so I don't know if I could go any bigger on the rotors without changing wheels. By the time I changed tires and wheels x8 and installed new brakes I could pay for a lot of rotors -- perhaps I should just keep some extras on hand and swap them in when necessary.
Or perhaps there are some premium quality rotors that would hold up better than the ones I have. Would slotted/drilled help? Is there any particular brand(s) that is better than others?


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## germancarnut51 (Mar 23, 2008)

*Re: rear drum to disc swap--worth it? (shoebear)*

Heat is going to warp rotors, no matter what brand you buy. Better brake pads are going to dump more heat into the rotors making the problem worse.
You're right about the wheel size. Bigger rotors are going to require bigger wheels. No way around that. I know when I got my Corrado G60 front brakes, I looked at the clearance on the 10.1" brakes with 14" wheels, and I said to myself, looks like that may clear. After I installed the Corrado front brakes I founf that they won't clear the 14" wheels. My Golf GL already had Corrado 15" X 6.5" Sebring wheels on it when I bought it, so the 11" brakes fit just fine.
I think you should look into bigger front brakes, and plan on a wheel change in the future. You can always sell your 14" wheels to get some money towards the 15" wheels you'll need.


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## shoebear (Nov 22, 2009)

*Re: rear drum to disc swap--worth it? (germancarnut51)*

Thanks, carnut, I agree. I guess I'll put up with the pulsing for now.
I may try a set of 256mm (stock size) slotted and/or drilled rotors on the theory that a) they might allow a bit more air flow and thus dissipate heat better or b) thet the slots or holes might help allow the rotors to expand without warping (like holes and slots in a table saw blade).


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## greyhare (Dec 24, 2003)

*Re: rear drum to disc swap--worth it? (shoebear)*

If you are getting the brakes hot enough to warp the rotors, you will more than likely have cracking with drilled rotors.
You need better cooling. Run ducts from the lower bumper vents to the back of the brakes.


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## The Big V (Jul 11, 1999)

hmmm where to begin. firstly, i have a mk3 2.0 5spd golf...it has rear drum brakes. i looked into swapping to discs and decided it wasn't worth it. i rebuilt the rear drums for about 35$ at the same time i did the rear wheel bearings and installed new parking brake cables. the parking brake cables and rear drum rebuild were very simple and very easy...i think Dan Reed's page has a DIY. the car's braking is much more stable now. 

as you know when you brake most of the weight transfer is to the front of the car, hence why you have larger front brakes than rear. there are many variables in driving and stopping in particular. i have 15inch lightweight kosei wheels on my car. they weigh about 12lbs each. the weight transfers that happen to a car effect it greater than most people imagine. having lighter wheels and brakes aid in your steering/handling because you have less unsprung weight. getting the larger 11in rotors with G60 calipers is most likely going to negate any braking advantages with weight disadvantages. those are hefty brakes even compared to the oem ones. i have 15in wheels like i said so i looked into this option. i am going to stay with the oem 10.1 inch rotor size. i will most likely use Brembo Blanks or Brembo Slotted 10.1 inch rotors. they are well made and do the job...the slotted help dissipate some heat as well as contact and bite on the brake pad. 

i race a mk3 golf as well. we use Brembo Blanks on it with Hawk black or blue pads. they generally last endurance races pretty well but i've seen people chew them up on occasion. for the street i'd recommend a few things that you can upgrade your system if you encounter hard braking (at high speeds). you're dealing with weight and friction (heat). sooo you can use better brake fluid...i recommend ATE Super Blue Racing Fluid...it's gonna hold up against temperature better and be more consistent. you can upgrade to Stainless Steel brake lines for a better, stiffer responding brake pedal and braking response (less susceptible to heat damage that happens on standard lines!!). you can use better brake pads...i'd recommend Hawk HPS pads...they will grip better regardless of temperature...they will prob create a little more heat in fact. you can upgrade to a Wilwood 4 piston lightweight caliper seen here http://www.momentummotorparts.com/store/brakingmk3.asp its lighter and stronger and fits oem setups....i have yet to try this final option but it's what i'm considering for my upgrade plan. 

lastly, who says you're warping the rotors? have you taken the rotor out and actually measured it? we most often find that people aren't bedding in their brakes properly and you get uneven wear patches of your pads on your rotors and that causes the vibration and unsteady braking. bedding in brakes is important on the street just as it is on a race track. i'm guessing you have crap pads that are wearing heavily under brake force/heat build up and causing the "warping" you mention. your rotors as well as lines and fluid can't handle the stress either. forget the big brake upgrade kits. try installing ss brake lines and getting a complete brake fluid flush w the ATE Super Blue Race (its still dot 4 don't overthink it) Fluid. then if you want try some HPS Hawk pads. and then do the slotted Brembo rotors if ya want something more than the Brembo "Blanks." 

BED IN YOUR BRAKES. straight line on highway...make sure NOBODY is behind you....55-70mph or whatever speed limit is, gently tap your brakes a couple times to start to warm them up...try three times from speed limit minus 5-10mph. ok then with a race pad we usually do about 75mph but since you're using a street pad i'd cut it in half. from about 40mph you need to press your brakes very very firmly in a straight line to 10mph without using ABS or screeching your tires etc..just a nice solid firm brake to 10mph and then speed back up right away to 40-50mph and do the same thing about 5 times. it is important not to come to a complete stop!!! it is also important to continue driving without using the brakes for another 5+ minutes on the highway afterwards to let your brakes cool down. what you've effectively done is put a smooth and EVEN coat of brake pad on the rotor and also put an initial wear on the pad so as to match the rotor shape. without this you can get strange pad to rotor bite reaction or uneven pad and rotor abuse. when you stomp on the brakes every now and then on your way to work from 70mph to 0 you are basically wearing the pad onto the rotor unevenly and at a complete stop without a coating on the rotor a chunk of pad is sticking to the rotor and then you have this vibration and lumpy brake feel. 

also--your tires could be a factor as well. if you don't have good grip then it doesn't matter what your brakes or your suspension is like cause its the only part of your car that actually touches the road!! get some good all season tires or if you commute a lot year round look into getting some decent summer tires and some excellent winter tires. 

i'd be curious to see if simply bedding in your brakes alone would solve your problem. it's something that you could need to do after a car wash or after the car has been sitting in the rain or snow parked after a drive on salty and sandy roads etc. that said i understand the need and desire for better braking performance and upgrading the components. try it step by step...i'd recommend a minimum of the ss brake lines and the fluid and then go from there w a pad and slotted rotor if ya must...etc. 

hope this helps and isn't toooo ramble-y. good luck 

here's a link to brake bed-procedure and other tech info (bleeding brakes page too)-- 

http://www.tirerack.com/brakes/tech/techpage.jsp?techid=85 
http://www.stoptech.com/tech_info/wp_bedintheory.shtml 
http://www.zeckhausen.com/bedding_in_brakes.htm 
http://www.zeckhausen.com/bleeding_brakes.htm


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