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Discussion Starter · #1 ·
I tried to upload the full article I wrote on this but It's a bit much. I'll post it in pieces instead.

I’ve been doing some brake upgrades while I did some motor upgrades. It passes the time while I wait for parts. A little while back I happened to have the luck of getting my hands on a complete upgrade set for the rear brakes. This included all hardware and fasteners to install a set of Isuzu rear calipers and rotors to my 72 GT. It did mean replacing the bearings, keepers and a reshim of the new axle bearings. The axle bearings weren’t needed but seemed like a good idea while I had it apart. This included mounting plates that were installed instead of the bearing retainers. These were from an early model Turbo Isuzu and will fit inside of 13 inch rims. Once installed I had very weak brakes and after doing a bit of math on cylinder sizing I found out why. The original rear cylinders are about a third smaller in volume than most calipers even the floating single sided ones from the Isuzu. I was faced with going back to the drums, restrict the fronts or come up with a new idea. I chose the new idea approach and used a 82 master cylinder from a BMW 528 I. It was made by ATE and looked to fit and used all the same sizing as an Opel for lines and banjo bolts. For that year BMW there are a couple used and I chose one that powered 4 wheel discs already and had a single front and rear outlet. I didn’t try the booster at the same time but it looks to be a good donor as well. It has front and back bores of 24 VS. the 17 or so from a stock GT master cylinder. I did have to split the fronts using a rear axle tee fitting. I was right and it was the same length as an Opel MC but had the outlet ports on the wrong side. I took it apart to see how it operated and check it for usability as it was a used part. It has much larger cylinders and the bias is set by 2 springs that can be changed to get the bias right if needed. I had some work to install it as the pictures show but it does fit. I had to cut some of the drivers side light bucket opening and use a line for the fronts turned as quick as possible to clear everything. I did use a banjo bolt on the back but to get it to turn and tighten I had to round off the corners of the square attaching bolt. An Opel reservoir doesn’t fit this master cylinder and a BMW one won’t clear the front sheet metal. I cut the BMW one at the full line for the forward half and reattached a new top for it made out of plastic, using Seal All. It did just that and has held up to the brake fluid as well. The function is exactly as planned. I’ve tested this at varying speeds up to 80 MPH and it is extremely firm and the nose dive or front lock up is no longer there. I do believe that this will allow for bigger front brakes to be used with no loss of pedal. I’ve also recently found out that BMW 320I front calipers will fit the GT if swapped side to side and quite possibly the stock non vented calipers may work as well. These would be from a 77 or so model I’ve been told. I’ve located a full used set locally that I’ll pick up as soon as the put the car out for parts. If the BMW front calipers and rotors do fit and only need pads and some light work my total cost for the complete upgrade will be around 275.00. I’ve been extremely lucky with parts on this and I know I could never hope to repeat it at that cost. This wasn’t the easiest upgrade but maybe the most important. If it won’t stop then what fun is going fast?

Parts list
Isuzu rear calipers with rubber lines
Emergency brake cable with hardware
Custom mounting brackets for the calipers
New Isuzu rotors
New brake pads
Axle bearings
Axle bearing retainers
Used Master Cylinder with reservoir
Rear axle Tee and short steel line from a stock caliper
Used front calipers and rotors
 

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Discussion Starter · #2 ·
these pics were originally attached to the full write up.
 

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Discussion Starter · #3 · (Edited)
I tried a couple of ways to get one of the more important pics of the full back set included and it said no way. Here is the link to the original post of them.

never mind I got it past the radar

Gary do whatever you want with the info. I'm not much on writing it all but building it sure is fun. If I missed something or didn't answer a question just ask.

One thing I have to mention is the rear set was done By GTJim in New Zealand and the work is phenomenal, I'll never be able to give enough praise for the work he did on this package.
 

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Discussion Starter · #4 ·
I've been doing some digging on this rear set of brakes and found an interesting turn. The pads for mine are a Raybestos D235 and do not fit any Isuzu imported to the United States. After getting them cross referenced I did find that the 1984 Mazda 1.1 uses these brake pads and calipers and were imported to the US. I haven't found the rotors yet but I'll keep digging.
 

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nobody said:
One thing I have to mention is the rear set was done By GTJim in New Zealand and the work is phenomenal, I'll never be able to give enough praise for the work he did on this package.
I am just glad the rear brake set made it into the right hands - did a bit of travelling before it got to you from the previous owner! Would not be able to go through making up more sets as parts are getting few and far between.
Just enough left for a set and a spare till I find more bits. Plus I do need toget a bit done on my GT...... but thanks for the mention :)
 

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Discussion Starter · #7 ·
here is a better shot of the E brake and caliper setup. It also shows an alternative exhuast system.
 

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Discussion Starter · #8 ·
A few items that I've found recently should go into this thread. The BMW ATE or Girlings from at least a 78 BMW 320I do fit but not the rotors. The seal all used on the brake reservoir didn't continue to hold up. Either the combination of the bigger fronts or the bigger master made bleeding the fronts a real challenge. It either had alot of pressure or not enough and a 1 man bleeder operation just wouldn't work. Brembo part # 25052 is a perfect match to an NOS front 75 rotor.
 

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Volvo front + rear drum= Will Stock MC hold?

I've read the threads and i am doing the Volvo front caliper upgrade. We have mounted the Calipers/Rotors successfully, we split the line at the caliper with a T fitting and when we bled the brakes i think the MC blew(it was old). We are installing a new MC but i have some doubts...1) Will the stock Opel MC have enough volume/strength to run these bigger brakes coupled with the rear drum brakes. There was no mention about upgrading the MC on the original Volvo Upgrade thread done by the gentleman in Sweden so i assumed it was not necessary to modify the MC. 2)What would happen in terms of the MC if we installed the rear izuzu disc brakes instead of the drums, would this help the MC or make matters worse? I would greatly appreciate any suggestions, we are in the middle of the conversion an need help. Thanks
Mauri :confused:
 

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Muari, "Nobody" did the izusu rear brake upgrade and had to mod the MC from a BMW, I believe, the stock Opel MC just doesn't have the volume to operate the larger calipers in the rear. Do a search for Brake Upgrades, you'll find the thread he did on that. HTH.
 

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Vovlo upgrade problems with MC

Thanks Ron, the problem is that the BMW reservoir did not fit well in the GT and the modification to it did not hold up, apparently the opel reservoir cannot be used on the BMW MC. Anastomotors mentioned he was using a Volvo MC, does anyone know if the Volvo MC for these Calipers (vented Rotors) fit on the GT booster and will it accept the opel reservoir or will the volvo reservoir fit the GT? Thanks Again :confused:
Mauri
 

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Discussion Starter · #12 ·
The first attempt at the modification didn't hold up for the BMW reservoir. Now it's all good and will be fine for a long time. The more brakes you add only make the Opel MC issue worse. From experience if your thinking of doing the backs too it is important to upgrade the MC. I do like the bias on the BMW one.
 

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Thanks Nobody for the response. How did you ultimately modify the BMW reservoir to make it work? If i keep the rear drums for now, do you think a new Opel MC would work ok? Thanks Again
Mauri
 

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Discussion Starter · #14 ·
I very carefully melted the seams back together so it had nothing but plastic holding it and the brake fluid couldn't act upon it.
 

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Discussion Starter · #15 ·
When I did the backs I noticed a change in braking, I also saw where Bob had mentioned that on some car with the bigger brakes and a stock MC it had to be pumped to stop. I was doing a bit more digging on this subject and found that the rear calipers from the injected 84 Mazda RX7 look to be the right ones. The Rotor off that car could work but it would need some work to drill another set of holes for 100 mm spacing instead of the 110 for the Mazda. This is just some things I've turned up so far but I'd need some dimensions like the spacing of the rear rotor and such to know for sure. Maybe if we talked Jim into it he might give up a drawing on that bracket. Maybe even the code file if possible.
 

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Ummm!

nobody said:
. This is just some things I've turned up so far but I'd need some dimensions like the spacing of the rear rotor and such to know for sure. Maybe if we talked Jim into it he might give up a drawing on that bracket. Maybe even the code file if possible.
Ummm! Well, there is no drawing ... I simply took the Isuzu and the GT mounting plates in to the profile cutting shop and said to the operator: "I need a bracket that is a combination of these two with the caliper holes orientated like so ... " His reply was: "Come back tomorrow and I will have them done for you."

That is how things are done here - cash payments and no drawings! :D

Saves heaps on paperwork and tax. ;)
 

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volvo brakes

Today we found an MC from a 3 series BMW with 4 wheel disk brakes and it had two front portals for the front lines and one rear portal for the rear line. It was a little challenging but we finally got it in and although this one had a lower fluid reservoir it still needed to be modified. The best thing is we got it at a pick your part for $15. Tommorrow we will bleed the brakes and test it out. My only concern is that now with this larger capacity MC, will it blow away the rear drum cylinders? We have the Izuzu rear axle with disks ready to be installed but wanted to wait on that for now. Thanks Again for your help.
Mauri
 

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Front Brake Upgrade

Now the rears are taken care of by the Isuzu Impulse disc set-up I have turned my attention to the front discs. Isuzu Impulse again ( of course ).
With my GT front suspension disassembled the similarity between Impulse and GT spindles cannot be ignored and it seems that a substitution into the GT suspension is the easiest way to fit the 16mm wide, 256mm diameter, vented Isuzu discs. The tapers on the ball joints are the same on the upper ball joint and the GT lower ball is either the same or just slightly larger so the Isuzu spindle can be reamed, just a wee bit, to fit. The major difference is the the Isuzu spindle is not quite as tall, but a 10mm spacer between the upper control arm and the ball joint will easily cure that. Also the Isuzu has a fixed steering arm and the turn stops will need to be altered slightly to line up correctly. Here are a couple of pics comparing the two spindles.
 

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Discussion Starter · #19 ·
Mauri
You could go to the larger rear cylinders now they aren't that expensive and I think you might like the results.
 

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No luck

I think there's a problem with matching the Volvo front Calipers(vented) with the BMW MC because today we bled the system and we are getting no resistance on the pedal as if there was a leak. The rear drums apparently are working, (you can hear the brake shoes hitting against the drum) but when we bleed the fronts there seems to be little fluid coming out of the Calipers. I think the problem is that the BMW MC does not push enough fluid to work these cylinders, but i don't understand why i am not getting ANY resistance on the pedal (system is closed, no leaks). I saw the Volvo MC at the pick your part and it's much longer besides the base is different and would not fit on the GT booster, I don't think it could be adapted. Should i drill one of the caliper inlets and make it a one line system or am i just not bleeding this right. I am on the verge of frustration, so any life saving suggestion would be greatly appreciated!! Thanks
Mauri
 
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